xref: /openbmc/linux/net/ipv4/ip_fragment.c (revision 275876e2) 
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 
52 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
53  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
54  * as well. Or notify me, at least. --ANK
55  */
56 
57 static int sysctl_ipfrag_max_dist __read_mostly = 64;
58 static const char ip_frag_cache_name[] = "ip4-frags";
59 
60 struct ipfrag_skb_cb
61 {
62 	struct inet_skb_parm	h;
63 	int			offset;
64 };
65 
66 #define FRAG_CB(skb)	((struct ipfrag_skb_cb *)((skb)->cb))
67 
68 /* Describe an entry in the "incomplete datagrams" queue. */
69 struct ipq {
70 	struct inet_frag_queue q;
71 
72 	u32		user;
73 	__be32		saddr;
74 	__be32		daddr;
75 	__be16		id;
76 	u8		protocol;
77 	u8		ecn; /* RFC3168 support */
78 	int             iif;
79 	unsigned int    rid;
80 	struct inet_peer *peer;
81 };
82 
83 static inline u8 ip4_frag_ecn(u8 tos)
84 {
85 	return 1 << (tos & INET_ECN_MASK);
86 }
87 
88 static struct inet_frags ip4_frags;
89 
90 int ip_frag_mem(struct net *net)
91 {
92 	return sum_frag_mem_limit(&net->ipv4.frags);
93 }
94 
95 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
96 			 struct net_device *dev);
97 
98 struct ip4_create_arg {
99 	struct iphdr *iph;
100 	u32 user;
101 };
102 
103 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
104 {
105 	net_get_random_once(&ip4_frags.rnd, sizeof(ip4_frags.rnd));
106 	return jhash_3words((__force u32)id << 16 | prot,
107 			    (__force u32)saddr, (__force u32)daddr,
108 			    ip4_frags.rnd);
109 }
110 
111 static unsigned int ip4_hashfn(const struct inet_frag_queue *q)
112 {
113 	const struct ipq *ipq;
114 
115 	ipq = container_of(q, struct ipq, q);
116 	return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
117 }
118 
119 static bool ip4_frag_match(const struct inet_frag_queue *q, const void *a)
120 {
121 	const struct ipq *qp;
122 	const struct ip4_create_arg *arg = a;
123 
124 	qp = container_of(q, struct ipq, q);
125 	return	qp->id == arg->iph->id &&
126 		qp->saddr == arg->iph->saddr &&
127 		qp->daddr == arg->iph->daddr &&
128 		qp->protocol == arg->iph->protocol &&
129 		qp->user == arg->user;
130 }
131 
132 static void ip4_frag_init(struct inet_frag_queue *q, const void *a)
133 {
134 	struct ipq *qp = container_of(q, struct ipq, q);
135 	struct netns_ipv4 *ipv4 = container_of(q->net, struct netns_ipv4,
136 					       frags);
137 	struct net *net = container_of(ipv4, struct net, ipv4);
138 
139 	const struct ip4_create_arg *arg = a;
140 
141 	qp->protocol = arg->iph->protocol;
142 	qp->id = arg->iph->id;
143 	qp->ecn = ip4_frag_ecn(arg->iph->tos);
144 	qp->saddr = arg->iph->saddr;
145 	qp->daddr = arg->iph->daddr;
146 	qp->user = arg->user;
147 	qp->peer = sysctl_ipfrag_max_dist ?
148 		inet_getpeer_v4(net->ipv4.peers, arg->iph->saddr, 1) : NULL;
149 }
150 
151 static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
152 {
153 	struct ipq *qp;
154 
155 	qp = container_of(q, struct ipq, q);
156 	if (qp->peer)
157 		inet_putpeer(qp->peer);
158 }
159 
160 
161 /* Destruction primitives. */
162 
163 static __inline__ void ipq_put(struct ipq *ipq)
164 {
165 	inet_frag_put(&ipq->q, &ip4_frags);
166 }
167 
168 /* Kill ipq entry. It is not destroyed immediately,
169  * because caller (and someone more) holds reference count.
170  */
171 static void ipq_kill(struct ipq *ipq)
172 {
173 	inet_frag_kill(&ipq->q, &ip4_frags);
174 }
175 
176 /*
177  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
178  */
179 static void ip_expire(unsigned long arg)
180 {
181 	struct ipq *qp;
182 	struct net *net;
183 
184 	qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
185 	net = container_of(qp->q.net, struct net, ipv4.frags);
186 
187 	spin_lock(&qp->q.lock);
188 
189 	if (qp->q.flags & INET_FRAG_COMPLETE)
190 		goto out;
191 
192 	ipq_kill(qp);
193 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
194 
195 	if (!(qp->q.flags & INET_FRAG_EVICTED)) {
196 		struct sk_buff *head = qp->q.fragments;
197 		const struct iphdr *iph;
198 		int err;
199 
200 		IP_INC_STATS_BH(net, IPSTATS_MIB_REASMTIMEOUT);
201 
202 		if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !qp->q.fragments)
203 			goto out;
204 
205 		rcu_read_lock();
206 		head->dev = dev_get_by_index_rcu(net, qp->iif);
207 		if (!head->dev)
208 			goto out_rcu_unlock;
209 
210 		/* skb has no dst, perform route lookup again */
211 		iph = ip_hdr(head);
212 		err = ip_route_input_noref(head, iph->daddr, iph->saddr,
213 					   iph->tos, head->dev);
214 		if (err)
215 			goto out_rcu_unlock;
216 
217 		/* Only an end host needs to send an ICMP
218 		 * "Fragment Reassembly Timeout" message, per RFC792.
219 		 */
220 		if (qp->user == IP_DEFRAG_AF_PACKET ||
221 		    ((qp->user >= IP_DEFRAG_CONNTRACK_IN) &&
222 		     (qp->user <= __IP_DEFRAG_CONNTRACK_IN_END) &&
223 		     (skb_rtable(head)->rt_type != RTN_LOCAL)))
224 			goto out_rcu_unlock;
225 
226 		/* Send an ICMP "Fragment Reassembly Timeout" message. */
227 		icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
228 out_rcu_unlock:
229 		rcu_read_unlock();
230 	}
231 out:
232 	spin_unlock(&qp->q.lock);
233 	ipq_put(qp);
234 }
235 
236 /* Find the correct entry in the "incomplete datagrams" queue for
237  * this IP datagram, and create new one, if nothing is found.
238  */
239 static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
240 {
241 	struct inet_frag_queue *q;
242 	struct ip4_create_arg arg;
243 	unsigned int hash;
244 
245 	arg.iph = iph;
246 	arg.user = user;
247 
248 	hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
249 
250 	q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
251 	if (IS_ERR_OR_NULL(q)) {
252 		inet_frag_maybe_warn_overflow(q, pr_fmt());
253 		return NULL;
254 	}
255 	return container_of(q, struct ipq, q);
256 }
257 
258 /* Is the fragment too far ahead to be part of ipq? */
259 static inline int ip_frag_too_far(struct ipq *qp)
260 {
261 	struct inet_peer *peer = qp->peer;
262 	unsigned int max = sysctl_ipfrag_max_dist;
263 	unsigned int start, end;
264 
265 	int rc;
266 
267 	if (!peer || !max)
268 		return 0;
269 
270 	start = qp->rid;
271 	end = atomic_inc_return(&peer->rid);
272 	qp->rid = end;
273 
274 	rc = qp->q.fragments && (end - start) > max;
275 
276 	if (rc) {
277 		struct net *net;
278 
279 		net = container_of(qp->q.net, struct net, ipv4.frags);
280 		IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
281 	}
282 
283 	return rc;
284 }
285 
286 static int ip_frag_reinit(struct ipq *qp)
287 {
288 	struct sk_buff *fp;
289 	unsigned int sum_truesize = 0;
290 
291 	if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
292 		atomic_inc(&qp->q.refcnt);
293 		return -ETIMEDOUT;
294 	}
295 
296 	fp = qp->q.fragments;
297 	do {
298 		struct sk_buff *xp = fp->next;
299 
300 		sum_truesize += fp->truesize;
301 		kfree_skb(fp);
302 		fp = xp;
303 	} while (fp);
304 	sub_frag_mem_limit(&qp->q, sum_truesize);
305 
306 	qp->q.flags = 0;
307 	qp->q.len = 0;
308 	qp->q.meat = 0;
309 	qp->q.fragments = NULL;
310 	qp->q.fragments_tail = NULL;
311 	qp->iif = 0;
312 	qp->ecn = 0;
313 
314 	return 0;
315 }
316 
317 /* Add new segment to existing queue. */
318 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
319 {
320 	struct sk_buff *prev, *next;
321 	struct net_device *dev;
322 	int flags, offset;
323 	int ihl, end;
324 	int err = -ENOENT;
325 	u8 ecn;
326 
327 	if (qp->q.flags & INET_FRAG_COMPLETE)
328 		goto err;
329 
330 	if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
331 	    unlikely(ip_frag_too_far(qp)) &&
332 	    unlikely(err = ip_frag_reinit(qp))) {
333 		ipq_kill(qp);
334 		goto err;
335 	}
336 
337 	ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
338 	offset = ntohs(ip_hdr(skb)->frag_off);
339 	flags = offset & ~IP_OFFSET;
340 	offset &= IP_OFFSET;
341 	offset <<= 3;		/* offset is in 8-byte chunks */
342 	ihl = ip_hdrlen(skb);
343 
344 	/* Determine the position of this fragment. */
345 	end = offset + skb->len - ihl;
346 	err = -EINVAL;
347 
348 	/* Is this the final fragment? */
349 	if ((flags & IP_MF) == 0) {
350 		/* If we already have some bits beyond end
351 		 * or have different end, the segment is corrupted.
352 		 */
353 		if (end < qp->q.len ||
354 		    ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
355 			goto err;
356 		qp->q.flags |= INET_FRAG_LAST_IN;
357 		qp->q.len = end;
358 	} else {
359 		if (end&7) {
360 			end &= ~7;
361 			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
362 				skb->ip_summed = CHECKSUM_NONE;
363 		}
364 		if (end > qp->q.len) {
365 			/* Some bits beyond end -> corruption. */
366 			if (qp->q.flags & INET_FRAG_LAST_IN)
367 				goto err;
368 			qp->q.len = end;
369 		}
370 	}
371 	if (end == offset)
372 		goto err;
373 
374 	err = -ENOMEM;
375 	if (pskb_pull(skb, ihl) == NULL)
376 		goto err;
377 
378 	err = pskb_trim_rcsum(skb, end - offset);
379 	if (err)
380 		goto err;
381 
382 	/* Find out which fragments are in front and at the back of us
383 	 * in the chain of fragments so far.  We must know where to put
384 	 * this fragment, right?
385 	 */
386 	prev = qp->q.fragments_tail;
387 	if (!prev || FRAG_CB(prev)->offset < offset) {
388 		next = NULL;
389 		goto found;
390 	}
391 	prev = NULL;
392 	for (next = qp->q.fragments; next != NULL; next = next->next) {
393 		if (FRAG_CB(next)->offset >= offset)
394 			break;	/* bingo! */
395 		prev = next;
396 	}
397 
398 found:
399 	/* We found where to put this one.  Check for overlap with
400 	 * preceding fragment, and, if needed, align things so that
401 	 * any overlaps are eliminated.
402 	 */
403 	if (prev) {
404 		int i = (FRAG_CB(prev)->offset + prev->len) - offset;
405 
406 		if (i > 0) {
407 			offset += i;
408 			err = -EINVAL;
409 			if (end <= offset)
410 				goto err;
411 			err = -ENOMEM;
412 			if (!pskb_pull(skb, i))
413 				goto err;
414 			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
415 				skb->ip_summed = CHECKSUM_NONE;
416 		}
417 	}
418 
419 	err = -ENOMEM;
420 
421 	while (next && FRAG_CB(next)->offset < end) {
422 		int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
423 
424 		if (i < next->len) {
425 			/* Eat head of the next overlapped fragment
426 			 * and leave the loop. The next ones cannot overlap.
427 			 */
428 			if (!pskb_pull(next, i))
429 				goto err;
430 			FRAG_CB(next)->offset += i;
431 			qp->q.meat -= i;
432 			if (next->ip_summed != CHECKSUM_UNNECESSARY)
433 				next->ip_summed = CHECKSUM_NONE;
434 			break;
435 		} else {
436 			struct sk_buff *free_it = next;
437 
438 			/* Old fragment is completely overridden with
439 			 * new one drop it.
440 			 */
441 			next = next->next;
442 
443 			if (prev)
444 				prev->next = next;
445 			else
446 				qp->q.fragments = next;
447 
448 			qp->q.meat -= free_it->len;
449 			sub_frag_mem_limit(&qp->q, free_it->truesize);
450 			kfree_skb(free_it);
451 		}
452 	}
453 
454 	FRAG_CB(skb)->offset = offset;
455 
456 	/* Insert this fragment in the chain of fragments. */
457 	skb->next = next;
458 	if (!next)
459 		qp->q.fragments_tail = skb;
460 	if (prev)
461 		prev->next = skb;
462 	else
463 		qp->q.fragments = skb;
464 
465 	dev = skb->dev;
466 	if (dev) {
467 		qp->iif = dev->ifindex;
468 		skb->dev = NULL;
469 	}
470 	qp->q.stamp = skb->tstamp;
471 	qp->q.meat += skb->len;
472 	qp->ecn |= ecn;
473 	add_frag_mem_limit(&qp->q, skb->truesize);
474 	if (offset == 0)
475 		qp->q.flags |= INET_FRAG_FIRST_IN;
476 
477 	if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
478 	    skb->len + ihl > qp->q.max_size)
479 		qp->q.max_size = skb->len + ihl;
480 
481 	if (qp->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
482 	    qp->q.meat == qp->q.len) {
483 		unsigned long orefdst = skb->_skb_refdst;
484 
485 		skb->_skb_refdst = 0UL;
486 		err = ip_frag_reasm(qp, prev, dev);
487 		skb->_skb_refdst = orefdst;
488 		return err;
489 	}
490 
491 	skb_dst_drop(skb);
492 	return -EINPROGRESS;
493 
494 err:
495 	kfree_skb(skb);
496 	return err;
497 }
498 
499 
500 /* Build a new IP datagram from all its fragments. */
501 
502 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
503 			 struct net_device *dev)
504 {
505 	struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
506 	struct iphdr *iph;
507 	struct sk_buff *fp, *head = qp->q.fragments;
508 	int len;
509 	int ihlen;
510 	int err;
511 	int sum_truesize;
512 	u8 ecn;
513 
514 	ipq_kill(qp);
515 
516 	ecn = ip_frag_ecn_table[qp->ecn];
517 	if (unlikely(ecn == 0xff)) {
518 		err = -EINVAL;
519 		goto out_fail;
520 	}
521 	/* Make the one we just received the head. */
522 	if (prev) {
523 		head = prev->next;
524 		fp = skb_clone(head, GFP_ATOMIC);
525 		if (!fp)
526 			goto out_nomem;
527 
528 		fp->next = head->next;
529 		if (!fp->next)
530 			qp->q.fragments_tail = fp;
531 		prev->next = fp;
532 
533 		skb_morph(head, qp->q.fragments);
534 		head->next = qp->q.fragments->next;
535 
536 		consume_skb(qp->q.fragments);
537 		qp->q.fragments = head;
538 	}
539 
540 	WARN_ON(head == NULL);
541 	WARN_ON(FRAG_CB(head)->offset != 0);
542 
543 	/* Allocate a new buffer for the datagram. */
544 	ihlen = ip_hdrlen(head);
545 	len = ihlen + qp->q.len;
546 
547 	err = -E2BIG;
548 	if (len > 65535)
549 		goto out_oversize;
550 
551 	/* Head of list must not be cloned. */
552 	if (skb_unclone(head, GFP_ATOMIC))
553 		goto out_nomem;
554 
555 	/* If the first fragment is fragmented itself, we split
556 	 * it to two chunks: the first with data and paged part
557 	 * and the second, holding only fragments. */
558 	if (skb_has_frag_list(head)) {
559 		struct sk_buff *clone;
560 		int i, plen = 0;
561 
562 		if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
563 			goto out_nomem;
564 		clone->next = head->next;
565 		head->next = clone;
566 		skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
567 		skb_frag_list_init(head);
568 		for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
569 			plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
570 		clone->len = clone->data_len = head->data_len - plen;
571 		head->data_len -= clone->len;
572 		head->len -= clone->len;
573 		clone->csum = 0;
574 		clone->ip_summed = head->ip_summed;
575 		add_frag_mem_limit(&qp->q, clone->truesize);
576 	}
577 
578 	skb_push(head, head->data - skb_network_header(head));
579 
580 	sum_truesize = head->truesize;
581 	for (fp = head->next; fp;) {
582 		bool headstolen;
583 		int delta;
584 		struct sk_buff *next = fp->next;
585 
586 		sum_truesize += fp->truesize;
587 		if (head->ip_summed != fp->ip_summed)
588 			head->ip_summed = CHECKSUM_NONE;
589 		else if (head->ip_summed == CHECKSUM_COMPLETE)
590 			head->csum = csum_add(head->csum, fp->csum);
591 
592 		if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
593 			kfree_skb_partial(fp, headstolen);
594 		} else {
595 			if (!skb_shinfo(head)->frag_list)
596 				skb_shinfo(head)->frag_list = fp;
597 			head->data_len += fp->len;
598 			head->len += fp->len;
599 			head->truesize += fp->truesize;
600 		}
601 		fp = next;
602 	}
603 	sub_frag_mem_limit(&qp->q, sum_truesize);
604 
605 	head->next = NULL;
606 	head->dev = dev;
607 	head->tstamp = qp->q.stamp;
608 	IPCB(head)->frag_max_size = qp->q.max_size;
609 
610 	iph = ip_hdr(head);
611 	/* max_size != 0 implies at least one fragment had IP_DF set */
612 	iph->frag_off = qp->q.max_size ? htons(IP_DF) : 0;
613 	iph->tot_len = htons(len);
614 	iph->tos |= ecn;
615 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
616 	qp->q.fragments = NULL;
617 	qp->q.fragments_tail = NULL;
618 	return 0;
619 
620 out_nomem:
621 	LIMIT_NETDEBUG(KERN_ERR pr_fmt("queue_glue: no memory for gluing queue %p\n"),
622 		       qp);
623 	err = -ENOMEM;
624 	goto out_fail;
625 out_oversize:
626 	net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->saddr);
627 out_fail:
628 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
629 	return err;
630 }
631 
632 /* Process an incoming IP datagram fragment. */
633 int ip_defrag(struct sk_buff *skb, u32 user)
634 {
635 	struct ipq *qp;
636 	struct net *net;
637 
638 	net = skb->dev ? dev_net(skb->dev) : dev_net(skb_dst(skb)->dev);
639 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);
640 
641 	/* Lookup (or create) queue header */
642 	if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
643 		int ret;
644 
645 		spin_lock(&qp->q.lock);
646 
647 		ret = ip_frag_queue(qp, skb);
648 
649 		spin_unlock(&qp->q.lock);
650 		ipq_put(qp);
651 		return ret;
652 	}
653 
654 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
655 	kfree_skb(skb);
656 	return -ENOMEM;
657 }
658 EXPORT_SYMBOL(ip_defrag);
659 
660 struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user)
661 {
662 	struct iphdr iph;
663 	u32 len;
664 
665 	if (skb->protocol != htons(ETH_P_IP))
666 		return skb;
667 
668 	if (!skb_copy_bits(skb, 0, &iph, sizeof(iph)))
669 		return skb;
670 
671 	if (iph.ihl < 5 || iph.version != 4)
672 		return skb;
673 
674 	len = ntohs(iph.tot_len);
675 	if (skb->len < len || len < (iph.ihl * 4))
676 		return skb;
677 
678 	if (ip_is_fragment(&iph)) {
679 		skb = skb_share_check(skb, GFP_ATOMIC);
680 		if (skb) {
681 			if (!pskb_may_pull(skb, iph.ihl*4))
682 				return skb;
683 			if (pskb_trim_rcsum(skb, len))
684 				return skb;
685 			memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
686 			if (ip_defrag(skb, user))
687 				return NULL;
688 			skb_clear_hash(skb);
689 		}
690 	}
691 	return skb;
692 }
693 EXPORT_SYMBOL(ip_check_defrag);
694 
695 #ifdef CONFIG_SYSCTL
696 static int zero;
697 
698 static struct ctl_table ip4_frags_ns_ctl_table[] = {
699 	{
700 		.procname	= "ipfrag_high_thresh",
701 		.data		= &init_net.ipv4.frags.high_thresh,
702 		.maxlen		= sizeof(int),
703 		.mode		= 0644,
704 		.proc_handler	= proc_dointvec_minmax,
705 		.extra1		= &init_net.ipv4.frags.low_thresh
706 	},
707 	{
708 		.procname	= "ipfrag_low_thresh",
709 		.data		= &init_net.ipv4.frags.low_thresh,
710 		.maxlen		= sizeof(int),
711 		.mode		= 0644,
712 		.proc_handler	= proc_dointvec_minmax,
713 		.extra1		= &zero,
714 		.extra2		= &init_net.ipv4.frags.high_thresh
715 	},
716 	{
717 		.procname	= "ipfrag_time",
718 		.data		= &init_net.ipv4.frags.timeout,
719 		.maxlen		= sizeof(int),
720 		.mode		= 0644,
721 		.proc_handler	= proc_dointvec_jiffies,
722 	},
723 	{ }
724 };
725 
726 /* secret interval has been deprecated */
727 static int ip4_frags_secret_interval_unused;
728 static struct ctl_table ip4_frags_ctl_table[] = {
729 	{
730 		.procname	= "ipfrag_secret_interval",
731 		.data		= &ip4_frags_secret_interval_unused,
732 		.maxlen		= sizeof(int),
733 		.mode		= 0644,
734 		.proc_handler	= proc_dointvec_jiffies,
735 	},
736 	{
737 		.procname	= "ipfrag_max_dist",
738 		.data		= &sysctl_ipfrag_max_dist,
739 		.maxlen		= sizeof(int),
740 		.mode		= 0644,
741 		.proc_handler	= proc_dointvec_minmax,
742 		.extra1		= &zero
743 	},
744 	{ }
745 };
746 
747 static int __net_init ip4_frags_ns_ctl_register(struct net *net)
748 {
749 	struct ctl_table *table;
750 	struct ctl_table_header *hdr;
751 
752 	table = ip4_frags_ns_ctl_table;
753 	if (!net_eq(net, &init_net)) {
754 		table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
755 		if (table == NULL)
756 			goto err_alloc;
757 
758 		table[0].data = &net->ipv4.frags.high_thresh;
759 		table[0].extra1 = &net->ipv4.frags.low_thresh;
760 		table[0].extra2 = &init_net.ipv4.frags.high_thresh;
761 		table[1].data = &net->ipv4.frags.low_thresh;
762 		table[1].extra2 = &net->ipv4.frags.high_thresh;
763 		table[2].data = &net->ipv4.frags.timeout;
764 
765 		/* Don't export sysctls to unprivileged users */
766 		if (net->user_ns != &init_user_ns)
767 			table[0].procname = NULL;
768 	}
769 
770 	hdr = register_net_sysctl(net, "net/ipv4", table);
771 	if (hdr == NULL)
772 		goto err_reg;
773 
774 	net->ipv4.frags_hdr = hdr;
775 	return 0;
776 
777 err_reg:
778 	if (!net_eq(net, &init_net))
779 		kfree(table);
780 err_alloc:
781 	return -ENOMEM;
782 }
783 
784 static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
785 {
786 	struct ctl_table *table;
787 
788 	table = net->ipv4.frags_hdr->ctl_table_arg;
789 	unregister_net_sysctl_table(net->ipv4.frags_hdr);
790 	kfree(table);
791 }
792 
793 static void ip4_frags_ctl_register(void)
794 {
795 	register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
796 }
797 #else
798 static inline int ip4_frags_ns_ctl_register(struct net *net)
799 {
800 	return 0;
801 }
802 
803 static inline void ip4_frags_ns_ctl_unregister(struct net *net)
804 {
805 }
806 
807 static inline void ip4_frags_ctl_register(void)
808 {
809 }
810 #endif
811 
812 static int __net_init ipv4_frags_init_net(struct net *net)
813 {
814 	/* Fragment cache limits.
815 	 *
816 	 * The fragment memory accounting code, (tries to) account for
817 	 * the real memory usage, by measuring both the size of frag
818 	 * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
819 	 * and the SKB's truesize.
820 	 *
821 	 * A 64K fragment consumes 129736 bytes (44*2944)+200
822 	 * (1500 truesize == 2944, sizeof(struct ipq) == 200)
823 	 *
824 	 * We will commit 4MB at one time. Should we cross that limit
825 	 * we will prune down to 3MB, making room for approx 8 big 64K
826 	 * fragments 8x128k.
827 	 */
828 	net->ipv4.frags.high_thresh = 4 * 1024 * 1024;
829 	net->ipv4.frags.low_thresh  = 3 * 1024 * 1024;
830 	/*
831 	 * Important NOTE! Fragment queue must be destroyed before MSL expires.
832 	 * RFC791 is wrong proposing to prolongate timer each fragment arrival
833 	 * by TTL.
834 	 */
835 	net->ipv4.frags.timeout = IP_FRAG_TIME;
836 
837 	inet_frags_init_net(&net->ipv4.frags);
838 
839 	return ip4_frags_ns_ctl_register(net);
840 }
841 
842 static void __net_exit ipv4_frags_exit_net(struct net *net)
843 {
844 	ip4_frags_ns_ctl_unregister(net);
845 	inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
846 }
847 
848 static struct pernet_operations ip4_frags_ops = {
849 	.init = ipv4_frags_init_net,
850 	.exit = ipv4_frags_exit_net,
851 };
852 
853 void __init ipfrag_init(void)
854 {
855 	ip4_frags_ctl_register();
856 	register_pernet_subsys(&ip4_frags_ops);
857 	ip4_frags.hashfn = ip4_hashfn;
858 	ip4_frags.constructor = ip4_frag_init;
859 	ip4_frags.destructor = ip4_frag_free;
860 	ip4_frags.skb_free = NULL;
861 	ip4_frags.qsize = sizeof(struct ipq);
862 	ip4_frags.match = ip4_frag_match;
863 	ip4_frags.frag_expire = ip_expire;
864 	ip4_frags.frags_cache_name = ip_frag_cache_name;
865 	if (inet_frags_init(&ip4_frags))
866 		panic("IP: failed to allocate ip4_frags cache\n");
867 }
868