xref: /linux/net/ipv6/reassembly.c (revision 7a9b709e7cc5ce1ffb84ce07bf6d157e1de758df) 
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  *	IPv6 fragment reassembly
4  *	Linux INET6 implementation
5  *
6  *	Authors:
7  *	Pedro Roque		<roque@di.fc.ul.pt>
8  *
9  *	Based on: net/ipv4/ip_fragment.c
10  */
11 
12 /*
13  *	Fixes:
14  *	Andi Kleen	Make it work with multiple hosts.
15  *			More RFC compliance.
16  *
17  *      Horst von Brand Add missing #include <linux/string.h>
18  *	Alexey Kuznetsov	SMP races, threading, cleanup.
19  *	Patrick McHardy		LRU queue of frag heads for evictor.
20  *	Mitsuru KANDA @USAGI	Register inet6_protocol{}.
21  *	David Stevens and
22  *	YOSHIFUJI,H. @USAGI	Always remove fragment header to
23  *				calculate ICV correctly.
24  */
25 
26 #define pr_fmt(fmt) "IPv6: " fmt
27 
28 #include <linux/errno.h>
29 #include <linux/types.h>
30 #include <linux/string.h>
31 #include <linux/socket.h>
32 #include <linux/sockios.h>
33 #include <linux/jiffies.h>
34 #include <linux/net.h>
35 #include <linux/list.h>
36 #include <linux/netdevice.h>
37 #include <linux/in6.h>
38 #include <linux/ipv6.h>
39 #include <linux/icmpv6.h>
40 #include <linux/random.h>
41 #include <linux/jhash.h>
42 #include <linux/skbuff.h>
43 #include <linux/slab.h>
44 #include <linux/export.h>
45 #include <linux/tcp.h>
46 #include <linux/udp.h>
47 
48 #include <net/sock.h>
49 #include <net/snmp.h>
50 
51 #include <net/ipv6.h>
52 #include <net/ip6_route.h>
53 #include <net/protocol.h>
54 #include <net/transp_v6.h>
55 #include <net/rawv6.h>
56 #include <net/ndisc.h>
57 #include <net/addrconf.h>
58 #include <net/ipv6_frag.h>
59 #include <net/inet_ecn.h>
60 
61 static const char ip6_frag_cache_name[] = "ip6-frags";
62 
63 static u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
64 {
65 	return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
66 }
67 
68 static struct inet_frags ip6_frags;
69 
70 static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
71 			  struct sk_buff *prev_tail, struct net_device *dev,
72 			  int *refs);
73 
74 static void ip6_frag_expire(struct timer_list *t)
75 {
76 	struct inet_frag_queue *frag = from_timer(frag, t, timer);
77 	struct frag_queue *fq;
78 
79 	fq = container_of(frag, struct frag_queue, q);
80 
81 	ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
82 }
83 
84 static struct frag_queue *
85 fq_find(struct net *net, __be32 id, const struct ipv6hdr *hdr, int iif)
86 {
87 	struct frag_v6_compare_key key = {
88 		.id = id,
89 		.saddr = hdr->saddr,
90 		.daddr = hdr->daddr,
91 		.user = IP6_DEFRAG_LOCAL_DELIVER,
92 		.iif = iif,
93 	};
94 	struct inet_frag_queue *q;
95 
96 	if (!(ipv6_addr_type(&hdr->daddr) & (IPV6_ADDR_MULTICAST |
97 					    IPV6_ADDR_LINKLOCAL)))
98 		key.iif = 0;
99 
100 	q = inet_frag_find(net->ipv6.fqdir, &key);
101 	if (!q)
102 		return NULL;
103 
104 	return container_of(q, struct frag_queue, q);
105 }
106 
107 static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
108 			  struct frag_hdr *fhdr, int nhoff,
109 			  u32 *prob_offset, int *refs)
110 {
111 	struct net *net = dev_net(skb_dst(skb)->dev);
112 	int offset, end, fragsize;
113 	struct sk_buff *prev_tail;
114 	struct net_device *dev;
115 	int err = -ENOENT;
116 	SKB_DR(reason);
117 	u8 ecn;
118 
119 	/* If reassembly is already done, @skb must be a duplicate frag. */
120 	if (fq->q.flags & INET_FRAG_COMPLETE) {
121 		SKB_DR_SET(reason, DUP_FRAG);
122 		goto err;
123 	}
124 
125 	err = -EINVAL;
126 	offset = ntohs(fhdr->frag_off) & ~0x7;
127 	end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
128 			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
129 
130 	if ((unsigned int)end > IPV6_MAXPLEN) {
131 		*prob_offset = (u8 *)&fhdr->frag_off - skb_network_header(skb);
132 		/* note that if prob_offset is set, the skb is freed elsewhere,
133 		 * we do not free it here.
134 		 */
135 		return -1;
136 	}
137 
138 	ecn = ip6_frag_ecn(ipv6_hdr(skb));
139 
140 	if (skb->ip_summed == CHECKSUM_COMPLETE) {
141 		const unsigned char *nh = skb_network_header(skb);
142 		skb->csum = csum_sub(skb->csum,
143 				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
144 						  0));
145 	}
146 
147 	/* Is this the final fragment? */
148 	if (!(fhdr->frag_off & htons(IP6_MF))) {
149 		/* If we already have some bits beyond end
150 		 * or have different end, the segment is corrupted.
151 		 */
152 		if (end < fq->q.len ||
153 		    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len))
154 			goto discard_fq;
155 		fq->q.flags |= INET_FRAG_LAST_IN;
156 		fq->q.len = end;
157 	} else {
158 		/* Check if the fragment is rounded to 8 bytes.
159 		 * Required by the RFC.
160 		 */
161 		if (end & 0x7) {
162 			/* RFC2460 says always send parameter problem in
163 			 * this case. -DaveM
164 			 */
165 			*prob_offset = offsetof(struct ipv6hdr, payload_len);
166 			return -1;
167 		}
168 		if (end > fq->q.len) {
169 			/* Some bits beyond end -> corruption. */
170 			if (fq->q.flags & INET_FRAG_LAST_IN)
171 				goto discard_fq;
172 			fq->q.len = end;
173 		}
174 	}
175 
176 	if (end == offset)
177 		goto discard_fq;
178 
179 	err = -ENOMEM;
180 	/* Point into the IP datagram 'data' part. */
181 	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
182 		goto discard_fq;
183 
184 	err = pskb_trim_rcsum(skb, end - offset);
185 	if (err)
186 		goto discard_fq;
187 
188 	/* Note : skb->rbnode and skb->dev share the same location. */
189 	dev = skb->dev;
190 	/* Makes sure compiler wont do silly aliasing games */
191 	barrier();
192 
193 	prev_tail = fq->q.fragments_tail;
194 	err = inet_frag_queue_insert(&fq->q, skb, offset, end);
195 	if (err)
196 		goto insert_error;
197 
198 	if (dev)
199 		fq->iif = dev->ifindex;
200 
201 	fq->q.stamp = skb->tstamp;
202 	fq->q.tstamp_type = skb->tstamp_type;
203 	fq->q.meat += skb->len;
204 	fq->ecn |= ecn;
205 	add_frag_mem_limit(fq->q.fqdir, skb->truesize);
206 
207 	fragsize = -skb_network_offset(skb) + skb->len;
208 	if (fragsize > fq->q.max_size)
209 		fq->q.max_size = fragsize;
210 
211 	/* The first fragment.
212 	 * nhoffset is obtained from the first fragment, of course.
213 	 */
214 	if (offset == 0) {
215 		fq->nhoffset = nhoff;
216 		fq->q.flags |= INET_FRAG_FIRST_IN;
217 	}
218 
219 	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
220 	    fq->q.meat == fq->q.len) {
221 		unsigned long orefdst = skb->_skb_refdst;
222 
223 		skb->_skb_refdst = 0UL;
224 		err = ip6_frag_reasm(fq, skb, prev_tail, dev, refs);
225 		skb->_skb_refdst = orefdst;
226 		return err;
227 	}
228 
229 	skb_dst_drop(skb);
230 	return -EINPROGRESS;
231 
232 insert_error:
233 	if (err == IPFRAG_DUP) {
234 		SKB_DR_SET(reason, DUP_FRAG);
235 		err = -EINVAL;
236 		goto err;
237 	}
238 	err = -EINVAL;
239 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
240 			IPSTATS_MIB_REASM_OVERLAPS);
241 discard_fq:
242 	inet_frag_kill(&fq->q, refs);
243 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
244 			IPSTATS_MIB_REASMFAILS);
245 err:
246 	kfree_skb_reason(skb, reason);
247 	return err;
248 }
249 
250 /*
251  *	Check if this packet is complete.
252  *
253  *	It is called with locked fq, and caller must check that
254  *	queue is eligible for reassembly i.e. it is not COMPLETE,
255  *	the last and the first frames arrived and all the bits are here.
256  */
257 static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
258 			  struct sk_buff *prev_tail, struct net_device *dev,
259 			  int *refs)
260 {
261 	struct net *net = fq->q.fqdir->net;
262 	unsigned int nhoff;
263 	void *reasm_data;
264 	int payload_len;
265 	u8 ecn;
266 
267 	inet_frag_kill(&fq->q, refs);
268 
269 	ecn = ip_frag_ecn_table[fq->ecn];
270 	if (unlikely(ecn == 0xff))
271 		goto out_fail;
272 
273 	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
274 	if (!reasm_data)
275 		goto out_oom;
276 
277 	payload_len = -skb_network_offset(skb) -
278 		       sizeof(struct ipv6hdr) + fq->q.len -
279 		       sizeof(struct frag_hdr);
280 	if (payload_len > IPV6_MAXPLEN)
281 		goto out_oversize;
282 
283 	/* We have to remove fragment header from datagram and to relocate
284 	 * header in order to calculate ICV correctly. */
285 	nhoff = fq->nhoffset;
286 	skb_network_header(skb)[nhoff] = skb_transport_header(skb)[0];
287 	memmove(skb->head + sizeof(struct frag_hdr), skb->head,
288 		(skb->data - skb->head) - sizeof(struct frag_hdr));
289 	if (skb_mac_header_was_set(skb))
290 		skb->mac_header += sizeof(struct frag_hdr);
291 	skb->network_header += sizeof(struct frag_hdr);
292 
293 	skb_reset_transport_header(skb);
294 
295 	inet_frag_reasm_finish(&fq->q, skb, reasm_data, true);
296 
297 	skb->dev = dev;
298 	ipv6_hdr(skb)->payload_len = htons(payload_len);
299 	ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
300 	IP6CB(skb)->nhoff = nhoff;
301 	IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
302 	IP6CB(skb)->frag_max_size = fq->q.max_size;
303 
304 	/* Yes, and fold redundant checksum back. 8) */
305 	skb_postpush_rcsum(skb, skb_network_header(skb),
306 			   skb_network_header_len(skb));
307 
308 	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMOKS);
309 	fq->q.rb_fragments = RB_ROOT;
310 	fq->q.fragments_tail = NULL;
311 	fq->q.last_run_head = NULL;
312 	return 1;
313 
314 out_oversize:
315 	net_dbg_ratelimited("ip6_frag_reasm: payload len = %d\n", payload_len);
316 	goto out_fail;
317 out_oom:
318 	net_dbg_ratelimited("ip6_frag_reasm: no memory for reassembly\n");
319 out_fail:
320 	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMFAILS);
321 	inet_frag_kill(&fq->q, refs);
322 	return -1;
323 }
324 
325 static int ipv6_frag_rcv(struct sk_buff *skb)
326 {
327 	struct frag_hdr *fhdr;
328 	struct frag_queue *fq;
329 	const struct ipv6hdr *hdr = ipv6_hdr(skb);
330 	struct net *net = dev_net(skb_dst(skb)->dev);
331 	u8 nexthdr;
332 	int iif;
333 
334 	if (IP6CB(skb)->flags & IP6SKB_FRAGMENTED)
335 		goto fail_hdr;
336 
337 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMREQDS);
338 
339 	/* Jumbo payload inhibits frag. header */
340 	if (hdr->payload_len == 0)
341 		goto fail_hdr;
342 
343 	if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
344 				 sizeof(struct frag_hdr))))
345 		goto fail_hdr;
346 
347 	hdr = ipv6_hdr(skb);
348 	fhdr = (struct frag_hdr *)skb_transport_header(skb);
349 
350 	if (!(fhdr->frag_off & htons(IP6_OFFSET | IP6_MF))) {
351 		/* It is not a fragmented frame */
352 		skb->transport_header += sizeof(struct frag_hdr);
353 		__IP6_INC_STATS(net,
354 				ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMOKS);
355 
356 		IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
357 		IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
358 		IP6CB(skb)->frag_max_size = ntohs(hdr->payload_len) +
359 					    sizeof(struct ipv6hdr);
360 		return 1;
361 	}
362 
363 	/* RFC 8200, Section 4.5 Fragment Header:
364 	 * If the first fragment does not include all headers through an
365 	 * Upper-Layer header, then that fragment should be discarded and
366 	 * an ICMP Parameter Problem, Code 3, message should be sent to
367 	 * the source of the fragment, with the Pointer field set to zero.
368 	 */
369 	nexthdr = hdr->nexthdr;
370 	if (ipv6frag_thdr_truncated(skb, skb_network_offset(skb) + sizeof(struct ipv6hdr), &nexthdr)) {
371 		__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
372 				IPSTATS_MIB_INHDRERRORS);
373 		icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
374 		return -1;
375 	}
376 
377 	iif = skb->dev ? skb->dev->ifindex : 0;
378 	rcu_read_lock();
379 	fq = fq_find(net, fhdr->identification, hdr, iif);
380 	if (fq) {
381 		u32 prob_offset = 0;
382 		int ret, refs = 0;
383 
384 		spin_lock(&fq->q.lock);
385 
386 		fq->iif = iif;
387 		ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff,
388 				     &prob_offset, &refs);
389 
390 		spin_unlock(&fq->q.lock);
391 		rcu_read_unlock();
392 		inet_frag_putn(&fq->q, refs);
393 		if (prob_offset) {
394 			__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
395 					IPSTATS_MIB_INHDRERRORS);
396 			/* icmpv6_param_prob() calls kfree_skb(skb) */
397 			icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, prob_offset);
398 		}
399 		return ret;
400 	}
401 	rcu_read_unlock();
402 
403 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMFAILS);
404 	kfree_skb(skb);
405 	return -1;
406 
407 fail_hdr:
408 	__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
409 			IPSTATS_MIB_INHDRERRORS);
410 	icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb_network_header_len(skb));
411 	return -1;
412 }
413 
414 static const struct inet6_protocol frag_protocol = {
415 	.handler	=	ipv6_frag_rcv,
416 	.flags		=	INET6_PROTO_NOPOLICY,
417 };
418 
419 #ifdef CONFIG_SYSCTL
420 
421 static struct ctl_table ip6_frags_ns_ctl_table[] = {
422 	{
423 		.procname	= "ip6frag_high_thresh",
424 		.maxlen		= sizeof(unsigned long),
425 		.mode		= 0644,
426 		.proc_handler	= proc_doulongvec_minmax,
427 	},
428 	{
429 		.procname	= "ip6frag_low_thresh",
430 		.maxlen		= sizeof(unsigned long),
431 		.mode		= 0644,
432 		.proc_handler	= proc_doulongvec_minmax,
433 	},
434 	{
435 		.procname	= "ip6frag_time",
436 		.maxlen		= sizeof(int),
437 		.mode		= 0644,
438 		.proc_handler	= proc_dointvec_jiffies,
439 	},
440 };
441 
442 /* secret interval has been deprecated */
443 static int ip6_frags_secret_interval_unused;
444 static struct ctl_table ip6_frags_ctl_table[] = {
445 	{
446 		.procname	= "ip6frag_secret_interval",
447 		.data		= &ip6_frags_secret_interval_unused,
448 		.maxlen		= sizeof(int),
449 		.mode		= 0644,
450 		.proc_handler	= proc_dointvec_jiffies,
451 	},
452 };
453 
454 static int __net_init ip6_frags_ns_sysctl_register(struct net *net)
455 {
456 	struct ctl_table *table;
457 	struct ctl_table_header *hdr;
458 
459 	table = ip6_frags_ns_ctl_table;
460 	if (!net_eq(net, &init_net)) {
461 		table = kmemdup(table, sizeof(ip6_frags_ns_ctl_table), GFP_KERNEL);
462 		if (!table)
463 			goto err_alloc;
464 
465 	}
466 	table[0].data	= &net->ipv6.fqdir->high_thresh;
467 	table[0].extra1	= &net->ipv6.fqdir->low_thresh;
468 	table[1].data	= &net->ipv6.fqdir->low_thresh;
469 	table[1].extra2	= &net->ipv6.fqdir->high_thresh;
470 	table[2].data	= &net->ipv6.fqdir->timeout;
471 
472 	hdr = register_net_sysctl_sz(net, "net/ipv6", table,
473 				     ARRAY_SIZE(ip6_frags_ns_ctl_table));
474 	if (!hdr)
475 		goto err_reg;
476 
477 	net->ipv6.sysctl.frags_hdr = hdr;
478 	return 0;
479 
480 err_reg:
481 	if (!net_eq(net, &init_net))
482 		kfree(table);
483 err_alloc:
484 	return -ENOMEM;
485 }
486 
487 static void __net_exit ip6_frags_ns_sysctl_unregister(struct net *net)
488 {
489 	const struct ctl_table *table;
490 
491 	table = net->ipv6.sysctl.frags_hdr->ctl_table_arg;
492 	unregister_net_sysctl_table(net->ipv6.sysctl.frags_hdr);
493 	if (!net_eq(net, &init_net))
494 		kfree(table);
495 }
496 
497 static struct ctl_table_header *ip6_ctl_header;
498 
499 static int ip6_frags_sysctl_register(void)
500 {
501 	ip6_ctl_header = register_net_sysctl(&init_net, "net/ipv6",
502 			ip6_frags_ctl_table);
503 	return ip6_ctl_header == NULL ? -ENOMEM : 0;
504 }
505 
506 static void ip6_frags_sysctl_unregister(void)
507 {
508 	unregister_net_sysctl_table(ip6_ctl_header);
509 }
510 #else
511 static int ip6_frags_ns_sysctl_register(struct net *net)
512 {
513 	return 0;
514 }
515 
516 static void ip6_frags_ns_sysctl_unregister(struct net *net)
517 {
518 }
519 
520 static int ip6_frags_sysctl_register(void)
521 {
522 	return 0;
523 }
524 
525 static void ip6_frags_sysctl_unregister(void)
526 {
527 }
528 #endif
529 
530 static int __net_init ipv6_frags_init_net(struct net *net)
531 {
532 	int res;
533 
534 	res = fqdir_init(&net->ipv6.fqdir, &ip6_frags, net);
535 	if (res < 0)
536 		return res;
537 
538 	net->ipv6.fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
539 	net->ipv6.fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
540 	net->ipv6.fqdir->timeout = IPV6_FRAG_TIMEOUT;
541 
542 	res = ip6_frags_ns_sysctl_register(net);
543 	if (res < 0)
544 		fqdir_exit(net->ipv6.fqdir);
545 	return res;
546 }
547 
548 static void __net_exit ipv6_frags_pre_exit_net(struct net *net)
549 {
550 	fqdir_pre_exit(net->ipv6.fqdir);
551 }
552 
553 static void __net_exit ipv6_frags_exit_net(struct net *net)
554 {
555 	ip6_frags_ns_sysctl_unregister(net);
556 	fqdir_exit(net->ipv6.fqdir);
557 }
558 
559 static struct pernet_operations ip6_frags_ops = {
560 	.init		= ipv6_frags_init_net,
561 	.pre_exit	= ipv6_frags_pre_exit_net,
562 	.exit		= ipv6_frags_exit_net,
563 };
564 
565 static const struct rhashtable_params ip6_rhash_params = {
566 	.head_offset		= offsetof(struct inet_frag_queue, node),
567 	.hashfn			= ip6frag_key_hashfn,
568 	.obj_hashfn		= ip6frag_obj_hashfn,
569 	.obj_cmpfn		= ip6frag_obj_cmpfn,
570 	.automatic_shrinking	= true,
571 };
572 
573 int __init ipv6_frag_init(void)
574 {
575 	int ret;
576 
577 	ip6_frags.constructor = ip6frag_init;
578 	ip6_frags.destructor = NULL;
579 	ip6_frags.qsize = sizeof(struct frag_queue);
580 	ip6_frags.frag_expire = ip6_frag_expire;
581 	ip6_frags.frags_cache_name = ip6_frag_cache_name;
582 	ip6_frags.rhash_params = ip6_rhash_params;
583 	ret = inet_frags_init(&ip6_frags);
584 	if (ret)
585 		goto out;
586 
587 	ret = inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT);
588 	if (ret)
589 		goto err_protocol;
590 
591 	ret = ip6_frags_sysctl_register();
592 	if (ret)
593 		goto err_sysctl;
594 
595 	ret = register_pernet_subsys(&ip6_frags_ops);
596 	if (ret)
597 		goto err_pernet;
598 
599 out:
600 	return ret;
601 
602 err_pernet:
603 	ip6_frags_sysctl_unregister();
604 err_sysctl:
605 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
606 err_protocol:
607 	inet_frags_fini(&ip6_frags);
608 	goto out;
609 }
610 
611 void ipv6_frag_exit(void)
612 {
613 	ip6_frags_sysctl_unregister();
614 	unregister_pernet_subsys(&ip6_frags_ops);
615 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
616 	inet_frags_fini(&ip6_frags);
617 }
618