nf_conntrack_reasm.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * IPv6 fragment reassembly for connection tracking
  4 *
  5 * Copyright (C)2004 USAGI/WIDE Project
  6 *
  7 * Author:
  8 *	Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
  9 *
 10 * Based on: net/ipv6/reassembly.c
 11 */
 12
 13#define pr_fmt(fmt) "IPv6-nf: " fmt
 14
 15#include <linux/errno.h>
 16#include <linux/types.h>
 17#include <linux/string.h>
 18#include <linux/net.h>
 19#include <linux/netdevice.h>
 20#include <linux/ipv6.h>
 21#include <linux/slab.h>
 22
 23#include <net/ipv6_frag.h>
 24
 25#include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
 26#include <linux/sysctl.h>
 27#include <linux/netfilter.h>
 28#include <linux/netfilter_ipv6.h>
 29#include <linux/kernel.h>
 30#include <linux/module.h>
 31#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 32#include <net/netns/generic.h>
 33
 34static const char nf_frags_cache_name[] = "nf-frags";
 35
 36static unsigned int nf_frag_pernet_id __read_mostly;
 37static struct inet_frags nf_frags;
 38
 39static struct nft_ct_frag6_pernet *nf_frag_pernet(struct net *net)
 40{
 41	return net_generic(net, nf_frag_pernet_id);
 42}
 43
 44#ifdef CONFIG_SYSCTL
 45
 46static struct ctl_table nf_ct_frag6_sysctl_table[] = {
 47	{
 48		.procname	= "nf_conntrack_frag6_timeout",
 49		.maxlen		= sizeof(unsigned int),
 50		.mode		= 0644,
 51		.proc_handler	= proc_dointvec_jiffies,
 52	},
 53	{
 54		.procname	= "nf_conntrack_frag6_low_thresh",
 55		.maxlen		= sizeof(unsigned long),
 56		.mode		= 0644,
 57		.proc_handler	= proc_doulongvec_minmax,
 58	},
 59	{
 60		.procname	= "nf_conntrack_frag6_high_thresh",
 61		.maxlen		= sizeof(unsigned long),
 62		.mode		= 0644,
 63		.proc_handler	= proc_doulongvec_minmax,
 64	},
 65};
 66
 67static int nf_ct_frag6_sysctl_register(struct net *net)
 68{
 69	struct nft_ct_frag6_pernet *nf_frag;
 70	struct ctl_table *table;
 71	struct ctl_table_header *hdr;
 72
 73	table = nf_ct_frag6_sysctl_table;
 74	if (!net_eq(net, &init_net)) {
 75		table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
 76				GFP_KERNEL);
 77		if (table == NULL)
 78			goto err_alloc;
 79	}
 80
 81	nf_frag = nf_frag_pernet(net);
 82
 83	table[0].data	= &nf_frag->fqdir->timeout;
 84	table[1].data	= &nf_frag->fqdir->low_thresh;
 85	table[1].extra2	= &nf_frag->fqdir->high_thresh;
 86	table[2].data	= &nf_frag->fqdir->high_thresh;
 87	table[2].extra1	= &nf_frag->fqdir->low_thresh;
 88
 89	hdr = register_net_sysctl_sz(net, "net/netfilter", table,
 90				     ARRAY_SIZE(nf_ct_frag6_sysctl_table));
 91	if (hdr == NULL)
 92		goto err_reg;
 93
 94	nf_frag->nf_frag_frags_hdr = hdr;
 95	return 0;
 96
 97err_reg:
 98	if (!net_eq(net, &init_net))
 99		kfree(table);
100err_alloc:
101	return -ENOMEM;
102}
103
104static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
105{
106	struct nft_ct_frag6_pernet *nf_frag = nf_frag_pernet(net);
107	const struct ctl_table *table;
108
109	table = nf_frag->nf_frag_frags_hdr->ctl_table_arg;
110	unregister_net_sysctl_table(nf_frag->nf_frag_frags_hdr);
111	if (!net_eq(net, &init_net))
112		kfree(table);
113}
114
115#else
116static int nf_ct_frag6_sysctl_register(struct net *net)
117{
118	return 0;
119}
120static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
121{
122}
123#endif
124
125static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
126			     struct sk_buff *prev_tail, struct net_device *dev,
127			     int *refs);
128
129static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
130{
131	return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
132}
133
134static void nf_ct_frag6_expire(struct timer_list *t)
135{
136	struct inet_frag_queue *frag = timer_container_of(frag, t, timer);
137	struct frag_queue *fq;
138
139	fq = container_of(frag, struct frag_queue, q);
140
141	ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
142}
143
144/* Creation primitives. */
145static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
146				  const struct ipv6hdr *hdr, int iif)
147{
148	struct nft_ct_frag6_pernet *nf_frag = nf_frag_pernet(net);
149	struct frag_v6_compare_key key = {
150		.id = id,
151		.saddr = hdr->saddr,
152		.daddr = hdr->daddr,
153		.user = user,
154		.iif = iif,
155	};
156	struct inet_frag_queue *q;
157
158	if (!(ipv6_addr_type(&hdr->daddr) & (IPV6_ADDR_MULTICAST |
159					    IPV6_ADDR_LINKLOCAL)))
160		key.iif = 0;
161
162	q = inet_frag_find(nf_frag->fqdir, &key);
163	if (!q)
164		return NULL;
165
166	return container_of(q, struct frag_queue, q);
167}
168
169
170static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
171			     const struct frag_hdr *fhdr, int nhoff,
172			     int *refs)
173{
174	unsigned int payload_len;
175	struct net_device *dev;
176	struct sk_buff *prev;
177	int offset, end, err;
178	u8 ecn;
179
180	if (fq->q.flags & INET_FRAG_COMPLETE) {
181		pr_debug("Already completed\n");
182		goto err;
183	}
184
185	payload_len = ntohs(ipv6_hdr(skb)->payload_len);
186
187	offset = ntohs(fhdr->frag_off) & ~0x7;
188	end = offset + (payload_len -
189			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
190
191	if ((unsigned int)end > IPV6_MAXPLEN) {
192		pr_debug("offset is too large.\n");
193		return -EINVAL;
194	}
195
196	ecn = ip6_frag_ecn(ipv6_hdr(skb));
197
198	if (skb->ip_summed == CHECKSUM_COMPLETE) {
199		const unsigned char *nh = skb_network_header(skb);
200		skb->csum = csum_sub(skb->csum,
201				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
202						  0));
203	}
204
205	/* Is this the final fragment? */
206	if (!(fhdr->frag_off & htons(IP6_MF))) {
207		/* If we already have some bits beyond end
208		 * or have different end, the segment is corrupted.
209		 */
210		if (end < fq->q.len ||
211		    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len)) {
212			pr_debug("already received last fragment\n");
213			goto err;
214		}
215		fq->q.flags |= INET_FRAG_LAST_IN;
216		fq->q.len = end;
217	} else {
218		/* Check if the fragment is rounded to 8 bytes.
219		 * Required by the RFC.
220		 */
221		if (end & 0x7) {
222			/* RFC2460 says always send parameter problem in
223			 * this case. -DaveM
224			 */
225			pr_debug("end of fragment not rounded to 8 bytes.\n");
226			inet_frag_kill(&fq->q, refs);
227			return -EPROTO;
228		}
229		if (end > fq->q.len) {
230			/* Some bits beyond end -> corruption. */
231			if (fq->q.flags & INET_FRAG_LAST_IN) {
232				pr_debug("last packet already reached.\n");
233				goto err;
234			}
235			fq->q.len = end;
236		}
237	}
238
239	if (end == offset)
240		goto err;
241
242	/* Point into the IP datagram 'data' part. */
243	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
244		pr_debug("queue: message is too short.\n");
245		goto err;
246	}
247	if (pskb_trim_rcsum(skb, end - offset)) {
248		pr_debug("Can't trim\n");
249		goto err;
250	}
251
252	/* Note : skb->rbnode and skb->dev share the same location. */
253	dev = skb->dev;
254	/* Makes sure compiler wont do silly aliasing games */
255	barrier();
256
257	prev = fq->q.fragments_tail;
258	err = inet_frag_queue_insert(&fq->q, skb, offset, end);
259	if (err) {
260		if (err == IPFRAG_DUP) {
261			/* No error for duplicates, pretend they got queued. */
262			kfree_skb_reason(skb, SKB_DROP_REASON_DUP_FRAG);
263			return -EINPROGRESS;
264		}
265		goto insert_error;
266	}
267
268	if (dev)
269		fq->iif = dev->ifindex;
270
271	fq->q.stamp = skb->tstamp;
272	fq->q.tstamp_type = skb->tstamp_type;
273	fq->q.meat += skb->len;
274	fq->ecn |= ecn;
275	if (payload_len > fq->q.max_size)
276		fq->q.max_size = payload_len;
277	add_frag_mem_limit(fq->q.fqdir, skb->truesize);
278
279	/* The first fragment.
280	 * nhoffset is obtained from the first fragment, of course.
281	 */
282	if (offset == 0) {
283		fq->nhoffset = nhoff;
284		fq->q.flags |= INET_FRAG_FIRST_IN;
285	}
286
287	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
288	    fq->q.meat == fq->q.len) {
289		unsigned long orefdst = skb->_skb_refdst;
290
291		skb->_skb_refdst = 0UL;
292		err = nf_ct_frag6_reasm(fq, skb, prev, dev, refs);
293		skb->_skb_refdst = orefdst;
294
295		/* After queue has assumed skb ownership, only 0 or
296		 * -EINPROGRESS must be returned.
297		 */
298		return err ? -EINPROGRESS : 0;
299	}
300
301	skb_dst_drop(skb);
302	skb_orphan(skb);
303	return -EINPROGRESS;
304
305insert_error:
306	inet_frag_kill(&fq->q, refs);
307err:
308	skb_dst_drop(skb);
309	return -EINVAL;
310}
311
312/*
313 *	Check if this packet is complete.
314 *
315 *	It is called with locked fq, and caller must check that
316 *	queue is eligible for reassembly i.e. it is not COMPLETE,
317 *	the last and the first frames arrived and all the bits are here.
318 */
319static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
320			     struct sk_buff *prev_tail, struct net_device *dev,
321			     int *refs)
322{
323	void *reasm_data;
324	int payload_len;
325	u8 ecn;
326
327	inet_frag_kill(&fq->q, refs);
328
329	ecn = ip_frag_ecn_table[fq->ecn];
330	if (unlikely(ecn == 0xff))
331		goto err;
332
333	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
334	if (!reasm_data)
335		goto err;
336
337	payload_len = -skb_network_offset(skb) -
338		       sizeof(struct ipv6hdr) + fq->q.len -
339		       sizeof(struct frag_hdr);
340	if (payload_len > IPV6_MAXPLEN) {
341		net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
342				    payload_len);
343		goto err;
344	}
345
346	/* We have to remove fragment header from datagram and to relocate
347	 * header in order to calculate ICV correctly. */
348	skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
349	memmove(skb->head + sizeof(struct frag_hdr), skb->head,
350		(skb->data - skb->head) - sizeof(struct frag_hdr));
351	skb->mac_header += sizeof(struct frag_hdr);
352	skb->network_header += sizeof(struct frag_hdr);
353
354	skb_reset_transport_header(skb);
355
356	inet_frag_reasm_finish(&fq->q, skb, reasm_data, false);
357
358	skb->ignore_df = 1;
359	skb->dev = dev;
360	ipv6_hdr(skb)->payload_len = htons(payload_len);
361	ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
362	IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
363	IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
364
365	/* Yes, and fold redundant checksum back. 8) */
366	if (skb->ip_summed == CHECKSUM_COMPLETE)
367		skb->csum = csum_partial(skb_network_header(skb),
368					 skb_network_header_len(skb),
369					 skb->csum);
370
371	fq->q.rb_fragments = RB_ROOT;
372	fq->q.fragments_tail = NULL;
373	fq->q.last_run_head = NULL;
374
375	return 0;
376
377err:
378	inet_frag_kill(&fq->q, refs);
379	return -EINVAL;
380}
381
382/*
383 * find the header just before Fragment Header.
384 *
385 * if success return 0 and set ...
386 * (*prevhdrp): the value of "Next Header Field" in the header
387 *		just before Fragment Header.
388 * (*prevhoff): the offset of "Next Header Field" in the header
389 *		just before Fragment Header.
390 * (*fhoff)   : the offset of Fragment Header.
391 *
392 * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
393 *
394 */
395static int
396find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
397{
398	u8 nexthdr = ipv6_hdr(skb)->nexthdr;
399	const int netoff = skb_network_offset(skb);
400	u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
401	int start = netoff + sizeof(struct ipv6hdr);
402	int len = skb->len - start;
403	u8 prevhdr = NEXTHDR_IPV6;
404
405	while (nexthdr != NEXTHDR_FRAGMENT) {
406		struct ipv6_opt_hdr hdr;
407		int hdrlen;
408
409		if (!ipv6_ext_hdr(nexthdr)) {
410			return -1;
411		}
412		if (nexthdr == NEXTHDR_NONE) {
413			pr_debug("next header is none\n");
414			return -1;
415		}
416		if (len < (int)sizeof(struct ipv6_opt_hdr)) {
417			pr_debug("too short\n");
418			return -1;
419		}
420		if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
421			BUG();
422		if (nexthdr == NEXTHDR_AUTH)
423			hdrlen = ipv6_authlen(&hdr);
424		else
425			hdrlen = ipv6_optlen(&hdr);
426
427		prevhdr = nexthdr;
428		prev_nhoff = start;
429
430		nexthdr = hdr.nexthdr;
431		len -= hdrlen;
432		start += hdrlen;
433	}
434
435	if (len < 0)
436		return -1;
437
438	*prevhdrp = prevhdr;
439	*prevhoff = prev_nhoff;
440	*fhoff = start;
441
442	return 0;
443}
444
445int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
446{
447	u16 savethdr = skb->transport_header;
448	u8 nexthdr = NEXTHDR_FRAGMENT;
449	int fhoff, nhoff, ret;
450	struct frag_hdr *fhdr;
451	struct frag_queue *fq;
452	struct ipv6hdr *hdr;
453	int refs = 0;
454	u8 prevhdr;
455
456	/* Jumbo payload inhibits frag. header */
457	if (ipv6_hdr(skb)->payload_len == 0) {
458		pr_debug("payload len = 0\n");
459		return 0;
460	}
461
462	if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
463		return 0;
464
465	/* Discard the first fragment if it does not include all headers
466	 * RFC 8200, Section 4.5
467	 */
468	if (ipv6frag_thdr_truncated(skb, fhoff, &nexthdr)) {
469		pr_debug("Drop incomplete fragment\n");
470		return 0;
471	}
472
473	if (!pskb_may_pull(skb, fhoff + sizeof(*fhdr)))
474		return -ENOMEM;
475
476	skb_set_transport_header(skb, fhoff);
477	hdr = ipv6_hdr(skb);
478	fhdr = (struct frag_hdr *)skb_transport_header(skb);
479
480	rcu_read_lock();
481	fq = fq_find(net, fhdr->identification, user, hdr,
482		     skb->dev ? skb->dev->ifindex : 0);
483	if (fq == NULL) {
484		rcu_read_unlock();
485		pr_debug("Can't find and can't create new queue\n");
486		return -ENOMEM;
487	}
488
489	spin_lock_bh(&fq->q.lock);
490
491	ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff, &refs);
492	if (ret == -EPROTO) {
493		skb->transport_header = savethdr;
494		ret = 0;
495	}
496
497	spin_unlock_bh(&fq->q.lock);
498	rcu_read_unlock();
499	inet_frag_putn(&fq->q, refs);
500	return ret;
501}
502EXPORT_SYMBOL_GPL(nf_ct_frag6_gather);
503
504static int nf_ct_net_init(struct net *net)
505{
506	struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);
507	int res;
508
509	res = fqdir_init(&nf_frag->fqdir, &nf_frags, net);
510	if (res < 0)
511		return res;
512
513	nf_frag->fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
514	nf_frag->fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
515	nf_frag->fqdir->timeout = IPV6_FRAG_TIMEOUT;
516
517	res = nf_ct_frag6_sysctl_register(net);
518	if (res < 0)
519		fqdir_exit(nf_frag->fqdir);
520	return res;
521}
522
523static void nf_ct_net_pre_exit(struct net *net)
524{
525	struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);
526
527	fqdir_pre_exit(nf_frag->fqdir);
528}
529
530static void nf_ct_net_exit(struct net *net)
531{
532	struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);
533
534	nf_ct_frags6_sysctl_unregister(net);
535	fqdir_exit(nf_frag->fqdir);
536}
537
538static struct pernet_operations nf_ct_net_ops = {
539	.init		= nf_ct_net_init,
540	.pre_exit	= nf_ct_net_pre_exit,
541	.exit		= nf_ct_net_exit,
542	.id		= &nf_frag_pernet_id,
543	.size		= sizeof(struct nft_ct_frag6_pernet),
544};
545
546static const struct rhashtable_params nfct_rhash_params = {
547	.head_offset		= offsetof(struct inet_frag_queue, node),
548	.hashfn			= ip6frag_key_hashfn,
549	.obj_hashfn		= ip6frag_obj_hashfn,
550	.obj_cmpfn		= ip6frag_obj_cmpfn,
551	.automatic_shrinking	= true,
552};
553
554int nf_ct_frag6_init(void)
555{
556	int ret = 0;
557
558	nf_frags.constructor = ip6frag_init;
559	nf_frags.destructor = NULL;
560	nf_frags.qsize = sizeof(struct frag_queue);
561	nf_frags.frag_expire = nf_ct_frag6_expire;
562	nf_frags.frags_cache_name = nf_frags_cache_name;
563	nf_frags.rhash_params = nfct_rhash_params;
564	ret = inet_frags_init(&nf_frags);
565	if (ret)
566		goto out;
567	ret = register_pernet_subsys(&nf_ct_net_ops);
568	if (ret)
569		inet_frags_fini(&nf_frags);
570
571out:
572	return ret;
573}
574
575void nf_ct_frag6_cleanup(void)
576{
577	unregister_pernet_subsys(&nf_ct_net_ops);
578	inet_frags_fini(&nf_frags);
579}