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Linux/net/ipv6/netfilter/nf_conntrack_reasm.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  * IPv6 fragment reassembly for connection tracking
  4  *
  5  * Copyright (C)2004 USAGI/WIDE Project
  6  *
  7  * Author:
  8  *      Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
  9  *
 10  * Based on: net/ipv6/reassembly.c
 11  */
 12 
 13 #define pr_fmt(fmt) "IPv6-nf: " fmt
 14 
 15 #include <linux/errno.h>
 16 #include <linux/types.h>
 17 #include <linux/string.h>
 18 #include <linux/socket.h>
 19 #include <linux/sockios.h>
 20 #include <linux/jiffies.h>
 21 #include <linux/net.h>
 22 #include <linux/list.h>
 23 #include <linux/netdevice.h>
 24 #include <linux/in6.h>
 25 #include <linux/ipv6.h>
 26 #include <linux/icmpv6.h>
 27 #include <linux/random.h>
 28 #include <linux/slab.h>
 29 
 30 #include <net/sock.h>
 31 #include <net/snmp.h>
 32 #include <net/ipv6_frag.h>
 33 
 34 #include <net/protocol.h>
 35 #include <net/transp_v6.h>
 36 #include <net/rawv6.h>
 37 #include <net/ndisc.h>
 38 #include <net/addrconf.h>
 39 #include <net/inet_ecn.h>
 40 #include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
 41 #include <linux/sysctl.h>
 42 #include <linux/netfilter.h>
 43 #include <linux/netfilter_ipv6.h>
 44 #include <linux/kernel.h>
 45 #include <linux/module.h>
 46 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 47 
 48 static const char nf_frags_cache_name[] = "nf-frags";
 49 
 50 static struct inet_frags nf_frags;
 51 
 52 #ifdef CONFIG_SYSCTL
 53 
 54 static struct ctl_table nf_ct_frag6_sysctl_table[] = {
 55         {
 56                 .procname       = "nf_conntrack_frag6_timeout",
 57                 .maxlen         = sizeof(unsigned int),
 58                 .mode           = 0644,
 59                 .proc_handler   = proc_dointvec_jiffies,
 60         },
 61         {
 62                 .procname       = "nf_conntrack_frag6_low_thresh",
 63                 .maxlen         = sizeof(unsigned long),
 64                 .mode           = 0644,
 65                 .proc_handler   = proc_doulongvec_minmax,
 66         },
 67         {
 68                 .procname       = "nf_conntrack_frag6_high_thresh",
 69                 .maxlen         = sizeof(unsigned long),
 70                 .mode           = 0644,
 71                 .proc_handler   = proc_doulongvec_minmax,
 72         },
 73         { }
 74 };
 75 
 76 static int nf_ct_frag6_sysctl_register(struct net *net)
 77 {
 78         struct ctl_table *table;
 79         struct ctl_table_header *hdr;
 80 
 81         table = nf_ct_frag6_sysctl_table;
 82         if (!net_eq(net, &init_net)) {
 83                 table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
 84                                 GFP_KERNEL);
 85                 if (table == NULL)
 86                         goto err_alloc;
 87         }
 88 
 89         table[0].data   = &net->nf_frag.fqdir->timeout;
 90         table[1].data   = &net->nf_frag.fqdir->low_thresh;
 91         table[1].extra2 = &net->nf_frag.fqdir->high_thresh;
 92         table[2].data   = &net->nf_frag.fqdir->high_thresh;
 93         table[2].extra1 = &net->nf_frag.fqdir->low_thresh;
 94         table[2].extra2 = &init_net.nf_frag.fqdir->high_thresh;
 95 
 96         hdr = register_net_sysctl(net, "net/netfilter", table);
 97         if (hdr == NULL)
 98                 goto err_reg;
 99 
100         net->nf_frag_frags_hdr = hdr;
101         return 0;
102 
103 err_reg:
104         if (!net_eq(net, &init_net))
105                 kfree(table);
106 err_alloc:
107         return -ENOMEM;
108 }
109 
110 static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
111 {
112         struct ctl_table *table;
113 
114         table = net->nf_frag_frags_hdr->ctl_table_arg;
115         unregister_net_sysctl_table(net->nf_frag_frags_hdr);
116         if (!net_eq(net, &init_net))
117                 kfree(table);
118 }
119 
120 #else
121 static int nf_ct_frag6_sysctl_register(struct net *net)
122 {
123         return 0;
124 }
125 static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
126 {
127 }
128 #endif
129 
130 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
131                              struct sk_buff *prev_tail, struct net_device *dev);
132 
133 static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
134 {
135         return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
136 }
137 
138 static void nf_ct_frag6_expire(struct timer_list *t)
139 {
140         struct inet_frag_queue *frag = from_timer(frag, t, timer);
141         struct frag_queue *fq;
142 
143         fq = container_of(frag, struct frag_queue, q);
144 
145         ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
146 }
147 
148 /* Creation primitives. */
149 static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
150                                   const struct ipv6hdr *hdr, int iif)
151 {
152         struct frag_v6_compare_key key = {
153                 .id = id,
154                 .saddr = hdr->saddr,
155                 .daddr = hdr->daddr,
156                 .user = user,
157                 .iif = iif,
158         };
159         struct inet_frag_queue *q;
160 
161         q = inet_frag_find(net->nf_frag.fqdir, &key);
162         if (!q)
163                 return NULL;
164 
165         return container_of(q, struct frag_queue, q);
166 }
167 
168 
169 static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
170                              const struct frag_hdr *fhdr, int nhoff)
171 {
172         unsigned int payload_len;
173         struct net_device *dev;
174         struct sk_buff *prev;
175         int offset, end, err;
176         u8 ecn;
177 
178         if (fq->q.flags & INET_FRAG_COMPLETE) {
179                 pr_debug("Already completed\n");
180                 goto err;
181         }
182 
183         payload_len = ntohs(ipv6_hdr(skb)->payload_len);
184 
185         offset = ntohs(fhdr->frag_off) & ~0x7;
186         end = offset + (payload_len -
187                         ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
188 
189         if ((unsigned int)end > IPV6_MAXPLEN) {
190                 pr_debug("offset is too large.\n");
191                 return -EINVAL;
192         }
193 
194         ecn = ip6_frag_ecn(ipv6_hdr(skb));
195 
196         if (skb->ip_summed == CHECKSUM_COMPLETE) {
197                 const unsigned char *nh = skb_network_header(skb);
198                 skb->csum = csum_sub(skb->csum,
199                                      csum_partial(nh, (u8 *)(fhdr + 1) - nh,
200                                                   0));
201         }
202 
203         /* Is this the final fragment? */
204         if (!(fhdr->frag_off & htons(IP6_MF))) {
205                 /* If we already have some bits beyond end
206                  * or have different end, the segment is corrupted.
207                  */
208                 if (end < fq->q.len ||
209                     ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len)) {
210                         pr_debug("already received last fragment\n");
211                         goto err;
212                 }
213                 fq->q.flags |= INET_FRAG_LAST_IN;
214                 fq->q.len = end;
215         } else {
216                 /* Check if the fragment is rounded to 8 bytes.
217                  * Required by the RFC.
218                  */
219                 if (end & 0x7) {
220                         /* RFC2460 says always send parameter problem in
221                          * this case. -DaveM
222                          */
223                         pr_debug("end of fragment not rounded to 8 bytes.\n");
224                         inet_frag_kill(&fq->q);
225                         return -EPROTO;
226                 }
227                 if (end > fq->q.len) {
228                         /* Some bits beyond end -> corruption. */
229                         if (fq->q.flags & INET_FRAG_LAST_IN) {
230                                 pr_debug("last packet already reached.\n");
231                                 goto err;
232                         }
233                         fq->q.len = end;
234                 }
235         }
236 
237         if (end == offset)
238                 goto err;
239 
240         /* Point into the IP datagram 'data' part. */
241         if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
242                 pr_debug("queue: message is too short.\n");
243                 goto err;
244         }
245         if (pskb_trim_rcsum(skb, end - offset)) {
246                 pr_debug("Can't trim\n");
247                 goto err;
248         }
249 
250         /* Note : skb->rbnode and skb->dev share the same location. */
251         dev = skb->dev;
252         /* Makes sure compiler wont do silly aliasing games */
253         barrier();
254 
255         prev = fq->q.fragments_tail;
256         err = inet_frag_queue_insert(&fq->q, skb, offset, end);
257         if (err) {
258                 if (err == IPFRAG_DUP) {
259                         /* No error for duplicates, pretend they got queued. */
260                         kfree_skb(skb);
261                         return -EINPROGRESS;
262                 }
263                 goto insert_error;
264         }
265 
266         if (dev)
267                 fq->iif = dev->ifindex;
268 
269         fq->q.stamp = skb->tstamp;
270         fq->q.meat += skb->len;
271         fq->ecn |= ecn;
272         if (payload_len > fq->q.max_size)
273                 fq->q.max_size = payload_len;
274         add_frag_mem_limit(fq->q.fqdir, skb->truesize);
275 
276         /* The first fragment.
277          * nhoffset is obtained from the first fragment, of course.
278          */
279         if (offset == 0) {
280                 fq->nhoffset = nhoff;
281                 fq->q.flags |= INET_FRAG_FIRST_IN;
282         }
283 
284         if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
285             fq->q.meat == fq->q.len) {
286                 unsigned long orefdst = skb->_skb_refdst;
287 
288                 skb->_skb_refdst = 0UL;
289                 err = nf_ct_frag6_reasm(fq, skb, prev, dev);
290                 skb->_skb_refdst = orefdst;
291 
292                 /* After queue has assumed skb ownership, only 0 or
293                  * -EINPROGRESS must be returned.
294                  */
295                 return err ? -EINPROGRESS : 0;
296         }
297 
298         skb_dst_drop(skb);
299         return -EINPROGRESS;
300 
301 insert_error:
302         inet_frag_kill(&fq->q);
303 err:
304         skb_dst_drop(skb);
305         return -EINVAL;
306 }
307 
308 /*
309  *      Check if this packet is complete.
310  *
311  *      It is called with locked fq, and caller must check that
312  *      queue is eligible for reassembly i.e. it is not COMPLETE,
313  *      the last and the first frames arrived and all the bits are here.
314  */
315 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
316                              struct sk_buff *prev_tail, struct net_device *dev)
317 {
318         void *reasm_data;
319         int payload_len;
320         u8 ecn;
321 
322         inet_frag_kill(&fq->q);
323 
324         ecn = ip_frag_ecn_table[fq->ecn];
325         if (unlikely(ecn == 0xff))
326                 goto err;
327 
328         reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
329         if (!reasm_data)
330                 goto err;
331 
332         payload_len = ((skb->data - skb_network_header(skb)) -
333                        sizeof(struct ipv6hdr) + fq->q.len -
334                        sizeof(struct frag_hdr));
335         if (payload_len > IPV6_MAXPLEN) {
336                 net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
337                                     payload_len);
338                 goto err;
339         }
340 
341         /* We have to remove fragment header from datagram and to relocate
342          * header in order to calculate ICV correctly. */
343         skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
344         memmove(skb->head + sizeof(struct frag_hdr), skb->head,
345                 (skb->data - skb->head) - sizeof(struct frag_hdr));
346         skb->mac_header += sizeof(struct frag_hdr);
347         skb->network_header += sizeof(struct frag_hdr);
348 
349         skb_reset_transport_header(skb);
350 
351         inet_frag_reasm_finish(&fq->q, skb, reasm_data, false);
352 
353         skb->ignore_df = 1;
354         skb->dev = dev;
355         ipv6_hdr(skb)->payload_len = htons(payload_len);
356         ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
357         IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
358         IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
359 
360         /* Yes, and fold redundant checksum back. 8) */
361         if (skb->ip_summed == CHECKSUM_COMPLETE)
362                 skb->csum = csum_partial(skb_network_header(skb),
363                                          skb_network_header_len(skb),
364                                          skb->csum);
365 
366         fq->q.rb_fragments = RB_ROOT;
367         fq->q.fragments_tail = NULL;
368         fq->q.last_run_head = NULL;
369 
370         return 0;
371 
372 err:
373         inet_frag_kill(&fq->q);
374         return -EINVAL;
375 }
376 
377 /*
378  * find the header just before Fragment Header.
379  *
380  * if success return 0 and set ...
381  * (*prevhdrp): the value of "Next Header Field" in the header
382  *              just before Fragment Header.
383  * (*prevhoff): the offset of "Next Header Field" in the header
384  *              just before Fragment Header.
385  * (*fhoff)   : the offset of Fragment Header.
386  *
387  * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
388  *
389  */
390 static int
391 find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
392 {
393         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
394         const int netoff = skb_network_offset(skb);
395         u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
396         int start = netoff + sizeof(struct ipv6hdr);
397         int len = skb->len - start;
398         u8 prevhdr = NEXTHDR_IPV6;
399 
400         while (nexthdr != NEXTHDR_FRAGMENT) {
401                 struct ipv6_opt_hdr hdr;
402                 int hdrlen;
403 
404                 if (!ipv6_ext_hdr(nexthdr)) {
405                         return -1;
406                 }
407                 if (nexthdr == NEXTHDR_NONE) {
408                         pr_debug("next header is none\n");
409                         return -1;
410                 }
411                 if (len < (int)sizeof(struct ipv6_opt_hdr)) {
412                         pr_debug("too short\n");
413                         return -1;
414                 }
415                 if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
416                         BUG();
417                 if (nexthdr == NEXTHDR_AUTH)
418                         hdrlen = ipv6_authlen(&hdr);
419                 else
420                         hdrlen = ipv6_optlen(&hdr);
421 
422                 prevhdr = nexthdr;
423                 prev_nhoff = start;
424 
425                 nexthdr = hdr.nexthdr;
426                 len -= hdrlen;
427                 start += hdrlen;
428         }
429 
430         if (len < 0)
431                 return -1;
432 
433         *prevhdrp = prevhdr;
434         *prevhoff = prev_nhoff;
435         *fhoff = start;
436 
437         return 0;
438 }
439 
440 int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
441 {
442         u16 savethdr = skb->transport_header;
443         u8 nexthdr = NEXTHDR_FRAGMENT;
444         int fhoff, nhoff, ret;
445         struct frag_hdr *fhdr;
446         struct frag_queue *fq;
447         struct ipv6hdr *hdr;
448         u8 prevhdr;
449 
450         /* Jumbo payload inhibits frag. header */
451         if (ipv6_hdr(skb)->payload_len == 0) {
452                 pr_debug("payload len = 0\n");
453                 return 0;
454         }
455 
456         if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
457                 return 0;
458 
459         /* Discard the first fragment if it does not include all headers
460          * RFC 8200, Section 4.5
461          */
462         if (ipv6frag_thdr_truncated(skb, fhoff, &nexthdr)) {
463                 pr_debug("Drop incomplete fragment\n");
464                 return 0;
465         }
466 
467         if (!pskb_may_pull(skb, fhoff + sizeof(*fhdr)))
468                 return -ENOMEM;
469 
470         skb_set_transport_header(skb, fhoff);
471         hdr = ipv6_hdr(skb);
472         fhdr = (struct frag_hdr *)skb_transport_header(skb);
473 
474         skb_orphan(skb);
475         fq = fq_find(net, fhdr->identification, user, hdr,
476                      skb->dev ? skb->dev->ifindex : 0);
477         if (fq == NULL) {
478                 pr_debug("Can't find and can't create new queue\n");
479                 return -ENOMEM;
480         }
481 
482         spin_lock_bh(&fq->q.lock);
483 
484         ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff);
485         if (ret == -EPROTO) {
486                 skb->transport_header = savethdr;
487                 ret = 0;
488         }
489 
490         spin_unlock_bh(&fq->q.lock);
491         inet_frag_put(&fq->q);
492         return ret;
493 }
494 EXPORT_SYMBOL_GPL(nf_ct_frag6_gather);
495 
496 static int nf_ct_net_init(struct net *net)
497 {
498         int res;
499 
500         res = fqdir_init(&net->nf_frag.fqdir, &nf_frags, net);
501         if (res < 0)
502                 return res;
503 
504         net->nf_frag.fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
505         net->nf_frag.fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
506         net->nf_frag.fqdir->timeout = IPV6_FRAG_TIMEOUT;
507 
508         res = nf_ct_frag6_sysctl_register(net);
509         if (res < 0)
510                 fqdir_exit(net->nf_frag.fqdir);
511         return res;
512 }
513 
514 static void nf_ct_net_pre_exit(struct net *net)
515 {
516         fqdir_pre_exit(net->nf_frag.fqdir);
517 }
518 
519 static void nf_ct_net_exit(struct net *net)
520 {
521         nf_ct_frags6_sysctl_unregister(net);
522         fqdir_exit(net->nf_frag.fqdir);
523 }
524 
525 static struct pernet_operations nf_ct_net_ops = {
526         .init           = nf_ct_net_init,
527         .pre_exit       = nf_ct_net_pre_exit,
528         .exit           = nf_ct_net_exit,
529 };
530 
531 static const struct rhashtable_params nfct_rhash_params = {
532         .head_offset            = offsetof(struct inet_frag_queue, node),
533         .hashfn                 = ip6frag_key_hashfn,
534         .obj_hashfn             = ip6frag_obj_hashfn,
535         .obj_cmpfn              = ip6frag_obj_cmpfn,
536         .automatic_shrinking    = true,
537 };
538 
539 int nf_ct_frag6_init(void)
540 {
541         int ret = 0;
542 
543         nf_frags.constructor = ip6frag_init;
544         nf_frags.destructor = NULL;
545         nf_frags.qsize = sizeof(struct frag_queue);
546         nf_frags.frag_expire = nf_ct_frag6_expire;
547         nf_frags.frags_cache_name = nf_frags_cache_name;
548         nf_frags.rhash_params = nfct_rhash_params;
549         ret = inet_frags_init(&nf_frags);
550         if (ret)
551                 goto out;
552         ret = register_pernet_subsys(&nf_ct_net_ops);
553         if (ret)
554                 inet_frags_fini(&nf_frags);
555 
556 out:
557         return ret;
558 }
559 
560 void nf_ct_frag6_cleanup(void)
561 {
562         unregister_pernet_subsys(&nf_ct_net_ops);
563         inet_frags_fini(&nf_frags);
564 }
565 

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