xref: /openbmc/linux/net/ipv4/ip_fragment.c (revision a1e58bbd) 
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  * Version:	$Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
9  *
10  * Authors:	Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
11  *		Alan Cox <Alan.Cox@linux.org>
12  *
13  * Fixes:
14  *		Alan Cox	:	Split from ip.c , see ip_input.c for history.
15  *		David S. Miller :	Begin massive cleanup...
16  *		Andi Kleen	:	Add sysctls.
17  *		xxxx		:	Overlapfrag bug.
18  *		Ultima          :       ip_expire() kernel panic.
19  *		Bill Hawes	:	Frag accounting and evictor fixes.
20  *		John McDonald	:	0 length frag bug.
21  *		Alexey Kuznetsov:	SMP races, threading, cleanup.
22  *		Patrick McHardy :	LRU queue of frag heads for evictor.
23  */
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 <net/sock.h>
38 #include <net/ip.h>
39 #include <net/icmp.h>
40 #include <net/checksum.h>
41 #include <net/inetpeer.h>
42 #include <net/inet_frag.h>
43 #include <linux/tcp.h>
44 #include <linux/udp.h>
45 #include <linux/inet.h>
46 #include <linux/netfilter_ipv4.h>
47 
48 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
49  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
50  * as well. Or notify me, at least. --ANK
51  */
52 
53 static int sysctl_ipfrag_max_dist __read_mostly = 64;
54 
55 struct ipfrag_skb_cb
56 {
57 	struct inet_skb_parm	h;
58 	int			offset;
59 };
60 
61 #define FRAG_CB(skb)	((struct ipfrag_skb_cb*)((skb)->cb))
62 
63 /* Describe an entry in the "incomplete datagrams" queue. */
64 struct ipq {
65 	struct inet_frag_queue q;
66 
67 	u32		user;
68 	__be32		saddr;
69 	__be32		daddr;
70 	__be16		id;
71 	u8		protocol;
72 	int             iif;
73 	unsigned int    rid;
74 	struct inet_peer *peer;
75 };
76 
77 static struct inet_frags ip4_frags;
78 
79 int ip_frag_nqueues(struct net *net)
80 {
81 	return net->ipv4.frags.nqueues;
82 }
83 
84 int ip_frag_mem(struct net *net)
85 {
86 	return atomic_read(&net->ipv4.frags.mem);
87 }
88 
89 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
90 			 struct net_device *dev);
91 
92 struct ip4_create_arg {
93 	struct iphdr *iph;
94 	u32 user;
95 };
96 
97 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
98 {
99 	return jhash_3words((__force u32)id << 16 | prot,
100 			    (__force u32)saddr, (__force u32)daddr,
101 			    ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
102 }
103 
104 static unsigned int ip4_hashfn(struct inet_frag_queue *q)
105 {
106 	struct ipq *ipq;
107 
108 	ipq = container_of(q, struct ipq, q);
109 	return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
110 }
111 
112 static int ip4_frag_match(struct inet_frag_queue *q, void *a)
113 {
114 	struct ipq *qp;
115 	struct ip4_create_arg *arg = a;
116 
117 	qp = container_of(q, struct ipq, q);
118 	return (qp->id == arg->iph->id &&
119 			qp->saddr == arg->iph->saddr &&
120 			qp->daddr == arg->iph->daddr &&
121 			qp->protocol == arg->iph->protocol &&
122 			qp->user == arg->user);
123 }
124 
125 /* Memory Tracking Functions. */
126 static __inline__ void frag_kfree_skb(struct netns_frags *nf,
127 		struct sk_buff *skb, int *work)
128 {
129 	if (work)
130 		*work -= skb->truesize;
131 	atomic_sub(skb->truesize, &nf->mem);
132 	kfree_skb(skb);
133 }
134 
135 static void ip4_frag_init(struct inet_frag_queue *q, void *a)
136 {
137 	struct ipq *qp = container_of(q, struct ipq, q);
138 	struct ip4_create_arg *arg = a;
139 
140 	qp->protocol = arg->iph->protocol;
141 	qp->id = arg->iph->id;
142 	qp->saddr = arg->iph->saddr;
143 	qp->daddr = arg->iph->daddr;
144 	qp->user = arg->user;
145 	qp->peer = sysctl_ipfrag_max_dist ?
146 		inet_getpeer(arg->iph->saddr, 1) : NULL;
147 }
148 
149 static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
150 {
151 	struct ipq *qp;
152 
153 	qp = container_of(q, struct ipq, q);
154 	if (qp->peer)
155 		inet_putpeer(qp->peer);
156 }
157 
158 
159 /* Destruction primitives. */
160 
161 static __inline__ void ipq_put(struct ipq *ipq)
162 {
163 	inet_frag_put(&ipq->q, &ip4_frags);
164 }
165 
166 /* Kill ipq entry. It is not destroyed immediately,
167  * because caller (and someone more) holds reference count.
168  */
169 static void ipq_kill(struct ipq *ipq)
170 {
171 	inet_frag_kill(&ipq->q, &ip4_frags);
172 }
173 
174 /* Memory limiting on fragments.  Evictor trashes the oldest
175  * fragment queue until we are back under the threshold.
176  */
177 static void ip_evictor(struct net *net)
178 {
179 	int evicted;
180 
181 	evicted = inet_frag_evictor(&net->ipv4.frags, &ip4_frags);
182 	if (evicted)
183 		IP_ADD_STATS_BH(IPSTATS_MIB_REASMFAILS, evicted);
184 }
185 
186 /*
187  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
188  */
189 static void ip_expire(unsigned long arg)
190 {
191 	struct ipq *qp;
192 
193 	qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
194 
195 	spin_lock(&qp->q.lock);
196 
197 	if (qp->q.last_in & COMPLETE)
198 		goto out;
199 
200 	ipq_kill(qp);
201 
202 	IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
203 	IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
204 
205 	if ((qp->q.last_in&FIRST_IN) && qp->q.fragments != NULL) {
206 		struct sk_buff *head = qp->q.fragments;
207 		/* Send an ICMP "Fragment Reassembly Timeout" message. */
208 		if ((head->dev = dev_get_by_index(&init_net, qp->iif)) != NULL) {
209 			icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
210 			dev_put(head->dev);
211 		}
212 	}
213 out:
214 	spin_unlock(&qp->q.lock);
215 	ipq_put(qp);
216 }
217 
218 /* Find the correct entry in the "incomplete datagrams" queue for
219  * this IP datagram, and create new one, if nothing is found.
220  */
221 static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
222 {
223 	struct inet_frag_queue *q;
224 	struct ip4_create_arg arg;
225 	unsigned int hash;
226 
227 	arg.iph = iph;
228 	arg.user = user;
229 	hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
230 
231 	q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
232 	if (q == NULL)
233 		goto out_nomem;
234 
235 	return container_of(q, struct ipq, q);
236 
237 out_nomem:
238 	LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
239 	return NULL;
240 }
241 
242 /* Is the fragment too far ahead to be part of ipq? */
243 static inline int ip_frag_too_far(struct ipq *qp)
244 {
245 	struct inet_peer *peer = qp->peer;
246 	unsigned int max = sysctl_ipfrag_max_dist;
247 	unsigned int start, end;
248 
249 	int rc;
250 
251 	if (!peer || !max)
252 		return 0;
253 
254 	start = qp->rid;
255 	end = atomic_inc_return(&peer->rid);
256 	qp->rid = end;
257 
258 	rc = qp->q.fragments && (end - start) > max;
259 
260 	if (rc) {
261 		IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
262 	}
263 
264 	return rc;
265 }
266 
267 static int ip_frag_reinit(struct ipq *qp)
268 {
269 	struct sk_buff *fp;
270 
271 	if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
272 		atomic_inc(&qp->q.refcnt);
273 		return -ETIMEDOUT;
274 	}
275 
276 	fp = qp->q.fragments;
277 	do {
278 		struct sk_buff *xp = fp->next;
279 		frag_kfree_skb(qp->q.net, fp, NULL);
280 		fp = xp;
281 	} while (fp);
282 
283 	qp->q.last_in = 0;
284 	qp->q.len = 0;
285 	qp->q.meat = 0;
286 	qp->q.fragments = NULL;
287 	qp->iif = 0;
288 
289 	return 0;
290 }
291 
292 /* Add new segment to existing queue. */
293 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
294 {
295 	struct sk_buff *prev, *next;
296 	struct net_device *dev;
297 	int flags, offset;
298 	int ihl, end;
299 	int err = -ENOENT;
300 
301 	if (qp->q.last_in & COMPLETE)
302 		goto err;
303 
304 	if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
305 	    unlikely(ip_frag_too_far(qp)) &&
306 	    unlikely(err = ip_frag_reinit(qp))) {
307 		ipq_kill(qp);
308 		goto err;
309 	}
310 
311 	offset = ntohs(ip_hdr(skb)->frag_off);
312 	flags = offset & ~IP_OFFSET;
313 	offset &= IP_OFFSET;
314 	offset <<= 3;		/* offset is in 8-byte chunks */
315 	ihl = ip_hdrlen(skb);
316 
317 	/* Determine the position of this fragment. */
318 	end = offset + skb->len - ihl;
319 	err = -EINVAL;
320 
321 	/* Is this the final fragment? */
322 	if ((flags & IP_MF) == 0) {
323 		/* If we already have some bits beyond end
324 		 * or have different end, the segment is corrrupted.
325 		 */
326 		if (end < qp->q.len ||
327 		    ((qp->q.last_in & LAST_IN) && end != qp->q.len))
328 			goto err;
329 		qp->q.last_in |= LAST_IN;
330 		qp->q.len = end;
331 	} else {
332 		if (end&7) {
333 			end &= ~7;
334 			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
335 				skb->ip_summed = CHECKSUM_NONE;
336 		}
337 		if (end > qp->q.len) {
338 			/* Some bits beyond end -> corruption. */
339 			if (qp->q.last_in & LAST_IN)
340 				goto err;
341 			qp->q.len = end;
342 		}
343 	}
344 	if (end == offset)
345 		goto err;
346 
347 	err = -ENOMEM;
348 	if (pskb_pull(skb, ihl) == NULL)
349 		goto err;
350 
351 	err = pskb_trim_rcsum(skb, end - offset);
352 	if (err)
353 		goto err;
354 
355 	/* Find out which fragments are in front and at the back of us
356 	 * in the chain of fragments so far.  We must know where to put
357 	 * this fragment, right?
358 	 */
359 	prev = NULL;
360 	for (next = qp->q.fragments; next != NULL; next = next->next) {
361 		if (FRAG_CB(next)->offset >= offset)
362 			break;	/* bingo! */
363 		prev = next;
364 	}
365 
366 	/* We found where to put this one.  Check for overlap with
367 	 * preceding fragment, and, if needed, align things so that
368 	 * any overlaps are eliminated.
369 	 */
370 	if (prev) {
371 		int i = (FRAG_CB(prev)->offset + prev->len) - offset;
372 
373 		if (i > 0) {
374 			offset += i;
375 			err = -EINVAL;
376 			if (end <= offset)
377 				goto err;
378 			err = -ENOMEM;
379 			if (!pskb_pull(skb, i))
380 				goto err;
381 			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
382 				skb->ip_summed = CHECKSUM_NONE;
383 		}
384 	}
385 
386 	err = -ENOMEM;
387 
388 	while (next && FRAG_CB(next)->offset < end) {
389 		int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
390 
391 		if (i < next->len) {
392 			/* Eat head of the next overlapped fragment
393 			 * and leave the loop. The next ones cannot overlap.
394 			 */
395 			if (!pskb_pull(next, i))
396 				goto err;
397 			FRAG_CB(next)->offset += i;
398 			qp->q.meat -= i;
399 			if (next->ip_summed != CHECKSUM_UNNECESSARY)
400 				next->ip_summed = CHECKSUM_NONE;
401 			break;
402 		} else {
403 			struct sk_buff *free_it = next;
404 
405 			/* Old fragment is completely overridden with
406 			 * new one drop it.
407 			 */
408 			next = next->next;
409 
410 			if (prev)
411 				prev->next = next;
412 			else
413 				qp->q.fragments = next;
414 
415 			qp->q.meat -= free_it->len;
416 			frag_kfree_skb(qp->q.net, free_it, NULL);
417 		}
418 	}
419 
420 	FRAG_CB(skb)->offset = offset;
421 
422 	/* Insert this fragment in the chain of fragments. */
423 	skb->next = next;
424 	if (prev)
425 		prev->next = skb;
426 	else
427 		qp->q.fragments = skb;
428 
429 	dev = skb->dev;
430 	if (dev) {
431 		qp->iif = dev->ifindex;
432 		skb->dev = NULL;
433 	}
434 	qp->q.stamp = skb->tstamp;
435 	qp->q.meat += skb->len;
436 	atomic_add(skb->truesize, &qp->q.net->mem);
437 	if (offset == 0)
438 		qp->q.last_in |= FIRST_IN;
439 
440 	if (qp->q.last_in == (FIRST_IN | LAST_IN) && qp->q.meat == qp->q.len)
441 		return ip_frag_reasm(qp, prev, dev);
442 
443 	write_lock(&ip4_frags.lock);
444 	list_move_tail(&qp->q.lru_list, &qp->q.net->lru_list);
445 	write_unlock(&ip4_frags.lock);
446 	return -EINPROGRESS;
447 
448 err:
449 	kfree_skb(skb);
450 	return err;
451 }
452 
453 
454 /* Build a new IP datagram from all its fragments. */
455 
456 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
457 			 struct net_device *dev)
458 {
459 	struct iphdr *iph;
460 	struct sk_buff *fp, *head = qp->q.fragments;
461 	int len;
462 	int ihlen;
463 	int err;
464 
465 	ipq_kill(qp);
466 
467 	/* Make the one we just received the head. */
468 	if (prev) {
469 		head = prev->next;
470 		fp = skb_clone(head, GFP_ATOMIC);
471 		if (!fp)
472 			goto out_nomem;
473 
474 		fp->next = head->next;
475 		prev->next = fp;
476 
477 		skb_morph(head, qp->q.fragments);
478 		head->next = qp->q.fragments->next;
479 
480 		kfree_skb(qp->q.fragments);
481 		qp->q.fragments = head;
482 	}
483 
484 	BUG_TRAP(head != NULL);
485 	BUG_TRAP(FRAG_CB(head)->offset == 0);
486 
487 	/* Allocate a new buffer for the datagram. */
488 	ihlen = ip_hdrlen(head);
489 	len = ihlen + qp->q.len;
490 
491 	err = -E2BIG;
492 	if (len > 65535)
493 		goto out_oversize;
494 
495 	/* Head of list must not be cloned. */
496 	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
497 		goto out_nomem;
498 
499 	/* If the first fragment is fragmented itself, we split
500 	 * it to two chunks: the first with data and paged part
501 	 * and the second, holding only fragments. */
502 	if (skb_shinfo(head)->frag_list) {
503 		struct sk_buff *clone;
504 		int i, plen = 0;
505 
506 		if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
507 			goto out_nomem;
508 		clone->next = head->next;
509 		head->next = clone;
510 		skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
511 		skb_shinfo(head)->frag_list = NULL;
512 		for (i=0; i<skb_shinfo(head)->nr_frags; i++)
513 			plen += skb_shinfo(head)->frags[i].size;
514 		clone->len = clone->data_len = head->data_len - plen;
515 		head->data_len -= clone->len;
516 		head->len -= clone->len;
517 		clone->csum = 0;
518 		clone->ip_summed = head->ip_summed;
519 		atomic_add(clone->truesize, &qp->q.net->mem);
520 	}
521 
522 	skb_shinfo(head)->frag_list = head->next;
523 	skb_push(head, head->data - skb_network_header(head));
524 	atomic_sub(head->truesize, &qp->q.net->mem);
525 
526 	for (fp=head->next; fp; fp = fp->next) {
527 		head->data_len += fp->len;
528 		head->len += fp->len;
529 		if (head->ip_summed != fp->ip_summed)
530 			head->ip_summed = CHECKSUM_NONE;
531 		else if (head->ip_summed == CHECKSUM_COMPLETE)
532 			head->csum = csum_add(head->csum, fp->csum);
533 		head->truesize += fp->truesize;
534 		atomic_sub(fp->truesize, &qp->q.net->mem);
535 	}
536 
537 	head->next = NULL;
538 	head->dev = dev;
539 	head->tstamp = qp->q.stamp;
540 
541 	iph = ip_hdr(head);
542 	iph->frag_off = 0;
543 	iph->tot_len = htons(len);
544 	IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
545 	qp->q.fragments = NULL;
546 	return 0;
547 
548 out_nomem:
549 	LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
550 			      "queue %p\n", qp);
551 	err = -ENOMEM;
552 	goto out_fail;
553 out_oversize:
554 	if (net_ratelimit())
555 		printk(KERN_INFO
556 			"Oversized IP packet from %d.%d.%d.%d.\n",
557 			NIPQUAD(qp->saddr));
558 out_fail:
559 	IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
560 	return err;
561 }
562 
563 /* Process an incoming IP datagram fragment. */
564 int ip_defrag(struct sk_buff *skb, u32 user)
565 {
566 	struct ipq *qp;
567 	struct net *net;
568 
569 	IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
570 
571 	net = skb->dev ? skb->dev->nd_net : skb->dst->dev->nd_net;
572 	/* Start by cleaning up the memory. */
573 	if (atomic_read(&net->ipv4.frags.mem) > net->ipv4.frags.high_thresh)
574 		ip_evictor(net);
575 
576 	/* Lookup (or create) queue header */
577 	if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
578 		int ret;
579 
580 		spin_lock(&qp->q.lock);
581 
582 		ret = ip_frag_queue(qp, skb);
583 
584 		spin_unlock(&qp->q.lock);
585 		ipq_put(qp);
586 		return ret;
587 	}
588 
589 	IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
590 	kfree_skb(skb);
591 	return -ENOMEM;
592 }
593 
594 #ifdef CONFIG_SYSCTL
595 static int zero;
596 
597 static struct ctl_table ip4_frags_ctl_table[] = {
598 	{
599 		.ctl_name	= NET_IPV4_IPFRAG_HIGH_THRESH,
600 		.procname	= "ipfrag_high_thresh",
601 		.data		= &init_net.ipv4.frags.high_thresh,
602 		.maxlen		= sizeof(int),
603 		.mode		= 0644,
604 		.proc_handler	= &proc_dointvec
605 	},
606 	{
607 		.ctl_name	= NET_IPV4_IPFRAG_LOW_THRESH,
608 		.procname	= "ipfrag_low_thresh",
609 		.data		= &init_net.ipv4.frags.low_thresh,
610 		.maxlen		= sizeof(int),
611 		.mode		= 0644,
612 		.proc_handler	= &proc_dointvec
613 	},
614 	{
615 		.ctl_name	= NET_IPV4_IPFRAG_TIME,
616 		.procname	= "ipfrag_time",
617 		.data		= &init_net.ipv4.frags.timeout,
618 		.maxlen		= sizeof(int),
619 		.mode		= 0644,
620 		.proc_handler	= &proc_dointvec_jiffies,
621 		.strategy	= &sysctl_jiffies
622 	},
623 	{
624 		.ctl_name	= NET_IPV4_IPFRAG_SECRET_INTERVAL,
625 		.procname	= "ipfrag_secret_interval",
626 		.data		= &ip4_frags.secret_interval,
627 		.maxlen		= sizeof(int),
628 		.mode		= 0644,
629 		.proc_handler	= &proc_dointvec_jiffies,
630 		.strategy	= &sysctl_jiffies
631 	},
632 	{
633 		.procname	= "ipfrag_max_dist",
634 		.data		= &sysctl_ipfrag_max_dist,
635 		.maxlen		= sizeof(int),
636 		.mode		= 0644,
637 		.proc_handler	= &proc_dointvec_minmax,
638 		.extra1		= &zero
639 	},
640 	{ }
641 };
642 
643 static int ip4_frags_ctl_register(struct net *net)
644 {
645 	struct ctl_table *table;
646 	struct ctl_table_header *hdr;
647 
648 	table = ip4_frags_ctl_table;
649 	if (net != &init_net) {
650 		table = kmemdup(table, sizeof(ip4_frags_ctl_table), GFP_KERNEL);
651 		if (table == NULL)
652 			goto err_alloc;
653 
654 		table[0].data = &net->ipv4.frags.high_thresh;
655 		table[1].data = &net->ipv4.frags.low_thresh;
656 		table[2].data = &net->ipv4.frags.timeout;
657 		table[3].mode &= ~0222;
658 		table[4].mode &= ~0222;
659 	}
660 
661 	hdr = register_net_sysctl_table(net, net_ipv4_ctl_path, table);
662 	if (hdr == NULL)
663 		goto err_reg;
664 
665 	net->ipv4.frags_hdr = hdr;
666 	return 0;
667 
668 err_reg:
669 	if (net != &init_net)
670 		kfree(table);
671 err_alloc:
672 	return -ENOMEM;
673 }
674 
675 static void ip4_frags_ctl_unregister(struct net *net)
676 {
677 	struct ctl_table *table;
678 
679 	table = net->ipv4.frags_hdr->ctl_table_arg;
680 	unregister_net_sysctl_table(net->ipv4.frags_hdr);
681 	kfree(table);
682 }
683 #else
684 static inline int ip4_frags_ctl_register(struct net *net)
685 {
686 	return 0;
687 }
688 
689 static inline void ip4_frags_ctl_unregister(struct net *net)
690 {
691 }
692 #endif
693 
694 static int ipv4_frags_init_net(struct net *net)
695 {
696 	/*
697 	 * Fragment cache limits. We will commit 256K at one time. Should we
698 	 * cross that limit we will prune down to 192K. This should cope with
699 	 * even the most extreme cases without allowing an attacker to
700 	 * measurably harm machine performance.
701 	 */
702 	net->ipv4.frags.high_thresh = 256 * 1024;
703 	net->ipv4.frags.low_thresh = 192 * 1024;
704 	/*
705 	 * Important NOTE! Fragment queue must be destroyed before MSL expires.
706 	 * RFC791 is wrong proposing to prolongate timer each fragment arrival
707 	 * by TTL.
708 	 */
709 	net->ipv4.frags.timeout = IP_FRAG_TIME;
710 
711 	inet_frags_init_net(&net->ipv4.frags);
712 
713 	return ip4_frags_ctl_register(net);
714 }
715 
716 static void ipv4_frags_exit_net(struct net *net)
717 {
718 	ip4_frags_ctl_unregister(net);
719 	inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
720 }
721 
722 static struct pernet_operations ip4_frags_ops = {
723 	.init = ipv4_frags_init_net,
724 	.exit = ipv4_frags_exit_net,
725 };
726 
727 void __init ipfrag_init(void)
728 {
729 	register_pernet_subsys(&ip4_frags_ops);
730 	ip4_frags.hashfn = ip4_hashfn;
731 	ip4_frags.constructor = ip4_frag_init;
732 	ip4_frags.destructor = ip4_frag_free;
733 	ip4_frags.skb_free = NULL;
734 	ip4_frags.qsize = sizeof(struct ipq);
735 	ip4_frags.match = ip4_frag_match;
736 	ip4_frags.frag_expire = ip_expire;
737 	ip4_frags.secret_interval = 10 * 60 * HZ;
738 	inet_frags_init(&ip4_frags);
739 }
740 
741 EXPORT_SYMBOL(ip_defrag);
742