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Linux/net/sctp/output.c

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  1 /* SCTP kernel implementation
  2  * (C) Copyright IBM Corp. 2001, 2004
  3  * Copyright (c) 1999-2000 Cisco, Inc.
  4  * Copyright (c) 1999-2001 Motorola, Inc.
  5  *
  6  * This file is part of the SCTP kernel implementation
  7  *
  8  * These functions handle output processing.
  9  *
 10  * This SCTP implementation is free software;
 11  * you can redistribute it and/or modify it under the terms of
 12  * the GNU General Public License as published by
 13  * the Free Software Foundation; either version 2, or (at your option)
 14  * any later version.
 15  *
 16  * This SCTP implementation is distributed in the hope that it
 17  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
 18  *                 ************************
 19  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 20  * See the GNU General Public License for more details.
 21  *
 22  * You should have received a copy of the GNU General Public License
 23  * along with GNU CC; see the file COPYING.  If not, see
 24  * <http://www.gnu.org/licenses/>.
 25  *
 26  * Please send any bug reports or fixes you make to the
 27  * email address(es):
 28  *    lksctp developers <linux-sctp@vger.kernel.org>
 29  *
 30  * Written or modified by:
 31  *    La Monte H.P. Yarroll <piggy@acm.org>
 32  *    Karl Knutson          <karl@athena.chicago.il.us>
 33  *    Jon Grimm             <jgrimm@austin.ibm.com>
 34  *    Sridhar Samudrala     <sri@us.ibm.com>
 35  */
 36 
 37 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 38 
 39 #include <linux/types.h>
 40 #include <linux/kernel.h>
 41 #include <linux/wait.h>
 42 #include <linux/time.h>
 43 #include <linux/ip.h>
 44 #include <linux/ipv6.h>
 45 #include <linux/init.h>
 46 #include <linux/slab.h>
 47 #include <net/inet_ecn.h>
 48 #include <net/ip.h>
 49 #include <net/icmp.h>
 50 #include <net/net_namespace.h>
 51 
 52 #include <linux/socket.h> /* for sa_family_t */
 53 #include <net/sock.h>
 54 
 55 #include <net/sctp/sctp.h>
 56 #include <net/sctp/sm.h>
 57 #include <net/sctp/checksum.h>
 58 
 59 /* Forward declarations for private helpers. */
 60 static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
 61                                               struct sctp_chunk *chunk);
 62 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
 63                                            struct sctp_chunk *chunk);
 64 static void sctp_packet_append_data(struct sctp_packet *packet,
 65                                            struct sctp_chunk *chunk);
 66 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
 67                                         struct sctp_chunk *chunk,
 68                                         u16 chunk_len);
 69 
 70 static void sctp_packet_reset(struct sctp_packet *packet)
 71 {
 72         packet->size = packet->overhead;
 73         packet->has_cookie_echo = 0;
 74         packet->has_sack = 0;
 75         packet->has_data = 0;
 76         packet->has_auth = 0;
 77         packet->ipfragok = 0;
 78         packet->auth = NULL;
 79 }
 80 
 81 /* Config a packet.
 82  * This appears to be a followup set of initializations.
 83  */
 84 struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
 85                                        __u32 vtag, int ecn_capable)
 86 {
 87         struct sctp_chunk *chunk = NULL;
 88 
 89         pr_debug("%s: packet:%p vtag:0x%x\n", __func__, packet, vtag);
 90 
 91         packet->vtag = vtag;
 92 
 93         if (ecn_capable && sctp_packet_empty(packet)) {
 94                 chunk = sctp_get_ecne_prepend(packet->transport->asoc);
 95 
 96                 /* If there a is a prepend chunk stick it on the list before
 97                  * any other chunks get appended.
 98                  */
 99                 if (chunk)
100                         sctp_packet_append_chunk(packet, chunk);
101         }
102 
103         return packet;
104 }
105 
106 /* Initialize the packet structure. */
107 struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
108                                      struct sctp_transport *transport,
109                                      __u16 sport, __u16 dport)
110 {
111         struct sctp_association *asoc = transport->asoc;
112         size_t overhead;
113 
114         pr_debug("%s: packet:%p transport:%p\n", __func__, packet, transport);
115 
116         packet->transport = transport;
117         packet->source_port = sport;
118         packet->destination_port = dport;
119         INIT_LIST_HEAD(&packet->chunk_list);
120         if (asoc) {
121                 struct sctp_sock *sp = sctp_sk(asoc->base.sk);
122                 overhead = sp->pf->af->net_header_len;
123         } else {
124                 overhead = sizeof(struct ipv6hdr);
125         }
126         overhead += sizeof(struct sctphdr);
127         packet->overhead = overhead;
128         sctp_packet_reset(packet);
129         packet->vtag = 0;
130 
131         return packet;
132 }
133 
134 /* Free a packet.  */
135 void sctp_packet_free(struct sctp_packet *packet)
136 {
137         struct sctp_chunk *chunk, *tmp;
138 
139         pr_debug("%s: packet:%p\n", __func__, packet);
140 
141         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
142                 list_del_init(&chunk->list);
143                 sctp_chunk_free(chunk);
144         }
145 }
146 
147 /* This routine tries to append the chunk to the offered packet. If adding
148  * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
149  * is not present in the packet, it transmits the input packet.
150  * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
151  * as it can fit in the packet, but any more data that does not fit in this
152  * packet can be sent only after receiving the COOKIE_ACK.
153  */
154 sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
155                                        struct sctp_chunk *chunk,
156                                        int one_packet)
157 {
158         sctp_xmit_t retval;
159         int error = 0;
160 
161         pr_debug("%s: packet:%p chunk:%p\n", __func__, packet, chunk);
162 
163         switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
164         case SCTP_XMIT_PMTU_FULL:
165                 if (!packet->has_cookie_echo) {
166                         error = sctp_packet_transmit(packet);
167                         if (error < 0)
168                                 chunk->skb->sk->sk_err = -error;
169 
170                         /* If we have an empty packet, then we can NOT ever
171                          * return PMTU_FULL.
172                          */
173                         if (!one_packet)
174                                 retval = sctp_packet_append_chunk(packet,
175                                                                   chunk);
176                 }
177                 break;
178 
179         case SCTP_XMIT_RWND_FULL:
180         case SCTP_XMIT_OK:
181         case SCTP_XMIT_NAGLE_DELAY:
182                 break;
183         }
184 
185         return retval;
186 }
187 
188 /* Try to bundle an auth chunk into the packet. */
189 static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
190                                            struct sctp_chunk *chunk)
191 {
192         struct sctp_association *asoc = pkt->transport->asoc;
193         struct sctp_chunk *auth;
194         sctp_xmit_t retval = SCTP_XMIT_OK;
195 
196         /* if we don't have an association, we can't do authentication */
197         if (!asoc)
198                 return retval;
199 
200         /* See if this is an auth chunk we are bundling or if
201          * auth is already bundled.
202          */
203         if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->has_auth)
204                 return retval;
205 
206         /* if the peer did not request this chunk to be authenticated,
207          * don't do it
208          */
209         if (!chunk->auth)
210                 return retval;
211 
212         auth = sctp_make_auth(asoc);
213         if (!auth)
214                 return retval;
215 
216         retval = __sctp_packet_append_chunk(pkt, auth);
217 
218         if (retval != SCTP_XMIT_OK)
219                 sctp_chunk_free(auth);
220 
221         return retval;
222 }
223 
224 /* Try to bundle a SACK with the packet. */
225 static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
226                                            struct sctp_chunk *chunk)
227 {
228         sctp_xmit_t retval = SCTP_XMIT_OK;
229 
230         /* If sending DATA and haven't aleady bundled a SACK, try to
231          * bundle one in to the packet.
232          */
233         if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
234             !pkt->has_cookie_echo) {
235                 struct sctp_association *asoc;
236                 struct timer_list *timer;
237                 asoc = pkt->transport->asoc;
238                 timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
239 
240                 /* If the SACK timer is running, we have a pending SACK */
241                 if (timer_pending(timer)) {
242                         struct sctp_chunk *sack;
243 
244                         if (pkt->transport->sack_generation !=
245                             pkt->transport->asoc->peer.sack_generation)
246                                 return retval;
247 
248                         asoc->a_rwnd = asoc->rwnd;
249                         sack = sctp_make_sack(asoc);
250                         if (sack) {
251                                 retval = __sctp_packet_append_chunk(pkt, sack);
252                                 if (retval != SCTP_XMIT_OK) {
253                                         sctp_chunk_free(sack);
254                                         goto out;
255                                 }
256                                 asoc->peer.sack_needed = 0;
257                                 if (del_timer(timer))
258                                         sctp_association_put(asoc);
259                         }
260                 }
261         }
262 out:
263         return retval;
264 }
265 
266 
267 /* Append a chunk to the offered packet reporting back any inability to do
268  * so.
269  */
270 static sctp_xmit_t __sctp_packet_append_chunk(struct sctp_packet *packet,
271                                               struct sctp_chunk *chunk)
272 {
273         sctp_xmit_t retval = SCTP_XMIT_OK;
274         __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
275 
276         /* Check to see if this chunk will fit into the packet */
277         retval = sctp_packet_will_fit(packet, chunk, chunk_len);
278         if (retval != SCTP_XMIT_OK)
279                 goto finish;
280 
281         /* We believe that this chunk is OK to add to the packet */
282         switch (chunk->chunk_hdr->type) {
283         case SCTP_CID_DATA:
284                 /* Account for the data being in the packet */
285                 sctp_packet_append_data(packet, chunk);
286                 /* Disallow SACK bundling after DATA. */
287                 packet->has_sack = 1;
288                 /* Disallow AUTH bundling after DATA */
289                 packet->has_auth = 1;
290                 /* Let it be knows that packet has DATA in it */
291                 packet->has_data = 1;
292                 /* timestamp the chunk for rtx purposes */
293                 chunk->sent_at = jiffies;
294                 break;
295         case SCTP_CID_COOKIE_ECHO:
296                 packet->has_cookie_echo = 1;
297                 break;
298 
299         case SCTP_CID_SACK:
300                 packet->has_sack = 1;
301                 if (chunk->asoc)
302                         chunk->asoc->stats.osacks++;
303                 break;
304 
305         case SCTP_CID_AUTH:
306                 packet->has_auth = 1;
307                 packet->auth = chunk;
308                 break;
309         }
310 
311         /* It is OK to send this chunk.  */
312         list_add_tail(&chunk->list, &packet->chunk_list);
313         packet->size += chunk_len;
314         chunk->transport = packet->transport;
315 finish:
316         return retval;
317 }
318 
319 /* Append a chunk to the offered packet reporting back any inability to do
320  * so.
321  */
322 sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
323                                      struct sctp_chunk *chunk)
324 {
325         sctp_xmit_t retval = SCTP_XMIT_OK;
326 
327         pr_debug("%s: packet:%p chunk:%p\n", __func__, packet, chunk);
328 
329         /* Data chunks are special.  Before seeing what else we can
330          * bundle into this packet, check to see if we are allowed to
331          * send this DATA.
332          */
333         if (sctp_chunk_is_data(chunk)) {
334                 retval = sctp_packet_can_append_data(packet, chunk);
335                 if (retval != SCTP_XMIT_OK)
336                         goto finish;
337         }
338 
339         /* Try to bundle AUTH chunk */
340         retval = sctp_packet_bundle_auth(packet, chunk);
341         if (retval != SCTP_XMIT_OK)
342                 goto finish;
343 
344         /* Try to bundle SACK chunk */
345         retval = sctp_packet_bundle_sack(packet, chunk);
346         if (retval != SCTP_XMIT_OK)
347                 goto finish;
348 
349         retval = __sctp_packet_append_chunk(packet, chunk);
350 
351 finish:
352         return retval;
353 }
354 
355 static void sctp_packet_release_owner(struct sk_buff *skb)
356 {
357         sk_free(skb->sk);
358 }
359 
360 static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
361 {
362         skb_orphan(skb);
363         skb->sk = sk;
364         skb->destructor = sctp_packet_release_owner;
365 
366         /*
367          * The data chunks have already been accounted for in sctp_sendmsg(),
368          * therefore only reserve a single byte to keep socket around until
369          * the packet has been transmitted.
370          */
371         atomic_inc(&sk->sk_wmem_alloc);
372 }
373 
374 /* All packets are sent to the network through this function from
375  * sctp_outq_tail().
376  *
377  * The return value is a normal kernel error return value.
378  */
379 int sctp_packet_transmit(struct sctp_packet *packet)
380 {
381         struct sctp_transport *tp = packet->transport;
382         struct sctp_association *asoc = tp->asoc;
383         struct sctphdr *sh;
384         struct sk_buff *nskb;
385         struct sctp_chunk *chunk, *tmp;
386         struct sock *sk;
387         int err = 0;
388         int padding;            /* How much padding do we need?  */
389         __u8 has_data = 0;
390         struct dst_entry *dst;
391         unsigned char *auth = NULL;     /* pointer to auth in skb data */
392 
393         pr_debug("%s: packet:%p\n", __func__, packet);
394 
395         /* Do NOT generate a chunkless packet. */
396         if (list_empty(&packet->chunk_list))
397                 return err;
398 
399         /* Set up convenience variables... */
400         chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
401         sk = chunk->skb->sk;
402 
403         /* Allocate the new skb.  */
404         nskb = alloc_skb(packet->size + MAX_HEADER, GFP_ATOMIC);
405         if (!nskb)
406                 goto nomem;
407 
408         /* Make sure the outbound skb has enough header room reserved. */
409         skb_reserve(nskb, packet->overhead + MAX_HEADER);
410 
411         /* Set the owning socket so that we know where to get the
412          * destination IP address.
413          */
414         sctp_packet_set_owner_w(nskb, sk);
415 
416         if (!sctp_transport_dst_check(tp)) {
417                 sctp_transport_route(tp, NULL, sctp_sk(sk));
418                 if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
419                         sctp_assoc_sync_pmtu(sk, asoc);
420                 }
421         }
422         dst = dst_clone(tp->dst);
423         if (!dst)
424                 goto no_route;
425         skb_dst_set(nskb, dst);
426 
427         /* Build the SCTP header.  */
428         sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
429         skb_reset_transport_header(nskb);
430         sh->source = htons(packet->source_port);
431         sh->dest   = htons(packet->destination_port);
432 
433         /* From 6.8 Adler-32 Checksum Calculation:
434          * After the packet is constructed (containing the SCTP common
435          * header and one or more control or DATA chunks), the
436          * transmitter shall:
437          *
438          * 1) Fill in the proper Verification Tag in the SCTP common
439          *    header and initialize the checksum field to 0's.
440          */
441         sh->vtag     = htonl(packet->vtag);
442         sh->checksum = 0;
443 
444         /**
445          * 6.10 Bundling
446          *
447          *    An endpoint bundles chunks by simply including multiple
448          *    chunks in one outbound SCTP packet.  ...
449          */
450 
451         /**
452          * 3.2  Chunk Field Descriptions
453          *
454          * The total length of a chunk (including Type, Length and
455          * Value fields) MUST be a multiple of 4 bytes.  If the length
456          * of the chunk is not a multiple of 4 bytes, the sender MUST
457          * pad the chunk with all zero bytes and this padding is not
458          * included in the chunk length field.  The sender should
459          * never pad with more than 3 bytes.
460          *
461          * [This whole comment explains WORD_ROUND() below.]
462          */
463 
464         pr_debug("***sctp_transmit_packet***\n");
465 
466         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
467                 list_del_init(&chunk->list);
468                 if (sctp_chunk_is_data(chunk)) {
469                         /* 6.3.1 C4) When data is in flight and when allowed
470                          * by rule C5, a new RTT measurement MUST be made each
471                          * round trip.  Furthermore, new RTT measurements
472                          * SHOULD be made no more than once per round-trip
473                          * for a given destination transport address.
474                          */
475 
476                         if (!chunk->resent && !tp->rto_pending) {
477                                 chunk->rtt_in_progress = 1;
478                                 tp->rto_pending = 1;
479                         }
480 
481                         has_data = 1;
482                 }
483 
484                 padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
485                 if (padding)
486                         memset(skb_put(chunk->skb, padding), 0, padding);
487 
488                 /* if this is the auth chunk that we are adding,
489                  * store pointer where it will be added and put
490                  * the auth into the packet.
491                  */
492                 if (chunk == packet->auth)
493                         auth = skb_tail_pointer(nskb);
494 
495                 memcpy(skb_put(nskb, chunk->skb->len),
496                                chunk->skb->data, chunk->skb->len);
497 
498                 pr_debug("*** Chunk:%p[%s] %s 0x%x, length:%d, chunk->skb->len:%d, "
499                          "rtt_in_progress:%d\n", chunk,
500                          sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)),
501                          chunk->has_tsn ? "TSN" : "No TSN",
502                          chunk->has_tsn ? ntohl(chunk->subh.data_hdr->tsn) : 0,
503                          ntohs(chunk->chunk_hdr->length), chunk->skb->len,
504                          chunk->rtt_in_progress);
505 
506                 /*
507                  * If this is a control chunk, this is our last
508                  * reference. Free data chunks after they've been
509                  * acknowledged or have failed.
510                  */
511                 if (!sctp_chunk_is_data(chunk))
512                         sctp_chunk_free(chunk);
513         }
514 
515         /* SCTP-AUTH, Section 6.2
516          *    The sender MUST calculate the MAC as described in RFC2104 [2]
517          *    using the hash function H as described by the MAC Identifier and
518          *    the shared association key K based on the endpoint pair shared key
519          *    described by the shared key identifier.  The 'data' used for the
520          *    computation of the AUTH-chunk is given by the AUTH chunk with its
521          *    HMAC field set to zero (as shown in Figure 6) followed by all
522          *    chunks that are placed after the AUTH chunk in the SCTP packet.
523          */
524         if (auth)
525                 sctp_auth_calculate_hmac(asoc, nskb,
526                                         (struct sctp_auth_chunk *)auth,
527                                         GFP_ATOMIC);
528 
529         /* 2) Calculate the Adler-32 checksum of the whole packet,
530          *    including the SCTP common header and all the
531          *    chunks.
532          *
533          * Note: Adler-32 is no longer applicable, as has been replaced
534          * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
535          */
536         if (!sctp_checksum_disable) {
537                 if (!(dst->dev->features & NETIF_F_SCTP_CSUM) ||
538                     (dst_xfrm(dst) != NULL) || packet->ipfragok) {
539                         sh->checksum = sctp_compute_cksum(nskb, 0);
540                 } else {
541                         /* no need to seed pseudo checksum for SCTP */
542                         nskb->ip_summed = CHECKSUM_PARTIAL;
543                         nskb->csum_start = skb_transport_header(nskb) - nskb->head;
544                         nskb->csum_offset = offsetof(struct sctphdr, checksum);
545                 }
546         }
547 
548         /* IP layer ECN support
549          * From RFC 2481
550          *  "The ECN-Capable Transport (ECT) bit would be set by the
551          *   data sender to indicate that the end-points of the
552          *   transport protocol are ECN-capable."
553          *
554          * Now setting the ECT bit all the time, as it should not cause
555          * any problems protocol-wise even if our peer ignores it.
556          *
557          * Note: The works for IPv6 layer checks this bit too later
558          * in transmission.  See IP6_ECN_flow_xmit().
559          */
560         tp->af_specific->ecn_capable(nskb->sk);
561 
562         /* Set up the IP options.  */
563         /* BUG: not implemented
564          * For v4 this all lives somewhere in sk->sk_opt...
565          */
566 
567         /* Dump that on IP!  */
568         if (asoc) {
569                 asoc->stats.opackets++;
570                 if (asoc->peer.last_sent_to != tp)
571                         /* Considering the multiple CPU scenario, this is a
572                          * "correcter" place for last_sent_to.  --xguo
573                          */
574                         asoc->peer.last_sent_to = tp;
575         }
576 
577         if (has_data) {
578                 struct timer_list *timer;
579                 unsigned long timeout;
580 
581                 /* Restart the AUTOCLOSE timer when sending data. */
582                 if (sctp_state(asoc, ESTABLISHED) &&
583                     asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE]) {
584                         timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
585                         timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
586 
587                         if (!mod_timer(timer, jiffies + timeout))
588                                 sctp_association_hold(asoc);
589                 }
590         }
591 
592         pr_debug("***sctp_transmit_packet*** skb->len:%d\n", nskb->len);
593 
594         nskb->local_df = packet->ipfragok;
595         tp->af_specific->sctp_xmit(nskb, tp);
596 
597 out:
598         sctp_packet_reset(packet);
599         return err;
600 no_route:
601         kfree_skb(nskb);
602 
603         if (asoc)
604                 IP_INC_STATS(sock_net(asoc->base.sk), IPSTATS_MIB_OUTNOROUTES);
605 
606         /* FIXME: Returning the 'err' will effect all the associations
607          * associated with a socket, although only one of the paths of the
608          * association is unreachable.
609          * The real failure of a transport or association can be passed on
610          * to the user via notifications. So setting this error may not be
611          * required.
612          */
613          /* err = -EHOSTUNREACH; */
614 err:
615         /* Control chunks are unreliable so just drop them.  DATA chunks
616          * will get resent or dropped later.
617          */
618 
619         list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
620                 list_del_init(&chunk->list);
621                 if (!sctp_chunk_is_data(chunk))
622                         sctp_chunk_free(chunk);
623         }
624         goto out;
625 nomem:
626         err = -ENOMEM;
627         goto err;
628 }
629 
630 /********************************************************************
631  * 2nd Level Abstractions
632  ********************************************************************/
633 
634 /* This private function check to see if a chunk can be added */
635 static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
636                                            struct sctp_chunk *chunk)
637 {
638         sctp_xmit_t retval = SCTP_XMIT_OK;
639         size_t datasize, rwnd, inflight, flight_size;
640         struct sctp_transport *transport = packet->transport;
641         struct sctp_association *asoc = transport->asoc;
642         struct sctp_outq *q = &asoc->outqueue;
643 
644         /* RFC 2960 6.1  Transmission of DATA Chunks
645          *
646          * A) At any given time, the data sender MUST NOT transmit new data to
647          * any destination transport address if its peer's rwnd indicates
648          * that the peer has no buffer space (i.e. rwnd is 0, see Section
649          * 6.2.1).  However, regardless of the value of rwnd (including if it
650          * is 0), the data sender can always have one DATA chunk in flight to
651          * the receiver if allowed by cwnd (see rule B below).  This rule
652          * allows the sender to probe for a change in rwnd that the sender
653          * missed due to the SACK having been lost in transit from the data
654          * receiver to the data sender.
655          */
656 
657         rwnd = asoc->peer.rwnd;
658         inflight = q->outstanding_bytes;
659         flight_size = transport->flight_size;
660 
661         datasize = sctp_data_size(chunk);
662 
663         if (datasize > rwnd) {
664                 if (inflight > 0) {
665                         /* We have (at least) one data chunk in flight,
666                          * so we can't fall back to rule 6.1 B).
667                          */
668                         retval = SCTP_XMIT_RWND_FULL;
669                         goto finish;
670                 }
671         }
672 
673         /* RFC 2960 6.1  Transmission of DATA Chunks
674          *
675          * B) At any given time, the sender MUST NOT transmit new data
676          * to a given transport address if it has cwnd or more bytes
677          * of data outstanding to that transport address.
678          */
679         /* RFC 7.2.4 & the Implementers Guide 2.8.
680          *
681          * 3) ...
682          *    When a Fast Retransmit is being performed the sender SHOULD
683          *    ignore the value of cwnd and SHOULD NOT delay retransmission.
684          */
685         if (chunk->fast_retransmit != SCTP_NEED_FRTX)
686                 if (flight_size >= transport->cwnd) {
687                         retval = SCTP_XMIT_RWND_FULL;
688                         goto finish;
689                 }
690 
691         /* Nagle's algorithm to solve small-packet problem:
692          * Inhibit the sending of new chunks when new outgoing data arrives
693          * if any previously transmitted data on the connection remains
694          * unacknowledged.
695          */
696         if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
697             inflight && sctp_state(asoc, ESTABLISHED)) {
698                 unsigned int max = transport->pathmtu - packet->overhead;
699                 unsigned int len = chunk->skb->len + q->out_qlen;
700 
701                 /* Check whether this chunk and all the rest of pending
702                  * data will fit or delay in hopes of bundling a full
703                  * sized packet.
704                  * Don't delay large message writes that may have been
705                  * fragmeneted into small peices.
706                  */
707                 if ((len < max) && chunk->msg->can_delay) {
708                         retval = SCTP_XMIT_NAGLE_DELAY;
709                         goto finish;
710                 }
711         }
712 
713 finish:
714         return retval;
715 }
716 
717 /* This private function does management things when adding DATA chunk */
718 static void sctp_packet_append_data(struct sctp_packet *packet,
719                                 struct sctp_chunk *chunk)
720 {
721         struct sctp_transport *transport = packet->transport;
722         size_t datasize = sctp_data_size(chunk);
723         struct sctp_association *asoc = transport->asoc;
724         u32 rwnd = asoc->peer.rwnd;
725 
726         /* Keep track of how many bytes are in flight over this transport. */
727         transport->flight_size += datasize;
728 
729         /* Keep track of how many bytes are in flight to the receiver. */
730         asoc->outqueue.outstanding_bytes += datasize;
731 
732         /* Update our view of the receiver's rwnd. */
733         if (datasize < rwnd)
734                 rwnd -= datasize;
735         else
736                 rwnd = 0;
737 
738         asoc->peer.rwnd = rwnd;
739         /* Has been accepted for transmission. */
740         if (!asoc->peer.prsctp_capable)
741                 chunk->msg->can_abandon = 0;
742         sctp_chunk_assign_tsn(chunk);
743         sctp_chunk_assign_ssn(chunk);
744 }
745 
746 static sctp_xmit_t sctp_packet_will_fit(struct sctp_packet *packet,
747                                         struct sctp_chunk *chunk,
748                                         u16 chunk_len)
749 {
750         size_t psize;
751         size_t pmtu;
752         int too_big;
753         sctp_xmit_t retval = SCTP_XMIT_OK;
754 
755         psize = packet->size;
756         pmtu  = ((packet->transport->asoc) ?
757                 (packet->transport->asoc->pathmtu) :
758                 (packet->transport->pathmtu));
759 
760         too_big = (psize + chunk_len > pmtu);
761 
762         /* Decide if we need to fragment or resubmit later. */
763         if (too_big) {
764                 /* It's OK to fragmet at IP level if any one of the following
765                  * is true:
766                  *      1. The packet is empty (meaning this chunk is greater
767                  *         the MTU)
768                  *      2. The chunk we are adding is a control chunk
769                  *      3. The packet doesn't have any data in it yet and data
770                  *      requires authentication.
771                  */
772                 if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
773                     (!packet->has_data && chunk->auth)) {
774                         /* We no longer do re-fragmentation.
775                          * Just fragment at the IP layer, if we
776                          * actually hit this condition
777                          */
778                         packet->ipfragok = 1;
779                 } else {
780                         retval = SCTP_XMIT_PMTU_FULL;
781                 }
782         }
783 
784         return retval;
785 }
786 

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