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TOMOYO Linux Cross Reference
Linux/net/ipv4/tcp_input.c

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  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              Implementation of the Transmission Control Protocol(TCP).
  7  *
  8  * Authors:     Ross Biro
  9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 10  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
 11  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
 12  *              Florian La Roche, <flla@stud.uni-sb.de>
 13  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 14  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
 15  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
 16  *              Matthew Dillon, <dillon@apollo.west.oic.com>
 17  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 18  *              Jorge Cwik, <jorge@laser.satlink.net>
 19  */
 20 
 21 /*
 22  * Changes:
 23  *              Pedro Roque     :       Fast Retransmit/Recovery.
 24  *                                      Two receive queues.
 25  *                                      Retransmit queue handled by TCP.
 26  *                                      Better retransmit timer handling.
 27  *                                      New congestion avoidance.
 28  *                                      Header prediction.
 29  *                                      Variable renaming.
 30  *
 31  *              Eric            :       Fast Retransmit.
 32  *              Randy Scott     :       MSS option defines.
 33  *              Eric Schenk     :       Fixes to slow start algorithm.
 34  *              Eric Schenk     :       Yet another double ACK bug.
 35  *              Eric Schenk     :       Delayed ACK bug fixes.
 36  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
 37  *              David S. Miller :       Don't allow zero congestion window.
 38  *              Eric Schenk     :       Fix retransmitter so that it sends
 39  *                                      next packet on ack of previous packet.
 40  *              Andi Kleen      :       Moved open_request checking here
 41  *                                      and process RSTs for open_requests.
 42  *              Andi Kleen      :       Better prune_queue, and other fixes.
 43  *              Andrey Savochkin:       Fix RTT measurements in the presence of
 44  *                                      timestamps.
 45  *              Andrey Savochkin:       Check sequence numbers correctly when
 46  *                                      removing SACKs due to in sequence incoming
 47  *                                      data segments.
 48  *              Andi Kleen:             Make sure we never ack data there is not
 49  *                                      enough room for. Also make this condition
 50  *                                      a fatal error if it might still happen.
 51  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
 52  *                                      connections with MSS<min(MTU,ann. MSS)
 53  *                                      work without delayed acks.
 54  *              Andi Kleen:             Process packets with PSH set in the
 55  *                                      fast path.
 56  *              J Hadi Salim:           ECN support
 57  *              Andrei Gurtov,
 58  *              Pasi Sarolahti,
 59  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
 60  *                                      engine. Lots of bugs are found.
 61  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
 62  */
 63 
 64 #include <linux/mm.h>
 65 #include <linux/slab.h>
 66 #include <linux/module.h>
 67 #include <linux/sysctl.h>
 68 #include <linux/kernel.h>
 69 #include <net/dst.h>
 70 #include <net/tcp.h>
 71 #include <net/inet_common.h>
 72 #include <linux/ipsec.h>
 73 #include <asm/unaligned.h>
 74 #include <net/netdma.h>
 75 
 76 int sysctl_tcp_timestamps __read_mostly = 1;
 77 int sysctl_tcp_window_scaling __read_mostly = 1;
 78 int sysctl_tcp_sack __read_mostly = 1;
 79 int sysctl_tcp_fack __read_mostly = 1;
 80 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
 81 EXPORT_SYMBOL(sysctl_tcp_reordering);
 82 int sysctl_tcp_ecn __read_mostly = 2;
 83 EXPORT_SYMBOL(sysctl_tcp_ecn);
 84 int sysctl_tcp_dsack __read_mostly = 1;
 85 int sysctl_tcp_app_win __read_mostly = 31;
 86 int sysctl_tcp_adv_win_scale __read_mostly = 1;
 87 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
 88 
 89 /* rfc5961 challenge ack rate limiting */
 90 int sysctl_tcp_challenge_ack_limit = 1000;
 91 
 92 int sysctl_tcp_stdurg __read_mostly;
 93 int sysctl_tcp_rfc1337 __read_mostly;
 94 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
 95 int sysctl_tcp_frto __read_mostly = 2;
 96 int sysctl_tcp_frto_response __read_mostly;
 97 int sysctl_tcp_nometrics_save __read_mostly;
 98 
 99 int sysctl_tcp_thin_dupack __read_mostly;
100 
101 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
102 int sysctl_tcp_abc __read_mostly;
103 
104 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
105 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
106 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
107 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
108 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
109 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
110 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
111 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
112 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
113 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
114 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
115 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
116 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
117 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
118 #define FLAG_UPDATE_TS_RECENT   0x4000 /* tcp_replace_ts_recent() */
119 
120 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
121 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
122 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
123 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
124 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
125 
126 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
127 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
128 
129 /* Adapt the MSS value used to make delayed ack decision to the
130  * real world.
131  */
132 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
133 {
134         struct inet_connection_sock *icsk = inet_csk(sk);
135         const unsigned int lss = icsk->icsk_ack.last_seg_size;
136         unsigned int len;
137 
138         icsk->icsk_ack.last_seg_size = 0;
139 
140         /* skb->len may jitter because of SACKs, even if peer
141          * sends good full-sized frames.
142          */
143         len = skb_shinfo(skb)->gso_size ? : skb->len;
144         if (len >= icsk->icsk_ack.rcv_mss) {
145                 icsk->icsk_ack.rcv_mss = len;
146         } else {
147                 /* Otherwise, we make more careful check taking into account,
148                  * that SACKs block is variable.
149                  *
150                  * "len" is invariant segment length, including TCP header.
151                  */
152                 len += skb->data - skb_transport_header(skb);
153                 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
154                     /* If PSH is not set, packet should be
155                      * full sized, provided peer TCP is not badly broken.
156                      * This observation (if it is correct 8)) allows
157                      * to handle super-low mtu links fairly.
158                      */
159                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
160                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
161                         /* Subtract also invariant (if peer is RFC compliant),
162                          * tcp header plus fixed timestamp option length.
163                          * Resulting "len" is MSS free of SACK jitter.
164                          */
165                         len -= tcp_sk(sk)->tcp_header_len;
166                         icsk->icsk_ack.last_seg_size = len;
167                         if (len == lss) {
168                                 icsk->icsk_ack.rcv_mss = len;
169                                 return;
170                         }
171                 }
172                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
173                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
174                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
175         }
176 }
177 
178 static void tcp_incr_quickack(struct sock *sk)
179 {
180         struct inet_connection_sock *icsk = inet_csk(sk);
181         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
182 
183         if (quickacks == 0)
184                 quickacks = 2;
185         if (quickacks > icsk->icsk_ack.quick)
186                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
187 }
188 
189 static void tcp_enter_quickack_mode(struct sock *sk)
190 {
191         struct inet_connection_sock *icsk = inet_csk(sk);
192         tcp_incr_quickack(sk);
193         icsk->icsk_ack.pingpong = 0;
194         icsk->icsk_ack.ato = TCP_ATO_MIN;
195 }
196 
197 /* Send ACKs quickly, if "quick" count is not exhausted
198  * and the session is not interactive.
199  */
200 
201 static inline int tcp_in_quickack_mode(const struct sock *sk)
202 {
203         const struct inet_connection_sock *icsk = inet_csk(sk);
204         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
205 }
206 
207 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
208 {
209         if (tp->ecn_flags & TCP_ECN_OK)
210                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
211 }
212 
213 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
214 {
215         if (tcp_hdr(skb)->cwr)
216                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
217 }
218 
219 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
220 {
221         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
222 }
223 
224 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
225 {
226         if (!(tp->ecn_flags & TCP_ECN_OK))
227                 return;
228 
229         switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
230         case INET_ECN_NOT_ECT:
231                 /* Funny extension: if ECT is not set on a segment,
232                  * and we already seen ECT on a previous segment,
233                  * it is probably a retransmit.
234                  */
235                 if (tp->ecn_flags & TCP_ECN_SEEN)
236                         tcp_enter_quickack_mode((struct sock *)tp);
237                 break;
238         case INET_ECN_CE:
239                 tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
240                 /* fallinto */
241         default:
242                 tp->ecn_flags |= TCP_ECN_SEEN;
243         }
244 }
245 
246 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
247 {
248         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
249                 tp->ecn_flags &= ~TCP_ECN_OK;
250 }
251 
252 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
253 {
254         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
255                 tp->ecn_flags &= ~TCP_ECN_OK;
256 }
257 
258 static inline int TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
259 {
260         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
261                 return 1;
262         return 0;
263 }
264 
265 /* Buffer size and advertised window tuning.
266  *
267  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
268  */
269 
270 static void tcp_fixup_sndbuf(struct sock *sk)
271 {
272         int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
273 
274         sndmem *= TCP_INIT_CWND;
275         if (sk->sk_sndbuf < sndmem)
276                 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
277 }
278 
279 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
280  *
281  * All tcp_full_space() is split to two parts: "network" buffer, allocated
282  * forward and advertised in receiver window (tp->rcv_wnd) and
283  * "application buffer", required to isolate scheduling/application
284  * latencies from network.
285  * window_clamp is maximal advertised window. It can be less than
286  * tcp_full_space(), in this case tcp_full_space() - window_clamp
287  * is reserved for "application" buffer. The less window_clamp is
288  * the smoother our behaviour from viewpoint of network, but the lower
289  * throughput and the higher sensitivity of the connection to losses. 8)
290  *
291  * rcv_ssthresh is more strict window_clamp used at "slow start"
292  * phase to predict further behaviour of this connection.
293  * It is used for two goals:
294  * - to enforce header prediction at sender, even when application
295  *   requires some significant "application buffer". It is check #1.
296  * - to prevent pruning of receive queue because of misprediction
297  *   of receiver window. Check #2.
298  *
299  * The scheme does not work when sender sends good segments opening
300  * window and then starts to feed us spaghetti. But it should work
301  * in common situations. Otherwise, we have to rely on queue collapsing.
302  */
303 
304 /* Slow part of check#2. */
305 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
306 {
307         struct tcp_sock *tp = tcp_sk(sk);
308         /* Optimize this! */
309         int truesize = tcp_win_from_space(skb->truesize) >> 1;
310         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
311 
312         while (tp->rcv_ssthresh <= window) {
313                 if (truesize <= skb->len)
314                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
315 
316                 truesize >>= 1;
317                 window >>= 1;
318         }
319         return 0;
320 }
321 
322 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
323 {
324         struct tcp_sock *tp = tcp_sk(sk);
325 
326         /* Check #1 */
327         if (tp->rcv_ssthresh < tp->window_clamp &&
328             (int)tp->rcv_ssthresh < tcp_space(sk) &&
329             !tcp_memory_pressure) {
330                 int incr;
331 
332                 /* Check #2. Increase window, if skb with such overhead
333                  * will fit to rcvbuf in future.
334                  */
335                 if (tcp_win_from_space(skb->truesize) <= skb->len)
336                         incr = 2 * tp->advmss;
337                 else
338                         incr = __tcp_grow_window(sk, skb);
339 
340                 if (incr) {
341                         incr = max_t(int, incr, 2 * skb->len);
342                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
343                                                tp->window_clamp);
344                         inet_csk(sk)->icsk_ack.quick |= 1;
345                 }
346         }
347 }
348 
349 /* 3. Tuning rcvbuf, when connection enters established state. */
350 
351 static void tcp_fixup_rcvbuf(struct sock *sk)
352 {
353         u32 mss = tcp_sk(sk)->advmss;
354         u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
355         int rcvmem;
356 
357         /* Limit to 10 segments if mss <= 1460,
358          * or 14600/mss segments, with a minimum of two segments.
359          */
360         if (mss > 1460)
361                 icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
362 
363         rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
364         while (tcp_win_from_space(rcvmem) < mss)
365                 rcvmem += 128;
366 
367         rcvmem *= icwnd;
368 
369         if (sk->sk_rcvbuf < rcvmem)
370                 sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
371 }
372 
373 /* 4. Try to fixup all. It is made immediately after connection enters
374  *    established state.
375  */
376 static void tcp_init_buffer_space(struct sock *sk)
377 {
378         struct tcp_sock *tp = tcp_sk(sk);
379         int maxwin;
380 
381         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
382                 tcp_fixup_rcvbuf(sk);
383         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
384                 tcp_fixup_sndbuf(sk);
385 
386         tp->rcvq_space.space = tp->rcv_wnd;
387 
388         maxwin = tcp_full_space(sk);
389 
390         if (tp->window_clamp >= maxwin) {
391                 tp->window_clamp = maxwin;
392 
393                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
394                         tp->window_clamp = max(maxwin -
395                                                (maxwin >> sysctl_tcp_app_win),
396                                                4 * tp->advmss);
397         }
398 
399         /* Force reservation of one segment. */
400         if (sysctl_tcp_app_win &&
401             tp->window_clamp > 2 * tp->advmss &&
402             tp->window_clamp + tp->advmss > maxwin)
403                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
404 
405         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
406         tp->snd_cwnd_stamp = tcp_time_stamp;
407 }
408 
409 /* 5. Recalculate window clamp after socket hit its memory bounds. */
410 static void tcp_clamp_window(struct sock *sk)
411 {
412         struct tcp_sock *tp = tcp_sk(sk);
413         struct inet_connection_sock *icsk = inet_csk(sk);
414 
415         icsk->icsk_ack.quick = 0;
416 
417         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
418             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
419             !tcp_memory_pressure &&
420             atomic_long_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
421                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
422                                     sysctl_tcp_rmem[2]);
423         }
424         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
425                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
426 }
427 
428 /* Initialize RCV_MSS value.
429  * RCV_MSS is an our guess about MSS used by the peer.
430  * We haven't any direct information about the MSS.
431  * It's better to underestimate the RCV_MSS rather than overestimate.
432  * Overestimations make us ACKing less frequently than needed.
433  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
434  */
435 void tcp_initialize_rcv_mss(struct sock *sk)
436 {
437         const struct tcp_sock *tp = tcp_sk(sk);
438         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
439 
440         hint = min(hint, tp->rcv_wnd / 2);
441         hint = min(hint, TCP_MSS_DEFAULT);
442         hint = max(hint, TCP_MIN_MSS);
443 
444         inet_csk(sk)->icsk_ack.rcv_mss = hint;
445 }
446 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
447 
448 /* Receiver "autotuning" code.
449  *
450  * The algorithm for RTT estimation w/o timestamps is based on
451  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
452  * <http://public.lanl.gov/radiant/pubs.html#DRS>
453  *
454  * More detail on this code can be found at
455  * <http://staff.psc.edu/jheffner/>,
456  * though this reference is out of date.  A new paper
457  * is pending.
458  */
459 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
460 {
461         u32 new_sample = tp->rcv_rtt_est.rtt;
462         long m = sample;
463 
464         if (m == 0)
465                 m = 1;
466 
467         if (new_sample != 0) {
468                 /* If we sample in larger samples in the non-timestamp
469                  * case, we could grossly overestimate the RTT especially
470                  * with chatty applications or bulk transfer apps which
471                  * are stalled on filesystem I/O.
472                  *
473                  * Also, since we are only going for a minimum in the
474                  * non-timestamp case, we do not smooth things out
475                  * else with timestamps disabled convergence takes too
476                  * long.
477                  */
478                 if (!win_dep) {
479                         m -= (new_sample >> 3);
480                         new_sample += m;
481                 } else {
482                         m <<= 3;
483                         if (m < new_sample)
484                                 new_sample = m;
485                 }
486         } else {
487                 /* No previous measure. */
488                 new_sample = m << 3;
489         }
490 
491         if (tp->rcv_rtt_est.rtt != new_sample)
492                 tp->rcv_rtt_est.rtt = new_sample;
493 }
494 
495 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
496 {
497         if (tp->rcv_rtt_est.time == 0)
498                 goto new_measure;
499         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
500                 return;
501         tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
502 
503 new_measure:
504         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
505         tp->rcv_rtt_est.time = tcp_time_stamp;
506 }
507 
508 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
509                                           const struct sk_buff *skb)
510 {
511         struct tcp_sock *tp = tcp_sk(sk);
512         if (tp->rx_opt.rcv_tsecr &&
513             (TCP_SKB_CB(skb)->end_seq -
514              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
515                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
516 }
517 
518 /*
519  * This function should be called every time data is copied to user space.
520  * It calculates the appropriate TCP receive buffer space.
521  */
522 void tcp_rcv_space_adjust(struct sock *sk)
523 {
524         struct tcp_sock *tp = tcp_sk(sk);
525         int time;
526         int space;
527 
528         if (tp->rcvq_space.time == 0)
529                 goto new_measure;
530 
531         time = tcp_time_stamp - tp->rcvq_space.time;
532         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
533                 return;
534 
535         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
536 
537         space = max(tp->rcvq_space.space, space);
538 
539         if (tp->rcvq_space.space != space) {
540                 int rcvmem;
541 
542                 tp->rcvq_space.space = space;
543 
544                 if (sysctl_tcp_moderate_rcvbuf &&
545                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
546                         int new_clamp = space;
547 
548                         /* Receive space grows, normalize in order to
549                          * take into account packet headers and sk_buff
550                          * structure overhead.
551                          */
552                         space /= tp->advmss;
553                         if (!space)
554                                 space = 1;
555                         rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
556                         while (tcp_win_from_space(rcvmem) < tp->advmss)
557                                 rcvmem += 128;
558                         space *= rcvmem;
559                         space = min(space, sysctl_tcp_rmem[2]);
560                         if (space > sk->sk_rcvbuf) {
561                                 sk->sk_rcvbuf = space;
562 
563                                 /* Make the window clamp follow along.  */
564                                 tp->window_clamp = new_clamp;
565                         }
566                 }
567         }
568 
569 new_measure:
570         tp->rcvq_space.seq = tp->copied_seq;
571         tp->rcvq_space.time = tcp_time_stamp;
572 }
573 
574 /* There is something which you must keep in mind when you analyze the
575  * behavior of the tp->ato delayed ack timeout interval.  When a
576  * connection starts up, we want to ack as quickly as possible.  The
577  * problem is that "good" TCP's do slow start at the beginning of data
578  * transmission.  The means that until we send the first few ACK's the
579  * sender will sit on his end and only queue most of his data, because
580  * he can only send snd_cwnd unacked packets at any given time.  For
581  * each ACK we send, he increments snd_cwnd and transmits more of his
582  * queue.  -DaveM
583  */
584 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
585 {
586         struct tcp_sock *tp = tcp_sk(sk);
587         struct inet_connection_sock *icsk = inet_csk(sk);
588         u32 now;
589 
590         inet_csk_schedule_ack(sk);
591 
592         tcp_measure_rcv_mss(sk, skb);
593 
594         tcp_rcv_rtt_measure(tp);
595 
596         now = tcp_time_stamp;
597 
598         if (!icsk->icsk_ack.ato) {
599                 /* The _first_ data packet received, initialize
600                  * delayed ACK engine.
601                  */
602                 tcp_incr_quickack(sk);
603                 icsk->icsk_ack.ato = TCP_ATO_MIN;
604         } else {
605                 int m = now - icsk->icsk_ack.lrcvtime;
606 
607                 if (m <= TCP_ATO_MIN / 2) {
608                         /* The fastest case is the first. */
609                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
610                 } else if (m < icsk->icsk_ack.ato) {
611                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
612                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
613                                 icsk->icsk_ack.ato = icsk->icsk_rto;
614                 } else if (m > icsk->icsk_rto) {
615                         /* Too long gap. Apparently sender failed to
616                          * restart window, so that we send ACKs quickly.
617                          */
618                         tcp_incr_quickack(sk);
619                         sk_mem_reclaim(sk);
620                 }
621         }
622         icsk->icsk_ack.lrcvtime = now;
623 
624         TCP_ECN_check_ce(tp, skb);
625 
626         if (skb->len >= 128)
627                 tcp_grow_window(sk, skb);
628 }
629 
630 /* Called to compute a smoothed rtt estimate. The data fed to this
631  * routine either comes from timestamps, or from segments that were
632  * known _not_ to have been retransmitted [see Karn/Partridge
633  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
634  * piece by Van Jacobson.
635  * NOTE: the next three routines used to be one big routine.
636  * To save cycles in the RFC 1323 implementation it was better to break
637  * it up into three procedures. -- erics
638  */
639 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
640 {
641         struct tcp_sock *tp = tcp_sk(sk);
642         long m = mrtt; /* RTT */
643 
644         /*      The following amusing code comes from Jacobson's
645          *      article in SIGCOMM '88.  Note that rtt and mdev
646          *      are scaled versions of rtt and mean deviation.
647          *      This is designed to be as fast as possible
648          *      m stands for "measurement".
649          *
650          *      On a 1990 paper the rto value is changed to:
651          *      RTO = rtt + 4 * mdev
652          *
653          * Funny. This algorithm seems to be very broken.
654          * These formulae increase RTO, when it should be decreased, increase
655          * too slowly, when it should be increased quickly, decrease too quickly
656          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
657          * does not matter how to _calculate_ it. Seems, it was trap
658          * that VJ failed to avoid. 8)
659          */
660         if (m == 0)
661                 m = 1;
662         if (tp->srtt != 0) {
663                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
664                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
665                 if (m < 0) {
666                         m = -m;         /* m is now abs(error) */
667                         m -= (tp->mdev >> 2);   /* similar update on mdev */
668                         /* This is similar to one of Eifel findings.
669                          * Eifel blocks mdev updates when rtt decreases.
670                          * This solution is a bit different: we use finer gain
671                          * for mdev in this case (alpha*beta).
672                          * Like Eifel it also prevents growth of rto,
673                          * but also it limits too fast rto decreases,
674                          * happening in pure Eifel.
675                          */
676                         if (m > 0)
677                                 m >>= 3;
678                 } else {
679                         m -= (tp->mdev >> 2);   /* similar update on mdev */
680                 }
681                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
682                 if (tp->mdev > tp->mdev_max) {
683                         tp->mdev_max = tp->mdev;
684                         if (tp->mdev_max > tp->rttvar)
685                                 tp->rttvar = tp->mdev_max;
686                 }
687                 if (after(tp->snd_una, tp->rtt_seq)) {
688                         if (tp->mdev_max < tp->rttvar)
689                                 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
690                         tp->rtt_seq = tp->snd_nxt;
691                         tp->mdev_max = tcp_rto_min(sk);
692                 }
693         } else {
694                 /* no previous measure. */
695                 tp->srtt = m << 3;      /* take the measured time to be rtt */
696                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
697                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
698                 tp->rtt_seq = tp->snd_nxt;
699         }
700 }
701 
702 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
703  * routine referred to above.
704  */
705 static inline void tcp_set_rto(struct sock *sk)
706 {
707         const struct tcp_sock *tp = tcp_sk(sk);
708         /* Old crap is replaced with new one. 8)
709          *
710          * More seriously:
711          * 1. If rtt variance happened to be less 50msec, it is hallucination.
712          *    It cannot be less due to utterly erratic ACK generation made
713          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
714          *    to do with delayed acks, because at cwnd>2 true delack timeout
715          *    is invisible. Actually, Linux-2.4 also generates erratic
716          *    ACKs in some circumstances.
717          */
718         inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
719 
720         /* 2. Fixups made earlier cannot be right.
721          *    If we do not estimate RTO correctly without them,
722          *    all the algo is pure shit and should be replaced
723          *    with correct one. It is exactly, which we pretend to do.
724          */
725 
726         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
727          * guarantees that rto is higher.
728          */
729         tcp_bound_rto(sk);
730 }
731 
732 /* Save metrics learned by this TCP session.
733    This function is called only, when TCP finishes successfully
734    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
735  */
736 void tcp_update_metrics(struct sock *sk)
737 {
738         struct tcp_sock *tp = tcp_sk(sk);
739         struct dst_entry *dst = __sk_dst_get(sk);
740 
741         if (sysctl_tcp_nometrics_save)
742                 return;
743 
744         dst_confirm(dst);
745 
746         if (dst && (dst->flags & DST_HOST)) {
747                 const struct inet_connection_sock *icsk = inet_csk(sk);
748                 int m;
749                 unsigned long rtt;
750 
751                 if (icsk->icsk_backoff || !tp->srtt) {
752                         /* This session failed to estimate rtt. Why?
753                          * Probably, no packets returned in time.
754                          * Reset our results.
755                          */
756                         if (!(dst_metric_locked(dst, RTAX_RTT)))
757                                 dst_metric_set(dst, RTAX_RTT, 0);
758                         return;
759                 }
760 
761                 rtt = dst_metric_rtt(dst, RTAX_RTT);
762                 m = rtt - tp->srtt;
763 
764                 /* If newly calculated rtt larger than stored one,
765                  * store new one. Otherwise, use EWMA. Remember,
766                  * rtt overestimation is always better than underestimation.
767                  */
768                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
769                         if (m <= 0)
770                                 set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
771                         else
772                                 set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
773                 }
774 
775                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
776                         unsigned long var;
777                         if (m < 0)
778                                 m = -m;
779 
780                         /* Scale deviation to rttvar fixed point */
781                         m >>= 1;
782                         if (m < tp->mdev)
783                                 m = tp->mdev;
784 
785                         var = dst_metric_rtt(dst, RTAX_RTTVAR);
786                         if (m >= var)
787                                 var = m;
788                         else
789                                 var -= (var - m) >> 2;
790 
791                         set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
792                 }
793 
794                 if (tcp_in_initial_slowstart(tp)) {
795                         /* Slow start still did not finish. */
796                         if (dst_metric(dst, RTAX_SSTHRESH) &&
797                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
798                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
799                                 dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
800                         if (!dst_metric_locked(dst, RTAX_CWND) &&
801                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
802                                 dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
803                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
804                            icsk->icsk_ca_state == TCP_CA_Open) {
805                         /* Cong. avoidance phase, cwnd is reliable. */
806                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
807                                 dst_metric_set(dst, RTAX_SSTHRESH,
808                                                max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
809                         if (!dst_metric_locked(dst, RTAX_CWND))
810                                 dst_metric_set(dst, RTAX_CWND,
811                                                (dst_metric(dst, RTAX_CWND) +
812                                                 tp->snd_cwnd) >> 1);
813                 } else {
814                         /* Else slow start did not finish, cwnd is non-sense,
815                            ssthresh may be also invalid.
816                          */
817                         if (!dst_metric_locked(dst, RTAX_CWND))
818                                 dst_metric_set(dst, RTAX_CWND,
819                                                (dst_metric(dst, RTAX_CWND) +
820                                                 tp->snd_ssthresh) >> 1);
821                         if (dst_metric(dst, RTAX_SSTHRESH) &&
822                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
823                             tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
824                                 dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
825                 }
826 
827                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
828                         if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
829                             tp->reordering != sysctl_tcp_reordering)
830                                 dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
831                 }
832         }
833 }
834 
835 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
836 {
837         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
838 
839         if (!cwnd)
840                 cwnd = TCP_INIT_CWND;
841         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
842 }
843 
844 /* Set slow start threshold and cwnd not falling to slow start */
845 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
846 {
847         struct tcp_sock *tp = tcp_sk(sk);
848         const struct inet_connection_sock *icsk = inet_csk(sk);
849 
850         tp->prior_ssthresh = 0;
851         tp->bytes_acked = 0;
852         if (icsk->icsk_ca_state < TCP_CA_CWR) {
853                 tp->undo_marker = 0;
854                 if (set_ssthresh)
855                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
856                 tp->snd_cwnd = min(tp->snd_cwnd,
857                                    tcp_packets_in_flight(tp) + 1U);
858                 tp->snd_cwnd_cnt = 0;
859                 tp->high_seq = tp->snd_nxt;
860                 tp->snd_cwnd_stamp = tcp_time_stamp;
861                 TCP_ECN_queue_cwr(tp);
862 
863                 tcp_set_ca_state(sk, TCP_CA_CWR);
864         }
865 }
866 
867 /*
868  * Packet counting of FACK is based on in-order assumptions, therefore TCP
869  * disables it when reordering is detected
870  */
871 static void tcp_disable_fack(struct tcp_sock *tp)
872 {
873         /* RFC3517 uses different metric in lost marker => reset on change */
874         if (tcp_is_fack(tp))
875                 tp->lost_skb_hint = NULL;
876         tp->rx_opt.sack_ok &= ~2;
877 }
878 
879 /* Take a notice that peer is sending D-SACKs */
880 static void tcp_dsack_seen(struct tcp_sock *tp)
881 {
882         tp->rx_opt.sack_ok |= 4;
883 }
884 
885 /* Initialize metrics on socket. */
886 
887 static void tcp_init_metrics(struct sock *sk)
888 {
889         struct tcp_sock *tp = tcp_sk(sk);
890         struct dst_entry *dst = __sk_dst_get(sk);
891 
892         if (dst == NULL)
893                 goto reset;
894 
895         dst_confirm(dst);
896 
897         if (dst_metric_locked(dst, RTAX_CWND))
898                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
899         if (dst_metric(dst, RTAX_SSTHRESH)) {
900                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
901                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
902                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
903         } else {
904                 /* ssthresh may have been reduced unnecessarily during.
905                  * 3WHS. Restore it back to its initial default.
906                  */
907                 tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
908         }
909         if (dst_metric(dst, RTAX_REORDERING) &&
910             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
911                 tcp_disable_fack(tp);
912                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
913         }
914 
915         if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
916                 goto reset;
917 
918         /* Initial rtt is determined from SYN,SYN-ACK.
919          * The segment is small and rtt may appear much
920          * less than real one. Use per-dst memory
921          * to make it more realistic.
922          *
923          * A bit of theory. RTT is time passed after "normal" sized packet
924          * is sent until it is ACKed. In normal circumstances sending small
925          * packets force peer to delay ACKs and calculation is correct too.
926          * The algorithm is adaptive and, provided we follow specs, it
927          * NEVER underestimate RTT. BUT! If peer tries to make some clever
928          * tricks sort of "quick acks" for time long enough to decrease RTT
929          * to low value, and then abruptly stops to do it and starts to delay
930          * ACKs, wait for troubles.
931          */
932         if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
933                 tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
934                 tp->rtt_seq = tp->snd_nxt;
935         }
936         if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
937                 tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
938                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
939         }
940         tcp_set_rto(sk);
941 reset:
942         if (tp->srtt == 0) {
943                 /* RFC2988bis: We've failed to get a valid RTT sample from
944                  * 3WHS. This is most likely due to retransmission,
945                  * including spurious one. Reset the RTO back to 3secs
946                  * from the more aggressive 1sec to avoid more spurious
947                  * retransmission.
948                  */
949                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
950                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
951         }
952         /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
953          * retransmitted. In light of RFC2988bis' more aggressive 1sec
954          * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
955          * retransmission has occurred.
956          */
957         if (tp->total_retrans > 1)
958                 tp->snd_cwnd = 1;
959         else
960                 tp->snd_cwnd = tcp_init_cwnd(tp, dst);
961         tp->snd_cwnd_stamp = tcp_time_stamp;
962 }
963 
964 static void tcp_update_reordering(struct sock *sk, const int metric,
965                                   const int ts)
966 {
967         struct tcp_sock *tp = tcp_sk(sk);
968         if (metric > tp->reordering) {
969                 int mib_idx;
970 
971                 tp->reordering = min(TCP_MAX_REORDERING, metric);
972 
973                 /* This exciting event is worth to be remembered. 8) */
974                 if (ts)
975                         mib_idx = LINUX_MIB_TCPTSREORDER;
976                 else if (tcp_is_reno(tp))
977                         mib_idx = LINUX_MIB_TCPRENOREORDER;
978                 else if (tcp_is_fack(tp))
979                         mib_idx = LINUX_MIB_TCPFACKREORDER;
980                 else
981                         mib_idx = LINUX_MIB_TCPSACKREORDER;
982 
983                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
984 #if FASTRETRANS_DEBUG > 1
985                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
986                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
987                        tp->reordering,
988                        tp->fackets_out,
989                        tp->sacked_out,
990                        tp->undo_marker ? tp->undo_retrans : 0);
991 #endif
992                 tcp_disable_fack(tp);
993         }
994 }
995 
996 /* This must be called before lost_out is incremented */
997 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
998 {
999         if ((tp->retransmit_skb_hint == NULL) ||
1000             before(TCP_SKB_CB(skb)->seq,
1001                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
1002                 tp->retransmit_skb_hint = skb;
1003 
1004         if (!tp->lost_out ||
1005             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
1006                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1007 }
1008 
1009 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
1010 {
1011         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1012                 tcp_verify_retransmit_hint(tp, skb);
1013 
1014                 tp->lost_out += tcp_skb_pcount(skb);
1015                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1016         }
1017 }
1018 
1019 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
1020                                             struct sk_buff *skb)
1021 {
1022         tcp_verify_retransmit_hint(tp, skb);
1023 
1024         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1025                 tp->lost_out += tcp_skb_pcount(skb);
1026                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1027         }
1028 }
1029 
1030 /* This procedure tags the retransmission queue when SACKs arrive.
1031  *
1032  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1033  * Packets in queue with these bits set are counted in variables
1034  * sacked_out, retrans_out and lost_out, correspondingly.
1035  *
1036  * Valid combinations are:
1037  * Tag  InFlight        Description
1038  * 0    1               - orig segment is in flight.
1039  * S    0               - nothing flies, orig reached receiver.
1040  * L    0               - nothing flies, orig lost by net.
1041  * R    2               - both orig and retransmit are in flight.
1042  * L|R  1               - orig is lost, retransmit is in flight.
1043  * S|R  1               - orig reached receiver, retrans is still in flight.
1044  * (L|S|R is logically valid, it could occur when L|R is sacked,
1045  *  but it is equivalent to plain S and code short-curcuits it to S.
1046  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1047  *
1048  * These 6 states form finite state machine, controlled by the following events:
1049  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1050  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1051  * 3. Loss detection event of one of three flavors:
1052  *      A. Scoreboard estimator decided the packet is lost.
1053  *         A'. Reno "three dupacks" marks head of queue lost.
1054  *         A''. Its FACK modfication, head until snd.fack is lost.
1055  *      B. SACK arrives sacking data transmitted after never retransmitted
1056  *         hole was sent out.
1057  *      C. SACK arrives sacking SND.NXT at the moment, when the
1058  *         segment was retransmitted.
1059  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1060  *
1061  * It is pleasant to note, that state diagram turns out to be commutative,
1062  * so that we are allowed not to be bothered by order of our actions,
1063  * when multiple events arrive simultaneously. (see the function below).
1064  *
1065  * Reordering detection.
1066  * --------------------
1067  * Reordering metric is maximal distance, which a packet can be displaced
1068  * in packet stream. With SACKs we can estimate it:
1069  *
1070  * 1. SACK fills old hole and the corresponding segment was not
1071  *    ever retransmitted -> reordering. Alas, we cannot use it
1072  *    when segment was retransmitted.
1073  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1074  *    for retransmitted and already SACKed segment -> reordering..
1075  * Both of these heuristics are not used in Loss state, when we cannot
1076  * account for retransmits accurately.
1077  *
1078  * SACK block validation.
1079  * ----------------------
1080  *
1081  * SACK block range validation checks that the received SACK block fits to
1082  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1083  * Note that SND.UNA is not included to the range though being valid because
1084  * it means that the receiver is rather inconsistent with itself reporting
1085  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1086  * perfectly valid, however, in light of RFC2018 which explicitly states
1087  * that "SACK block MUST reflect the newest segment.  Even if the newest
1088  * segment is going to be discarded ...", not that it looks very clever
1089  * in case of head skb. Due to potentional receiver driven attacks, we
1090  * choose to avoid immediate execution of a walk in write queue due to
1091  * reneging and defer head skb's loss recovery to standard loss recovery
1092  * procedure that will eventually trigger (nothing forbids us doing this).
1093  *
1094  * Implements also blockage to start_seq wrap-around. Problem lies in the
1095  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1096  * there's no guarantee that it will be before snd_nxt (n). The problem
1097  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1098  * wrap (s_w):
1099  *
1100  *         <- outs wnd ->                          <- wrapzone ->
1101  *         u     e      n                         u_w   e_w  s n_w
1102  *         |     |      |                          |     |   |  |
1103  * |<------------+------+----- TCP seqno space --------------+---------->|
1104  * ...-- <2^31 ->|                                           |<--------...
1105  * ...---- >2^31 ------>|                                    |<--------...
1106  *
1107  * Current code wouldn't be vulnerable but it's better still to discard such
1108  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1109  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1110  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1111  * equal to the ideal case (infinite seqno space without wrap caused issues).
1112  *
1113  * With D-SACK the lower bound is extended to cover sequence space below
1114  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1115  * again, D-SACK block must not to go across snd_una (for the same reason as
1116  * for the normal SACK blocks, explained above). But there all simplicity
1117  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1118  * fully below undo_marker they do not affect behavior in anyway and can
1119  * therefore be safely ignored. In rare cases (which are more or less
1120  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1121  * fragmentation and packet reordering past skb's retransmission. To consider
1122  * them correctly, the acceptable range must be extended even more though
1123  * the exact amount is rather hard to quantify. However, tp->max_window can
1124  * be used as an exaggerated estimate.
1125  */
1126 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1127                                   u32 start_seq, u32 end_seq)
1128 {
1129         /* Too far in future, or reversed (interpretation is ambiguous) */
1130         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1131                 return 0;
1132 
1133         /* Nasty start_seq wrap-around check (see comments above) */
1134         if (!before(start_seq, tp->snd_nxt))
1135                 return 0;
1136 
1137         /* In outstanding window? ...This is valid exit for D-SACKs too.
1138          * start_seq == snd_una is non-sensical (see comments above)
1139          */
1140         if (after(start_seq, tp->snd_una))
1141                 return 1;
1142 
1143         if (!is_dsack || !tp->undo_marker)
1144                 return 0;
1145 
1146         /* ...Then it's D-SACK, and must reside below snd_una completely */
1147         if (after(end_seq, tp->snd_una))
1148                 return 0;
1149 
1150         if (!before(start_seq, tp->undo_marker))
1151                 return 1;
1152 
1153         /* Too old */
1154         if (!after(end_seq, tp->undo_marker))
1155                 return 0;
1156 
1157         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1158          *   start_seq < undo_marker and end_seq >= undo_marker.
1159          */
1160         return !before(start_seq, end_seq - tp->max_window);
1161 }
1162 
1163 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1164  * Event "C". Later note: FACK people cheated me again 8), we have to account
1165  * for reordering! Ugly, but should help.
1166  *
1167  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1168  * less than what is now known to be received by the other end (derived from
1169  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1170  * retransmitted skbs to avoid some costly processing per ACKs.
1171  */
1172 static void tcp_mark_lost_retrans(struct sock *sk)
1173 {
1174         const struct inet_connection_sock *icsk = inet_csk(sk);
1175         struct tcp_sock *tp = tcp_sk(sk);
1176         struct sk_buff *skb;
1177         int cnt = 0;
1178         u32 new_low_seq = tp->snd_nxt;
1179         u32 received_upto = tcp_highest_sack_seq(tp);
1180 
1181         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1182             !after(received_upto, tp->lost_retrans_low) ||
1183             icsk->icsk_ca_state != TCP_CA_Recovery)
1184                 return;
1185 
1186         tcp_for_write_queue(skb, sk) {
1187                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1188 
1189                 if (skb == tcp_send_head(sk))
1190                         break;
1191                 if (cnt == tp->retrans_out)
1192                         break;
1193                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1194                         continue;
1195 
1196                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1197                         continue;
1198 
1199                 /* TODO: We would like to get rid of tcp_is_fack(tp) only
1200                  * constraint here (see above) but figuring out that at
1201                  * least tp->reordering SACK blocks reside between ack_seq
1202                  * and received_upto is not easy task to do cheaply with
1203                  * the available datastructures.
1204                  *
1205                  * Whether FACK should check here for tp->reordering segs
1206                  * in-between one could argue for either way (it would be
1207                  * rather simple to implement as we could count fack_count
1208                  * during the walk and do tp->fackets_out - fack_count).
1209                  */
1210                 if (after(received_upto, ack_seq)) {
1211                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1212                         tp->retrans_out -= tcp_skb_pcount(skb);
1213 
1214                         tcp_skb_mark_lost_uncond_verify(tp, skb);
1215                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1216                 } else {
1217                         if (before(ack_seq, new_low_seq))
1218                                 new_low_seq = ack_seq;
1219                         cnt += tcp_skb_pcount(skb);
1220                 }
1221         }
1222 
1223         if (tp->retrans_out)
1224                 tp->lost_retrans_low = new_low_seq;
1225 }
1226 
1227 static int tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1228                            struct tcp_sack_block_wire *sp, int num_sacks,
1229                            u32 prior_snd_una)
1230 {
1231         struct tcp_sock *tp = tcp_sk(sk);
1232         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1233         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1234         int dup_sack = 0;
1235 
1236         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1237                 dup_sack = 1;
1238                 tcp_dsack_seen(tp);
1239                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1240         } else if (num_sacks > 1) {
1241                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1242                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1243 
1244                 if (!after(end_seq_0, end_seq_1) &&
1245                     !before(start_seq_0, start_seq_1)) {
1246                         dup_sack = 1;
1247                         tcp_dsack_seen(tp);
1248                         NET_INC_STATS_BH(sock_net(sk),
1249                                         LINUX_MIB_TCPDSACKOFORECV);
1250                 }
1251         }
1252 
1253         /* D-SACK for already forgotten data... Do dumb counting. */
1254         if (dup_sack && tp->undo_marker && tp->undo_retrans &&
1255             !after(end_seq_0, prior_snd_una) &&
1256             after(end_seq_0, tp->undo_marker))
1257                 tp->undo_retrans--;
1258 
1259         return dup_sack;
1260 }
1261 
1262 struct tcp_sacktag_state {
1263         int reord;
1264         int fack_count;
1265         int flag;
1266 };
1267 
1268 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1269  * the incoming SACK may not exactly match but we can find smaller MSS
1270  * aligned portion of it that matches. Therefore we might need to fragment
1271  * which may fail and creates some hassle (caller must handle error case
1272  * returns).
1273  *
1274  * FIXME: this could be merged to shift decision code
1275  */
1276 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1277                                  u32 start_seq, u32 end_seq)
1278 {
1279         int in_sack, err;
1280         unsigned int pkt_len;
1281         unsigned int mss;
1282 
1283         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1284                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1285 
1286         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1287             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1288                 mss = tcp_skb_mss(skb);
1289                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1290 
1291                 if (!in_sack) {
1292                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1293                         if (pkt_len < mss)
1294                                 pkt_len = mss;
1295                 } else {
1296                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1297                         if (pkt_len < mss)
1298                                 return -EINVAL;
1299                 }
1300 
1301                 /* Round if necessary so that SACKs cover only full MSSes
1302                  * and/or the remaining small portion (if present)
1303                  */
1304                 if (pkt_len > mss) {
1305                         unsigned int new_len = (pkt_len / mss) * mss;
1306                         if (!in_sack && new_len < pkt_len)
1307                                 new_len += mss;
1308                         pkt_len = new_len;
1309                 }
1310 
1311                 if (pkt_len >= skb->len && !in_sack)
1312                         return 0;
1313 
1314                 err = tcp_fragment(sk, skb, pkt_len, mss);
1315                 if (err < 0)
1316                         return err;
1317         }
1318 
1319         return in_sack;
1320 }
1321 
1322 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1323 static u8 tcp_sacktag_one(struct sock *sk,
1324                           struct tcp_sacktag_state *state, u8 sacked,
1325                           u32 start_seq, u32 end_seq,
1326                           int dup_sack, int pcount)
1327 {
1328         struct tcp_sock *tp = tcp_sk(sk);
1329         int fack_count = state->fack_count;
1330 
1331         /* Account D-SACK for retransmitted packet. */
1332         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1333                 if (tp->undo_marker && tp->undo_retrans &&
1334                     after(end_seq, tp->undo_marker))
1335                         tp->undo_retrans--;
1336                 if (sacked & TCPCB_SACKED_ACKED)
1337                         state->reord = min(fack_count, state->reord);
1338         }
1339 
1340         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1341         if (!after(end_seq, tp->snd_una))
1342                 return sacked;
1343 
1344         if (!(sacked & TCPCB_SACKED_ACKED)) {
1345                 if (sacked & TCPCB_SACKED_RETRANS) {
1346                         /* If the segment is not tagged as lost,
1347                          * we do not clear RETRANS, believing
1348                          * that retransmission is still in flight.
1349                          */
1350                         if (sacked & TCPCB_LOST) {
1351                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1352                                 tp->lost_out -= pcount;
1353                                 tp->retrans_out -= pcount;
1354                         }
1355                 } else {
1356                         if (!(sacked & TCPCB_RETRANS)) {
1357                                 /* New sack for not retransmitted frame,
1358                                  * which was in hole. It is reordering.
1359                                  */
1360                                 if (before(start_seq,
1361                                            tcp_highest_sack_seq(tp)))
1362                                         state->reord = min(fack_count,
1363                                                            state->reord);
1364 
1365                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1366                                 if (!after(end_seq, tp->frto_highmark))
1367                                         state->flag |= FLAG_ONLY_ORIG_SACKED;
1368                         }
1369 
1370                         if (sacked & TCPCB_LOST) {
1371                                 sacked &= ~TCPCB_LOST;
1372                                 tp->lost_out -= pcount;
1373                         }
1374                 }
1375 
1376                 sacked |= TCPCB_SACKED_ACKED;
1377                 state->flag |= FLAG_DATA_SACKED;
1378                 tp->sacked_out += pcount;
1379 
1380                 fack_count += pcount;
1381 
1382                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1383                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1384                     before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1385                         tp->lost_cnt_hint += pcount;
1386 
1387                 if (fack_count > tp->fackets_out)
1388                         tp->fackets_out = fack_count;
1389         }
1390 
1391         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1392          * frames and clear it. undo_retrans is decreased above, L|R frames
1393          * are accounted above as well.
1394          */
1395         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1396                 sacked &= ~TCPCB_SACKED_RETRANS;
1397                 tp->retrans_out -= pcount;
1398         }
1399 
1400         return sacked;
1401 }
1402 
1403 /* Shift newly-SACKed bytes from this skb to the immediately previous
1404  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1405  */
1406 static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1407                            struct tcp_sacktag_state *state,
1408                            unsigned int pcount, int shifted, int mss,
1409                            int dup_sack)
1410 {
1411         struct tcp_sock *tp = tcp_sk(sk);
1412         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1413         u32 start_seq = TCP_SKB_CB(skb)->seq;   /* start of newly-SACKed */
1414         u32 end_seq = start_seq + shifted;      /* end of newly-SACKed */
1415 
1416         BUG_ON(!pcount);
1417 
1418         /* Adjust counters and hints for the newly sacked sequence
1419          * range but discard the return value since prev is already
1420          * marked. We must tag the range first because the seq
1421          * advancement below implicitly advances
1422          * tcp_highest_sack_seq() when skb is highest_sack.
1423          */
1424         tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1425                         start_seq, end_seq, dup_sack, pcount);
1426 
1427         if (skb == tp->lost_skb_hint)
1428                 tp->lost_cnt_hint += pcount;
1429 
1430         TCP_SKB_CB(prev)->end_seq += shifted;
1431         TCP_SKB_CB(skb)->seq += shifted;
1432 
1433         skb_shinfo(prev)->gso_segs += pcount;
1434         BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1435         skb_shinfo(skb)->gso_segs -= pcount;
1436 
1437         /* When we're adding to gso_segs == 1, gso_size will be zero,
1438          * in theory this shouldn't be necessary but as long as DSACK
1439          * code can come after this skb later on it's better to keep
1440          * setting gso_size to something.
1441          */
1442         if (!skb_shinfo(prev)->gso_size) {
1443                 skb_shinfo(prev)->gso_size = mss;
1444                 skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1445         }
1446 
1447         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1448         if (skb_shinfo(skb)->gso_segs <= 1) {
1449                 skb_shinfo(skb)->gso_size = 0;
1450                 skb_shinfo(skb)->gso_type = 0;
1451         }
1452 
1453         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1454         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1455 
1456         if (skb->len > 0) {
1457                 BUG_ON(!tcp_skb_pcount(skb));
1458                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1459                 return 0;
1460         }
1461 
1462         /* Whole SKB was eaten :-) */
1463 
1464         if (skb == tp->retransmit_skb_hint)
1465                 tp->retransmit_skb_hint = prev;
1466         if (skb == tp->scoreboard_skb_hint)
1467                 tp->scoreboard_skb_hint = prev;
1468         if (skb == tp->lost_skb_hint) {
1469                 tp->lost_skb_hint = prev;
1470                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1471         }
1472 
1473         TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1474         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1475                 TCP_SKB_CB(prev)->end_seq++;
1476 
1477         if (skb == tcp_highest_sack(sk))
1478                 tcp_advance_highest_sack(sk, skb);
1479 
1480         tcp_unlink_write_queue(skb, sk);
1481         sk_wmem_free_skb(sk, skb);
1482 
1483         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1484 
1485         return 1;
1486 }
1487 
1488 /* I wish gso_size would have a bit more sane initialization than
1489  * something-or-zero which complicates things
1490  */
1491 static int tcp_skb_seglen(const struct sk_buff *skb)
1492 {
1493         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1494 }
1495 
1496 /* Shifting pages past head area doesn't work */
1497 static int skb_can_shift(const struct sk_buff *skb)
1498 {
1499         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1500 }
1501 
1502 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1503  * skb.
1504  */
1505 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1506                                           struct tcp_sacktag_state *state,
1507                                           u32 start_seq, u32 end_seq,
1508                                           int dup_sack)
1509 {
1510         struct tcp_sock *tp = tcp_sk(sk);
1511         struct sk_buff *prev;
1512         int mss;
1513         int pcount = 0;
1514         int len;
1515         int in_sack;
1516 
1517         if (!sk_can_gso(sk))
1518                 goto fallback;
1519 
1520         /* Normally R but no L won't result in plain S */
1521         if (!dup_sack &&
1522             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1523                 goto fallback;
1524         if (!skb_can_shift(skb))
1525                 goto fallback;
1526         /* This frame is about to be dropped (was ACKed). */
1527         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1528                 goto fallback;
1529 
1530         /* Can only happen with delayed DSACK + discard craziness */
1531         if (unlikely(skb == tcp_write_queue_head(sk)))
1532                 goto fallback;
1533         prev = tcp_write_queue_prev(sk, skb);
1534 
1535         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1536                 goto fallback;
1537 
1538         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1539                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1540 
1541         if (in_sack) {
1542                 len = skb->len;
1543                 pcount = tcp_skb_pcount(skb);
1544                 mss = tcp_skb_seglen(skb);
1545 
1546                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1547                  * drop this restriction as unnecessary
1548                  */
1549                 if (mss != tcp_skb_seglen(prev))
1550                         goto fallback;
1551         } else {
1552                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1553                         goto noop;
1554                 /* CHECKME: This is non-MSS split case only?, this will
1555                  * cause skipped skbs due to advancing loop btw, original
1556                  * has that feature too
1557                  */
1558                 if (tcp_skb_pcount(skb) <= 1)
1559                         goto noop;
1560 
1561                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1562                 if (!in_sack) {
1563                         /* TODO: head merge to next could be attempted here
1564                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1565                          * though it might not be worth of the additional hassle
1566                          *
1567                          * ...we can probably just fallback to what was done
1568                          * previously. We could try merging non-SACKed ones
1569                          * as well but it probably isn't going to buy off
1570                          * because later SACKs might again split them, and
1571                          * it would make skb timestamp tracking considerably
1572                          * harder problem.
1573                          */
1574                         goto fallback;
1575                 }
1576 
1577                 len = end_seq - TCP_SKB_CB(skb)->seq;
1578                 BUG_ON(len < 0);
1579                 BUG_ON(len > skb->len);
1580 
1581                 /* MSS boundaries should be honoured or else pcount will
1582                  * severely break even though it makes things bit trickier.
1583                  * Optimize common case to avoid most of the divides
1584                  */
1585                 mss = tcp_skb_mss(skb);
1586 
1587                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1588                  * drop this restriction as unnecessary
1589                  */
1590                 if (mss != tcp_skb_seglen(prev))
1591                         goto fallback;
1592 
1593                 if (len == mss) {
1594                         pcount = 1;
1595                 } else if (len < mss) {
1596                         goto noop;
1597                 } else {
1598                         pcount = len / mss;
1599                         len = pcount * mss;
1600                 }
1601         }
1602 
1603         /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1604         if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1605                 goto fallback;
1606 
1607         if (!skb_shift(prev, skb, len))
1608                 goto fallback;
1609         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1610                 goto out;
1611 
1612         /* Hole filled allows collapsing with the next as well, this is very
1613          * useful when hole on every nth skb pattern happens
1614          */
1615         if (prev == tcp_write_queue_tail(sk))
1616                 goto out;
1617         skb = tcp_write_queue_next(sk, prev);
1618 
1619         if (!skb_can_shift(skb) ||
1620             (skb == tcp_send_head(sk)) ||
1621             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1622             (mss != tcp_skb_seglen(skb)))
1623                 goto out;
1624 
1625         len = skb->len;
1626         if (skb_shift(prev, skb, len)) {
1627                 pcount += tcp_skb_pcount(skb);
1628                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1629         }
1630 
1631 out:
1632         state->fack_count += pcount;
1633         return prev;
1634 
1635 noop:
1636         return skb;
1637 
1638 fallback:
1639         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1640         return NULL;
1641 }
1642 
1643 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1644                                         struct tcp_sack_block *next_dup,
1645                                         struct tcp_sacktag_state *state,
1646                                         u32 start_seq, u32 end_seq,
1647                                         int dup_sack_in)
1648 {
1649         struct tcp_sock *tp = tcp_sk(sk);
1650         struct sk_buff *tmp;
1651 
1652         tcp_for_write_queue_from(skb, sk) {
1653                 int in_sack = 0;
1654                 int dup_sack = dup_sack_in;
1655 
1656                 if (skb == tcp_send_head(sk))
1657                         break;
1658 
1659                 /* queue is in-order => we can short-circuit the walk early */
1660                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1661                         break;
1662 
1663                 if ((next_dup != NULL) &&
1664                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1665                         in_sack = tcp_match_skb_to_sack(sk, skb,
1666                                                         next_dup->start_seq,
1667                                                         next_dup->end_seq);
1668                         if (in_sack > 0)
1669                                 dup_sack = 1;
1670                 }
1671 
1672                 /* skb reference here is a bit tricky to get right, since
1673                  * shifting can eat and free both this skb and the next,
1674                  * so not even _safe variant of the loop is enough.
1675                  */
1676                 if (in_sack <= 0) {
1677                         tmp = tcp_shift_skb_data(sk, skb, state,
1678                                                  start_seq, end_seq, dup_sack);
1679                         if (tmp != NULL) {
1680                                 if (tmp != skb) {
1681                                         skb = tmp;
1682                                         continue;
1683                                 }
1684 
1685                                 in_sack = 0;
1686                         } else {
1687                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1688                                                                 start_seq,
1689                                                                 end_seq);
1690                         }
1691                 }
1692 
1693                 if (unlikely(in_sack < 0))
1694                         break;
1695 
1696                 if (in_sack) {
1697                         TCP_SKB_CB(skb)->sacked =
1698                                 tcp_sacktag_one(sk,
1699                                                 state,
1700                                                 TCP_SKB_CB(skb)->sacked,
1701                                                 TCP_SKB_CB(skb)->seq,
1702                                                 TCP_SKB_CB(skb)->end_seq,
1703                                                 dup_sack,
1704                                                 tcp_skb_pcount(skb));
1705 
1706                         if (!before(TCP_SKB_CB(skb)->seq,
1707                                     tcp_highest_sack_seq(tp)))
1708                                 tcp_advance_highest_sack(sk, skb);
1709                 }
1710 
1711                 state->fack_count += tcp_skb_pcount(skb);
1712         }
1713         return skb;
1714 }
1715 
1716 /* Avoid all extra work that is being done by sacktag while walking in
1717  * a normal way
1718  */
1719 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1720                                         struct tcp_sacktag_state *state,
1721                                         u32 skip_to_seq)
1722 {
1723         tcp_for_write_queue_from(skb, sk) {
1724                 if (skb == tcp_send_head(sk))
1725                         break;
1726 
1727                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1728                         break;
1729 
1730                 state->fack_count += tcp_skb_pcount(skb);
1731         }
1732         return skb;
1733 }
1734 
1735 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1736                                                 struct sock *sk,
1737                                                 struct tcp_sack_block *next_dup,
1738                                                 struct tcp_sacktag_state *state,
1739                                                 u32 skip_to_seq)
1740 {
1741         if (next_dup == NULL)
1742                 return skb;
1743 
1744         if (before(next_dup->start_seq, skip_to_seq)) {
1745                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1746                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1747                                        next_dup->start_seq, next_dup->end_seq,
1748                                        1);
1749         }
1750 
1751         return skb;
1752 }
1753 
1754 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1755 {
1756         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1757 }
1758 
1759 static int
1760 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1761                         u32 prior_snd_una)
1762 {
1763         const struct inet_connection_sock *icsk = inet_csk(sk);
1764         struct tcp_sock *tp = tcp_sk(sk);
1765         const unsigned char *ptr = (skb_transport_header(ack_skb) +
1766                                     TCP_SKB_CB(ack_skb)->sacked);
1767         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1768         struct tcp_sack_block sp[TCP_NUM_SACKS];
1769         struct tcp_sack_block *cache;
1770         struct tcp_sacktag_state state;
1771         struct sk_buff *skb;
1772         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1773         int used_sacks;
1774         int found_dup_sack = 0;
1775         int i, j;
1776         int first_sack_index;
1777 
1778         state.flag = 0;
1779         state.reord = tp->packets_out;
1780 
1781         if (!tp->sacked_out) {
1782                 if (WARN_ON(tp->fackets_out))
1783                         tp->fackets_out = 0;
1784                 tcp_highest_sack_reset(sk);
1785         }
1786 
1787         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1788                                          num_sacks, prior_snd_una);
1789         if (found_dup_sack)
1790                 state.flag |= FLAG_DSACKING_ACK;
1791 
1792         /* Eliminate too old ACKs, but take into
1793          * account more or less fresh ones, they can
1794          * contain valid SACK info.
1795          */
1796         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1797                 return 0;
1798 
1799         if (!tp->packets_out)
1800                 goto out;
1801 
1802         used_sacks = 0;
1803         first_sack_index = 0;
1804         for (i = 0; i < num_sacks; i++) {
1805                 int dup_sack = !i && found_dup_sack;
1806 
1807                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1808                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1809 
1810                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1811                                             sp[used_sacks].start_seq,
1812                                             sp[used_sacks].end_seq)) {
1813                         int mib_idx;
1814 
1815                         if (dup_sack) {
1816                                 if (!tp->undo_marker)
1817                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1818                                 else
1819                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1820                         } else {
1821                                 /* Don't count olds caused by ACK reordering */
1822                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1823                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1824                                         continue;
1825                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1826                         }
1827 
1828                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1829                         if (i == 0)
1830                                 first_sack_index = -1;
1831                         continue;
1832                 }
1833 
1834                 /* Ignore very old stuff early */
1835                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1836                         continue;
1837 
1838                 used_sacks++;
1839         }
1840 
1841         /* order SACK blocks to allow in order walk of the retrans queue */
1842         for (i = used_sacks - 1; i > 0; i--) {
1843                 for (j = 0; j < i; j++) {
1844                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1845                                 swap(sp[j], sp[j + 1]);
1846 
1847                                 /* Track where the first SACK block goes to */
1848                                 if (j == first_sack_index)
1849                                         first_sack_index = j + 1;
1850                         }
1851                 }
1852         }
1853 
1854         skb = tcp_write_queue_head(sk);
1855         state.fack_count = 0;
1856         i = 0;
1857 
1858         if (!tp->sacked_out) {
1859                 /* It's already past, so skip checking against it */
1860                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1861         } else {
1862                 cache = tp->recv_sack_cache;
1863                 /* Skip empty blocks in at head of the cache */
1864                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1865                        !cache->end_seq)
1866                         cache++;
1867         }
1868 
1869         while (i < used_sacks) {
1870                 u32 start_seq = sp[i].start_seq;
1871                 u32 end_seq = sp[i].end_seq;
1872                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1873                 struct tcp_sack_block *next_dup = NULL;
1874 
1875                 if (found_dup_sack && ((i + 1) == first_sack_index))
1876                         next_dup = &sp[i + 1];
1877 
1878                 /* Event "B" in the comment above. */
1879                 if (after(end_seq, tp->high_seq))
1880                         state.flag |= FLAG_DATA_LOST;
1881 
1882                 /* Skip too early cached blocks */
1883                 while (tcp_sack_cache_ok(tp, cache) &&
1884                        !before(start_seq, cache->end_seq))
1885                         cache++;
1886 
1887                 /* Can skip some work by looking recv_sack_cache? */
1888                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1889                     after(end_seq, cache->start_seq)) {
1890 
1891                         /* Head todo? */
1892                         if (before(start_seq, cache->start_seq)) {
1893                                 skb = tcp_sacktag_skip(skb, sk, &state,
1894                                                        start_seq);
1895                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1896                                                        &state,
1897                                                        start_seq,
1898                                                        cache->start_seq,
1899                                                        dup_sack);
1900                         }
1901 
1902                         /* Rest of the block already fully processed? */
1903                         if (!after(end_seq, cache->end_seq))
1904                                 goto advance_sp;
1905 
1906                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1907                                                        &state,
1908                                                        cache->end_seq);
1909 
1910                         /* ...tail remains todo... */
1911                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1912                                 /* ...but better entrypoint exists! */
1913                                 skb = tcp_highest_sack(sk);
1914                                 if (skb == NULL)
1915                                         break;
1916                                 state.fack_count = tp->fackets_out;
1917                                 cache++;
1918                                 goto walk;
1919                         }
1920 
1921                         skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1922                         /* Check overlap against next cached too (past this one already) */
1923                         cache++;
1924                         continue;
1925                 }
1926 
1927                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1928                         skb = tcp_highest_sack(sk);
1929                         if (skb == NULL)
1930                                 break;
1931                         state.fack_count = tp->fackets_out;
1932                 }
1933                 skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1934 
1935 walk:
1936                 skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1937                                        start_seq, end_seq, dup_sack);
1938 
1939 advance_sp:
1940                 /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1941                  * due to in-order walk
1942                  */
1943                 if (after(end_seq, tp->frto_highmark))
1944                         state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1945 
1946                 i++;
1947         }
1948 
1949         /* Clear the head of the cache sack blocks so we can skip it next time */
1950         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1951                 tp->recv_sack_cache[i].start_seq = 0;
1952                 tp->recv_sack_cache[i].end_seq = 0;
1953         }
1954         for (j = 0; j < used_sacks; j++)
1955                 tp->recv_sack_cache[i++] = sp[j];
1956 
1957         tcp_mark_lost_retrans(sk);
1958 
1959         tcp_verify_left_out(tp);
1960 
1961         if ((state.reord < tp->fackets_out) &&
1962             ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1963             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1964                 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1965 
1966 out:
1967 
1968 #if FASTRETRANS_DEBUG > 0
1969         WARN_ON((int)tp->sacked_out < 0);
1970         WARN_ON((int)tp->lost_out < 0);
1971         WARN_ON((int)tp->retrans_out < 0);
1972         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1973 #endif
1974         return state.flag;
1975 }
1976 
1977 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1978  * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1979  */
1980 static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1981 {
1982         u32 holes;
1983 
1984         holes = max(tp->lost_out, 1U);
1985         holes = min(holes, tp->packets_out);
1986 
1987         if ((tp->sacked_out + holes) > tp->packets_out) {
1988                 tp->sacked_out = tp->packets_out - holes;
1989                 return 1;
1990         }
1991         return 0;
1992 }
1993 
1994 /* If we receive more dupacks than we expected counting segments
1995  * in assumption of absent reordering, interpret this as reordering.
1996  * The only another reason could be bug in receiver TCP.
1997  */
1998 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1999 {
2000         struct tcp_sock *tp = tcp_sk(sk);
2001         if (tcp_limit_reno_sacked(tp))
2002                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
2003 }
2004 
2005 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2006 
2007 static void tcp_add_reno_sack(struct sock *sk)
2008 {
2009         struct tcp_sock *tp = tcp_sk(sk);
2010         tp->sacked_out++;
2011         tcp_check_reno_reordering(sk, 0);
2012         tcp_verify_left_out(tp);
2013 }
2014 
2015 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2016 
2017 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
2018 {
2019         struct tcp_sock *tp = tcp_sk(sk);
2020 
2021         if (acked > 0) {
2022                 /* One ACK acked hole. The rest eat duplicate ACKs. */
2023                 if (acked - 1 >= tp->sacked_out)
2024                         tp->sacked_out = 0;
2025                 else
2026                         tp->sacked_out -= acked - 1;
2027         }
2028         tcp_check_reno_reordering(sk, acked);
2029         tcp_verify_left_out(tp);
2030 }
2031 
2032 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2033 {
2034         tp->sacked_out = 0;
2035 }
2036 
2037 static int tcp_is_sackfrto(const struct tcp_sock *tp)
2038 {
2039         return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
2040 }
2041 
2042 /* F-RTO can only be used if TCP has never retransmitted anything other than
2043  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
2044  */
2045 int tcp_use_frto(struct sock *sk)
2046 {
2047         const struct tcp_sock *tp = tcp_sk(sk);
2048         const struct inet_connection_sock *icsk = inet_csk(sk);
2049         struct sk_buff *skb;
2050 
2051         if (!sysctl_tcp_frto)
2052                 return 0;
2053 
2054         /* MTU probe and F-RTO won't really play nicely along currently */
2055         if (icsk->icsk_mtup.probe_size)
2056                 return 0;
2057 
2058         if (tcp_is_sackfrto(tp))
2059                 return 1;
2060 
2061         /* Avoid expensive walking of rexmit queue if possible */
2062         if (tp->retrans_out > 1)
2063                 return 0;
2064 
2065         skb = tcp_write_queue_head(sk);
2066         if (tcp_skb_is_last(sk, skb))
2067                 return 1;
2068         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
2069         tcp_for_write_queue_from(skb, sk) {
2070                 if (skb == tcp_send_head(sk))
2071                         break;
2072                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2073                         return 0;
2074                 /* Short-circuit when first non-SACKed skb has been checked */
2075                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2076                         break;
2077         }
2078         return 1;
2079 }
2080 
2081 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2082  * recovery a bit and use heuristics in tcp_process_frto() to detect if
2083  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2084  * keep retrans_out counting accurate (with SACK F-RTO, other than head
2085  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2086  * bits are handled if the Loss state is really to be entered (in
2087  * tcp_enter_frto_loss).
2088  *
2089  * Do like tcp_enter_loss() would; when RTO expires the second time it
2090  * does:
2091  *  "Reduce ssthresh if it has not yet been made inside this window."
2092  */
2093 void tcp_enter_frto(struct sock *sk)
2094 {
2095         const struct inet_connection_sock *icsk = inet_csk(sk);
2096         struct tcp_sock *tp = tcp_sk(sk);
2097         struct sk_buff *skb;
2098 
2099         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2100             tp->snd_una == tp->high_seq ||
2101             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2102              !icsk->icsk_retransmits)) {
2103                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2104                 /* Our state is too optimistic in ssthresh() call because cwnd
2105                  * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2106                  * recovery has not yet completed. Pattern would be this: RTO,
2107                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
2108                  * up here twice).
2109                  * RFC4138 should be more specific on what to do, even though
2110                  * RTO is quite unlikely to occur after the first Cumulative ACK
2111                  * due to back-off and complexity of triggering events ...
2112                  */
2113                 if (tp->frto_counter) {
2114                         u32 stored_cwnd;
2115                         stored_cwnd = tp->snd_cwnd;
2116                         tp->snd_cwnd = 2;
2117                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2118                         tp->snd_cwnd = stored_cwnd;
2119                 } else {
2120                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2121                 }
2122                 /* ... in theory, cong.control module could do "any tricks" in
2123                  * ssthresh(), which means that ca_state, lost bits and lost_out
2124                  * counter would have to be faked before the call occurs. We
2125                  * consider that too expensive, unlikely and hacky, so modules
2126                  * using these in ssthresh() must deal these incompatibility
2127                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2128                  */
2129                 tcp_ca_event(sk, CA_EVENT_FRTO);
2130         }
2131 
2132         tp->undo_marker = tp->snd_una;
2133         tp->undo_retrans = 0;
2134 
2135         skb = tcp_write_queue_head(sk);
2136         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2137                 tp->undo_marker = 0;
2138         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2139                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2140                 tp->retrans_out -= tcp_skb_pcount(skb);
2141         }
2142         tcp_verify_left_out(tp);
2143 
2144         /* Too bad if TCP was application limited */
2145         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2146 
2147         /* Earlier loss recovery underway (see RFC4138; Appendix B).
2148          * The last condition is necessary at least in tp->frto_counter case.
2149          */
2150         if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2151             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2152             after(tp->high_seq, tp->snd_una)) {
2153                 tp->frto_highmark = tp->high_seq;
2154         } else {
2155                 tp->frto_highmark = tp->snd_nxt;
2156         }
2157         tcp_set_ca_state(sk, TCP_CA_Disorder);
2158         tp->high_seq = tp->snd_nxt;
2159         tp->frto_counter = 1;
2160 }
2161 
2162 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2163  * which indicates that we should follow the traditional RTO recovery,
2164  * i.e. mark everything lost and do go-back-N retransmission.
2165  */
2166 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2167 {
2168         struct tcp_sock *tp = tcp_sk(sk);
2169         struct sk_buff *skb;
2170 
2171         tp->lost_out = 0;
2172         tp->retrans_out = 0;
2173         if (tcp_is_reno(tp))
2174                 tcp_reset_reno_sack(tp);
2175 
2176         tcp_for_write_queue(skb, sk) {
2177                 if (skb == tcp_send_head(sk))
2178                         break;
2179 
2180                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2181                 /*
2182                  * Count the retransmission made on RTO correctly (only when
2183                  * waiting for the first ACK and did not get it)...
2184                  */
2185                 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2186                         /* For some reason this R-bit might get cleared? */
2187                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2188                                 tp->retrans_out += tcp_skb_pcount(skb);
2189                         /* ...enter this if branch just for the first segment */
2190                         flag |= FLAG_DATA_ACKED;
2191                 } else {
2192                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2193                                 tp->undo_marker = 0;
2194                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2195                 }
2196 
2197                 /* Marking forward transmissions that were made after RTO lost
2198                  * can cause unnecessary retransmissions in some scenarios,
2199                  * SACK blocks will mitigate that in some but not in all cases.
2200                  * We used to not mark them but it was causing break-ups with
2201                  * receivers that do only in-order receival.
2202                  *
2203                  * TODO: we could detect presence of such receiver and select
2204                  * different behavior per flow.
2205                  */
2206                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2207                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2208                         tp->lost_out += tcp_skb_pcount(skb);
2209                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2210                 }
2211         }
2212         tcp_verify_left_out(tp);
2213 
2214         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2215         tp->snd_cwnd_cnt = 0;
2216         tp->snd_cwnd_stamp = tcp_time_stamp;
2217         tp->frto_counter = 0;
2218         tp->bytes_acked = 0;
2219 
2220         tp->reordering = min_t(unsigned int, tp->reordering,
2221                                sysctl_tcp_reordering);
2222         tcp_set_ca_state(sk, TCP_CA_Loss);
2223         tp->high_seq = tp->snd_nxt;
2224         TCP_ECN_queue_cwr(tp);
2225 
2226         tcp_clear_all_retrans_hints(tp);
2227 }
2228 
2229 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2230 {
2231         tp->retrans_out = 0;
2232         tp->lost_out = 0;
2233 
2234         tp->undo_marker = 0;
2235         tp->undo_retrans = 0;
2236 }
2237 
2238 void tcp_clear_retrans(struct tcp_sock *tp)
2239 {
2240         tcp_clear_retrans_partial(tp);
2241 
2242         tp->fackets_out = 0;
2243         tp->sacked_out = 0;
2244 }
2245 
2246 /* Enter Loss state. If "how" is not zero, forget all SACK information
2247  * and reset tags completely, otherwise preserve SACKs. If receiver
2248  * dropped its ofo queue, we will know this due to reneging detection.
2249  */
2250 void tcp_enter_loss(struct sock *sk, int how)
2251 {
2252         const struct inet_connection_sock *icsk = inet_csk(sk);
2253         struct tcp_sock *tp = tcp_sk(sk);
2254         struct sk_buff *skb;
2255 
2256         /* Reduce ssthresh if it has not yet been made inside this window. */
2257         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2258             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2259                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2260                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2261                 tcp_ca_event(sk, CA_EVENT_LOSS);
2262         }
2263         tp->snd_cwnd       = 1;
2264         tp->snd_cwnd_cnt   = 0;
2265         tp->snd_cwnd_stamp = tcp_time_stamp;
2266 
2267         tp->bytes_acked = 0;
2268         tcp_clear_retrans_partial(tp);
2269 
2270         if (tcp_is_reno(tp))
2271                 tcp_reset_reno_sack(tp);
2272 
2273         tp->undo_marker = tp->snd_una;
2274         if (how) {
2275                 tp->sacked_out = 0;
2276                 tp->fackets_out = 0;
2277         }
2278         tcp_clear_all_retrans_hints(tp);
2279 
2280         tcp_for_write_queue(skb, sk) {
2281                 if (skb == tcp_send_head(sk))
2282                         break;
2283 
2284                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2285                         tp->undo_marker = 0;
2286                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2287                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2288                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2289                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2290                         tp->lost_out += tcp_skb_pcount(skb);
2291                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2292                 }
2293         }
2294         tcp_verify_left_out(tp);
2295 
2296         tp->reordering = min_t(unsigned int, tp->reordering,
2297                                sysctl_tcp_reordering);
2298         tcp_set_ca_state(sk, TCP_CA_Loss);
2299         tp->high_seq = tp->snd_nxt;
2300         TCP_ECN_queue_cwr(tp);
2301         /* Abort F-RTO algorithm if one is in progress */
2302         tp->frto_counter = 0;
2303 }
2304 
2305 /* If ACK arrived pointing to a remembered SACK, it means that our
2306  * remembered SACKs do not reflect real state of receiver i.e.
2307  * receiver _host_ is heavily congested (or buggy).
2308  *
2309  * Do processing similar to RTO timeout.
2310  */
2311 static int tcp_check_sack_reneging(struct sock *sk, int flag)
2312 {
2313         if (flag & FLAG_SACK_RENEGING) {
2314                 struct inet_connection_sock *icsk = inet_csk(sk);
2315                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2316 
2317                 tcp_enter_loss(sk, 1);
2318                 icsk->icsk_retransmits++;
2319                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2320                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2321                                           icsk->icsk_rto, TCP_RTO_MAX);
2322                 return 1;
2323         }
2324         return 0;
2325 }
2326 
2327 static inline int tcp_fackets_out(const struct tcp_sock *tp)
2328 {
2329         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2330 }
2331 
2332 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2333  * counter when SACK is enabled (without SACK, sacked_out is used for
2334  * that purpose).
2335  *
2336  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2337  * segments up to the highest received SACK block so far and holes in
2338  * between them.
2339  *
2340  * With reordering, holes may still be in flight, so RFC3517 recovery
2341  * uses pure sacked_out (total number of SACKed segments) even though
2342  * it violates the RFC that uses duplicate ACKs, often these are equal
2343  * but when e.g. out-of-window ACKs or packet duplication occurs,
2344  * they differ. Since neither occurs due to loss, TCP should really
2345  * ignore them.
2346  */
2347 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2348 {
2349         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2350 }
2351 
2352 static inline int tcp_skb_timedout(const struct sock *sk,
2353                                    const struct sk_buff *skb)
2354 {
2355         return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
2356 }
2357 
2358 static inline int tcp_head_timedout(const struct sock *sk)
2359 {
2360         const struct tcp_sock *tp = tcp_sk(sk);
2361 
2362         return tp->packets_out &&
2363                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2364 }
2365 
2366 /* Linux NewReno/SACK/FACK/ECN state machine.
2367  * --------------------------------------
2368  *
2369  * "Open"       Normal state, no dubious events, fast path.
2370  * "Disorder"   In all the respects it is "Open",
2371  *              but requires a bit more attention. It is entered when
2372  *              we see some SACKs or dupacks. It is split of "Open"
2373  *              mainly to move some processing from fast path to slow one.
2374  * "CWR"        CWND was reduced due to some Congestion Notification event.
2375  *              It can be ECN, ICMP source quench, local device congestion.
2376  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2377  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2378  *
2379  * tcp_fastretrans_alert() is entered:
2380  * - each incoming ACK, if state is not "Open"
2381  * - when arrived ACK is unusual, namely:
2382  *      * SACK
2383  *      * Duplicate ACK.
2384  *      * ECN ECE.
2385  *
2386  * Counting packets in flight is pretty simple.
2387  *
2388  *      in_flight = packets_out - left_out + retrans_out
2389  *
2390  *      packets_out is SND.NXT-SND.UNA counted in packets.
2391  *
2392  *      retrans_out is number of retransmitted segments.
2393  *
2394  *      left_out is number of segments left network, but not ACKed yet.
2395  *
2396  *              left_out = sacked_out + lost_out
2397  *
2398  *     sacked_out: Packets, which arrived to receiver out of order
2399  *                 and hence not ACKed. With SACKs this number is simply
2400  *                 amount of SACKed data. Even without SACKs
2401  *                 it is easy to give pretty reliable estimate of this number,
2402  *                 counting duplicate ACKs.
2403  *
2404  *       lost_out: Packets lost by network. TCP has no explicit
2405  *                 "loss notification" feedback from network (for now).
2406  *                 It means that this number can be only _guessed_.
2407  *                 Actually, it is the heuristics to predict lossage that
2408  *                 distinguishes different algorithms.
2409  *
2410  *      F.e. after RTO, when all the queue is considered as lost,
2411  *      lost_out = packets_out and in_flight = retrans_out.
2412  *
2413  *              Essentially, we have now two algorithms counting
2414  *              lost packets.
2415  *
2416  *              FACK: It is the simplest heuristics. As soon as we decided
2417  *              that something is lost, we decide that _all_ not SACKed
2418  *              packets until the most forward SACK are lost. I.e.
2419  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2420  *              It is absolutely correct estimate, if network does not reorder
2421  *              packets. And it loses any connection to reality when reordering
2422  *              takes place. We use FACK by default until reordering
2423  *              is suspected on the path to this destination.
2424  *
2425  *              NewReno: when Recovery is entered, we assume that one segment
2426  *              is lost (classic Reno). While we are in Recovery and
2427  *              a partial ACK arrives, we assume that one more packet
2428  *              is lost (NewReno). This heuristics are the same in NewReno
2429  *              and SACK.
2430  *
2431  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2432  *  deflation etc. CWND is real congestion window, never inflated, changes
2433  *  only according to classic VJ rules.
2434  *
2435  * Really tricky (and requiring careful tuning) part of algorithm
2436  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2437  * The first determines the moment _when_ we should reduce CWND and,
2438  * hence, slow down forward transmission. In fact, it determines the moment
2439  * when we decide that hole is caused by loss, rather than by a reorder.
2440  *
2441  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2442  * holes, caused by lost packets.
2443  *
2444  * And the most logically complicated part of algorithm is undo
2445  * heuristics. We detect false retransmits due to both too early
2446  * fast retransmit (reordering) and underestimated RTO, analyzing
2447  * timestamps and D-SACKs. When we detect that some segments were
2448  * retransmitted by mistake and CWND reduction was wrong, we undo
2449  * window reduction and abort recovery phase. This logic is hidden
2450  * inside several functions named tcp_try_undo_<something>.
2451  */
2452 
2453 /* This function decides, when we should leave Disordered state
2454  * and enter Recovery phase, reducing congestion window.
2455  *
2456  * Main question: may we further continue forward transmission
2457  * with the same cwnd?
2458  */
2459 static int tcp_time_to_recover(struct sock *sk)
2460 {
2461         struct tcp_sock *tp = tcp_sk(sk);
2462         __u32 packets_out;
2463 
2464         /* Do not perform any recovery during F-RTO algorithm */
2465         if (tp->frto_counter)
2466                 return 0;
2467 
2468         /* Trick#1: The loss is proven. */
2469         if (tp->lost_out)
2470                 return 1;
2471 
2472         /* Not-A-Trick#2 : Classic rule... */
2473         if (tcp_dupack_heuristics(tp) > tp->reordering)
2474                 return 1;
2475 
2476         /* Trick#3 : when we use RFC2988 timer restart, fast
2477          * retransmit can be triggered by timeout of queue head.
2478          */
2479         if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2480                 return 1;
2481 
2482         /* Trick#4: It is still not OK... But will it be useful to delay
2483          * recovery more?
2484          */
2485         packets_out = tp->packets_out;
2486         if (packets_out <= tp->reordering &&
2487             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2488             !tcp_may_send_now(sk)) {
2489                 /* We have nothing to send. This connection is limited
2490                  * either by receiver window or by application.
2491                  */
2492                 return 1;
2493         }
2494 
2495         /* If a thin stream is detected, retransmit after first
2496          * received dupack. Employ only if SACK is supported in order
2497          * to avoid possible corner-case series of spurious retransmissions
2498          * Use only if there are no unsent data.
2499          */
2500         if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2501             tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2502             tcp_is_sack(tp) && !tcp_send_head(sk))
2503                 return 1;
2504 
2505         return 0;
2506 }
2507 
2508 /* New heuristics: it is possible only after we switched to restart timer
2509  * each time when something is ACKed. Hence, we can detect timed out packets
2510  * during fast retransmit without falling to slow start.
2511  *
2512  * Usefulness of this as is very questionable, since we should know which of
2513  * the segments is the next to timeout which is relatively expensive to find
2514  * in general case unless we add some data structure just for that. The
2515  * current approach certainly won't find the right one too often and when it
2516  * finally does find _something_ it usually marks large part of the window
2517  * right away (because a retransmission with a larger timestamp blocks the
2518  * loop from advancing). -ij
2519  */
2520 static void tcp_timeout_skbs(struct sock *sk)
2521 {
2522         struct tcp_sock *tp = tcp_sk(sk);
2523         struct sk_buff *skb;
2524 
2525         if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2526                 return;
2527 
2528         skb = tp->scoreboard_skb_hint;
2529         if (tp->scoreboard_skb_hint == NULL)
2530                 skb = tcp_write_queue_head(sk);
2531 
2532         tcp_for_write_queue_from(skb, sk) {
2533                 if (skb == tcp_send_head(sk))
2534                         break;
2535                 if (!tcp_skb_timedout(sk, skb))
2536                         break;
2537 
2538                 tcp_skb_mark_lost(tp, skb);
2539         }
2540 
2541         tp->scoreboard_skb_hint = skb;
2542 
2543         tcp_verify_left_out(tp);
2544 }
2545 
2546 /* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2547  * is against sacked "cnt", otherwise it's against facked "cnt"
2548  */
2549 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2550 {
2551         struct tcp_sock *tp = tcp_sk(sk);
2552         struct sk_buff *skb;
2553         int cnt, oldcnt;
2554         int err;
2555         unsigned int mss;
2556 
2557         WARN_ON(packets > tp->packets_out);
2558         if (tp->lost_skb_hint) {
2559                 skb = tp->lost_skb_hint;
2560                 cnt = tp->lost_cnt_hint;
2561                 /* Head already handled? */
2562                 if (mark_head && skb != tcp_write_queue_head(sk))
2563                         return;
2564         } else {
2565                 skb = tcp_write_queue_head(sk);
2566                 cnt = 0;
2567         }
2568 
2569         tcp_for_write_queue_from(skb, sk) {
2570                 if (skb == tcp_send_head(sk))
2571                         break;
2572                 /* TODO: do this better */
2573                 /* this is not the most efficient way to do this... */
2574                 tp->lost_skb_hint = skb;
2575                 tp->lost_cnt_hint = cnt;
2576 
2577                 if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2578                         break;
2579 
2580                 oldcnt = cnt;
2581                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2582                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2583                         cnt += tcp_skb_pcount(skb);
2584 
2585                 if (cnt > packets) {
2586                         if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2587                             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2588                             (oldcnt >= packets))
2589                                 break;
2590 
2591                         mss = skb_shinfo(skb)->gso_size;
2592                         err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2593                         if (err < 0)
2594                                 break;
2595                         cnt = packets;
2596                 }
2597 
2598                 tcp_skb_mark_lost(tp, skb);
2599 
2600                 if (mark_head)
2601                         break;
2602         }
2603         tcp_verify_left_out(tp);
2604 }
2605 
2606 /* Account newly detected lost packet(s) */
2607 
2608 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2609 {
2610         struct tcp_sock *tp = tcp_sk(sk);
2611 
2612         if (tcp_is_reno(tp)) {
2613                 tcp_mark_head_lost(sk, 1, 1);
2614         } else if (tcp_is_fack(tp)) {
2615                 int lost = tp->fackets_out - tp->reordering;
2616                 if (lost <= 0)
2617                         lost = 1;
2618                 tcp_mark_head_lost(sk, lost, 0);
2619         } else {
2620                 int sacked_upto = tp->sacked_out - tp->reordering;
2621                 if (sacked_upto >= 0)
2622                         tcp_mark_head_lost(sk, sacked_upto, 0);
2623                 else if (fast_rexmit)
2624                         tcp_mark_head_lost(sk, 1, 1);
2625         }
2626 
2627         tcp_timeout_skbs(sk);
2628 }
2629 
2630 /* CWND moderation, preventing bursts due to too big ACKs
2631  * in dubious situations.
2632  */
2633 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2634 {
2635         tp->snd_cwnd = min(tp->snd_cwnd,
2636                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2637         tp->snd_cwnd_stamp = tcp_time_stamp;
2638 }
2639 
2640 /* Lower bound on congestion window is slow start threshold
2641  * unless congestion avoidance choice decides to overide it.
2642  */
2643 static inline u32 tcp_cwnd_min(const struct sock *sk)
2644 {
2645         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2646 
2647         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2648 }
2649 
2650 /* Decrease cwnd each second ack. */
2651 static void tcp_cwnd_down(struct sock *sk, int flag)
2652 {
2653         struct tcp_sock *tp = tcp_sk(sk);
2654         int decr = tp->snd_cwnd_cnt + 1;
2655 
2656         if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2657             (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2658                 tp->snd_cwnd_cnt = decr & 1;
2659                 decr >>= 1;
2660 
2661                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2662                         tp->snd_cwnd -= decr;
2663 
2664                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2665                 tp->snd_cwnd_stamp = tcp_time_stamp;
2666         }
2667 }
2668 
2669 /* Nothing was retransmitted or returned timestamp is less
2670  * than timestamp of the first retransmission.
2671  */
2672 static inline int tcp_packet_delayed(const struct tcp_sock *tp)
2673 {
2674         return !tp->retrans_stamp ||
2675                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2676                  before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2677 }
2678 
2679 /* Undo procedures. */
2680 
2681 #if FASTRETRANS_DEBUG > 1
2682 static void DBGUNDO(struct sock *sk, const char *msg)
2683 {
2684         struct tcp_sock *tp = tcp_sk(sk);
2685         struct inet_sock *inet = inet_sk(sk);
2686 
2687         if (sk->sk_family == AF_INET) {
2688                 printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2689                        msg,
2690                        &inet->inet_daddr, ntohs(inet->inet_dport),
2691                        tp->snd_cwnd, tcp_left_out(tp),
2692                        tp->snd_ssthresh, tp->prior_ssthresh,
2693                        tp->packets_out);
2694         }
2695 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2696         else if (sk->sk_family == AF_INET6) {
2697                 struct ipv6_pinfo *np = inet6_sk(sk);
2698                 printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2699                        msg,
2700                        &np->daddr, ntohs(inet->inet_dport),
2701                        tp->snd_cwnd, tcp_left_out(tp),
2702                        tp->snd_ssthresh, tp->prior_ssthresh,
2703                        tp->packets_out);
2704         }
2705 #endif
2706 }
2707 #else
2708 #define DBGUNDO(x...) do { } while (0)
2709 #endif
2710 
2711 static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
2712 {
2713         struct tcp_sock *tp = tcp_sk(sk);
2714 
2715         if (tp->prior_ssthresh) {
2716                 const struct inet_connection_sock *icsk = inet_csk(sk);
2717 
2718                 if (icsk->icsk_ca_ops->undo_cwnd)
2719                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2720                 else
2721                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2722 
2723                 if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
2724                         tp->snd_ssthresh = tp->prior_ssthresh;
2725                         TCP_ECN_withdraw_cwr(tp);
2726                 }
2727         } else {
2728                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2729         }
2730         tp->snd_cwnd_stamp = tcp_time_stamp;
2731 }
2732 
2733 static inline int tcp_may_undo(const struct tcp_sock *tp)
2734 {
2735         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2736 }
2737 
2738 /* People celebrate: "We love our President!" */
2739 static int tcp_try_undo_recovery(struct sock *sk)
2740 {
2741         struct tcp_sock *tp = tcp_sk(sk);
2742 
2743         if (tcp_may_undo(tp)) {
2744                 int mib_idx;
2745 
2746                 /* Happy end! We did not retransmit anything
2747                  * or our original transmission succeeded.
2748                  */
2749                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2750                 tcp_undo_cwr(sk, true);
2751                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2752                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2753                 else
2754                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2755 
2756                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2757                 tp->undo_marker = 0;
2758         }
2759         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2760                 /* Hold old state until something *above* high_seq
2761                  * is ACKed. For Reno it is MUST to prevent false
2762                  * fast retransmits (RFC2582). SACK TCP is safe. */
2763                 tcp_moderate_cwnd(tp);
2764                 return 1;
2765         }
2766         tcp_set_ca_state(sk, TCP_CA_Open);
2767         return 0;
2768 }
2769 
2770 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2771 static void tcp_try_undo_dsack(struct sock *sk)
2772 {
2773         struct tcp_sock *tp = tcp_sk(sk);
2774 
2775         if (tp->undo_marker && !tp->undo_retrans) {
2776                 DBGUNDO(sk, "D-SACK");
2777                 tcp_undo_cwr(sk, true);
2778                 tp->undo_marker = 0;
2779                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2780         }
2781 }
2782 
2783 /* We can clear retrans_stamp when there are no retransmissions in the
2784  * window. It would seem that it is trivially available for us in
2785  * tp->retrans_out, however, that kind of assumptions doesn't consider
2786  * what will happen if errors occur when sending retransmission for the
2787  * second time. ...It could the that such segment has only
2788  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2789  * the head skb is enough except for some reneging corner cases that
2790  * are not worth the effort.
2791  *
2792  * Main reason for all this complexity is the fact that connection dying
2793  * time now depends on the validity of the retrans_stamp, in particular,
2794  * that successive retransmissions of a segment must not advance
2795  * retrans_stamp under any conditions.
2796  */
2797 static int tcp_any_retrans_done(const struct sock *sk)
2798 {
2799         const struct tcp_sock *tp = tcp_sk(sk);
2800         struct sk_buff *skb;
2801 
2802         if (tp->retrans_out)
2803                 return 1;
2804 
2805         skb = tcp_write_queue_head(sk);
2806         if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2807                 return 1;
2808 
2809         return 0;
2810 }
2811 
2812 /* Undo during fast recovery after partial ACK. */
2813 
2814 static int tcp_try_undo_partial(struct sock *sk, int acked)
2815 {
2816         struct tcp_sock *tp = tcp_sk(sk);
2817         /* Partial ACK arrived. Force Hoe's retransmit. */
2818         int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2819 
2820         if (tcp_may_undo(tp)) {
2821                 /* Plain luck! Hole if filled with delayed
2822                  * packet, rather than with a retransmit.
2823                  */
2824                 if (!tcp_any_retrans_done(sk))
2825                         tp->retrans_stamp = 0;
2826 
2827                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2828 
2829                 DBGUNDO(sk, "Hoe");
2830                 tcp_undo_cwr(sk, false);
2831                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2832 
2833                 /* So... Do not make Hoe's retransmit yet.
2834                  * If the first packet was delayed, the rest
2835                  * ones are most probably delayed as well.
2836                  */
2837                 failed = 0;
2838         }
2839         return failed;
2840 }
2841 
2842 /* Undo during loss recovery after partial ACK. */
2843 static int tcp_try_undo_loss(struct sock *sk)
2844 {
2845         struct tcp_sock *tp = tcp_sk(sk);
2846 
2847         if (tcp_may_undo(tp)) {
2848                 struct sk_buff *skb;
2849                 tcp_for_write_queue(skb, sk) {
2850                         if (skb == tcp_send_head(sk))
2851                                 break;
2852                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2853                 }
2854 
2855                 tcp_clear_all_retrans_hints(tp);
2856 
2857                 DBGUNDO(sk, "partial loss");
2858                 tp->lost_out = 0;
2859                 tcp_undo_cwr(sk, true);
2860                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2861                 inet_csk(sk)->icsk_retransmits = 0;
2862                 tp->undo_marker = 0;
2863                 if (tcp_is_sack(tp))
2864                         tcp_set_ca_state(sk, TCP_CA_Open);
2865                 return 1;
2866         }
2867         return 0;
2868 }
2869 
2870 static inline void tcp_complete_cwr(struct sock *sk)
2871 {
2872         struct tcp_sock *tp = tcp_sk(sk);
2873 
2874         /* Do not moderate cwnd if it's already undone in cwr or recovery. */
2875         if (tp->undo_marker) {
2876                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
2877                         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2878                         tp->snd_cwnd_stamp = tcp_time_stamp;
2879                 } else if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH) {
2880                         /* PRR algorithm. */
2881                         tp->snd_cwnd = tp->snd_ssthresh;
2882                         tp->snd_cwnd_stamp = tcp_time_stamp;
2883                 }
2884         }
2885         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2886 }
2887 
2888 static void tcp_try_keep_open(struct sock *sk)
2889 {
2890         struct tcp_sock *tp = tcp_sk(sk);
2891         int state = TCP_CA_Open;
2892 
2893         if (tcp_left_out(tp) || tcp_any_retrans_done(sk) || tp->undo_marker)
2894                 state = TCP_CA_Disorder;
2895 
2896         if (inet_csk(sk)->icsk_ca_state != state) {
2897                 tcp_set_ca_state(sk, state);
2898                 tp->high_seq = tp->snd_nxt;
2899         }
2900 }
2901 
2902 static void tcp_try_to_open(struct sock *sk, int flag)
2903 {
2904         struct tcp_sock *tp = tcp_sk(sk);
2905 
2906         tcp_verify_left_out(tp);
2907 
2908         if (!tp->frto_counter && !tcp_any_retrans_done(sk))
2909                 tp->retrans_stamp = 0;
2910 
2911         if (flag & FLAG_ECE)
2912                 tcp_enter_cwr(sk, 1);
2913 
2914         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2915                 tcp_try_keep_open(sk);
2916                 tcp_moderate_cwnd(tp);
2917         } else {
2918                 tcp_cwnd_down(sk, flag);
2919         }
2920 }
2921 
2922 static void tcp_mtup_probe_failed(struct sock *sk)
2923 {
2924         struct inet_connection_sock *icsk = inet_csk(sk);
2925 
2926         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2927         icsk->icsk_mtup.probe_size = 0;
2928 }
2929 
2930 static void tcp_mtup_probe_success(struct sock *sk)
2931 {
2932         struct tcp_sock *tp = tcp_sk(sk);
2933         struct inet_connection_sock *icsk = inet_csk(sk);
2934 
2935         /* FIXME: breaks with very large cwnd */
2936         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2937         tp->snd_cwnd = tp->snd_cwnd *
2938                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2939                        icsk->icsk_mtup.probe_size;
2940         tp->snd_cwnd_cnt = 0;
2941         tp->snd_cwnd_stamp = tcp_time_stamp;
2942         tp->snd_ssthresh = tcp_current_ssthresh(sk);
2943 
2944         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2945         icsk->icsk_mtup.probe_size = 0;
2946         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2947 }
2948 
2949 /* Do a simple retransmit without using the backoff mechanisms in
2950  * tcp_timer. This is used for path mtu discovery.
2951  * The socket is already locked here.
2952  */
2953 void tcp_simple_retransmit(struct sock *sk)
2954 {
2955         const struct inet_connection_sock *icsk = inet_csk(sk);
2956         struct tcp_sock *tp = tcp_sk(sk);
2957         struct sk_buff *skb;
2958         unsigned int mss = tcp_current_mss(sk);
2959         u32 prior_lost = tp->lost_out;
2960 
2961         tcp_for_write_queue(skb, sk) {
2962                 if (skb == tcp_send_head(sk))
2963                         break;
2964                 if (tcp_skb_seglen(skb) > mss &&
2965                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2966                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2967                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2968                                 tp->retrans_out -= tcp_skb_pcount(skb);
2969                         }
2970                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2971                 }
2972         }
2973 
2974         tcp_clear_retrans_hints_partial(tp);
2975 
2976         if (prior_lost == tp->lost_out)
2977                 return;
2978 
2979         if (tcp_is_reno(tp))
2980                 tcp_limit_reno_sacked(tp);
2981 
2982         tcp_verify_left_out(tp);
2983 
2984         /* Don't muck with the congestion window here.
2985          * Reason is that we do not increase amount of _data_
2986          * in network, but units changed and effective
2987          * cwnd/ssthresh really reduced now.
2988          */
2989         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2990                 tp->high_seq = tp->snd_nxt;
2991                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2992                 tp->prior_ssthresh = 0;
2993                 tp->undo_marker = 0;
2994                 tcp_set_ca_state(sk, TCP_CA_Loss);
2995         }
2996         tcp_xmit_retransmit_queue(sk);
2997 }
2998 EXPORT_SYMBOL(tcp_simple_retransmit);
2999 
3000 /* This function implements the PRR algorithm, specifcally the PRR-SSRB
3001  * (proportional rate reduction with slow start reduction bound) as described in
3002  * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt.
3003  * It computes the number of packets to send (sndcnt) based on packets newly
3004  * delivered:
3005  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
3006  *      cwnd reductions across a full RTT.
3007  *   2) If packets in flight is lower than ssthresh (such as due to excess
3008  *      losses and/or application stalls), do not perform any further cwnd
3009  *      reductions, but instead slow start up to ssthresh.
3010  */
3011 static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
3012                                         int fast_rexmit, int flag)
3013 {
3014         struct tcp_sock *tp = tcp_sk(sk);
3015         int sndcnt = 0;
3016         int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
3017 
3018         if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
3019                 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
3020                                tp->prior_cwnd - 1;
3021                 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
3022         } else {
3023                 sndcnt = min_t(int, delta,
3024                                max_t(int, tp->prr_delivered - tp->prr_out,
3025                                      newly_acked_sacked) + 1);
3026         }
3027 
3028         sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
3029         tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
3030 }
3031 
3032 /* Process an event, which can update packets-in-flight not trivially.
3033  * Main goal of this function is to calculate new estimate for left_out,
3034  * taking into account both packets sitting in receiver's buffer and
3035  * packets lost by network.
3036  *
3037  * Besides that it does CWND reduction, when packet loss is detected
3038  * and changes state of machine.
3039  *
3040  * It does _not_ decide what to send, it is made in function
3041  * tcp_xmit_retransmit_queue().
3042  */
3043 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
3044                                   int newly_acked_sacked, int flag)
3045 {
3046         struct inet_connection_sock *icsk = inet_csk(sk);
3047         struct tcp_sock *tp = tcp_sk(sk);
3048         int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3049         int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
3050                                     (tcp_fackets_out(tp) > tp->reordering));
3051         int fast_rexmit = 0, mib_idx;
3052 
3053         if (WARN_ON(!tp->packets_out && tp->sacked_out))
3054                 tp->sacked_out = 0;
3055         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
3056                 tp->fackets_out = 0;
3057 
3058         /* Now state machine starts.
3059          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3060         if (flag & FLAG_ECE)
3061                 tp->prior_ssthresh = 0;
3062 
3063         /* B. In all the states check for reneging SACKs. */
3064         if (tcp_check_sack_reneging(sk, flag))
3065                 return;
3066 
3067         /* C. Process data loss notification, provided it is valid. */
3068         if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
3069             before(tp->snd_una, tp->high_seq) &&
3070             icsk->icsk_ca_state != TCP_CA_Open &&
3071             tp->fackets_out > tp->reordering) {
3072                 tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
3073                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
3074         }
3075 
3076         /* D. Check consistency of the current state. */
3077         tcp_verify_left_out(tp);
3078 
3079         /* E. Check state exit conditions. State can be terminated
3080          *    when high_seq is ACKed. */
3081         if (icsk->icsk_ca_state == TCP_CA_Open) {
3082                 WARN_ON(tp->retrans_out != 0);
3083                 tp->retrans_stamp = 0;
3084         } else if (!before(tp->snd_una, tp->high_seq)) {
3085                 switch (icsk->icsk_ca_state) {
3086                 case TCP_CA_Loss:
3087                         icsk->icsk_retransmits = 0;
3088                         if (tcp_try_undo_recovery(sk))
3089                                 return;
3090                         break;
3091 
3092                 case TCP_CA_CWR:
3093                         /* CWR is to be held something *above* high_seq
3094                          * is ACKed for CWR bit to reach receiver. */
3095                         if (tp->snd_una != tp->high_seq) {
3096                                 tcp_complete_cwr(sk);
3097                                 tcp_set_ca_state(sk, TCP_CA_Open);
3098                         }
3099                         break;
3100 
3101                 case TCP_CA_Disorder:
3102                         tcp_try_undo_dsack(sk);
3103                         if (!tp->undo_marker ||
3104                             /* For SACK case do not Open to allow to undo
3105                              * catching for all duplicate ACKs. */
3106                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
3107                                 tp->undo_marker = 0;
3108                                 tcp_set_ca_state(sk, TCP_CA_Open);
3109                         }
3110                         break;
3111 
3112                 case TCP_CA_Recovery:
3113                         if (tcp_is_reno(tp))
3114                                 tcp_reset_reno_sack(tp);
3115                         if (tcp_try_undo_recovery(sk))
3116                                 return;
3117                         tcp_complete_cwr(sk);
3118                         break;
3119                 }
3120         }
3121 
3122         /* F. Process state. */
3123         switch (icsk->icsk_ca_state) {
3124         case TCP_CA_Recovery:
3125                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3126                         if (tcp_is_reno(tp) && is_dupack)
3127                                 tcp_add_reno_sack(sk);
3128                 } else
3129                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
3130                 break;
3131         case TCP_CA_Loss:
3132                 if (flag & FLAG_DATA_ACKED)
3133                         icsk->icsk_retransmits = 0;
3134                 if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
3135                         tcp_reset_reno_sack(tp);
3136                 if (!tcp_try_undo_loss(sk)) {
3137                         tcp_moderate_cwnd(tp);
3138                         tcp_xmit_retransmit_queue(sk);
3139                         return;
3140                 }
3141                 if (icsk->icsk_ca_state != TCP_CA_Open)
3142                         return;
3143                 /* Loss is undone; fall through to processing in Open state. */
3144         default:
3145                 if (tcp_is_reno(tp)) {
3146                         if (flag & FLAG_SND_UNA_ADVANCED)
3147                                 tcp_reset_reno_sack(tp);
3148                         if (is_dupack)
3149                                 tcp_add_reno_sack(sk);
3150                 }
3151 
3152                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
3153                         tcp_try_undo_dsack(sk);
3154 
3155                 if (!tcp_time_to_recover(sk)) {
3156                         tcp_try_to_open(sk, flag);
3157                         return;
3158                 }
3159 
3160                 /* MTU probe failure: don't reduce cwnd */
3161                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
3162                     icsk->icsk_mtup.probe_size &&
3163                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
3164                         tcp_mtup_probe_failed(sk);
3165                         /* Restores the reduction we did in tcp_mtup_probe() */
3166                         tp->snd_cwnd++;
3167                         tcp_simple_retransmit(sk);
3168                         return;
3169                 }
3170 
3171                 /* Otherwise enter Recovery state */
3172 
3173                 if (tcp_is_reno(tp))
3174                         mib_idx = LINUX_MIB_TCPRENORECOVERY;
3175                 else
3176                         mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3177 
3178                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
3179 
3180                 tp->high_seq = tp->snd_nxt;
3181                 tp->prior_ssthresh = 0;
3182                 tp->undo_marker = tp->snd_una;
3183                 tp->undo_retrans = tp->retrans_out;
3184 
3185                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
3186                         if (!(flag & FLAG_ECE))
3187                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
3188                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3189                         TCP_ECN_queue_cwr(tp);
3190                 }
3191 
3192                 tp->bytes_acked = 0;
3193                 tp->snd_cwnd_cnt = 0;
3194                 tp->prior_cwnd = tp->snd_cwnd;
3195                 tp->prr_delivered = 0;
3196                 tp->prr_out = 0;
3197                 tcp_set_ca_state(sk, TCP_CA_Recovery);
3198                 fast_rexmit = 1;
3199         }
3200 
3201         if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3202                 tcp_update_scoreboard(sk, fast_rexmit);
3203         tp->prr_delivered += newly_acked_sacked;
3204         tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag);
3205         tcp_xmit_retransmit_queue(sk);
3206 }
3207 
3208 void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3209 {
3210         tcp_rtt_estimator(sk, seq_rtt);
3211         tcp_set_rto(sk);
3212         inet_csk(sk)->icsk_backoff = 0;
3213 }
3214 EXPORT_SYMBOL(tcp_valid_rtt_meas);
3215 
3216 /* Read draft-ietf-tcplw-high-performance before mucking
3217  * with this code. (Supersedes RFC1323)
3218  */
3219 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3220 {
3221         /* RTTM Rule: A TSecr value received in a segment is used to
3222          * update the averaged RTT measurement only if the segment
3223          * acknowledges some new data, i.e., only if it advances the
3224          * left edge of the send window.
3225          *
3226          * See draft-ietf-tcplw-high-performance-00, section 3.3.
3227          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3228          *
3229          * Changed: reset backoff as soon as we see the first valid sample.
3230          * If we do not, we get strongly overestimated rto. With timestamps
3231          * samples are accepted even from very old segments: f.e., when rtt=1
3232          * increases to 8, we retransmit 5 times and after 8 seconds delayed
3233          * answer arrives rto becomes 120 seconds! If at least one of segments
3234          * in window is lost... Voila.                          --ANK (010210)
3235          */
3236         struct tcp_sock *tp = tcp_sk(sk);
3237 
3238         tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3239 }
3240 
3241 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3242 {
3243         /* We don't have a timestamp. Can only use
3244          * packets that are not retransmitted to determine
3245          * rtt estimates. Also, we must not reset the
3246          * backoff for rto until we get a non-retransmitted
3247          * packet. This allows us to deal with a situation
3248          * where the network delay has increased suddenly.
3249          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3250          */
3251 
3252         if (flag & FLAG_RETRANS_DATA_ACKED)
3253                 return;
3254 
3255         tcp_valid_rtt_meas(sk, seq_rtt);
3256 }
3257 
3258 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3259                                       const s32 seq_rtt)
3260 {
3261         const struct tcp_sock *tp = tcp_sk(sk);
3262         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3263         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3264                 tcp_ack_saw_tstamp(sk, flag);
3265         else if (seq_rtt >= 0)
3266                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
3267 }
3268 
3269 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3270 {
3271         const struct inet_connection_sock *icsk = inet_csk(sk);
3272         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3273         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3274 }
3275 
3276 /* Restart timer after forward progress on connection.
3277  * RFC2988 recommends to restart timer to now+rto.
3278  */
3279 static void tcp_rearm_rto(struct sock *sk)
3280 {
3281         const struct tcp_sock *tp = tcp_sk(sk);
3282 
3283         if (!tp->packets_out) {
3284                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3285         } else {
3286                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3287                                           inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3288         }
3289 }
3290 
3291 /* If we get here, the whole TSO packet has not been acked. */
3292 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3293 {
3294         struct tcp_sock *tp = tcp_sk(sk);
3295         u32 packets_acked;
3296 
3297         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3298 
3299         packets_acked = tcp_skb_pcount(skb);
3300         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3301                 return 0;
3302         packets_acked -= tcp_skb_pcount(skb);
3303 
3304         if (packets_acked) {
3305                 BUG_ON(tcp_skb_pcount(skb) == 0);
3306                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3307         }
3308 
3309         return packets_acked;
3310 }
3311 
3312 /* Remove acknowledged frames from the retransmission queue. If our packet
3313  * is before the ack sequence we can discard it as it's confirmed to have
3314  * arrived at the other end.
3315  */
3316 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3317                                u32 prior_snd_una)
3318 {
3319         struct tcp_sock *tp = tcp_sk(sk);
3320         const struct inet_connection_sock *icsk = inet_csk(sk);
3321         struct sk_buff *skb;
3322         u32 now = tcp_time_stamp;
3323         int fully_acked = 1;
3324         int flag = 0;
3325         u32 pkts_acked = 0;
3326         u32 reord = tp->packets_out;
3327         u32 prior_sacked = tp->sacked_out;
3328         s32 seq_rtt = -1;
3329         s32 ca_seq_rtt = -1;
3330         ktime_t last_ackt = net_invalid_timestamp();
3331 
3332         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3333                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3334                 u32 acked_pcount;
3335                 u8 sacked = scb->sacked;
3336 
3337                 /* Determine how many packets and what bytes were acked, tso and else */
3338                 if (after(scb->end_seq, tp->snd_una)) {
3339                         if (tcp_skb_pcount(skb) == 1 ||
3340                             !after(tp->snd_una, scb->seq))
3341                                 break;
3342 
3343                         acked_pcount = tcp_tso_acked(sk, skb);
3344                         if (!acked_pcount)
3345                                 break;
3346 
3347                         fully_acked = 0;
3348                 } else {
3349                         acked_pcount = tcp_skb_pcount(skb);
3350                 }
3351 
3352                 if (sacked & TCPCB_RETRANS) {
3353                         if (sacked & TCPCB_SACKED_RETRANS)
3354                                 tp->retrans_out -= acked_pcount;
3355                         flag |= FLAG_RETRANS_DATA_ACKED;
3356                         ca_seq_rtt = -1;
3357                         seq_rtt = -1;
3358                         if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3359                                 flag |= FLAG_NONHEAD_RETRANS_ACKED;
3360                 } else {
3361                         ca_seq_rtt = now - scb->when;
3362                         last_ackt = skb->tstamp;
3363                         if (seq_rtt < 0) {
3364                                 seq_rtt = ca_seq_rtt;
3365                         }
3366                         if (!(sacked & TCPCB_SACKED_ACKED))
3367                                 reord = min(pkts_acked, reord);
3368                 }
3369 
3370                 if (sacked & TCPCB_SACKED_ACKED)
3371                         tp->sacked_out -= acked_pcount;
3372                 if (sacked & TCPCB_LOST)
3373                         tp->lost_out -= acked_pcount;
3374 
3375                 tp->packets_out -= acked_pcount;
3376                 pkts_acked += acked_pcount;
3377 
3378                 /* Initial outgoing SYN's get put onto the write_queue
3379                  * just like anything else we transmit.  It is not
3380                  * true data, and if we misinform our callers that
3381                  * this ACK acks real data, we will erroneously exit
3382                  * connection startup slow start one packet too
3383                  * quickly.  This is severely frowned upon behavior.
3384                  */
3385                 if (!(scb->tcp_flags & TCPHDR_SYN)) {
3386                         flag |= FLAG_DATA_ACKED;
3387                 } else {
3388                         flag |= FLAG_SYN_ACKED;
3389                         tp->retrans_stamp = 0;
3390                 }
3391 
3392                 if (!fully_acked)
3393                         break;
3394 
3395                 tcp_unlink_write_queue(skb, sk);
3396                 sk_wmem_free_skb(sk, skb);
3397                 tp->scoreboard_skb_hint = NULL;
3398                 if (skb == tp->retransmit_skb_hint)
3399                         tp->retransmit_skb_hint = NULL;
3400                 if (skb == tp->lost_skb_hint)
3401                         tp->lost_skb_hint = NULL;
3402         }
3403 
3404         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3405                 tp->snd_up = tp->snd_una;
3406 
3407         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3408                 flag |= FLAG_SACK_RENEGING;
3409 
3410         if (flag & FLAG_ACKED) {
3411                 const struct tcp_congestion_ops *ca_ops
3412                         = inet_csk(sk)->icsk_ca_ops;
3413 
3414                 if (unlikely(icsk->icsk_mtup.probe_size &&
3415                              !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3416                         tcp_mtup_probe_success(sk);
3417                 }
3418 
3419                 tcp_ack_update_rtt(sk, flag, seq_rtt);
3420                 tcp_rearm_rto(sk);
3421 
3422                 if (tcp_is_reno(tp)) {
3423                         tcp_remove_reno_sacks(sk, pkts_acked);
3424                 } else {
3425                         int delta;
3426 
3427                         /* Non-retransmitted hole got filled? That's reordering */
3428                         if (reord < prior_fackets && reord <= tp->fackets_out)
3429                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3430 
3431                         delta = tcp_is_fack(tp) ? pkts_acked :
3432                                                   prior_sacked - tp->sacked_out;
3433                         tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3434                 }
3435 
3436                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3437 
3438                 if (ca_ops->pkts_acked) {
3439                         s32 rtt_us = -1;
3440 
3441                         /* Is the ACK triggering packet unambiguous? */
3442                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3443                                 /* High resolution needed and available? */
3444                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3445                                     !ktime_equal(last_ackt,
3446                                                  net_invalid_timestamp()))
3447                                         rtt_us = ktime_us_delta(ktime_get_real(),
3448                                                                 last_ackt);
3449                                 else if (ca_seq_rtt >= 0)
3450                                         rtt_us = jiffies_to_usecs(ca_seq_rtt);
3451                         }
3452 
3453                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3454                 }
3455         }
3456 
3457 #if FASTRETRANS_DEBUG > 0
3458         WARN_ON((int)tp->sacked_out < 0);
3459         WARN_ON((int)tp->lost_out < 0);
3460         WARN_ON((int)tp->retrans_out < 0);
3461         if (!tp->packets_out && tcp_is_sack(tp)) {
3462                 icsk = inet_csk(sk);
3463                 if (tp->lost_out) {
3464                         printk(KERN_DEBUG "Leak l=%u %d\n",
3465                                tp->lost_out, icsk->icsk_ca_state);
3466                         tp->lost_out = 0;
3467                 }
3468                 if (tp->sacked_out) {
3469                         printk(KERN_DEBUG "Leak s=%u %d\n",
3470                                tp->sacked_out, icsk->icsk_ca_state);
3471                         tp->sacked_out = 0;
3472                 }
3473                 if (tp->retrans_out) {
3474                         printk(KERN_DEBUG "Leak r=%u %d\n",
3475                                tp->retrans_out, icsk->icsk_ca_state);
3476                         tp->retrans_out = 0;
3477                 }
3478         }
3479 #endif
3480         return flag;
3481 }
3482 
3483 static void tcp_ack_probe(struct sock *sk)
3484 {
3485         const struct tcp_sock *tp = tcp_sk(sk);
3486         struct inet_connection_sock *icsk = inet_csk(sk);
3487 
3488         /* Was it a usable window open? */
3489 
3490         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3491                 icsk->icsk_backoff = 0;
3492                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3493                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3494                  * This function is not for random using!
3495                  */
3496         } else {
3497                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3498                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3499                                           TCP_RTO_MAX);
3500         }
3501 }
3502 
3503 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3504 {
3505         return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3506                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3507 }
3508 
3509 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3510 {
3511         const struct tcp_sock *tp = tcp_sk(sk);
3512         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3513                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3514 }
3515 
3516 /* Check that window update is acceptable.
3517  * The function assumes that snd_una<=ack<=snd_next.
3518  */
3519 static inline int tcp_may_update_window(const struct tcp_sock *tp,
3520                                         const u32 ack, const u32 ack_seq,
3521                                         const u32 nwin)
3522 {
3523         return  after(ack, tp->snd_una) ||
3524                 after(ack_seq, tp->snd_wl1) ||
3525                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3526 }
3527 
3528 /* Update our send window.
3529  *
3530  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3531  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3532  */
3533 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3534                                  u32 ack_seq)
3535 {
3536         struct tcp_sock *tp = tcp_sk(sk);
3537         int flag = 0;
3538         u32 nwin = ntohs(tcp_hdr(skb)->window);
3539 
3540         if (likely(!tcp_hdr(skb)->syn))
3541                 nwin <<= tp->rx_opt.snd_wscale;
3542 
3543         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3544                 flag |= FLAG_WIN_UPDATE;
3545                 tcp_update_wl(tp, ack_seq);
3546 
3547                 if (tp->snd_wnd != nwin) {
3548                         tp->snd_wnd = nwin;
3549 
3550                         /* Note, it is the only place, where
3551                          * fast path is recovered for sending TCP.
3552                          */
3553                         tp->pred_flags = 0;
3554                         tcp_fast_path_check(sk);
3555 
3556                         if (nwin > tp->max_window) {
3557                                 tp->max_window = nwin;
3558                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3559                         }
3560                 }
3561         }
3562 
3563         tp->snd_una = ack;
3564 
3565         return flag;
3566 }
3567 
3568 /* A very conservative spurious RTO response algorithm: reduce cwnd and
3569  * continue in congestion avoidance.
3570  */
3571 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3572 {
3573         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3574         tp->snd_cwnd_cnt = 0;
3575         tp->bytes_acked = 0;
3576         TCP_ECN_queue_cwr(tp);
3577         tcp_moderate_cwnd(tp);
3578 }
3579 
3580 /* A conservative spurious RTO response algorithm: reduce cwnd using
3581  * rate halving and continue in congestion avoidance.
3582  */
3583 static void tcp_ratehalving_spur_to_response(struct sock *sk)
3584 {
3585         tcp_enter_cwr(sk, 0);
3586 }
3587 
3588 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3589 {
3590         if (flag & FLAG_ECE)
3591                 tcp_ratehalving_spur_to_response(sk);
3592         else
3593                 tcp_undo_cwr(sk, true);
3594 }
3595 
3596 /* F-RTO spurious RTO detection algorithm (RFC4138)
3597  *
3598  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3599  * comments). State (ACK number) is kept in frto_counter. When ACK advances
3600  * window (but not to or beyond highest sequence sent before RTO):
3601  *   On First ACK,  send two new segments out.
3602  *   On Second ACK, RTO was likely spurious. Do spurious response (response
3603  *                  algorithm is not part of the F-RTO detection algorithm
3604  *                  given in RFC4138 but can be selected separately).
3605  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3606  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3607  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3608  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3609  *
3610  * Rationale: if the RTO was spurious, new ACKs should arrive from the
3611  * original window even after we transmit two new data segments.
3612  *
3613  * SACK version:
3614  *   on first step, wait until first cumulative ACK arrives, then move to
3615  *   the second step. In second step, the next ACK decides.
3616  *
3617  * F-RTO is implemented (mainly) in four functions:
3618  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3619  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3620  *     called when tcp_use_frto() showed green light
3621  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3622  *   - tcp_enter_frto_loss() is called if there is not enough evidence
3623  *     to prove that the RTO is indeed spurious. It transfers the control
3624  *     from F-RTO to the conventional RTO recovery
3625  */
3626 static int tcp_process_frto(struct sock *sk, int flag)
3627 {
3628         struct tcp_sock *tp = tcp_sk(sk);
3629 
3630         tcp_verify_left_out(tp);
3631 
3632         /* Duplicate the behavior from Loss state (fastretrans_alert) */
3633         if (flag & FLAG_DATA_ACKED)
3634                 inet_csk(sk)->icsk_retransmits = 0;
3635 
3636         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3637             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3638                 tp->undo_marker = 0;
3639 
3640         if (!before(tp->snd_una, tp->frto_highmark)) {
3641                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3642                 return 1;
3643         }
3644 
3645         if (!tcp_is_sackfrto(tp)) {
3646                 /* RFC4138 shortcoming in step 2; should also have case c):
3647                  * ACK isn't duplicate nor advances window, e.g., opposite dir
3648                  * data, winupdate
3649                  */
3650                 if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3651                         return 1;
3652 
3653                 if (!(flag & FLAG_DATA_ACKED)) {
3654                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3655                                             flag);
3656                         return 1;
3657                 }
3658         } else {
3659                 if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3660                         if (!tcp_packets_in_flight(tp)) {
3661                                 tcp_enter_frto_loss(sk, 2, flag);
3662                                 return true;
3663                         }
3664 
3665                         /* Prevent sending of new data. */
3666                         tp->snd_cwnd = min(tp->snd_cwnd,
3667                                            tcp_packets_in_flight(tp));
3668                         return 1;
3669                 }
3670 
3671                 if ((tp->frto_counter >= 2) &&
3672                     (!(flag & FLAG_FORWARD_PROGRESS) ||
3673                      ((flag & FLAG_DATA_SACKED) &&
3674                       !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3675                         /* RFC4138 shortcoming (see comment above) */
3676                         if (!(flag & FLAG_FORWARD_PROGRESS) &&
3677                             (flag & FLAG_NOT_DUP))
3678                                 return 1;
3679 
3680                         tcp_enter_frto_loss(sk, 3, flag);
3681                         return 1;
3682                 }
3683         }
3684 
3685         if (tp->frto_counter == 1) {
3686                 /* tcp_may_send_now needs to see updated state */
3687                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3688                 tp->frto_counter = 2;
3689 
3690                 if (!tcp_may_send_now(sk))
3691                         tcp_enter_frto_loss(sk, 2, flag);
3692 
3693                 return 1;
3694         } else {
3695                 switch (sysctl_tcp_frto_response) {
3696                 case 2:
3697                         tcp_undo_spur_to_response(sk, flag);
3698                         break;
3699                 case 1:
3700                         tcp_conservative_spur_to_response(tp);
3701                         break;
3702                 default:
3703                         tcp_ratehalving_spur_to_response(sk);
3704                         break;
3705                 }
3706                 tp->frto_counter = 0;
3707                 tp->undo_marker = 0;
3708                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3709         }
3710         return 0;
3711 }
3712 
3713 /* RFC 5961 7 [ACK Throttling] */
3714 static void tcp_send_challenge_ack(struct sock *sk)
3715 {
3716         /* unprotected vars, we dont care of overwrites */
3717         static u32 challenge_timestamp;
3718         static unsigned int challenge_count;
3719         u32 count, now = jiffies / HZ;
3720 
3721         if (now != challenge_timestamp) {
3722                 u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;
3723 
3724                 challenge_timestamp = now;
3725                 ACCESS_ONCE(challenge_count) =
3726                         half + (u32)(
3727                         ((u64) random32() * sysctl_tcp_challenge_ack_limit)
3728                         >> 32);
3729         }
3730         count = ACCESS_ONCE(challenge_count);
3731         if (count > 0) {
3732                 ACCESS_ONCE(challenge_count) = count - 1;
3733                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3734                 tcp_send_ack(sk);
3735         }
3736 }
3737 
3738 static void tcp_store_ts_recent(struct tcp_sock *tp)
3739 {
3740         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3741         tp->rx_opt.ts_recent_stamp = get_seconds();
3742 }
3743 
3744 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3745 {
3746         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3747                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3748                  * extra check below makes sure this can only happen
3749                  * for pure ACK frames.  -DaveM
3750                  *
3751                  * Not only, also it occurs for expired timestamps.
3752                  */
3753 
3754                 if (tcp_paws_check(&tp->rx_opt, 0))
3755                         tcp_store_ts_recent(tp);
3756         }
3757 }
3758 
3759 /* This routine deals with incoming acks, but not outgoing ones. */
3760 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3761 {
3762         struct inet_connection_sock *icsk = inet_csk(sk);
3763         struct tcp_sock *tp = tcp_sk(sk);
3764         u32 prior_snd_una = tp->snd_una;
3765         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3766         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3767         u32 prior_in_flight;
3768         u32 prior_fackets;
3769         int prior_packets;
3770         int prior_sacked = tp->sacked_out;
3771         int newly_acked_sacked = 0;
3772         int frto_cwnd = 0;
3773 
3774         /* If the ack is older than previous acks
3775          * then we can probably ignore it.
3776          */
3777         if (before(ack, prior_snd_una)) {
3778                 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3779                 if (before(ack, prior_snd_una - tp->max_window)) {
3780                         tcp_send_challenge_ack(sk);
3781                         return -1;
3782                 }
3783                 goto old_ack;
3784         }
3785 
3786         /* If the ack includes data we haven't sent yet, discard
3787          * this segment (RFC793 Section 3.9).
3788          */
3789         if (after(ack, tp->snd_nxt))
3790                 goto invalid_ack;
3791 
3792         if (after(ack, prior_snd_una))
3793                 flag |= FLAG_SND_UNA_ADVANCED;
3794 
3795         if (sysctl_tcp_abc) {
3796                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3797                         tp->bytes_acked += ack - prior_snd_una;
3798                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3799                         /* we assume just one segment left network */
3800                         tp->bytes_acked += min(ack - prior_snd_una,
3801                                                tp->mss_cache);
3802         }
3803 
3804         prior_fackets = tp->fackets_out;
3805         prior_in_flight = tcp_packets_in_flight(tp);
3806 
3807         /* ts_recent update must be made after we are sure that the packet
3808          * is in window.
3809          */
3810         if (flag & FLAG_UPDATE_TS_RECENT)
3811                 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3812 
3813         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3814                 /* Window is constant, pure forward advance.
3815                  * No more checks are required.
3816                  * Note, we use the fact that SND.UNA>=SND.WL2.
3817                  */
3818                 tcp_update_wl(tp, ack_seq);
3819                 tp->snd_una = ack;
3820                 flag |= FLAG_WIN_UPDATE;
3821 
3822                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3823 
3824                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3825         } else {
3826                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3827                         flag |= FLAG_DATA;
3828                 else
3829                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3830 
3831                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3832 
3833                 if (TCP_SKB_CB(skb)->sacked)
3834                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3835 
3836                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3837                         flag |= FLAG_ECE;
3838 
3839                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3840         }
3841 
3842         /* We passed data and got it acked, remove any soft error
3843          * log. Something worked...
3844          */
3845         sk->sk_err_soft = 0;
3846         icsk->icsk_probes_out = 0;
3847         tp->rcv_tstamp = tcp_time_stamp;
3848         prior_packets = tp->packets_out;
3849         if (!prior_packets)
3850                 goto no_queue;
3851 
3852         /* See if we can take anything off of the retransmit queue. */
3853         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3854 
3855         newly_acked_sacked = (prior_packets - prior_sacked) -
3856                              (tp->packets_out - tp->sacked_out);
3857 
3858         if (tp->frto_counter)
3859                 frto_cwnd = tcp_process_frto(sk, flag);
3860         /* Guarantee sacktag reordering detection against wrap-arounds */
3861         if (before(tp->frto_highmark, tp->snd_una))
3862                 tp->frto_highmark = 0;
3863 
3864         if (tcp_ack_is_dubious(sk, flag)) {
3865                 /* Advance CWND, if state allows this. */
3866                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3867                     tcp_may_raise_cwnd(sk, flag))
3868                         tcp_cong_avoid(sk, ack, prior_in_flight);
3869                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3870                                       newly_acked_sacked, flag);
3871         } else {
3872                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3873                         tcp_cong_avoid(sk, ack, prior_in_flight);
3874         }
3875 
3876         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3877                 dst_confirm(__sk_dst_get(sk));
3878 
3879         return 1;
3880 
3881 no_queue:
3882         /* If this ack opens up a zero window, clear backoff.  It was
3883          * being used to time the probes, and is probably far higher than
3884          * it needs to be for normal retransmission.
3885          */
3886         if (tcp_send_head(sk))
3887                 tcp_ack_probe(sk);
3888         return 1;
3889 
3890 invalid_ack:
3891         SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3892         return -1;
3893 
3894 old_ack:
3895         if (TCP_SKB_CB(skb)->sacked) {
3896                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3897                 if (icsk->icsk_ca_state == TCP_CA_Open)
3898                         tcp_try_keep_open(sk);
3899         }
3900 
3901         SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3902         return 0;
3903 }
3904 
3905 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3906  * But, this can also be called on packets in the established flow when
3907  * the fast version below fails.
3908  */
3909 void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
3910                        const u8 **hvpp, int estab)
3911 {
3912         const unsigned char *ptr;
3913         const struct tcphdr *th = tcp_hdr(skb);
3914         int length = (th->doff * 4) - sizeof(struct tcphdr);
3915 
3916         ptr = (const unsigned char *)(th + 1);
3917         opt_rx->saw_tstamp = 0;
3918 
3919         while (length > 0) {
3920                 int opcode = *ptr++;
3921                 int opsize;
3922 
3923                 switch (opcode) {
3924                 case TCPOPT_EOL:
3925                         return;
3926                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3927                         length--;
3928                         continue;
3929                 default:
3930                         opsize = *ptr++;
3931                         if (opsize < 2) /* "silly options" */
3932                                 return;
3933                         if (opsize > length)
3934                                 return; /* don't parse partial options */
3935                         switch (opcode) {
3936                         case TCPOPT_MSS:
3937                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3938                                         u16 in_mss = get_unaligned_be16(ptr);
3939                                         if (in_mss) {
3940                                                 if (opt_rx->user_mss &&
3941                                                     opt_rx->user_mss < in_mss)
3942                                                         in_mss = opt_rx->user_mss;
3943                                                 opt_rx->mss_clamp = in_mss;
3944                                         }
3945                                 }
3946                                 break;
3947                         case TCPOPT_WINDOW:
3948                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3949                                     !estab && sysctl_tcp_window_scaling) {
3950                                         __u8 snd_wscale = *(__u8 *)ptr;
3951                                         opt_rx->wscale_ok = 1;
3952                                         if (snd_wscale > 14) {
3953                                                 if (net_ratelimit())
3954                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3955                                                                "scaling value %d >14 received.\n",
3956                                                                snd_wscale);
3957                                                 snd_wscale = 14;
3958                                         }
3959                                         opt_rx->snd_wscale = snd_wscale;
3960                                 }
3961                                 break;
3962                         case TCPOPT_TIMESTAMP:
3963                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3964                                     ((estab && opt_rx->tstamp_ok) ||
3965                                      (!estab && sysctl_tcp_timestamps))) {
3966                                         opt_rx->saw_tstamp = 1;
3967                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3968                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3969                                 }
3970                                 break;
3971                         case TCPOPT_SACK_PERM:
3972                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3973                                     !estab && sysctl_tcp_sack) {
3974                                         opt_rx->sack_ok = 1;
3975                                         tcp_sack_reset(opt_rx);
3976                                 }
3977                                 break;
3978 
3979                         case TCPOPT_SACK:
3980                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3981                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3982                                    opt_rx->sack_ok) {
3983                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3984                                 }
3985                                 break;
3986 #ifdef CONFIG_TCP_MD5SIG
3987                         case TCPOPT_MD5SIG:
3988                                 /*
3989                                  * The MD5 Hash has already been
3990                                  * checked (see tcp_v{4,6}_do_rcv()).
3991                                  */
3992                                 break;
3993 #endif
3994                         case TCPOPT_COOKIE:
3995                                 /* This option is variable length.
3996                                  */
3997                                 switch (opsize) {
3998                                 case TCPOLEN_COOKIE_BASE:
3999                                         /* not yet implemented */
4000                                         break;
4001                                 case TCPOLEN_COOKIE_PAIR:
4002                                         /* not yet implemented */
4003                                         break;
4004                                 case TCPOLEN_COOKIE_MIN+0:
4005                                 case TCPOLEN_COOKIE_MIN+2:
4006                                 case TCPOLEN_COOKIE_MIN+4:
4007                                 case TCPOLEN_COOKIE_MIN+6:
4008                                 case TCPOLEN_COOKIE_MAX:
4009                                         /* 16-bit multiple */
4010                                         opt_rx->cookie_plus = opsize;
4011                                         *hvpp = ptr;
4012                                         break;
4013                                 default:
4014                                         /* ignore option */
4015                                         break;
4016                                 }
4017                                 break;
4018                         }
4019 
4020                         ptr += opsize-2;
4021                         length -= opsize;
4022                 }
4023         }
4024 }
4025 EXPORT_SYMBOL(tcp_parse_options);
4026 
4027 static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4028 {
4029         const __be32 *ptr = (const __be32 *)(th + 1);
4030 
4031         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4032                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4033                 tp->rx_opt.saw_tstamp = 1;
4034                 ++ptr;
4035                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
4036                 ++ptr;
4037                 tp->rx_opt.rcv_tsecr = ntohl(*ptr);
4038                 return 1;
4039         }
4040         return 0;
4041 }
4042 
4043 /* Fast parse options. This hopes to only see timestamps.
4044  * If it is wrong it falls back on tcp_parse_options().
4045  */
4046 static int tcp_fast_parse_options(const struct sk_buff *skb,
4047                                   const struct tcphdr *th,
4048                                   struct tcp_sock *tp, const u8 **hvpp)
4049 {
4050         /* In the spirit of fast parsing, compare doff directly to constant
4051          * values.  Because equality is used, short doff can be ignored here.
4052          */
4053         if (th->doff == (sizeof(*th) / 4)) {
4054                 tp->rx_opt.saw_tstamp = 0;
4055                 return 0;
4056         } else if (tp->rx_opt.tstamp_ok &&
4057                    th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4058                 if (tcp_parse_aligned_timestamp(tp, th))
4059                         return 1;
4060         }
4061         tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
4062         return 1;
4063 }
4064 
4065 #ifdef CONFIG_TCP_MD5SIG
4066 /*
4067  * Parse MD5 Signature option
4068  */
4069 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4070 {
4071         int length = (th->doff << 2) - sizeof(*th);
4072         const u8 *ptr = (const u8 *)(th + 1);
4073 
4074         /* If the TCP option is too short, we can short cut */
4075         if (length < TCPOLEN_MD5SIG)
4076                 return NULL;
4077 
4078         while (length > 0) {
4079                 int opcode = *ptr++;
4080                 int opsize;
4081 
4082                 switch(opcode) {
4083                 case TCPOPT_EOL:
4084                         return NULL;
4085                 case TCPOPT_NOP:
4086                         length--;
4087                         continue;
4088                 default:
4089                         opsize = *ptr++;
4090                         if (opsize < 2 || opsize > length)
4091                                 return NULL;
4092                         if (opcode == TCPOPT_MD5SIG)
4093                                 return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4094                 }
4095                 ptr += opsize - 2;
4096                 length -= opsize;
4097         }
4098         return NULL;
4099 }
4100 EXPORT_SYMBOL(tcp_parse_md5sig_option);
4101 #endif
4102 
4103 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4104  *
4105  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4106  * it can pass through stack. So, the following predicate verifies that
4107  * this segment is not used for anything but congestion avoidance or
4108  * fast retransmit. Moreover, we even are able to eliminate most of such
4109  * second order effects, if we apply some small "replay" window (~RTO)
4110  * to timestamp space.
4111  *
4112  * All these measures still do not guarantee that we reject wrapped ACKs
4113  * on networks with high bandwidth, when sequence space is recycled fastly,
4114  * but it guarantees that such events will be very rare and do not affect
4115  * connection seriously. This doesn't look nice, but alas, PAWS is really
4116  * buggy extension.
4117  *
4118  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4119  * states that events when retransmit arrives after original data are rare.
4120  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4121  * the biggest problem on large power networks even with minor reordering.
4122  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4123  * up to bandwidth of 18Gigabit/sec. 8) ]
4124  */
4125 
4126 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4127 {
4128         const struct tcp_sock *tp = tcp_sk(sk);
4129         const struct tcphdr *th = tcp_hdr(skb);
4130         u32 seq = TCP_SKB_CB(skb)->seq;
4131         u32 ack = TCP_SKB_CB(skb)->ack_seq;
4132 
4133         return (/* 1. Pure ACK with correct sequence number. */
4134                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4135 
4136                 /* 2. ... and duplicate ACK. */
4137                 ack == tp->snd_una &&
4138 
4139                 /* 3. ... and does not update window. */
4140                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4141 
4142                 /* 4. ... and sits in replay window. */
4143                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4144 }
4145 
4146 static inline int tcp_paws_discard(const struct sock *sk,
4147                                    const struct sk_buff *skb)
4148 {
4149         const struct tcp_sock *tp = tcp_sk(sk);
4150 
4151         return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4152                !tcp_disordered_ack(sk, skb);
4153 }
4154 
4155 /* Check segment sequence number for validity.
4156  *
4157  * Segment controls are considered valid, if the segment
4158  * fits to the window after truncation to the window. Acceptability
4159  * of data (and SYN, FIN, of course) is checked separately.
4160  * See tcp_data_queue(), for example.
4161  *
4162  * Also, controls (RST is main one) are accepted using RCV.WUP instead
4163  * of RCV.NXT. Peer still did not advance his SND.UNA when we
4164  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4165  * (borrowed from freebsd)
4166  */
4167 
4168 static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4169 {
4170         return  !before(end_seq, tp->rcv_wup) &&
4171                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4172 }
4173 
4174 /* When we get a reset we do this. */
4175 static void tcp_reset(struct sock *sk)
4176 {
4177         /* We want the right error as BSD sees it (and indeed as we do). */
4178         switch (sk->sk_state) {
4179         case TCP_SYN_SENT:
4180                 sk->sk_err = ECONNREFUSED;
4181                 break;
4182         case TCP_CLOSE_WAIT:
4183                 sk->sk_err = EPIPE;
4184                 break;
4185         case TCP_CLOSE:
4186                 return;
4187         default:
4188                 sk->sk_err = ECONNRESET;
4189         }
4190         /* This barrier is coupled with smp_rmb() in tcp_poll() */
4191         smp_wmb();
4192 
4193         if (!sock_flag(sk, SOCK_DEAD))
4194                 sk->sk_error_report(sk);
4195 
4196         tcp_done(sk);
4197 }
4198 
4199 /*
4200  *      Process the FIN bit. This now behaves as it is supposed to work
4201  *      and the FIN takes effect when it is validly part of sequence
4202  *      space. Not before when we get holes.
4203  *
4204  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4205  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
4206  *      TIME-WAIT)
4207  *
4208  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
4209  *      close and we go into CLOSING (and later onto TIME-WAIT)
4210  *
4211  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4212  */
4213 static void tcp_fin(struct sock *sk)
4214 {
4215         struct tcp_sock *tp = tcp_sk(sk);
4216 
4217         inet_csk_schedule_ack(sk);
4218 
4219         sk->sk_shutdown |= RCV_SHUTDOWN;
4220         sock_set_flag(sk, SOCK_DONE);
4221 
4222         switch (sk->sk_state) {
4223         case TCP_SYN_RECV:
4224         case TCP_ESTABLISHED:
4225                 /* Move to CLOSE_WAIT */
4226                 tcp_set_state(sk, TCP_CLOSE_WAIT);
4227                 inet_csk(sk)->icsk_ack.pingpong = 1;
4228                 break;
4229 
4230         case TCP_CLOSE_WAIT:
4231         case TCP_CLOSING:
4232                 /* Received a retransmission of the FIN, do
4233                  * nothing.
4234                  */
4235                 break;
4236         case TCP_LAST_ACK:
4237                 /* RFC793: Remain in the LAST-ACK state. */
4238                 break;
4239 
4240         case TCP_FIN_WAIT1:
4241                 /* This case occurs when a simultaneous close
4242                  * happens, we must ack the received FIN and
4243                  * enter the CLOSING state.
4244                  */
4245                 tcp_send_ack(sk);
4246                 tcp_set_state(sk, TCP_CLOSING);
4247                 break;
4248         case TCP_FIN_WAIT2:
4249                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4250                 tcp_send_ack(sk);
4251                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4252                 break;
4253         default:
4254                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4255                  * cases we should never reach this piece of code.
4256                  */
4257                 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4258                        __func__, sk->sk_state);
4259                 break;
4260         }
4261 
4262         /* It _is_ possible, that we have something out-of-order _after_ FIN.
4263          * Probably, we should reset in this case. For now drop them.
4264          */
4265         __skb_queue_purge(&tp->out_of_order_queue);
4266         if (tcp_is_sack(tp))
4267                 tcp_sack_reset(&tp->rx_opt);
4268         sk_mem_reclaim(sk);
4269 
4270         if (!sock_flag(sk, SOCK_DEAD)) {
4271                 sk->sk_state_change(sk);
4272 
4273                 /* Do not send POLL_HUP for half duplex close. */
4274                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4275                     sk->sk_state == TCP_CLOSE)
4276                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4277                 else
4278                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4279         }
4280 }
4281 
4282 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4283                                   u32 end_seq)
4284 {
4285         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4286                 if (before(seq, sp->start_seq))
4287                         sp->start_seq = seq;
4288                 if (after(end_seq, sp->end_seq))
4289                         sp->end_seq = end_seq;
4290                 return 1;
4291         }
4292         return 0;
4293 }
4294 
4295 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4296 {
4297         struct tcp_sock *tp = tcp_sk(sk);
4298 
4299         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4300                 int mib_idx;
4301 
4302                 if (before(seq, tp->rcv_nxt))
4303                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4304                 else
4305                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4306 
4307                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4308 
4309                 tp->rx_opt.dsack = 1;
4310                 tp->duplicate_sack[0].start_seq = seq;
4311                 tp->duplicate_sack[0].end_seq = end_seq;
4312         }
4313 }
4314 
4315 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4316 {
4317         struct tcp_sock *tp = tcp_sk(sk);
4318 
4319         if (!tp->rx_opt.dsack)
4320                 tcp_dsack_set(sk, seq, end_seq);
4321         else
4322                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4323 }
4324 
4325 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4326 {
4327         struct tcp_sock *tp = tcp_sk(sk);
4328 
4329         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4330             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4331                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4332                 tcp_enter_quickack_mode(sk);
4333 
4334                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4335                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4336 
4337                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4338                                 end_seq = tp->rcv_nxt;
4339                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4340                 }
4341         }
4342 
4343         tcp_send_ack(sk);
4344 }
4345 
4346 /* These routines update the SACK block as out-of-order packets arrive or
4347  * in-order packets close up the sequence space.
4348  */
4349 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4350 {
4351         int this_sack;
4352         struct tcp_sack_block *sp = &tp->selective_acks[0];
4353         struct tcp_sack_block *swalk = sp + 1;
4354 
4355         /* See if the recent change to the first SACK eats into
4356          * or hits the sequence space of other SACK blocks, if so coalesce.
4357          */
4358         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4359                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4360                         int i;
4361 
4362                         /* Zap SWALK, by moving every further SACK up by one slot.
4363                          * Decrease num_sacks.
4364                          */
4365                         tp->rx_opt.num_sacks--;
4366                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4367                                 sp[i] = sp[i + 1];
4368                         continue;
4369                 }
4370                 this_sack++, swalk++;
4371         }
4372 }
4373 
4374 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4375 {
4376         struct tcp_sock *tp = tcp_sk(sk);
4377         struct tcp_sack_block *sp = &tp->selective_acks[0];
4378         int cur_sacks = tp->rx_opt.num_sacks;
4379         int this_sack;
4380 
4381         if (!cur_sacks)
4382                 goto new_sack;
4383 
4384         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4385                 if (tcp_sack_extend(sp, seq, end_seq)) {
4386                         /* Rotate this_sack to the first one. */
4387                         for (; this_sack > 0; this_sack--, sp--)
4388                                 swap(*sp, *(sp - 1));
4389                         if (cur_sacks > 1)
4390                                 tcp_sack_maybe_coalesce(tp);
4391                         return;
4392                 }
4393         }
4394 
4395         /* Could not find an adjacent existing SACK, build a new one,
4396          * put it at the front, and shift everyone else down.  We
4397          * always know there is at least one SACK present already here.
4398          *
4399          * If the sack array is full, forget about the last one.
4400          */
4401         if (this_sack >= TCP_NUM_SACKS) {
4402                 this_sack--;
4403                 tp->rx_opt.num_sacks--;
4404                 sp--;
4405         }
4406         for (; this_sack > 0; this_sack--, sp--)
4407                 *sp = *(sp - 1);
4408 
4409 new_sack:
4410         /* Build the new head SACK, and we're done. */
4411         sp->start_seq = seq;
4412         sp->end_seq = end_seq;
4413         tp->rx_opt.num_sacks++;
4414 }
4415 
4416 /* RCV.NXT advances, some SACKs should be eaten. */
4417 
4418 static void tcp_sack_remove(struct tcp_sock *tp)
4419 {
4420         struct tcp_sack_block *sp = &tp->selective_acks[0];
4421         int num_sacks = tp->rx_opt.num_sacks;
4422         int this_sack;
4423 
4424         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4425         if (skb_queue_empty(&tp->out_of_order_queue)) {
4426                 tp->rx_opt.num_sacks = 0;
4427                 return;
4428         }
4429 
4430         for (this_sack = 0; this_sack < num_sacks;) {
4431                 /* Check if the start of the sack is covered by RCV.NXT. */
4432                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4433                         int i;
4434 
4435                         /* RCV.NXT must cover all the block! */
4436                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4437 
4438                         /* Zap this SACK, by moving forward any other SACKS. */
4439                         for (i=this_sack+1; i < num_sacks; i++)
4440                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4441                         num_sacks--;
4442                         continue;
4443                 }
4444                 this_sack++;
4445                 sp++;
4446         }
4447         tp->rx_opt.num_sacks = num_sacks;
4448 }
4449 
4450 /* This one checks to see if we can put data from the
4451  * out_of_order queue into the receive_queue.
4452  */
4453 static void tcp_ofo_queue(struct sock *sk)
4454 {
4455         struct tcp_sock *tp = tcp_sk(sk);
4456         __u32 dsack_high = tp->rcv_nxt;
4457         struct sk_buff *skb;
4458 
4459         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4460                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4461                         break;
4462 
4463                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4464                         __u32 dsack = dsack_high;
4465                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4466                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4467                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4468                 }
4469 
4470                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4471                         SOCK_DEBUG(sk, "ofo packet was already received\n");
4472                         __skb_unlink(skb, &tp->out_of_order_queue);
4473                         __kfree_skb(skb);
4474                         continue;
4475                 }
4476                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4477                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4478                            TCP_SKB_CB(skb)->end_seq);
4479 
4480                 __skb_unlink(skb, &tp->out_of_order_queue);
4481                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4482                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4483                 if (tcp_hdr(skb)->fin)
4484                         tcp_fin(sk);
4485         }
4486 }
4487 
4488 static int tcp_prune_ofo_queue(struct sock *sk);
4489 static int tcp_prune_queue(struct sock *sk);
4490 
4491 static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4492 {
4493         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4494             !sk_rmem_schedule(sk, size)) {
4495 
4496                 if (tcp_prune_queue(sk) < 0)
4497                         return -1;
4498 
4499                 if (!sk_rmem_schedule(sk, size)) {
4500                         if (!tcp_prune_ofo_queue(sk))
4501                                 return -1;
4502 
4503                         if (!sk_rmem_schedule(sk, size))
4504                                 return -1;
4505                 }
4506         }
4507         return 0;
4508 }
4509 
4510 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4511 {
4512         const struct tcphdr *th = tcp_hdr(skb);
4513         struct tcp_sock *tp = tcp_sk(sk);
4514         int eaten = -1;
4515 
4516         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4517                 goto drop;
4518 
4519         skb_dst_drop(skb);
4520         __skb_pull(skb, th->doff * 4);
4521 
4522         TCP_ECN_accept_cwr(tp, skb);
4523 
4524         tp->rx_opt.dsack = 0;
4525 
4526         /*  Queue data for delivery to the user.
4527          *  Packets in sequence go to the receive queue.
4528          *  Out of sequence packets to the out_of_order_queue.
4529          */
4530         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4531                 if (tcp_receive_window(tp) == 0)
4532                         goto out_of_window;
4533 
4534                 /* Ok. In sequence. In window. */
4535                 if (tp->ucopy.task == current &&
4536                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4537                     sock_owned_by_user(sk) && !tp->urg_data) {
4538                         int chunk = min_t(unsigned int, skb->len,
4539                                           tp->ucopy.len);
4540 
4541                         __set_current_state(TASK_RUNNING);
4542 
4543                         local_bh_enable();
4544                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4545                                 tp->ucopy.len -= chunk;
4546                                 tp->copied_seq += chunk;
4547                                 eaten = (chunk == skb->len);
4548                                 tcp_rcv_space_adjust(sk);
4549                         }
4550                         local_bh_disable();
4551                 }
4552 
4553                 if (eaten <= 0) {
4554 queue_and_out:
4555                         if (eaten < 0 &&
4556                             tcp_try_rmem_schedule(sk, skb->truesize))
4557                                 goto drop;
4558 
4559                         skb_set_owner_r(skb, sk);
4560                         __skb_queue_tail(&sk->sk_receive_queue, skb);
4561                 }
4562                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4563                 if (skb->len)
4564                         tcp_event_data_recv(sk, skb);
4565                 if (th->fin)
4566                         tcp_fin(sk);
4567 
4568                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4569                         tcp_ofo_queue(sk);
4570 
4571                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4572                          * gap in queue is filled.
4573                          */
4574                         if (skb_queue_empty(&tp->out_of_order_queue))
4575                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4576                 }
4577 
4578                 if (tp->rx_opt.num_sacks)
4579                         tcp_sack_remove(tp);
4580 
4581                 tcp_fast_path_check(sk);
4582 
4583                 if (eaten > 0)
4584                         __kfree_skb(skb);
4585                 else if (!sock_flag(sk, SOCK_DEAD))
4586                         sk->sk_data_ready(sk, 0);
4587                 return;
4588         }
4589 
4590         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4591                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4592                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4593                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4594 
4595 out_of_window:
4596                 tcp_enter_quickack_mode(sk);
4597                 inet_csk_schedule_ack(sk);
4598 drop:
4599                 __kfree_skb(skb);
4600                 return;
4601         }
4602 
4603         /* Out of window. F.e. zero window probe. */
4604         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4605                 goto out_of_window;
4606 
4607         tcp_enter_quickack_mode(sk);
4608 
4609         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4610                 /* Partial packet, seq < rcv_next < end_seq */
4611                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4612                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4613                            TCP_SKB_CB(skb)->end_seq);
4614 
4615                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4616 
4617                 /* If window is closed, drop tail of packet. But after
4618                  * remembering D-SACK for its head made in previous line.
4619                  */
4620                 if (!tcp_receive_window(tp))
4621                         goto out_of_window;
4622                 goto queue_and_out;
4623         }
4624 
4625         TCP_ECN_check_ce(tp, skb);
4626 
4627         if (tcp_try_rmem_schedule(sk, skb->truesize))
4628                 goto drop;
4629 
4630         /* Disable header prediction. */
4631         tp->pred_flags = 0;
4632         inet_csk_schedule_ack(sk);
4633 
4634         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4635                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4636 
4637         skb_set_owner_r(skb, sk);
4638 
4639         if (!skb_peek(&tp->out_of_order_queue)) {
4640                 /* Initial out of order segment, build 1 SACK. */
4641                 if (tcp_is_sack(tp)) {
4642                         tp->rx_opt.num_sacks = 1;
4643                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4644                         tp->selective_acks[0].end_seq =
4645                                                 TCP_SKB_CB(skb)->end_seq;
4646                 }
4647                 __skb_queue_head(&tp->out_of_order_queue, skb);
4648         } else {
4649                 struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue);
4650                 u32 seq = TCP_SKB_CB(skb)->seq;
4651                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4652 
4653                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
4654                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4655 
4656                         if (!tp->rx_opt.num_sacks ||
4657                             tp->selective_acks[0].end_seq != seq)
4658                                 goto add_sack;
4659 
4660                         /* Common case: data arrive in order after hole. */
4661                         tp->selective_acks[0].end_seq = end_seq;
4662                         return;
4663                 }
4664 
4665                 /* Find place to insert this segment. */
4666                 while (1) {
4667                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
4668                                 break;
4669                         if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4670                                 skb1 = NULL;
4671                                 break;
4672                         }
4673                         skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4674                 }
4675 
4676                 /* Do skb overlap to previous one? */
4677                 if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4678                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4679                                 /* All the bits are present. Drop. */
4680                                 __kfree_skb(skb);
4681                                 tcp_dsack_set(sk, seq, end_seq);
4682                                 goto add_sack;
4683                         }
4684                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4685                                 /* Partial overlap. */
4686                                 tcp_dsack_set(sk, seq,
4687                                               TCP_SKB_CB(skb1)->end_seq);
4688                         } else {
4689                                 if (skb_queue_is_first(&tp->out_of_order_queue,
4690                                                        skb1))
4691                                         skb1 = NULL;
4692                                 else
4693                                         skb1 = skb_queue_prev(
4694                                                 &tp->out_of_order_queue,
4695                                                 skb1);
4696                         }
4697                 }
4698                 if (!skb1)
4699                         __skb_queue_head(&tp->out_of_order_queue, skb);
4700                 else
4701                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4702 
4703                 /* And clean segments covered by new one as whole. */
4704                 while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4705                         skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4706 
4707                         if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4708                                 break;
4709                         if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4710                                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4711                                                  end_seq);
4712                                 break;
4713                         }
4714                         __skb_unlink(skb1, &tp->out_of_order_queue);
4715                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4716                                          TCP_SKB_CB(skb1)->end_seq);
4717                         __kfree_skb(skb1);
4718                 }
4719 
4720 add_sack:
4721                 if (tcp_is_sack(tp))
4722                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
4723         }
4724 }
4725 
4726 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4727                                         struct sk_buff_head *list)
4728 {
4729         struct sk_buff *next = NULL;
4730 
4731         if (!skb_queue_is_last(list, skb))
4732                 next = skb_queue_next(list, skb);
4733 
4734         __skb_unlink(skb, list);
4735         __kfree_skb(skb);
4736         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4737 
4738         return next;
4739 }
4740 
4741 /* Collapse contiguous sequence of skbs head..tail with
4742  * sequence numbers start..end.
4743  *
4744  * If tail is NULL, this means until the end of the list.
4745  *
4746  * Segments with FIN/SYN are not collapsed (only because this
4747  * simplifies code)
4748  */
4749 static void
4750 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4751              struct sk_buff *head, struct sk_buff *tail,
4752              u32 start, u32 end)
4753 {
4754         struct sk_buff *skb, *n;
4755         bool end_of_skbs;
4756 
4757         /* First, check that queue is collapsible and find
4758          * the point where collapsing can be useful. */
4759         skb = head;
4760 restart:
4761         end_of_skbs = true;
4762         skb_queue_walk_from_safe(list, skb, n) {
4763                 if (skb == tail)
4764                         break;
4765                 /* No new bits? It is possible on ofo queue. */
4766                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4767                         skb = tcp_collapse_one(sk, skb, list);
4768                         if (!skb)
4769                                 break;
4770                         goto restart;
4771                 }
4772 
4773                 /* The first skb to collapse is:
4774                  * - not SYN/FIN and
4775                  * - bloated or contains data before "start" or
4776                  *   overlaps to the next one.
4777                  */
4778                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4779                     (tcp_win_from_space(skb->truesize) > skb->len ||
4780                      before(TCP_SKB_CB(skb)->seq, start))) {
4781                         end_of_skbs = false;
4782                         break;
4783                 }
4784 
4785                 if (!skb_queue_is_last(list, skb)) {
4786                         struct sk_buff *next = skb_queue_next(list, skb);
4787                         if (next != tail &&
4788                             TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4789                                 end_of_skbs = false;
4790                                 break;
4791                         }
4792                 }
4793 
4794                 /* Decided to skip this, advance start seq. */
4795                 start = TCP_SKB_CB(skb)->end_seq;
4796         }
4797         if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4798                 return;
4799 
4800         while (before(start, end)) {
4801                 struct sk_buff *nskb;
4802                 unsigned int header = skb_headroom(skb);
4803                 int copy = SKB_MAX_ORDER(header, 0);
4804 
4805                 /* Too big header? This can happen with IPv6. */
4806                 if (copy < 0)
4807                         return;
4808                 if (end - start < copy)
4809                         copy = end - start;
4810                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4811                 if (!nskb)
4812                         return;
4813 
4814                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4815                 skb_set_network_header(nskb, (skb_network_header(skb) -
4816                                               skb->head));
4817                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4818                                                 skb->head));
4819                 skb_reserve(nskb, header);
4820                 memcpy(nskb->head, skb->head, header);
4821                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4822                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4823                 __skb_queue_before(list, skb, nskb);
4824                 skb_set_owner_r(nskb, sk);
4825 
4826                 /* Copy data, releasing collapsed skbs. */
4827                 while (copy > 0) {
4828                         int offset = start - TCP_SKB_CB(skb)->seq;
4829                         int size = TCP_SKB_CB(skb)->end_seq - start;
4830 
4831                         BUG_ON(offset < 0);
4832                         if (size > 0) {
4833                                 size = min(copy, size);
4834                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4835                                         BUG();
4836                                 TCP_SKB_CB(nskb)->end_seq += size;
4837                                 copy -= size;
4838                                 start += size;
4839                         }
4840                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4841                                 skb = tcp_collapse_one(sk, skb, list);
4842                                 if (!skb ||
4843                                     skb == tail ||
4844                                     tcp_hdr(skb)->syn ||
4845                                     tcp_hdr(skb)->fin)
4846                                         return;
4847                         }
4848                 }
4849         }
4850 }
4851 
4852 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4853  * and tcp_collapse() them until all the queue is collapsed.
4854  */
4855 static void tcp_collapse_ofo_queue(struct sock *sk)
4856 {
4857         struct tcp_sock *tp = tcp_sk(sk);
4858         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4859         struct sk_buff *head;
4860         u32 start, end;
4861 
4862         if (skb == NULL)
4863                 return;
4864 
4865         start = TCP_SKB_CB(skb)->seq;
4866         end = TCP_SKB_CB(skb)->end_seq;
4867         head = skb;
4868 
4869         for (;;) {
4870                 struct sk_buff *next = NULL;
4871 
4872                 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4873                         next = skb_queue_next(&tp->out_of_order_queue, skb);
4874                 skb = next;
4875 
4876                 /* Segment is terminated when we see gap or when
4877                  * we are at the end of all the queue. */
4878                 if (!skb ||
4879                     after(TCP_SKB_CB(skb)->seq, end) ||
4880                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4881                         tcp_collapse(sk, &tp->out_of_order_queue,
4882                                      head, skb, start, end);
4883                         head = skb;
4884                         if (!skb)
4885                                 break;
4886                         /* Start new segment */
4887                         start = TCP_SKB_CB(skb)->seq;
4888                         end = TCP_SKB_CB(skb)->end_seq;
4889                 } else {
4890                         if (before(TCP_SKB_CB(skb)->seq, start))
4891                                 start = TCP_SKB_CB(skb)->seq;
4892                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4893                                 end = TCP_SKB_CB(skb)->end_seq;
4894                 }
4895         }
4896 }
4897 
4898 /*
4899  * Purge the out-of-order queue.
4900  * Return true if queue was pruned.
4901  */
4902 static int tcp_prune_ofo_queue(struct sock *sk)
4903 {
4904         struct tcp_sock *tp = tcp_sk(sk);
4905         int res = 0;
4906 
4907         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4908                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4909                 __skb_queue_purge(&tp->out_of_order_queue);
4910 
4911                 /* Reset SACK state.  A conforming SACK implementation will
4912                  * do the same at a timeout based retransmit.  When a connection
4913                  * is in a sad state like this, we care only about integrity
4914                  * of the connection not performance.
4915                  */
4916                 if (tp->rx_opt.sack_ok)
4917                         tcp_sack_reset(&tp->rx_opt);
4918                 sk_mem_reclaim(sk);
4919                 res = 1;
4920         }
4921         return res;
4922 }
4923 
4924 /* Reduce allocated memory if we can, trying to get
4925  * the socket within its memory limits again.
4926  *
4927  * Return less than zero if we should start dropping frames
4928  * until the socket owning process reads some of the data
4929  * to stabilize the situation.
4930  */
4931 static int tcp_prune_queue(struct sock *sk)
4932 {
4933         struct tcp_sock *tp = tcp_sk(sk);
4934 
4935         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4936 
4937         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4938 
4939         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4940                 tcp_clamp_window(sk);
4941         else if (tcp_memory_pressure)
4942                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4943 
4944         tcp_collapse_ofo_queue(sk);
4945         if (!skb_queue_empty(&sk->sk_receive_queue))
4946                 tcp_collapse(sk, &sk->sk_receive_queue,
4947                              skb_peek(&sk->sk_receive_queue),
4948                              NULL,
4949                              tp->copied_seq, tp->rcv_nxt);
4950         sk_mem_reclaim(sk);
4951 
4952         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4953                 return 0;
4954 
4955         /* Collapsing did not help, destructive actions follow.
4956          * This must not ever occur. */
4957 
4958         tcp_prune_ofo_queue(sk);
4959 
4960         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4961                 return 0;
4962 
4963         /* If we are really being abused, tell the caller to silently
4964          * drop receive data on the floor.  It will get retransmitted
4965          * and hopefully then we'll have sufficient space.
4966          */
4967         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4968 
4969         /* Massive buffer overcommit. */
4970         tp->pred_flags = 0;
4971         return -1;
4972 }
4973 
4974 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4975  * As additional protections, we do not touch cwnd in retransmission phases,
4976  * and if application hit its sndbuf limit recently.
4977  */
4978 void tcp_cwnd_application_limited(struct sock *sk)
4979 {
4980         struct tcp_sock *tp = tcp_sk(sk);
4981 
4982         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4983             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4984                 /* Limited by application or receiver window. */
4985                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4986                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4987                 if (win_used < tp->snd_cwnd) {
4988                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4989                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4990                 }
4991                 tp->snd_cwnd_used = 0;
4992         }
4993         tp->snd_cwnd_stamp = tcp_time_stamp;
4994 }
4995 
4996 static int tcp_should_expand_sndbuf(const struct sock *sk)
4997 {
4998         const struct tcp_sock *tp = tcp_sk(sk);
4999 
5000         /* If the user specified a specific send buffer setting, do
5001          * not modify it.
5002          */
5003         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5004                 return 0;
5005 
5006         /* If we are under global TCP memory pressure, do not expand.  */
5007         if (tcp_memory_pressure)
5008                 return 0;
5009 
5010         /* If we are under soft global TCP memory pressure, do not expand.  */
5011         if (atomic_long_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
5012                 return 0;
5013 
5014         /* If we filled the congestion window, do not expand.  */
5015         if (tp->packets_out >= tp->snd_cwnd)
5016                 return 0;
5017 
5018         return 1;
5019 }
5020 
5021 /* When incoming ACK allowed to free some skb from write_queue,
5022  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
5023  * on the exit from tcp input handler.
5024  *
5025  * PROBLEM: sndbuf expansion does not work well with largesend.
5026  */
5027 static void tcp_new_space(struct sock *sk)
5028 {
5029         struct tcp_sock *tp = tcp_sk(sk);
5030 
5031         if (tcp_should_expand_sndbuf(sk)) {
5032                 int sndmem = SKB_TRUESIZE(max_t(u32,
5033                                                 tp->rx_opt.mss_clamp,
5034                                                 tp->mss_cache) +
5035                                           MAX_TCP_HEADER);
5036                 int demanded = max_t(unsigned int, tp->snd_cwnd,
5037                                      tp->reordering + 1);
5038                 sndmem *= 2 * demanded;
5039                 if (sndmem > sk->sk_sndbuf)
5040                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
5041                 tp->snd_cwnd_stamp = tcp_time_stamp;
5042         }
5043 
5044         sk->sk_write_space(sk);
5045 }
5046 
5047 static void tcp_check_space(struct sock *sk)
5048 {
5049         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
5050                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
5051                 if (sk->sk_socket &&
5052                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5053                         tcp_new_space(sk);
5054         }
5055 }
5056 
5057 static inline void tcp_data_snd_check(struct sock *sk)
5058 {
5059         tcp_push_pending_frames(sk);
5060         tcp_check_space(sk);
5061 }
5062 
5063 /*
5064  * Check if sending an ack is needed.
5065  */
5066 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5067 {
5068         struct tcp_sock *tp = tcp_sk(sk);
5069 
5070             /* More than one full frame received... */
5071         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5072              /* ... and right edge of window advances far enough.
5073               * (tcp_recvmsg() will send ACK otherwise). Or...
5074               */
5075              __tcp_select_window(sk) >= tp->rcv_wnd) ||
5076             /* We ACK each frame or... */
5077             tcp_in_quickack_mode(sk) ||
5078             /* We have out of order data. */
5079             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
5080                 /* Then ack it now */
5081                 tcp_send_ack(sk);
5082         } else {
5083                 /* Else, send delayed ack. */
5084                 tcp_send_delayed_ack(sk);
5085         }
5086 }
5087 
5088 static inline void tcp_ack_snd_check(struct sock *sk)
5089 {
5090         if (!inet_csk_ack_scheduled(sk)) {
5091                 /* We sent a data segment already. */
5092                 return;
5093         }
5094         __tcp_ack_snd_check(sk, 1);
5095 }
5096 
5097 /*
5098  *      This routine is only called when we have urgent data
5099  *      signaled. Its the 'slow' part of tcp_urg. It could be
5100  *      moved inline now as tcp_urg is only called from one
5101  *      place. We handle URGent data wrong. We have to - as
5102  *      BSD still doesn't use the correction from RFC961.
5103  *      For 1003.1g we should support a new option TCP_STDURG to permit
5104  *      either form (or just set the sysctl tcp_stdurg).
5105  */
5106 
5107 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5108 {
5109         struct tcp_sock *tp = tcp_sk(sk);
5110         u32 ptr = ntohs(th->urg_ptr);
5111 
5112         if (ptr && !sysctl_tcp_stdurg)
5113                 ptr--;
5114         ptr += ntohl(th->seq);
5115 
5116         /* Ignore urgent data that we've already seen and read. */
5117         if (after(tp->copied_seq, ptr))
5118                 return;
5119 
5120         /* Do not replay urg ptr.
5121          *
5122          * NOTE: interesting situation not covered by specs.
5123          * Misbehaving sender may send urg ptr, pointing to segment,
5124          * which we already have in ofo queue. We are not able to fetch
5125          * such data and will stay in TCP_URG_NOTYET until will be eaten
5126          * by recvmsg(). Seems, we are not obliged to handle such wicked
5127          * situations. But it is worth to think about possibility of some
5128          * DoSes using some hypothetical application level deadlock.
5129          */
5130         if (before(ptr, tp->rcv_nxt))
5131                 return;
5132 
5133         /* Do we already have a newer (or duplicate) urgent pointer? */
5134         if (tp->urg_data && !after(ptr, tp->urg_seq))
5135                 return;
5136 
5137         /* Tell the world about our new urgent pointer. */
5138         sk_send_sigurg(sk);
5139 
5140         /* We may be adding urgent data when the last byte read was
5141          * urgent. To do this requires some care. We cannot just ignore
5142          * tp->copied_seq since we would read the last urgent byte again
5143          * as data, nor can we alter copied_seq until this data arrives
5144          * or we break the semantics of SIOCATMARK (and thus sockatmark())
5145          *
5146          * NOTE. Double Dutch. Rendering to plain English: author of comment
5147          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
5148          * and expect that both A and B disappear from stream. This is _wrong_.
5149          * Though this happens in BSD with high probability, this is occasional.
5150          * Any application relying on this is buggy. Note also, that fix "works"
5151          * only in this artificial test. Insert some normal data between A and B and we will
5152          * decline of BSD again. Verdict: it is better to remove to trap
5153          * buggy users.
5154          */
5155         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5156             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5157                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5158                 tp->copied_seq++;
5159                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5160                         __skb_unlink(skb, &sk->sk_receive_queue);
5161                         __kfree_skb(skb);
5162                 }
5163         }
5164 
5165         tp->urg_data = TCP_URG_NOTYET;
5166         tp->urg_seq = ptr;
5167 
5168         /* Disable header prediction. */
5169         tp->pred_flags = 0;
5170 }
5171 
5172 /* This is the 'fast' part of urgent handling. */
5173 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5174 {
5175         struct tcp_sock *tp = tcp_sk(sk);
5176 
5177         /* Check if we get a new urgent pointer - normally not. */
5178         if (th->urg)
5179                 tcp_check_urg(sk, th);
5180 
5181         /* Do we wait for any urgent data? - normally not... */
5182         if (tp->urg_data == TCP_URG_NOTYET) {
5183                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5184                           th->syn;
5185 
5186                 /* Is the urgent pointer pointing into this packet? */
5187                 if (ptr < skb->len) {
5188                         u8 tmp;
5189                         if (skb_copy_bits(skb, ptr, &tmp, 1))
5190                                 BUG();
5191                         tp->urg_data = TCP_URG_VALID | tmp;
5192                         if (!sock_flag(sk, SOCK_DEAD))
5193                                 sk->sk_data_ready(sk, 0);
5194                 }
5195         }
5196 }
5197 
5198 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5199 {
5200         struct tcp_sock *tp = tcp_sk(sk);
5201         int chunk = skb->len - hlen;
5202         int err;
5203 
5204         local_bh_enable();
5205         if (skb_csum_unnecessary(skb))
5206                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
5207         else
5208                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
5209                                                        tp->ucopy.iov);
5210 
5211         if (!err) {
5212                 tp->ucopy.len -= chunk;
5213                 tp->copied_seq += chunk;
5214                 tcp_rcv_space_adjust(sk);
5215         }
5216 
5217         local_bh_disable();
5218         return err;
5219 }
5220 
5221 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5222                                             struct sk_buff *skb)
5223 {
5224         __sum16 result;
5225 
5226         if (sock_owned_by_user(sk)) {
5227                 local_bh_enable();
5228                 result = __tcp_checksum_complete(skb);
5229                 local_bh_disable();
5230         } else {
5231                 result = __tcp_checksum_complete(skb);
5232         }
5233         return result;
5234 }
5235 
5236 static inline int tcp_checksum_complete_user(struct sock *sk,
5237                                              struct sk_buff *skb)
5238 {
5239         return !skb_csum_unnecessary(skb) &&
5240                __tcp_checksum_complete_user(sk, skb);
5241 }
5242 
5243 #ifdef CONFIG_NET_DMA
5244 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
5245                                   int hlen)
5246 {
5247         struct tcp_sock *tp = tcp_sk(sk);
5248         int chunk = skb->len - hlen;
5249         int dma_cookie;
5250         int copied_early = 0;
5251 
5252         if (tp->ucopy.wakeup)
5253                 return 0;
5254 
5255         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5256                 tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
5257 
5258         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5259 
5260                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5261                                                          skb, hlen,
5262                                                          tp->ucopy.iov, chunk,
5263                                                          tp->ucopy.pinned_list);
5264 
5265                 if (dma_cookie < 0)
5266                         goto out;
5267 
5268                 tp->ucopy.dma_cookie = dma_cookie;
5269                 copied_early = 1;
5270 
5271                 tp->ucopy.len -= chunk;
5272                 tp->copied_seq += chunk;
5273                 tcp_rcv_space_adjust(sk);
5274 
5275                 if ((tp->ucopy.len == 0) ||
5276                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5277                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5278                         tp->ucopy.wakeup = 1;
5279                         sk->sk_data_ready(sk, 0);
5280                 }
5281         } else if (chunk > 0) {
5282                 tp->ucopy.wakeup = 1;
5283                 sk->sk_data_ready(sk, 0);
5284         }
5285 out:
5286         return copied_early;
5287 }
5288 #endif /* CONFIG_NET_DMA */
5289 
5290 /* Does PAWS and seqno based validation of an incoming segment, flags will
5291  * play significant role here.
5292  */
5293 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5294                                   const struct tcphdr *th, int syn_inerr)
5295 {
5296         const u8 *hash_location;
5297         struct tcp_sock *tp = tcp_sk(sk);
5298 
5299         /* RFC1323: H1. Apply PAWS check first. */
5300         if (tcp_fast_parse_options(skb, th, tp, &hash_location) &&
5301             tp->rx_opt.saw_tstamp &&
5302             tcp_paws_discard(sk, skb)) {
5303                 if (!th->rst) {
5304                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5305                         tcp_send_dupack(sk, skb);
5306                         goto discard;
5307                 }
5308                 /* Reset is accepted even if it did not pass PAWS. */
5309         }
5310 
5311         /* Step 1: check sequence number */
5312         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5313                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5314                  * (RST) segments are validated by checking their SEQ-fields."
5315                  * And page 69: "If an incoming segment is not acceptable,
5316                  * an acknowledgment should be sent in reply (unless the RST
5317                  * bit is set, if so drop the segment and return)".
5318                  */
5319                 if (!th->rst) {
5320                         if (th->syn)
5321                                 goto syn_challenge;
5322                         tcp_send_dupack(sk, skb);
5323                 }
5324                 goto discard;
5325         }
5326 
5327         /* Step 2: check RST bit */
5328         if (th->rst) {
5329                 /* RFC 5961 3.2 :
5330                  * If sequence number exactly matches RCV.NXT, then
5331                  *     RESET the connection
5332                  * else
5333                  *     Send a challenge ACK
5334                  */
5335                 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5336                         tcp_reset(sk);
5337                 else
5338                         tcp_send_challenge_ack(sk);
5339                 goto discard;
5340         }
5341 
5342         /* step 3: check security and precedence [ignored] */
5343 
5344         /* step 4: Check for a SYN
5345          * RFC 5691 4.2 : Send a challenge ack
5346          */
5347         if (th->syn) {
5348 syn_challenge:
5349                 if (syn_inerr)
5350                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5351                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5352                 tcp_send_challenge_ack(sk);
5353                 goto discard;
5354         }
5355 
5356         return true;
5357 
5358 discard:
5359         __kfree_skb(skb);
5360         return false;
5361 }
5362 
5363 /*
5364  *      TCP receive function for the ESTABLISHED state.
5365  *
5366  *      It is split into a fast path and a slow path. The fast path is
5367  *      disabled when:
5368  *      - A zero window was announced from us - zero window probing
5369  *        is only handled properly in the slow path.
5370  *      - Out of order segments arrived.
5371  *      - Urgent data is expected.
5372  *      - There is no buffer space left
5373  *      - Unexpected TCP flags/window values/header lengths are received
5374  *        (detected by checking the TCP header against pred_flags)
5375  *      - Data is sent in both directions. Fast path only supports pure senders
5376  *        or pure receivers (this means either the sequence number or the ack
5377  *        value must stay constant)
5378  *      - Unexpected TCP option.
5379  *
5380  *      When these conditions are not satisfied it drops into a standard
5381  *      receive procedure patterned after RFC793 to handle all cases.
5382  *      The first three cases are guaranteed by proper pred_flags setting,
5383  *      the rest is checked inline. Fast processing is turned on in
5384  *      tcp_data_queue when everything is OK.
5385  */
5386 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5387                         const struct tcphdr *th, unsigned int len)
5388 {
5389         struct tcp_sock *tp = tcp_sk(sk);
5390 
5391         /*
5392          *      Header prediction.
5393          *      The code loosely follows the one in the famous
5394          *      "30 instruction TCP receive" Van Jacobson mail.
5395          *
5396          *      Van's trick is to deposit buffers into socket queue
5397          *      on a device interrupt, to call tcp_recv function
5398          *      on the receive process context and checksum and copy
5399          *      the buffer to user space. smart...
5400          *
5401          *      Our current scheme is not silly either but we take the
5402          *      extra cost of the net_bh soft interrupt processing...
5403          *      We do checksum and copy also but from device to kernel.
5404          */
5405 
5406         tp->rx_opt.saw_tstamp = 0;
5407 
5408         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5409          *      if header_prediction is to be made
5410          *      'S' will always be tp->tcp_header_len >> 2
5411          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5412          *  turn it off (when there are holes in the receive
5413          *       space for instance)
5414          *      PSH flag is ignored.
5415          */
5416 
5417         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5418             TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5419             !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5420                 int tcp_header_len = tp->tcp_header_len;
5421 
5422                 /* Timestamp header prediction: tcp_header_len
5423                  * is automatically equal to th->doff*4 due to pred_flags
5424                  * match.
5425                  */
5426 
5427                 /* Check timestamp */
5428                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5429                         /* No? Slow path! */
5430                         if (!tcp_parse_aligned_timestamp(tp, th))
5431                                 goto slow_path;
5432 
5433                         /* If PAWS failed, check it more carefully in slow path */
5434                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5435                                 goto slow_path;
5436 
5437                         /* DO NOT update ts_recent here, if checksum fails
5438                          * and timestamp was corrupted part, it will result
5439                          * in a hung connection since we will drop all
5440                          * future packets due to the PAWS test.
5441                          */
5442                 }
5443 
5444                 if (len <= tcp_header_len) {
5445                         /* Bulk data transfer: sender */
5446                         if (len == tcp_header_len) {
5447                                 /* Predicted packet is in window by definition.
5448                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5449                                  * Hence, check seq<=rcv_wup reduces to:
5450                                  */
5451                                 if (tcp_header_len ==
5452                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5453                                     tp->rcv_nxt == tp->rcv_wup)
5454                                         tcp_store_ts_recent(tp);
5455 
5456                                 /* We know that such packets are checksummed
5457                                  * on entry.
5458                                  */
5459                                 tcp_ack(sk, skb, 0);
5460                                 __kfree_skb(skb);
5461                                 tcp_data_snd_check(sk);
5462                                 return 0;
5463                         } else { /* Header too small */
5464                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5465                                 goto discard;
5466                         }
5467                 } else {
5468                         int eaten = 0;
5469                         int copied_early = 0;
5470 
5471                         if (tp->copied_seq == tp->rcv_nxt &&
5472                             len - tcp_header_len <= tp->ucopy.len) {
5473 #ifdef CONFIG_NET_DMA
5474                                 if (tp->ucopy.task == current &&
5475                                     sock_owned_by_user(sk) &&
5476                                     tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5477                                         copied_early = 1;
5478                                         eaten = 1;
5479                                 }
5480 #endif
5481                                 if (tp->ucopy.task == current &&
5482                                     sock_owned_by_user(sk) && !copied_early) {
5483                                         __set_current_state(TASK_RUNNING);
5484 
5485                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5486                                                 eaten = 1;
5487                                 }
5488                                 if (eaten) {
5489                                         /* Predicted packet is in window by definition.
5490                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5491                                          * Hence, check seq<=rcv_wup reduces to:
5492                                          */
5493                                         if (tcp_header_len ==
5494                                             (sizeof(struct tcphdr) +
5495                                              TCPOLEN_TSTAMP_ALIGNED) &&
5496                                             tp->rcv_nxt == tp->rcv_wup)
5497                                                 tcp_store_ts_recent(tp);
5498 
5499                                         tcp_rcv_rtt_measure_ts(sk, skb);
5500 
5501                                         __skb_pull(skb, tcp_header_len);
5502                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5503                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5504                                 }
5505                                 if (copied_early)
5506                                         tcp_cleanup_rbuf(sk, skb->len);
5507                         }
5508                         if (!eaten) {
5509                                 if (tcp_checksum_complete_user(sk, skb))
5510                                         goto csum_error;
5511 
5512                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5513                                         goto step5;
5514 
5515                                 /* Predicted packet is in window by definition.
5516                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5517                                  * Hence, check seq<=rcv_wup reduces to:
5518                                  */
5519                                 if (tcp_header_len ==
5520                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5521                                     tp->rcv_nxt == tp->rcv_wup)
5522                                         tcp_store_ts_recent(tp);
5523 
5524                                 tcp_rcv_rtt_measure_ts(sk, skb);
5525 
5526                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5527 
5528                                 /* Bulk data transfer: receiver */
5529                                 __skb_pull(skb, tcp_header_len);
5530                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
5531                                 skb_set_owner_r(skb, sk);
5532                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5533                         }
5534 
5535                         tcp_event_data_recv(sk, skb);
5536 
5537                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5538                                 /* Well, only one small jumplet in fast path... */
5539                                 tcp_ack(sk, skb, FLAG_DATA);
5540                                 tcp_data_snd_check(sk);
5541                                 if (!inet_csk_ack_scheduled(sk))
5542                                         goto no_ack;
5543                         }
5544 
5545                         if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5546                                 __tcp_ack_snd_check(sk, 0);
5547 no_ack:
5548 #ifdef CONFIG_NET_DMA
5549                         if (copied_early)
5550                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5551                         else
5552 #endif
5553                         if (eaten)
5554                                 __kfree_skb(skb);
5555                         else
5556                                 sk->sk_data_ready(sk, 0);
5557                         return 0;
5558                 }
5559         }
5560 
5561 slow_path:
5562         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5563                 goto csum_error;
5564 
5565         /*
5566          *      Standard slow path.
5567          */
5568 
5569         if (!tcp_validate_incoming(sk, skb, th, 1))
5570                 return 0;
5571 
5572 step5:
5573         if (th->ack &&
5574             tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5575                 goto discard;
5576 
5577         tcp_rcv_rtt_measure_ts(sk, skb);
5578 
5579         /* Process urgent data. */
5580         tcp_urg(sk, skb, th);
5581 
5582         /* step 7: process the segment text */
5583         tcp_data_queue(sk, skb);
5584 
5585         tcp_data_snd_check(sk);
5586         tcp_ack_snd_check(sk);
5587         return 0;
5588 
5589 csum_error:
5590         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5591 
5592 discard:
5593         __kfree_skb(skb);
5594         return 0;
5595 }
5596 EXPORT_SYMBOL(tcp_rcv_established);
5597 
5598 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5599                                          const struct tcphdr *th, unsigned int len)
5600 {
5601         const u8 *hash_location;
5602         struct inet_connection_sock *icsk = inet_csk(sk);
5603         struct tcp_sock *tp = tcp_sk(sk);
5604         struct tcp_cookie_values *cvp = tp->cookie_values;
5605         int saved_clamp = tp->rx_opt.mss_clamp;
5606 
5607         tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
5608 
5609         if (th->ack) {
5610                 /* rfc793:
5611                  * "If the state is SYN-SENT then
5612                  *    first check the ACK bit
5613                  *      If the ACK bit is set
5614                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5615                  *        a reset (unless the RST bit is set, if so drop
5616                  *        the segment and return)"
5617                  *
5618                  *  We do not send data with SYN, so that RFC-correct
5619                  *  test reduces to:
5620                  */
5621                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
5622                         goto reset_and_undo;
5623 
5624                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5625                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5626                              tcp_time_stamp)) {
5627                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5628                         goto reset_and_undo;
5629                 }
5630 
5631                 /* Now ACK is acceptable.
5632                  *
5633                  * "If the RST bit is set
5634                  *    If the ACK was acceptable then signal the user "error:
5635                  *    connection reset", drop the segment, enter CLOSED state,
5636                  *    delete TCB, and return."
5637                  */
5638 
5639                 if (th->rst) {
5640                         tcp_reset(sk);
5641                         goto discard;
5642                 }
5643 
5644                 /* rfc793:
5645                  *   "fifth, if neither of the SYN or RST bits is set then
5646                  *    drop the segment and return."
5647                  *
5648                  *    See note below!
5649                  *                                        --ANK(990513)
5650                  */
5651                 if (!th->syn)
5652                         goto discard_and_undo;
5653 
5654                 /* rfc793:
5655                  *   "If the SYN bit is on ...
5656                  *    are acceptable then ...
5657                  *    (our SYN has been ACKed), change the connection
5658                  *    state to ESTABLISHED..."
5659                  */
5660 
5661                 TCP_ECN_rcv_synack(tp, th);
5662 
5663                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5664                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5665 
5666                 /* Ok.. it's good. Set up sequence numbers and
5667                  * move to established.
5668                  */
5669                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5670                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5671 
5672                 /* RFC1323: The window in SYN & SYN/ACK segments is
5673                  * never scaled.
5674                  */
5675                 tp->snd_wnd = ntohs(th->window);
5676                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5677 
5678                 if (!tp->rx_opt.wscale_ok) {
5679                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5680                         tp->window_clamp = min(tp->window_clamp, 65535U);
5681                 }
5682 
5683                 if (tp->rx_opt.saw_tstamp) {
5684                         tp->rx_opt.tstamp_ok       = 1;
5685                         tp->tcp_header_len =
5686                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5687                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5688                         tcp_store_ts_recent(tp);
5689                 } else {
5690                         tp->tcp_header_len = sizeof(struct tcphdr);
5691                 }
5692 
5693                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5694                         tcp_enable_fack(tp);
5695 
5696                 tcp_mtup_init(sk);
5697                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5698                 tcp_initialize_rcv_mss(sk);
5699 
5700                 /* Remember, tcp_poll() does not lock socket!
5701                  * Change state from SYN-SENT only after copied_seq
5702                  * is initialized. */
5703                 tp->copied_seq = tp->rcv_nxt;
5704 
5705                 if (cvp != NULL &&
5706                     cvp->cookie_pair_size > 0 &&
5707                     tp->rx_opt.cookie_plus > 0) {
5708                         int cookie_size = tp->rx_opt.cookie_plus
5709                                         - TCPOLEN_COOKIE_BASE;
5710                         int cookie_pair_size = cookie_size
5711                                              + cvp->cookie_desired;
5712 
5713                         /* A cookie extension option was sent and returned.
5714                          * Note that each incoming SYNACK replaces the
5715                          * Responder cookie.  The initial exchange is most
5716                          * fragile, as protection against spoofing relies
5717                          * entirely upon the sequence and timestamp (above).
5718                          * This replacement strategy allows the correct pair to
5719                          * pass through, while any others will be filtered via
5720                          * Responder verification later.
5721                          */
5722                         if (sizeof(cvp->cookie_pair) >= cookie_pair_size) {
5723                                 memcpy(&cvp->cookie_pair[cvp->cookie_desired],
5724                                        hash_location, cookie_size);
5725                                 cvp->cookie_pair_size = cookie_pair_size;
5726                         }
5727                 }
5728 
5729                 smp_mb();
5730                 tcp_set_state(sk, TCP_ESTABLISHED);
5731 
5732                 security_inet_conn_established(sk, skb);
5733 
5734                 /* Make sure socket is routed, for correct metrics.  */
5735                 icsk->icsk_af_ops->rebuild_header(sk);
5736 
5737                 tcp_init_metrics(sk);
5738 
5739                 tcp_init_congestion_control(sk);
5740 
5741                 /* Prevent spurious tcp_cwnd_restart() on first data
5742                  * packet.
5743                  */
5744                 tp->lsndtime = tcp_time_stamp;
5745 
5746                 tcp_init_buffer_space(sk);
5747 
5748                 if (sock_flag(sk, SOCK_KEEPOPEN))
5749                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5750 
5751                 if (!tp->rx_opt.snd_wscale)
5752                         __tcp_fast_path_on(tp, tp->snd_wnd);
5753                 else
5754                         tp->pred_flags = 0;
5755 
5756                 if (!sock_flag(sk, SOCK_DEAD)) {
5757                         sk->sk_state_change(sk);
5758                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5759                 }
5760 
5761                 if (sk->sk_write_pending ||
5762                     icsk->icsk_accept_queue.rskq_defer_accept ||
5763                     icsk->icsk_ack.pingpong) {
5764                         /* Save one ACK. Data will be ready after
5765                          * several ticks, if write_pending is set.
5766                          *
5767                          * It may be deleted, but with this feature tcpdumps
5768                          * look so _wonderfully_ clever, that I was not able
5769                          * to stand against the temptation 8)     --ANK
5770                          */
5771                         inet_csk_schedule_ack(sk);
5772                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5773                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
5774                         tcp_incr_quickack(sk);
5775                         tcp_enter_quickack_mode(sk);
5776                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5777                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5778 
5779 discard:
5780                         __kfree_skb(skb);
5781                         return 0;
5782                 } else {
5783                         tcp_send_ack(sk);
5784                 }
5785                 return -1;
5786         }
5787 
5788         /* No ACK in the segment */
5789 
5790         if (th->rst) {
5791                 /* rfc793:
5792                  * "If the RST bit is set
5793                  *
5794                  *      Otherwise (no ACK) drop the segment and return."
5795                  */
5796 
5797                 goto discard_and_undo;
5798         }
5799 
5800         /* PAWS check. */
5801         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5802             tcp_paws_reject(&tp->rx_opt, 0))
5803                 goto discard_and_undo;
5804 
5805         if (th->syn) {
5806                 /* We see SYN without ACK. It is attempt of
5807                  * simultaneous connect with crossed SYNs.
5808                  * Particularly, it can be connect to self.
5809                  */
5810                 tcp_set_state(sk, TCP_SYN_RECV);
5811 
5812                 if (tp->rx_opt.saw_tstamp) {
5813                         tp->rx_opt.tstamp_ok = 1;
5814                         tcp_store_ts_recent(tp);
5815                         tp->tcp_header_len =
5816                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5817                 } else {
5818                         tp->tcp_header_len = sizeof(struct tcphdr);
5819                 }
5820 
5821                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5822                 tp->copied_seq = tp->rcv_nxt;
5823                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5824 
5825                 /* RFC1323: The window in SYN & SYN/ACK segments is
5826                  * never scaled.
5827                  */
5828                 tp->snd_wnd    = ntohs(th->window);
5829                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5830                 tp->max_window = tp->snd_wnd;
5831 
5832                 TCP_ECN_rcv_syn(tp, th);
5833 
5834                 tcp_mtup_init(sk);
5835                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5836                 tcp_initialize_rcv_mss(sk);
5837 
5838                 tcp_send_synack(sk);
5839 #if 0
5840                 /* Note, we could accept data and URG from this segment.
5841                  * There are no obstacles to make this.
5842                  *
5843                  * However, if we ignore data in ACKless segments sometimes,
5844                  * we have no reasons to accept it sometimes.
5845                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5846                  * is not flawless. So, discard packet for sanity.
5847                  * Uncomment this return to process the data.
5848                  */
5849                 return -1;
5850 #else
5851                 goto discard;
5852 #endif
5853         }
5854         /* "fifth, if neither of the SYN or RST bits is set then
5855          * drop the segment and return."
5856          */
5857 
5858 discard_and_undo:
5859         tcp_clear_options(&tp->rx_opt);
5860         tp->rx_opt.mss_clamp = saved_clamp;
5861         goto discard;
5862 
5863 reset_and_undo:
5864         tcp_clear_options(&tp->rx_opt);
5865         tp->rx_opt.mss_clamp = saved_clamp;
5866         return 1;
5867 }
5868 
5869 /*
5870  *      This function implements the receiving procedure of RFC 793 for
5871  *      all states except ESTABLISHED and TIME_WAIT.
5872  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5873  *      address independent.
5874  */
5875 
5876 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5877                           const struct tcphdr *th, unsigned int len)
5878 {
5879         struct tcp_sock *tp = tcp_sk(sk);
5880         struct inet_connection_sock *icsk = inet_csk(sk);
5881         int queued = 0;
5882 
5883         tp->rx_opt.saw_tstamp = 0;
5884 
5885         switch (sk->sk_state) {
5886         case TCP_CLOSE:
5887                 goto discard;
5888 
5889         case TCP_LISTEN:
5890                 if (th->ack)
5891                         return 1;
5892 
5893                 if (th->rst)
5894                         goto discard;
5895 
5896                 if (th->syn) {
5897                         if (th->fin)
5898                                 goto discard;
5899                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5900                                 return 1;
5901 
5902                         /* Now we have several options: In theory there is
5903                          * nothing else in the frame. KA9Q has an option to
5904                          * send data with the syn, BSD accepts data with the
5905                          * syn up to the [to be] advertised window and
5906                          * Solaris 2.1 gives you a protocol error. For now
5907                          * we just ignore it, that fits the spec precisely
5908                          * and avoids incompatibilities. It would be nice in
5909                          * future to drop through and process the data.
5910                          *
5911                          * Now that TTCP is starting to be used we ought to
5912                          * queue this data.
5913                          * But, this leaves one open to an easy denial of
5914                          * service attack, and SYN cookies can't defend
5915                          * against this problem. So, we drop the data
5916                          * in the interest of security over speed unless
5917                          * it's still in use.
5918                          */
5919                         kfree_skb(skb);
5920                         return 0;
5921                 }
5922                 goto discard;
5923 
5924         case TCP_SYN_SENT:
5925                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5926                 if (queued >= 0)
5927                         return queued;
5928 
5929                 /* Do step6 onward by hand. */
5930                 tcp_urg(sk, skb, th);
5931                 __kfree_skb(skb);
5932                 tcp_data_snd_check(sk);
5933                 return 0;
5934         }
5935 
5936         if (!tcp_validate_incoming(sk, skb, th, 0))
5937                 return 0;
5938 
5939         /* step 5: check the ACK field */
5940         if (th->ack) {
5941                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5942                                                   FLAG_UPDATE_TS_RECENT) > 0;
5943 
5944                 switch (sk->sk_state) {
5945                 case TCP_SYN_RECV:
5946                         if (acceptable) {
5947                                 tp->copied_seq = tp->rcv_nxt;
5948                                 smp_mb();
5949                                 tcp_set_state(sk, TCP_ESTABLISHED);
5950                                 sk->sk_state_change(sk);
5951 
5952                                 /* Note, that this wakeup is only for marginal
5953                                  * crossed SYN case. Passively open sockets
5954                                  * are not waked up, because sk->sk_sleep ==
5955                                  * NULL and sk->sk_socket == NULL.
5956                                  */
5957                                 if (sk->sk_socket)
5958                                         sk_wake_async(sk,
5959                                                       SOCK_WAKE_IO, POLL_OUT);
5960 
5961                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5962                                 tp->snd_wnd = ntohs(th->window) <<
5963                                               tp->rx_opt.snd_wscale;
5964                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5965 
5966                                 if (tp->rx_opt.tstamp_ok)
5967                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5968 
5969                                 /* Make sure socket is routed, for
5970                                  * correct metrics.
5971                                  */
5972                                 icsk->icsk_af_ops->rebuild_header(sk);
5973 
5974                                 tcp_init_metrics(sk);
5975 
5976                                 tcp_init_congestion_control(sk);
5977 
5978                                 /* Prevent spurious tcp_cwnd_restart() on
5979                                  * first data packet.
5980                                  */
5981                                 tp->lsndtime = tcp_time_stamp;
5982 
5983                                 tcp_mtup_init(sk);
5984                                 tcp_initialize_rcv_mss(sk);
5985                                 tcp_init_buffer_space(sk);
5986                                 tcp_fast_path_on(tp);
5987                         } else {
5988                                 return 1;
5989                         }
5990                         break;
5991 
5992                 case TCP_FIN_WAIT1:
5993                         if (tp->snd_una == tp->write_seq) {
5994                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5995                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5996                                 dst_confirm(__sk_dst_get(sk));
5997 
5998                                 if (!sock_flag(sk, SOCK_DEAD))
5999                                         /* Wake up lingering close() */
6000                                         sk->sk_state_change(sk);
6001                                 else {
6002                                         int tmo;
6003 
6004                                         if (tp->linger2 < 0 ||
6005                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6006                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
6007                                                 tcp_done(sk);