nf_conntrack_reasm.c revision e97c3e278e951501c2f385de70c3ceacdea78c4a 
1/*
2 * IPv6 fragment reassembly for connection tracking
3 *
4 * Copyright (C)2004 USAGI/WIDE Project
5 *
6 * Author:
7 *	Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
8 *
9 * Based on: net/ipv6/reassembly.c
10 *
11 * This program is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU General Public License
13 * as published by the Free Software Foundation; either version
14 * 2 of the License, or (at your option) any later version.
15 */
16
17#include <linux/errno.h>
18#include <linux/types.h>
19#include <linux/string.h>
20#include <linux/socket.h>
21#include <linux/sockios.h>
22#include <linux/jiffies.h>
23#include <linux/net.h>
24#include <linux/list.h>
25#include <linux/netdevice.h>
26#include <linux/in6.h>
27#include <linux/ipv6.h>
28#include <linux/icmpv6.h>
29#include <linux/random.h>
30#include <linux/slab.h>
31
32#include <net/sock.h>
33#include <net/snmp.h>
34#include <net/inet_frag.h>
35
36#include <net/ipv6.h>
37#include <net/protocol.h>
38#include <net/transp_v6.h>
39#include <net/rawv6.h>
40#include <net/ndisc.h>
41#include <net/addrconf.h>
42#include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
43#include <linux/sysctl.h>
44#include <linux/netfilter.h>
45#include <linux/netfilter_ipv6.h>
46#include <linux/kernel.h>
47#include <linux/module.h>
48
49
50struct nf_ct_frag6_skb_cb
51{
52	struct inet6_skb_parm	h;
53	int			offset;
54	struct sk_buff		*orig;
55};
56
57#define NFCT_FRAG6_CB(skb)	((struct nf_ct_frag6_skb_cb*)((skb)->cb))
58
59struct nf_ct_frag6_queue
60{
61	struct inet_frag_queue	q;
62
63	__be32			id;		/* fragment id		*/
64	u32			user;
65	struct in6_addr		saddr;
66	struct in6_addr		daddr;
67
68	unsigned int		csum;
69	__u16			nhoffset;
70};
71
72static struct inet_frags nf_frags;
73static struct netns_frags nf_init_frags;
74
75#ifdef CONFIG_SYSCTL
76struct ctl_table nf_ct_frag6_sysctl_table[] = {
77	{
78		.procname	= "nf_conntrack_frag6_timeout",
79		.data		= &nf_init_frags.timeout,
80		.maxlen		= sizeof(unsigned int),
81		.mode		= 0644,
82		.proc_handler	= proc_dointvec_jiffies,
83	},
84	{
85		.procname	= "nf_conntrack_frag6_low_thresh",
86		.data		= &nf_init_frags.low_thresh,
87		.maxlen		= sizeof(unsigned int),
88		.mode		= 0644,
89		.proc_handler	= proc_dointvec,
90	},
91	{
92		.procname	= "nf_conntrack_frag6_high_thresh",
93		.data		= &nf_init_frags.high_thresh,
94		.maxlen		= sizeof(unsigned int),
95		.mode		= 0644,
96		.proc_handler	= proc_dointvec,
97	},
98	{ }
99};
100
101static struct ctl_table_header *nf_ct_frag6_sysctl_header;
102#endif
103
104static unsigned int nf_hashfn(struct inet_frag_queue *q)
105{
106	const struct nf_ct_frag6_queue *nq;
107
108	nq = container_of(q, struct nf_ct_frag6_queue, q);
109	return inet6_hash_frag(nq->id, &nq->saddr, &nq->daddr, nf_frags.rnd);
110}
111
112static void nf_skb_free(struct sk_buff *skb)
113{
114	if (NFCT_FRAG6_CB(skb)->orig)
115		kfree_skb(NFCT_FRAG6_CB(skb)->orig);
116}
117
118/* Destruction primitives. */
119
120static __inline__ void fq_put(struct nf_ct_frag6_queue *fq)
121{
122	inet_frag_put(&fq->q, &nf_frags);
123}
124
125/* Kill fq entry. It is not destroyed immediately,
126 * because caller (and someone more) holds reference count.
127 */
128static __inline__ void fq_kill(struct nf_ct_frag6_queue *fq)
129{
130	inet_frag_kill(&fq->q, &nf_frags);
131}
132
133static void nf_ct_frag6_evictor(void)
134{
135	local_bh_disable();
136	inet_frag_evictor(&nf_init_frags, &nf_frags);
137	local_bh_enable();
138}
139
140static void nf_ct_frag6_expire(unsigned long data)
141{
142	struct nf_ct_frag6_queue *fq;
143
144	fq = container_of((struct inet_frag_queue *)data,
145			struct nf_ct_frag6_queue, q);
146
147	spin_lock(&fq->q.lock);
148
149	if (fq->q.last_in & INET_FRAG_COMPLETE)
150		goto out;
151
152	fq_kill(fq);
153
154out:
155	spin_unlock(&fq->q.lock);
156	fq_put(fq);
157}
158
159/* Creation primitives. */
160
161static __inline__ struct nf_ct_frag6_queue *
162fq_find(__be32 id, u32 user, struct in6_addr *src, struct in6_addr *dst)
163{
164	struct inet_frag_queue *q;
165	struct ip6_create_arg arg;
166	unsigned int hash;
167
168	arg.id = id;
169	arg.user = user;
170	arg.src = src;
171	arg.dst = dst;
172
173	read_lock_bh(&nf_frags.lock);
174	hash = inet6_hash_frag(id, src, dst, nf_frags.rnd);
175
176	q = inet_frag_find(&nf_init_frags, &nf_frags, &arg, hash);
177	local_bh_enable();
178	if (q == NULL)
179		goto oom;
180
181	return container_of(q, struct nf_ct_frag6_queue, q);
182
183oom:
184	pr_debug("Can't alloc new queue\n");
185	return NULL;
186}
187
188
189static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
190			     const struct frag_hdr *fhdr, int nhoff)
191{
192	struct sk_buff *prev, *next;
193	int offset, end;
194
195	if (fq->q.last_in & INET_FRAG_COMPLETE) {
196		pr_debug("Already completed\n");
197		goto err;
198	}
199
200	offset = ntohs(fhdr->frag_off) & ~0x7;
201	end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
202			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
203
204	if ((unsigned int)end > IPV6_MAXPLEN) {
205		pr_debug("offset is too large.\n");
206		return -1;
207	}
208
209	if (skb->ip_summed == CHECKSUM_COMPLETE) {
210		const unsigned char *nh = skb_network_header(skb);
211		skb->csum = csum_sub(skb->csum,
212				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
213						  0));
214	}
215
216	/* Is this the final fragment? */
217	if (!(fhdr->frag_off & htons(IP6_MF))) {
218		/* If we already have some bits beyond end
219		 * or have different end, the segment is corrupted.
220		 */
221		if (end < fq->q.len ||
222		    ((fq->q.last_in & INET_FRAG_LAST_IN) && end != fq->q.len)) {
223			pr_debug("already received last fragment\n");
224			goto err;
225		}
226		fq->q.last_in |= INET_FRAG_LAST_IN;
227		fq->q.len = end;
228	} else {
229		/* Check if the fragment is rounded to 8 bytes.
230		 * Required by the RFC.
231		 */
232		if (end & 0x7) {
233			/* RFC2460 says always send parameter problem in
234			 * this case. -DaveM
235			 */
236			pr_debug("end of fragment not rounded to 8 bytes.\n");
237			return -1;
238		}
239		if (end > fq->q.len) {
240			/* Some bits beyond end -> corruption. */
241			if (fq->q.last_in & INET_FRAG_LAST_IN) {
242				pr_debug("last packet already reached.\n");
243				goto err;
244			}
245			fq->q.len = end;
246		}
247	}
248
249	if (end == offset)
250		goto err;
251
252	/* Point into the IP datagram 'data' part. */
253	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
254		pr_debug("queue: message is too short.\n");
255		goto err;
256	}
257	if (pskb_trim_rcsum(skb, end - offset)) {
258		pr_debug("Can't trim\n");
259		goto err;
260	}
261
262	/* Find out which fragments are in front and at the back of us
263	 * in the chain of fragments so far.  We must know where to put
264	 * this fragment, right?
265	 */
266	prev = fq->q.fragments_tail;
267	if (!prev || NFCT_FRAG6_CB(prev)->offset < offset) {
268		next = NULL;
269		goto found;
270	}
271	prev = NULL;
272	for (next = fq->q.fragments; next != NULL; next = next->next) {
273		if (NFCT_FRAG6_CB(next)->offset >= offset)
274			break;	/* bingo! */
275		prev = next;
276	}
277
278found:
279	/* RFC5722, Section 4:
280	 *                                  When reassembling an IPv6 datagram, if
281	 *   one or more its constituent fragments is determined to be an
282	 *   overlapping fragment, the entire datagram (and any constituent
283	 *   fragments, including those not yet received) MUST be silently
284	 *   discarded.
285	 */
286
287	/* Check for overlap with preceding fragment. */
288	if (prev &&
289	    (NFCT_FRAG6_CB(prev)->offset + prev->len) - offset > 0)
290		goto discard_fq;
291
292	/* Look for overlap with succeeding segment. */
293	if (next && NFCT_FRAG6_CB(next)->offset < end)
294		goto discard_fq;
295
296	NFCT_FRAG6_CB(skb)->offset = offset;
297
298	/* Insert this fragment in the chain of fragments. */
299	skb->next = next;
300	if (!next)
301		fq->q.fragments_tail = skb;
302	if (prev)
303		prev->next = skb;
304	else
305		fq->q.fragments = skb;
306
307	skb->dev = NULL;
308	fq->q.stamp = skb->tstamp;
309	fq->q.meat += skb->len;
310	atomic_add(skb->truesize, &nf_init_frags.mem);
311
312	/* The first fragment.
313	 * nhoffset is obtained from the first fragment, of course.
314	 */
315	if (offset == 0) {
316		fq->nhoffset = nhoff;
317		fq->q.last_in |= INET_FRAG_FIRST_IN;
318	}
319	write_lock(&nf_frags.lock);
320	list_move_tail(&fq->q.lru_list, &nf_init_frags.lru_list);
321	write_unlock(&nf_frags.lock);
322	return 0;
323
324discard_fq:
325	fq_kill(fq);
326err:
327	return -1;
328}
329
330/*
331 *	Check if this packet is complete.
332 *	Returns NULL on failure by any reason, and pointer
333 *	to current nexthdr field in reassembled frame.
334 *
335 *	It is called with locked fq, and caller must check that
336 *	queue is eligible for reassembly i.e. it is not COMPLETE,
337 *	the last and the first frames arrived and all the bits are here.
338 */
339static struct sk_buff *
340nf_ct_frag6_reasm(struct nf_ct_frag6_queue *fq, struct net_device *dev)
341{
342	struct sk_buff *fp, *op, *head = fq->q.fragments;
343	int    payload_len;
344
345	fq_kill(fq);
346
347	WARN_ON(head == NULL);
348	WARN_ON(NFCT_FRAG6_CB(head)->offset != 0);
349
350	/* Unfragmented part is taken from the first segment. */
351	payload_len = ((head->data - skb_network_header(head)) -
352		       sizeof(struct ipv6hdr) + fq->q.len -
353		       sizeof(struct frag_hdr));
354	if (payload_len > IPV6_MAXPLEN) {
355		pr_debug("payload len is too large.\n");
356		goto out_oversize;
357	}
358
359	/* Head of list must not be cloned. */
360	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
361		pr_debug("skb is cloned but can't expand head");
362		goto out_oom;
363	}
364
365	/* If the first fragment is fragmented itself, we split
366	 * it to two chunks: the first with data and paged part
367	 * and the second, holding only fragments. */
368	if (skb_has_frag_list(head)) {
369		struct sk_buff *clone;
370		int i, plen = 0;
371
372		if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) {
373			pr_debug("Can't alloc skb\n");
374			goto out_oom;
375		}
376		clone->next = head->next;
377		head->next = clone;
378		skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
379		skb_frag_list_init(head);
380		for (i=0; i<skb_shinfo(head)->nr_frags; i++)
381			plen += skb_shinfo(head)->frags[i].size;
382		clone->len = clone->data_len = head->data_len - plen;
383		head->data_len -= clone->len;
384		head->len -= clone->len;
385		clone->csum = 0;
386		clone->ip_summed = head->ip_summed;
387
388		NFCT_FRAG6_CB(clone)->orig = NULL;
389		atomic_add(clone->truesize, &nf_init_frags.mem);
390	}
391
392	/* We have to remove fragment header from datagram and to relocate
393	 * header in order to calculate ICV correctly. */
394	skb_network_header(head)[fq->nhoffset] = skb_transport_header(head)[0];
395	memmove(head->head + sizeof(struct frag_hdr), head->head,
396		(head->data - head->head) - sizeof(struct frag_hdr));
397	head->mac_header += sizeof(struct frag_hdr);
398	head->network_header += sizeof(struct frag_hdr);
399
400	skb_shinfo(head)->frag_list = head->next;
401	skb_reset_transport_header(head);
402	skb_push(head, head->data - skb_network_header(head));
403
404	for (fp=head->next; fp; fp = fp->next) {
405		head->data_len += fp->len;
406		head->len += fp->len;
407		if (head->ip_summed != fp->ip_summed)
408			head->ip_summed = CHECKSUM_NONE;
409		else if (head->ip_summed == CHECKSUM_COMPLETE)
410			head->csum = csum_add(head->csum, fp->csum);
411		head->truesize += fp->truesize;
412	}
413	atomic_sub(head->truesize, &nf_init_frags.mem);
414
415	head->next = NULL;
416	head->dev = dev;
417	head->tstamp = fq->q.stamp;
418	ipv6_hdr(head)->payload_len = htons(payload_len);
419
420	/* Yes, and fold redundant checksum back. 8) */
421	if (head->ip_summed == CHECKSUM_COMPLETE)
422		head->csum = csum_partial(skb_network_header(head),
423					  skb_network_header_len(head),
424					  head->csum);
425
426	fq->q.fragments = NULL;
427	fq->q.fragments_tail = NULL;
428
429	/* all original skbs are linked into the NFCT_FRAG6_CB(head).orig */
430	fp = skb_shinfo(head)->frag_list;
431	if (fp && NFCT_FRAG6_CB(fp)->orig == NULL)
432		/* at above code, head skb is divided into two skbs. */
433		fp = fp->next;
434
435	op = NFCT_FRAG6_CB(head)->orig;
436	for (; fp; fp = fp->next) {
437		struct sk_buff *orig = NFCT_FRAG6_CB(fp)->orig;
438
439		op->next = orig;
440		op = orig;
441		NFCT_FRAG6_CB(fp)->orig = NULL;
442	}
443
444	return head;
445
446out_oversize:
447	if (net_ratelimit())
448		printk(KERN_DEBUG "nf_ct_frag6_reasm: payload len = %d\n", payload_len);
449	goto out_fail;
450out_oom:
451	if (net_ratelimit())
452		printk(KERN_DEBUG "nf_ct_frag6_reasm: no memory for reassembly\n");
453out_fail:
454	return NULL;
455}
456
457/*
458 * find the header just before Fragment Header.
459 *
460 * if success return 0 and set ...
461 * (*prevhdrp): the value of "Next Header Field" in the header
462 *		just before Fragment Header.
463 * (*prevhoff): the offset of "Next Header Field" in the header
464 *		just before Fragment Header.
465 * (*fhoff)   : the offset of Fragment Header.
466 *
467 * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
468 *
469 */
470static int
471find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
472{
473	u8 nexthdr = ipv6_hdr(skb)->nexthdr;
474	const int netoff = skb_network_offset(skb);
475	u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
476	int start = netoff + sizeof(struct ipv6hdr);
477	int len = skb->len - start;
478	u8 prevhdr = NEXTHDR_IPV6;
479
480	while (nexthdr != NEXTHDR_FRAGMENT) {
481		struct ipv6_opt_hdr hdr;
482		int hdrlen;
483
484		if (!ipv6_ext_hdr(nexthdr)) {
485			return -1;
486		}
487		if (nexthdr == NEXTHDR_NONE) {
488			pr_debug("next header is none\n");
489			return -1;
490		}
491		if (len < (int)sizeof(struct ipv6_opt_hdr)) {
492			pr_debug("too short\n");
493			return -1;
494		}
495		if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
496			BUG();
497		if (nexthdr == NEXTHDR_AUTH)
498			hdrlen = (hdr.hdrlen+2)<<2;
499		else
500			hdrlen = ipv6_optlen(&hdr);
501
502		prevhdr = nexthdr;
503		prev_nhoff = start;
504
505		nexthdr = hdr.nexthdr;
506		len -= hdrlen;
507		start += hdrlen;
508	}
509
510	if (len < 0)
511		return -1;
512
513	*prevhdrp = prevhdr;
514	*prevhoff = prev_nhoff;
515	*fhoff = start;
516
517	return 0;
518}
519
520struct sk_buff *nf_ct_frag6_gather(struct sk_buff *skb, u32 user)
521{
522	struct sk_buff *clone;
523	struct net_device *dev = skb->dev;
524	struct frag_hdr *fhdr;
525	struct nf_ct_frag6_queue *fq;
526	struct ipv6hdr *hdr;
527	int fhoff, nhoff;
528	u8 prevhdr;
529	struct sk_buff *ret_skb = NULL;
530
531	/* Jumbo payload inhibits frag. header */
532	if (ipv6_hdr(skb)->payload_len == 0) {
533		pr_debug("payload len = 0\n");
534		return skb;
535	}
536
537	if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
538		return skb;
539
540	clone = skb_clone(skb, GFP_ATOMIC);
541	if (clone == NULL) {
542		pr_debug("Can't clone skb\n");
543		return skb;
544	}
545
546	NFCT_FRAG6_CB(clone)->orig = skb;
547
548	if (!pskb_may_pull(clone, fhoff + sizeof(*fhdr))) {
549		pr_debug("message is too short.\n");
550		goto ret_orig;
551	}
552
553	skb_set_transport_header(clone, fhoff);
554	hdr = ipv6_hdr(clone);
555	fhdr = (struct frag_hdr *)skb_transport_header(clone);
556
557	if (atomic_read(&nf_init_frags.mem) > nf_init_frags.high_thresh)
558		nf_ct_frag6_evictor();
559
560	fq = fq_find(fhdr->identification, user, &hdr->saddr, &hdr->daddr);
561	if (fq == NULL) {
562		pr_debug("Can't find and can't create new queue\n");
563		goto ret_orig;
564	}
565
566	spin_lock_bh(&fq->q.lock);
567
568	if (nf_ct_frag6_queue(fq, clone, fhdr, nhoff) < 0) {
569		spin_unlock_bh(&fq->q.lock);
570		pr_debug("Can't insert skb to queue\n");
571		fq_put(fq);
572		goto ret_orig;
573	}
574
575	if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
576	    fq->q.meat == fq->q.len) {
577		ret_skb = nf_ct_frag6_reasm(fq, dev);
578		if (ret_skb == NULL)
579			pr_debug("Can't reassemble fragmented packets\n");
580	}
581	spin_unlock_bh(&fq->q.lock);
582
583	fq_put(fq);
584	return ret_skb;
585
586ret_orig:
587	kfree_skb(clone);
588	return skb;
589}
590
591void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb,
592			struct net_device *in, struct net_device *out,
593			int (*okfn)(struct sk_buff *))
594{
595	struct sk_buff *s, *s2;
596
597	for (s = NFCT_FRAG6_CB(skb)->orig; s;) {
598		nf_conntrack_put_reasm(s->nfct_reasm);
599		nf_conntrack_get_reasm(skb);
600		s->nfct_reasm = skb;
601
602		s2 = s->next;
603		s->next = NULL;
604
605		NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s, in, out, okfn,
606			       NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
607		s = s2;
608	}
609	nf_conntrack_put_reasm(skb);
610}
611
612int nf_ct_frag6_init(void)
613{
614	nf_frags.hashfn = nf_hashfn;
615	nf_frags.constructor = ip6_frag_init;
616	nf_frags.destructor = NULL;
617	nf_frags.skb_free = nf_skb_free;
618	nf_frags.qsize = sizeof(struct nf_ct_frag6_queue);
619	nf_frags.match = ip6_frag_match;
620	nf_frags.frag_expire = nf_ct_frag6_expire;
621	nf_frags.secret_interval = 10 * 60 * HZ;
622	nf_init_frags.timeout = IPV6_FRAG_TIMEOUT;
623	nf_init_frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
624	nf_init_frags.low_thresh = IPV6_FRAG_LOW_THRESH;
625	inet_frags_init_net(&nf_init_frags);
626	inet_frags_init(&nf_frags);
627
628	nf_ct_frag6_sysctl_header = register_sysctl_paths(nf_net_netfilter_sysctl_path,
629							  nf_ct_frag6_sysctl_table);
630	if (!nf_ct_frag6_sysctl_header) {
631		inet_frags_fini(&nf_frags);
632		return -ENOMEM;
633	}
634
635	return 0;
636}
637
638void nf_ct_frag6_cleanup(void)
639{
640	unregister_sysctl_table(nf_ct_frag6_sysctl_header);
641	nf_ct_frag6_sysctl_header = NULL;
642
643	inet_frags_fini(&nf_frags);
644
645	nf_init_frags.low_thresh = 0;
646	nf_ct_frag6_evictor();
647}
648