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Linux/net/ipv4/ip_fragment.c

  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  *              The IP fragmentation functionality.
  7  *
  8  * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
  9  *              Alan Cox <alan@lxorguk.ukuu.org.uk>
 10  *
 11  * Fixes:
 12  *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
 13  *              David S. Miller :       Begin massive cleanup...
 14  *              Andi Kleen      :       Add sysctls.
 15  *              xxxx            :       Overlapfrag bug.
 16  *              Ultima          :       ip_expire() kernel panic.
 17  *              Bill Hawes      :       Frag accounting and evictor fixes.
 18  *              John McDonald   :       0 length frag bug.
 19  *              Alexey Kuznetsov:       SMP races, threading, cleanup.
 20  *              Patrick McHardy :       LRU queue of frag heads for evictor.
 21  */
 22 
 23 #define pr_fmt(fmt) "IPv4: " fmt
 24 
 25 #include <linux/compiler.h>
 26 #include <linux/module.h>
 27 #include <linux/types.h>
 28 #include <linux/mm.h>
 29 #include <linux/jiffies.h>
 30 #include <linux/skbuff.h>
 31 #include <linux/list.h>
 32 #include <linux/ip.h>
 33 #include <linux/icmp.h>
 34 #include <linux/netdevice.h>
 35 #include <linux/jhash.h>
 36 #include <linux/random.h>
 37 #include <linux/slab.h>
 38 #include <net/route.h>
 39 #include <net/dst.h>
 40 #include <net/sock.h>
 41 #include <net/ip.h>
 42 #include <net/icmp.h>
 43 #include <net/checksum.h>
 44 #include <net/inetpeer.h>
 45 #include <net/inet_frag.h>
 46 #include <linux/tcp.h>
 47 #include <linux/udp.h>
 48 #include <linux/inet.h>
 49 #include <linux/netfilter_ipv4.h>
 50 #include <net/inet_ecn.h>
 51 #include <net/l3mdev.h>
 52 
 53 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
 54  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
 55  * as well. Or notify me, at least. --ANK
 56  */
 57 static const char ip_frag_cache_name[] = "ip4-frags";
 58 
 59 struct ipfrag_skb_cb
 60 {
 61         struct inet_skb_parm    h;
 62         int                     offset;
 63 };
 64 
 65 #define FRAG_CB(skb)    ((struct ipfrag_skb_cb *)((skb)->cb))
 66 
 67 /* Describe an entry in the "incomplete datagrams" queue. */
 68 struct ipq {
 69         struct inet_frag_queue q;
 70 
 71         u32             user;
 72         __be32          saddr;
 73         __be32          daddr;
 74         __be16          id;
 75         u8              protocol;
 76         u8              ecn; /* RFC3168 support */
 77         u16             max_df_size; /* largest frag with DF set seen */
 78         int             iif;
 79         int             vif;   /* L3 master device index */
 80         unsigned int    rid;
 81         struct inet_peer *peer;
 82 };
 83 
 84 static u8 ip4_frag_ecn(u8 tos)
 85 {
 86         return 1 << (tos & INET_ECN_MASK);
 87 }
 88 
 89 static struct inet_frags ip4_frags;
 90 
 91 int ip_frag_mem(struct net *net)
 92 {
 93         return sum_frag_mem_limit(&net->ipv4.frags);
 94 }
 95 
 96 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
 97                          struct net_device *dev);
 98 
 99 struct ip4_create_arg {
100         struct iphdr *iph;
101         u32 user;
102         int vif;
103 };
104 
105 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
106 {
107         net_get_random_once(&ip4_frags.rnd, sizeof(ip4_frags.rnd));
108         return jhash_3words((__force u32)id << 16 | prot,
109                             (__force u32)saddr, (__force u32)daddr,
110                             ip4_frags.rnd);
111 }
112 
113 static unsigned int ip4_hashfn(const struct inet_frag_queue *q)
114 {
115         const struct ipq *ipq;
116 
117         ipq = container_of(q, struct ipq, q);
118         return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
119 }
120 
121 static bool ip4_frag_match(const struct inet_frag_queue *q, const void *a)
122 {
123         const struct ipq *qp;
124         const struct ip4_create_arg *arg = a;
125 
126         qp = container_of(q, struct ipq, q);
127         return  qp->id == arg->iph->id &&
128                 qp->saddr == arg->iph->saddr &&
129                 qp->daddr == arg->iph->daddr &&
130                 qp->protocol == arg->iph->protocol &&
131                 qp->user == arg->user &&
132                 qp->vif == arg->vif;
133 }
134 
135 static void ip4_frag_init(struct inet_frag_queue *q, const void *a)
136 {
137         struct ipq *qp = container_of(q, struct ipq, q);
138         struct netns_ipv4 *ipv4 = container_of(q->net, struct netns_ipv4,
139                                                frags);
140         struct net *net = container_of(ipv4, struct net, ipv4);
141 
142         const struct ip4_create_arg *arg = a;
143 
144         qp->protocol = arg->iph->protocol;
145         qp->id = arg->iph->id;
146         qp->ecn = ip4_frag_ecn(arg->iph->tos);
147         qp->saddr = arg->iph->saddr;
148         qp->daddr = arg->iph->daddr;
149         qp->vif = arg->vif;
150         qp->user = arg->user;
151         qp->peer = q->net->max_dist ?
152                 inet_getpeer_v4(net->ipv4.peers, arg->iph->saddr, arg->vif, 1) :
153                 NULL;
154 }
155 
156 static void ip4_frag_free(struct inet_frag_queue *q)
157 {
158         struct ipq *qp;
159 
160         qp = container_of(q, struct ipq, q);
161         if (qp->peer)
162                 inet_putpeer(qp->peer);
163 }
164 
165 
166 /* Destruction primitives. */
167 
168 static void ipq_put(struct ipq *ipq)
169 {
170         inet_frag_put(&ipq->q, &ip4_frags);
171 }
172 
173 /* Kill ipq entry. It is not destroyed immediately,
174  * because caller (and someone more) holds reference count.
175  */
176 static void ipq_kill(struct ipq *ipq)
177 {
178         inet_frag_kill(&ipq->q, &ip4_frags);
179 }
180 
181 static bool frag_expire_skip_icmp(u32 user)
182 {
183         return user == IP_DEFRAG_AF_PACKET ||
184                ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_IN,
185                                          __IP_DEFRAG_CONNTRACK_IN_END) ||
186                ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_BRIDGE_IN,
187                                          __IP_DEFRAG_CONNTRACK_BRIDGE_IN);
188 }
189 
190 /*
191  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
192  */
193 static void ip_expire(unsigned long arg)
194 {
195         struct ipq *qp;
196         struct net *net;
197 
198         qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
199         net = container_of(qp->q.net, struct net, ipv4.frags);
200 
201         spin_lock(&qp->q.lock);
202 
203         if (qp->q.flags & INET_FRAG_COMPLETE)
204                 goto out;
205 
206         ipq_kill(qp);
207         __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
208 
209         if (!inet_frag_evicting(&qp->q)) {
210                 struct sk_buff *head = qp->q.fragments;
211                 const struct iphdr *iph;
212                 int err;
213 
214                 __IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);
215 
216                 if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !qp->q.fragments)
217                         goto out;
218 
219                 rcu_read_lock();
220                 head->dev = dev_get_by_index_rcu(net, qp->iif);
221                 if (!head->dev)
222                         goto out_rcu_unlock;
223 
224                 /* skb has no dst, perform route lookup again */
225                 iph = ip_hdr(head);
226                 err = ip_route_input_noref(head, iph->daddr, iph->saddr,
227                                            iph->tos, head->dev);
228                 if (err)
229                         goto out_rcu_unlock;
230 
231                 /* Only an end host needs to send an ICMP
232                  * "Fragment Reassembly Timeout" message, per RFC792.
233                  */
234                 if (frag_expire_skip_icmp(qp->user) &&
235                     (skb_rtable(head)->rt_type != RTN_LOCAL))
236                         goto out_rcu_unlock;
237 
238                 /* Send an ICMP "Fragment Reassembly Timeout" message. */
239                 icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
240 out_rcu_unlock:
241                 rcu_read_unlock();
242         }
243 out:
244         spin_unlock(&qp->q.lock);
245         ipq_put(qp);
246 }
247 
248 /* Find the correct entry in the "incomplete datagrams" queue for
249  * this IP datagram, and create new one, if nothing is found.
250  */
251 static struct ipq *ip_find(struct net *net, struct iphdr *iph,
252                            u32 user, int vif)
253 {
254         struct inet_frag_queue *q;
255         struct ip4_create_arg arg;
256         unsigned int hash;
257 
258         arg.iph = iph;
259         arg.user = user;
260         arg.vif = vif;
261 
262         hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
263 
264         q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
265         if (IS_ERR_OR_NULL(q)) {
266                 inet_frag_maybe_warn_overflow(q, pr_fmt());
267                 return NULL;
268         }
269         return container_of(q, struct ipq, q);
270 }
271 
272 /* Is the fragment too far ahead to be part of ipq? */
273 static int ip_frag_too_far(struct ipq *qp)
274 {
275         struct inet_peer *peer = qp->peer;
276         unsigned int max = qp->q.net->max_dist;
277         unsigned int start, end;
278 
279         int rc;
280 
281         if (!peer || !max)
282                 return 0;
283 
284         start = qp->rid;
285         end = atomic_inc_return(&peer->rid);
286         qp->rid = end;
287 
288         rc = qp->q.fragments && (end - start) > max;
289 
290         if (rc) {
291                 struct net *net;
292 
293                 net = container_of(qp->q.net, struct net, ipv4.frags);
294                 __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
295         }
296 
297         return rc;
298 }
299 
300 static int ip_frag_reinit(struct ipq *qp)
301 {
302         struct sk_buff *fp;
303         unsigned int sum_truesize = 0;
304 
305         if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
306                 atomic_inc(&qp->q.refcnt);
307                 return -ETIMEDOUT;
308         }
309 
310         fp = qp->q.fragments;
311         do {
312                 struct sk_buff *xp = fp->next;
313 
314                 sum_truesize += fp->truesize;
315                 kfree_skb(fp);
316                 fp = xp;
317         } while (fp);
318         sub_frag_mem_limit(qp->q.net, sum_truesize);
319 
320         qp->q.flags = 0;
321         qp->q.len = 0;
322         qp->q.meat = 0;
323         qp->q.fragments = NULL;
324         qp->q.fragments_tail = NULL;
325         qp->iif = 0;
326         qp->ecn = 0;
327 
328         return 0;
329 }
330 
331 /* Add new segment to existing queue. */
332 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
333 {
334         struct sk_buff *prev, *next;
335         struct net_device *dev;
336         unsigned int fragsize;
337         int flags, offset;
338         int ihl, end;
339         int err = -ENOENT;
340         u8 ecn;
341 
342         if (qp->q.flags & INET_FRAG_COMPLETE)
343                 goto err;
344 
345         if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
346             unlikely(ip_frag_too_far(qp)) &&
347             unlikely(err = ip_frag_reinit(qp))) {
348                 ipq_kill(qp);
349                 goto err;
350         }
351 
352         ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
353         offset = ntohs(ip_hdr(skb)->frag_off);
354         flags = offset & ~IP_OFFSET;
355         offset &= IP_OFFSET;
356         offset <<= 3;           /* offset is in 8-byte chunks */
357         ihl = ip_hdrlen(skb);
358 
359         /* Determine the position of this fragment. */
360         end = offset + skb->len - skb_network_offset(skb) - ihl;
361         err = -EINVAL;
362 
363         /* Is this the final fragment? */
364         if ((flags & IP_MF) == 0) {
365                 /* If we already have some bits beyond end
366                  * or have different end, the segment is corrupted.
367                  */
368                 if (end < qp->q.len ||
369                     ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
370                         goto err;
371                 qp->q.flags |= INET_FRAG_LAST_IN;
372                 qp->q.len = end;
373         } else {
374                 if (end&7) {
375                         end &= ~7;
376                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
377                                 skb->ip_summed = CHECKSUM_NONE;
378                 }
379                 if (end > qp->q.len) {
380                         /* Some bits beyond end -> corruption. */
381                         if (qp->q.flags & INET_FRAG_LAST_IN)
382                                 goto err;
383                         qp->q.len = end;
384                 }
385         }
386         if (end == offset)
387                 goto err;
388 
389         err = -ENOMEM;
390         if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
391                 goto err;
392 
393         err = pskb_trim_rcsum(skb, end - offset);
394         if (err)
395                 goto err;
396 
397         /* Find out which fragments are in front and at the back of us
398          * in the chain of fragments so far.  We must know where to put
399          * this fragment, right?
400          */
401         prev = qp->q.fragments_tail;
402         if (!prev || FRAG_CB(prev)->offset < offset) {
403                 next = NULL;
404                 goto found;
405         }
406         prev = NULL;
407         for (next = qp->q.fragments; next != NULL; next = next->next) {
408                 if (FRAG_CB(next)->offset >= offset)
409                         break;  /* bingo! */
410                 prev = next;
411         }
412 
413 found:
414         /* We found where to put this one.  Check for overlap with
415          * preceding fragment, and, if needed, align things so that
416          * any overlaps are eliminated.
417          */
418         if (prev) {
419                 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
420 
421                 if (i > 0) {
422                         offset += i;
423                         err = -EINVAL;
424                         if (end <= offset)
425                                 goto err;
426                         err = -ENOMEM;
427                         if (!pskb_pull(skb, i))
428                                 goto err;
429                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
430                                 skb->ip_summed = CHECKSUM_NONE;
431                 }
432         }
433 
434         err = -ENOMEM;
435 
436         while (next && FRAG_CB(next)->offset < end) {
437                 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
438 
439                 if (i < next->len) {
440                         /* Eat head of the next overlapped fragment
441                          * and leave the loop. The next ones cannot overlap.
442                          */
443                         if (!pskb_pull(next, i))
444                                 goto err;
445                         FRAG_CB(next)->offset += i;
446                         qp->q.meat -= i;
447                         if (next->ip_summed != CHECKSUM_UNNECESSARY)
448                                 next->ip_summed = CHECKSUM_NONE;
449                         break;
450                 } else {
451                         struct sk_buff *free_it = next;
452 
453                         /* Old fragment is completely overridden with
454                          * new one drop it.
455                          */
456                         next = next->next;
457 
458                         if (prev)
459                                 prev->next = next;
460                         else
461                                 qp->q.fragments = next;
462 
463                         qp->q.meat -= free_it->len;
464                         sub_frag_mem_limit(qp->q.net, free_it->truesize);
465                         kfree_skb(free_it);
466                 }
467         }
468 
469         FRAG_CB(skb)->offset = offset;
470 
471         /* Insert this fragment in the chain of fragments. */
472         skb->next = next;
473         if (!next)
474                 qp->q.fragments_tail = skb;
475         if (prev)
476                 prev->next = skb;
477         else
478                 qp->q.fragments = skb;
479 
480         dev = skb->dev;
481         if (dev) {
482                 qp->iif = dev->ifindex;
483                 skb->dev = NULL;
484         }
485         qp->q.stamp = skb->tstamp;
486         qp->q.meat += skb->len;
487         qp->ecn |= ecn;
488         add_frag_mem_limit(qp->q.net, skb->truesize);
489         if (offset == 0)
490                 qp->q.flags |= INET_FRAG_FIRST_IN;
491 
492         fragsize = skb->len + ihl;
493 
494         if (fragsize > qp->q.max_size)
495                 qp->q.max_size = fragsize;
496 
497         if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
498             fragsize > qp->max_df_size)
499                 qp->max_df_size = fragsize;
500 
501         if (qp->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
502             qp->q.meat == qp->q.len) {
503                 unsigned long orefdst = skb->_skb_refdst;
504 
505                 skb->_skb_refdst = 0UL;
506                 err = ip_frag_reasm(qp, prev, dev);
507                 skb->_skb_refdst = orefdst;
508                 return err;
509         }
510 
511         skb_dst_drop(skb);
512         return -EINPROGRESS;
513 
514 err:
515         kfree_skb(skb);
516         return err;
517 }
518 
519 
520 /* Build a new IP datagram from all its fragments. */
521 
522 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
523                          struct net_device *dev)
524 {
525         struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
526         struct iphdr *iph;
527         struct sk_buff *fp, *head = qp->q.fragments;
528         int len;
529         int ihlen;
530         int err;
531         u8 ecn;
532 
533         ipq_kill(qp);
534 
535         ecn = ip_frag_ecn_table[qp->ecn];
536         if (unlikely(ecn == 0xff)) {
537                 err = -EINVAL;
538                 goto out_fail;
539         }
540         /* Make the one we just received the head. */
541         if (prev) {
542                 head = prev->next;
543                 fp = skb_clone(head, GFP_ATOMIC);
544                 if (!fp)
545                         goto out_nomem;
546 
547                 fp->next = head->next;
548                 if (!fp->next)
549                         qp->q.fragments_tail = fp;
550                 prev->next = fp;
551 
552                 skb_morph(head, qp->q.fragments);
553                 head->next = qp->q.fragments->next;
554 
555                 consume_skb(qp->q.fragments);
556                 qp->q.fragments = head;
557         }
558 
559         WARN_ON(!head);
560         WARN_ON(FRAG_CB(head)->offset != 0);
561 
562         /* Allocate a new buffer for the datagram. */
563         ihlen = ip_hdrlen(head);
564         len = ihlen + qp->q.len;
565 
566         err = -E2BIG;
567         if (len > 65535)
568                 goto out_oversize;
569 
570         /* Head of list must not be cloned. */
571         if (skb_unclone(head, GFP_ATOMIC))
572                 goto out_nomem;
573 
574         /* If the first fragment is fragmented itself, we split
575          * it to two chunks: the first with data and paged part
576          * and the second, holding only fragments. */
577         if (skb_has_frag_list(head)) {
578                 struct sk_buff *clone;
579                 int i, plen = 0;
580 
581                 clone = alloc_skb(0, GFP_ATOMIC);
582                 if (!clone)
583                         goto out_nomem;
584                 clone->next = head->next;
585                 head->next = clone;
586                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
587                 skb_frag_list_init(head);
588                 for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
589                         plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
590                 clone->len = clone->data_len = head->data_len - plen;
591                 head->data_len -= clone->len;
592                 head->len -= clone->len;
593                 clone->csum = 0;
594                 clone->ip_summed = head->ip_summed;
595                 add_frag_mem_limit(qp->q.net, clone->truesize);
596         }
597 
598         skb_shinfo(head)->frag_list = head->next;
599         skb_push(head, head->data - skb_network_header(head));
600 
601         for (fp=head->next; fp; fp = fp->next) {
602                 head->data_len += fp->len;
603                 head->len += fp->len;
604                 if (head->ip_summed != fp->ip_summed)
605                         head->ip_summed = CHECKSUM_NONE;
606                 else if (head->ip_summed == CHECKSUM_COMPLETE)
607                         head->csum = csum_add(head->csum, fp->csum);
608                 head->truesize += fp->truesize;
609         }
610         sub_frag_mem_limit(qp->q.net, head->truesize);
611 
612         head->next = NULL;
613         head->dev = dev;
614         head->tstamp = qp->q.stamp;
615         IPCB(head)->frag_max_size = max(qp->max_df_size, qp->q.max_size);
616 
617         iph = ip_hdr(head);
618         iph->tot_len = htons(len);
619         iph->tos |= ecn;
620 
621         /* When we set IP_DF on a refragmented skb we must also force a
622          * call to ip_fragment to avoid forwarding a DF-skb of size s while
623          * original sender only sent fragments of size f (where f < s).
624          *
625          * We only set DF/IPSKB_FRAG_PMTU if such DF fragment was the largest
626          * frag seen to avoid sending tiny DF-fragments in case skb was built
627          * from one very small df-fragment and one large non-df frag.
628          */
629         if (qp->max_df_size == qp->q.max_size) {
630                 IPCB(head)->flags |= IPSKB_FRAG_PMTU;
631                 iph->frag_off = htons(IP_DF);
632         } else {
633                 iph->frag_off = 0;
634         }
635 
636         ip_send_check(iph);
637 
638         __IP_INC_STATS(net, IPSTATS_MIB_REASMOKS);
639         qp->q.fragments = NULL;
640         qp->q.fragments_tail = NULL;
641         return 0;
642 
643 out_nomem:
644         net_dbg_ratelimited("queue_glue: no memory for gluing queue %p\n", qp);
645         err = -ENOMEM;
646         goto out_fail;
647 out_oversize:
648         net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->saddr);
649 out_fail:
650         __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
651         return err;
652 }
653 
654 /* Process an incoming IP datagram fragment. */
655 int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
656 {
657         struct net_device *dev = skb->dev ? : skb_dst(skb)->dev;
658         int vif = l3mdev_master_ifindex_rcu(dev);
659         struct ipq *qp;
660 
661         __IP_INC_STATS(net, IPSTATS_MIB_REASMREQDS);
662         skb_orphan(skb);
663 
664         /* Lookup (or create) queue header */
665         qp = ip_find(net, ip_hdr(skb), user, vif);
666         if (qp) {
667                 int ret;
668 
669                 spin_lock(&qp->q.lock);
670 
671                 ret = ip_frag_queue(qp, skb);
672 
673                 spin_unlock(&qp->q.lock);
674                 ipq_put(qp);
675                 return ret;
676         }
677 
678         __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
679         kfree_skb(skb);
680         return -ENOMEM;
681 }
682 EXPORT_SYMBOL(ip_defrag);
683 
684 struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
685 {
686         struct iphdr iph;
687         int netoff;
688         u32 len;
689 
690         if (skb->protocol != htons(ETH_P_IP))
691                 return skb;
692 
693         netoff = skb_network_offset(skb);
694 
695         if (skb_copy_bits(skb, netoff, &iph, sizeof(iph)) < 0)
696                 return skb;
697 
698         if (iph.ihl < 5 || iph.version != 4)
699                 return skb;
700 
701         len = ntohs(iph.tot_len);
702         if (skb->len < netoff + len || len < (iph.ihl * 4))
703                 return skb;
704 
705         if (ip_is_fragment(&iph)) {
706                 skb = skb_share_check(skb, GFP_ATOMIC);
707                 if (skb) {
708                         if (!pskb_may_pull(skb, netoff + iph.ihl * 4))
709                                 return skb;
710                         if (pskb_trim_rcsum(skb, netoff + len))
711                                 return skb;
712                         memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
713                         if (ip_defrag(net, skb, user))
714                                 return NULL;
715                         skb_clear_hash(skb);
716                 }
717         }
718         return skb;
719 }
720 EXPORT_SYMBOL(ip_check_defrag);
721 
722 #ifdef CONFIG_SYSCTL
723 static int zero;
724 
725 static struct ctl_table ip4_frags_ns_ctl_table[] = {
726         {
727                 .procname       = "ipfrag_high_thresh",
728                 .data           = &init_net.ipv4.frags.high_thresh,
729                 .maxlen         = sizeof(int),
730                 .mode           = 0644,
731                 .proc_handler   = proc_dointvec_minmax,
732                 .extra1         = &init_net.ipv4.frags.low_thresh
733         },
734         {
735                 .procname       = "ipfrag_low_thresh",
736                 .data           = &init_net.ipv4.frags.low_thresh,
737                 .maxlen         = sizeof(int),
738                 .mode           = 0644,
739                 .proc_handler   = proc_dointvec_minmax,
740                 .extra1         = &zero,
741                 .extra2         = &init_net.ipv4.frags.high_thresh
742         },
743         {
744                 .procname       = "ipfrag_time",
745                 .data           = &init_net.ipv4.frags.timeout,
746                 .maxlen         = sizeof(int),
747                 .mode           = 0644,
748                 .proc_handler   = proc_dointvec_jiffies,
749         },
750         {
751                 .procname       = "ipfrag_max_dist",
752                 .data           = &init_net.ipv4.frags.max_dist,
753                 .maxlen         = sizeof(int),
754                 .mode           = 0644,
755                 .proc_handler   = proc_dointvec_minmax,
756                 .extra1         = &zero
757         },
758         { }
759 };
760 
761 /* secret interval has been deprecated */
762 static int ip4_frags_secret_interval_unused;
763 static struct ctl_table ip4_frags_ctl_table[] = {
764         {
765                 .procname       = "ipfrag_secret_interval",
766                 .data           = &ip4_frags_secret_interval_unused,
767                 .maxlen         = sizeof(int),
768                 .mode           = 0644,
769                 .proc_handler   = proc_dointvec_jiffies,
770         },
771         { }
772 };
773 
774 static int __net_init ip4_frags_ns_ctl_register(struct net *net)
775 {
776         struct ctl_table *table;
777         struct ctl_table_header *hdr;
778 
779         table = ip4_frags_ns_ctl_table;
780         if (!net_eq(net, &init_net)) {
781                 table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
782                 if (!table)
783                         goto err_alloc;
784 
785                 table[0].data = &net->ipv4.frags.high_thresh;
786                 table[0].extra1 = &net->ipv4.frags.low_thresh;
787                 table[0].extra2 = &init_net.ipv4.frags.high_thresh;
788                 table[1].data = &net->ipv4.frags.low_thresh;
789                 table[1].extra2 = &net->ipv4.frags.high_thresh;
790                 table[2].data = &net->ipv4.frags.timeout;
791                 table[3].data = &net->ipv4.frags.max_dist;
792         }
793 
794         hdr = register_net_sysctl(net, "net/ipv4", table);
795         if (!hdr)
796                 goto err_reg;
797 
798         net->ipv4.frags_hdr = hdr;
799         return 0;
800 
801 err_reg:
802         if (!net_eq(net, &init_net))
803                 kfree(table);
804 err_alloc:
805         return -ENOMEM;
806 }
807 
808 static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
809 {
810         struct ctl_table *table;
811 
812         table = net->ipv4.frags_hdr->ctl_table_arg;
813         unregister_net_sysctl_table(net->ipv4.frags_hdr);
814         kfree(table);
815 }
816 
817 static void __init ip4_frags_ctl_register(void)
818 {
819         register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
820 }
821 #else
822 static int ip4_frags_ns_ctl_register(struct net *net)
823 {
824         return 0;
825 }
826 
827 static void ip4_frags_ns_ctl_unregister(struct net *net)
828 {
829 }
830 
831 static void __init ip4_frags_ctl_register(void)
832 {
833 }
834 #endif
835 
836 static int __net_init ipv4_frags_init_net(struct net *net)
837 {
838         int res;
839 
840         /* Fragment cache limits.
841          *
842          * The fragment memory accounting code, (tries to) account for
843          * the real memory usage, by measuring both the size of frag
844          * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
845          * and the SKB's truesize.
846          *
847          * A 64K fragment consumes 129736 bytes (44*2944)+200
848          * (1500 truesize == 2944, sizeof(struct ipq) == 200)
849          *
850          * We will commit 4MB at one time. Should we cross that limit
851          * we will prune down to 3MB, making room for approx 8 big 64K
852          * fragments 8x128k.
853          */
854         net->ipv4.frags.high_thresh = 4 * 1024 * 1024;
855         net->ipv4.frags.low_thresh  = 3 * 1024 * 1024;
856         /*
857          * Important NOTE! Fragment queue must be destroyed before MSL expires.
858          * RFC791 is wrong proposing to prolongate timer each fragment arrival
859          * by TTL.
860          */
861         net->ipv4.frags.timeout = IP_FRAG_TIME;
862 
863         net->ipv4.frags.max_dist = 64;
864 
865         res = inet_frags_init_net(&net->ipv4.frags);
866         if (res)
867                 return res;
868         res = ip4_frags_ns_ctl_register(net);
869         if (res)
870                 inet_frags_uninit_net(&net->ipv4.frags);
871         return res;
872 }
873 
874 static void __net_exit ipv4_frags_exit_net(struct net *net)
875 {
876         ip4_frags_ns_ctl_unregister(net);
877         inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
878 }
879 
880 static struct pernet_operations ip4_frags_ops = {
881         .init = ipv4_frags_init_net,
882         .exit = ipv4_frags_exit_net,
883 };
884 
885 void __init ipfrag_init(void)
886 {
887         ip4_frags_ctl_register();
888         register_pernet_subsys(&ip4_frags_ops);
889         ip4_frags.hashfn = ip4_hashfn;
890         ip4_frags.constructor = ip4_frag_init;
891         ip4_frags.destructor = ip4_frag_free;
892         ip4_frags.qsize = sizeof(struct ipq);
893         ip4_frags.match = ip4_frag_match;
894         ip4_frags.frag_expire = ip_expire;
895         ip4_frags.frags_cache_name = ip_frag_cache_name;
896         if (inet_frags_init(&ip4_frags))
897                 panic("IP: failed to allocate ip4_frags cache\n");
898 }
899 

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