xref: /linux/net/ipv6/reassembly.c (revision c532de5a67a70f8533d495f8f2aaa9a0491c3ad0) 
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 
73 static void ip6_frag_expire(struct timer_list *t)
74 {
75 	struct inet_frag_queue *frag = from_timer(frag, t, timer);
76 	struct frag_queue *fq;
77 
78 	fq = container_of(frag, struct frag_queue, q);
79 
80 	ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
81 }
82 
83 static struct frag_queue *
84 fq_find(struct net *net, __be32 id, const struct ipv6hdr *hdr, int iif)
85 {
86 	struct frag_v6_compare_key key = {
87 		.id = id,
88 		.saddr = hdr->saddr,
89 		.daddr = hdr->daddr,
90 		.user = IP6_DEFRAG_LOCAL_DELIVER,
91 		.iif = iif,
92 	};
93 	struct inet_frag_queue *q;
94 
95 	if (!(ipv6_addr_type(&hdr->daddr) & (IPV6_ADDR_MULTICAST |
96 					    IPV6_ADDR_LINKLOCAL)))
97 		key.iif = 0;
98 
99 	q = inet_frag_find(net->ipv6.fqdir, &key);
100 	if (!q)
101 		return NULL;
102 
103 	return container_of(q, struct frag_queue, q);
104 }
105 
106 static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
107 			  struct frag_hdr *fhdr, int nhoff,
108 			  u32 *prob_offset)
109 {
110 	struct net *net = dev_net(skb_dst(skb)->dev);
111 	int offset, end, fragsize;
112 	struct sk_buff *prev_tail;
113 	struct net_device *dev;
114 	int err = -ENOENT;
115 	SKB_DR(reason);
116 	u8 ecn;
117 
118 	/* If reassembly is already done, @skb must be a duplicate frag. */
119 	if (fq->q.flags & INET_FRAG_COMPLETE) {
120 		SKB_DR_SET(reason, DUP_FRAG);
121 		goto err;
122 	}
123 
124 	err = -EINVAL;
125 	offset = ntohs(fhdr->frag_off) & ~0x7;
126 	end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
127 			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
128 
129 	if ((unsigned int)end > IPV6_MAXPLEN) {
130 		*prob_offset = (u8 *)&fhdr->frag_off - skb_network_header(skb);
131 		/* note that if prob_offset is set, the skb is freed elsewhere,
132 		 * we do not free it here.
133 		 */
134 		return -1;
135 	}
136 
137 	ecn = ip6_frag_ecn(ipv6_hdr(skb));
138 
139 	if (skb->ip_summed == CHECKSUM_COMPLETE) {
140 		const unsigned char *nh = skb_network_header(skb);
141 		skb->csum = csum_sub(skb->csum,
142 				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
143 						  0));
144 	}
145 
146 	/* Is this the final fragment? */
147 	if (!(fhdr->frag_off & htons(IP6_MF))) {
148 		/* If we already have some bits beyond end
149 		 * or have different end, the segment is corrupted.
150 		 */
151 		if (end < fq->q.len ||
152 		    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len))
153 			goto discard_fq;
154 		fq->q.flags |= INET_FRAG_LAST_IN;
155 		fq->q.len = end;
156 	} else {
157 		/* Check if the fragment is rounded to 8 bytes.
158 		 * Required by the RFC.
159 		 */
160 		if (end & 0x7) {
161 			/* RFC2460 says always send parameter problem in
162 			 * this case. -DaveM
163 			 */
164 			*prob_offset = offsetof(struct ipv6hdr, payload_len);
165 			return -1;
166 		}
167 		if (end > fq->q.len) {
168 			/* Some bits beyond end -> corruption. */
169 			if (fq->q.flags & INET_FRAG_LAST_IN)
170 				goto discard_fq;
171 			fq->q.len = end;
172 		}
173 	}
174 
175 	if (end == offset)
176 		goto discard_fq;
177 
178 	err = -ENOMEM;
179 	/* Point into the IP datagram 'data' part. */
180 	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
181 		goto discard_fq;
182 
183 	err = pskb_trim_rcsum(skb, end - offset);
184 	if (err)
185 		goto discard_fq;
186 
187 	/* Note : skb->rbnode and skb->dev share the same location. */
188 	dev = skb->dev;
189 	/* Makes sure compiler wont do silly aliasing games */
190 	barrier();
191 
192 	prev_tail = fq->q.fragments_tail;
193 	err = inet_frag_queue_insert(&fq->q, skb, offset, end);
194 	if (err)
195 		goto insert_error;
196 
197 	if (dev)
198 		fq->iif = dev->ifindex;
199 
200 	fq->q.stamp = skb->tstamp;
201 	fq->q.tstamp_type = skb->tstamp_type;
202 	fq->q.meat += skb->len;
203 	fq->ecn |= ecn;
204 	add_frag_mem_limit(fq->q.fqdir, skb->truesize);
205 
206 	fragsize = -skb_network_offset(skb) + skb->len;
207 	if (fragsize > fq->q.max_size)
208 		fq->q.max_size = fragsize;
209 
210 	/* The first fragment.
211 	 * nhoffset is obtained from the first fragment, of course.
212 	 */
213 	if (offset == 0) {
214 		fq->nhoffset = nhoff;
215 		fq->q.flags |= INET_FRAG_FIRST_IN;
216 	}
217 
218 	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
219 	    fq->q.meat == fq->q.len) {
220 		unsigned long orefdst = skb->_skb_refdst;
221 
222 		skb->_skb_refdst = 0UL;
223 		err = ip6_frag_reasm(fq, skb, prev_tail, dev);
224 		skb->_skb_refdst = orefdst;
225 		return err;
226 	}
227 
228 	skb_dst_drop(skb);
229 	return -EINPROGRESS;
230 
231 insert_error:
232 	if (err == IPFRAG_DUP) {
233 		SKB_DR_SET(reason, DUP_FRAG);
234 		err = -EINVAL;
235 		goto err;
236 	}
237 	err = -EINVAL;
238 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
239 			IPSTATS_MIB_REASM_OVERLAPS);
240 discard_fq:
241 	inet_frag_kill(&fq->q);
242 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
243 			IPSTATS_MIB_REASMFAILS);
244 err:
245 	kfree_skb_reason(skb, reason);
246 	return err;
247 }
248 
249 /*
250  *	Check if this packet is complete.
251  *
252  *	It is called with locked fq, and caller must check that
253  *	queue is eligible for reassembly i.e. it is not COMPLETE,
254  *	the last and the first frames arrived and all the bits are here.
255  */
256 static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
257 			  struct sk_buff *prev_tail, struct net_device *dev)
258 {
259 	struct net *net = fq->q.fqdir->net;
260 	unsigned int nhoff;
261 	void *reasm_data;
262 	int payload_len;
263 	u8 ecn;
264 
265 	inet_frag_kill(&fq->q);
266 
267 	ecn = ip_frag_ecn_table[fq->ecn];
268 	if (unlikely(ecn == 0xff))
269 		goto out_fail;
270 
271 	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
272 	if (!reasm_data)
273 		goto out_oom;
274 
275 	payload_len = -skb_network_offset(skb) -
276 		       sizeof(struct ipv6hdr) + fq->q.len -
277 		       sizeof(struct frag_hdr);
278 	if (payload_len > IPV6_MAXPLEN)
279 		goto out_oversize;
280 
281 	/* We have to remove fragment header from datagram and to relocate
282 	 * header in order to calculate ICV correctly. */
283 	nhoff = fq->nhoffset;
284 	skb_network_header(skb)[nhoff] = skb_transport_header(skb)[0];
285 	memmove(skb->head + sizeof(struct frag_hdr), skb->head,
286 		(skb->data - skb->head) - sizeof(struct frag_hdr));
287 	if (skb_mac_header_was_set(skb))
288 		skb->mac_header += sizeof(struct frag_hdr);
289 	skb->network_header += sizeof(struct frag_hdr);
290 
291 	skb_reset_transport_header(skb);
292 
293 	inet_frag_reasm_finish(&fq->q, skb, reasm_data, true);
294 
295 	skb->dev = dev;
296 	ipv6_hdr(skb)->payload_len = htons(payload_len);
297 	ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
298 	IP6CB(skb)->nhoff = nhoff;
299 	IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
300 	IP6CB(skb)->frag_max_size = fq->q.max_size;
301 
302 	/* Yes, and fold redundant checksum back. 8) */
303 	skb_postpush_rcsum(skb, skb_network_header(skb),
304 			   skb_network_header_len(skb));
305 
306 	rcu_read_lock();
307 	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMOKS);
308 	rcu_read_unlock();
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 	rcu_read_lock();
321 	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMFAILS);
322 	rcu_read_unlock();
323 	inet_frag_kill(&fq->q);
324 	return -1;
325 }
326 
327 static int ipv6_frag_rcv(struct sk_buff *skb)
328 {
329 	struct frag_hdr *fhdr;
330 	struct frag_queue *fq;
331 	const struct ipv6hdr *hdr = ipv6_hdr(skb);
332 	struct net *net = dev_net(skb_dst(skb)->dev);
333 	u8 nexthdr;
334 	int iif;
335 
336 	if (IP6CB(skb)->flags & IP6SKB_FRAGMENTED)
337 		goto fail_hdr;
338 
339 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMREQDS);
340 
341 	/* Jumbo payload inhibits frag. header */
342 	if (hdr->payload_len == 0)
343 		goto fail_hdr;
344 
345 	if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
346 				 sizeof(struct frag_hdr))))
347 		goto fail_hdr;
348 
349 	hdr = ipv6_hdr(skb);
350 	fhdr = (struct frag_hdr *)skb_transport_header(skb);
351 
352 	if (!(fhdr->frag_off & htons(IP6_OFFSET | IP6_MF))) {
353 		/* It is not a fragmented frame */
354 		skb->transport_header += sizeof(struct frag_hdr);
355 		__IP6_INC_STATS(net,
356 				ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMOKS);
357 
358 		IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
359 		IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
360 		IP6CB(skb)->frag_max_size = ntohs(hdr->payload_len) +
361 					    sizeof(struct ipv6hdr);
362 		return 1;
363 	}
364 
365 	/* RFC 8200, Section 4.5 Fragment Header:
366 	 * If the first fragment does not include all headers through an
367 	 * Upper-Layer header, then that fragment should be discarded and
368 	 * an ICMP Parameter Problem, Code 3, message should be sent to
369 	 * the source of the fragment, with the Pointer field set to zero.
370 	 */
371 	nexthdr = hdr->nexthdr;
372 	if (ipv6frag_thdr_truncated(skb, skb_network_offset(skb) + sizeof(struct ipv6hdr), &nexthdr)) {
373 		__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
374 				IPSTATS_MIB_INHDRERRORS);
375 		icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
376 		return -1;
377 	}
378 
379 	iif = skb->dev ? skb->dev->ifindex : 0;
380 	fq = fq_find(net, fhdr->identification, hdr, iif);
381 	if (fq) {
382 		u32 prob_offset = 0;
383 		int ret;
384 
385 		spin_lock(&fq->q.lock);
386 
387 		fq->iif = iif;
388 		ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff,
389 				     &prob_offset);
390 
391 		spin_unlock(&fq->q.lock);
392 		inet_frag_put(&fq->q);
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 
402 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_REASMFAILS);
403 	kfree_skb(skb);
404 	return -1;
405 
406 fail_hdr:
407 	__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
408 			IPSTATS_MIB_INHDRERRORS);
409 	icmpv6_param_prob(skb, ICMPV6_HDR_FIELD, skb_network_header_len(skb));
410 	return -1;
411 }
412 
413 static const struct inet6_protocol frag_protocol = {
414 	.handler	=	ipv6_frag_rcv,
415 	.flags		=	INET6_PROTO_NOPOLICY,
416 };
417 
418 #ifdef CONFIG_SYSCTL
419 
420 static struct ctl_table ip6_frags_ns_ctl_table[] = {
421 	{
422 		.procname	= "ip6frag_high_thresh",
423 		.maxlen		= sizeof(unsigned long),
424 		.mode		= 0644,
425 		.proc_handler	= proc_doulongvec_minmax,
426 	},
427 	{
428 		.procname	= "ip6frag_low_thresh",
429 		.maxlen		= sizeof(unsigned long),
430 		.mode		= 0644,
431 		.proc_handler	= proc_doulongvec_minmax,
432 	},
433 	{
434 		.procname	= "ip6frag_time",
435 		.maxlen		= sizeof(int),
436 		.mode		= 0644,
437 		.proc_handler	= proc_dointvec_jiffies,
438 	},
439 };
440 
441 /* secret interval has been deprecated */
442 static int ip6_frags_secret_interval_unused;
443 static struct ctl_table ip6_frags_ctl_table[] = {
444 	{
445 		.procname	= "ip6frag_secret_interval",
446 		.data		= &ip6_frags_secret_interval_unused,
447 		.maxlen		= sizeof(int),
448 		.mode		= 0644,
449 		.proc_handler	= proc_dointvec_jiffies,
450 	},
451 };
452 
453 static int __net_init ip6_frags_ns_sysctl_register(struct net *net)
454 {
455 	struct ctl_table *table;
456 	struct ctl_table_header *hdr;
457 
458 	table = ip6_frags_ns_ctl_table;
459 	if (!net_eq(net, &init_net)) {
460 		table = kmemdup(table, sizeof(ip6_frags_ns_ctl_table), GFP_KERNEL);
461 		if (!table)
462 			goto err_alloc;
463 
464 	}
465 	table[0].data	= &net->ipv6.fqdir->high_thresh;
466 	table[0].extra1	= &net->ipv6.fqdir->low_thresh;
467 	table[1].data	= &net->ipv6.fqdir->low_thresh;
468 	table[1].extra2	= &net->ipv6.fqdir->high_thresh;
469 	table[2].data	= &net->ipv6.fqdir->timeout;
470 
471 	hdr = register_net_sysctl_sz(net, "net/ipv6", table,
472 				     ARRAY_SIZE(ip6_frags_ns_ctl_table));
473 	if (!hdr)
474 		goto err_reg;
475 
476 	net->ipv6.sysctl.frags_hdr = hdr;
477 	return 0;
478 
479 err_reg:
480 	if (!net_eq(net, &init_net))
481 		kfree(table);
482 err_alloc:
483 	return -ENOMEM;
484 }
485 
486 static void __net_exit ip6_frags_ns_sysctl_unregister(struct net *net)
487 {
488 	const struct ctl_table *table;
489 
490 	table = net->ipv6.sysctl.frags_hdr->ctl_table_arg;
491 	unregister_net_sysctl_table(net->ipv6.sysctl.frags_hdr);
492 	if (!net_eq(net, &init_net))
493 		kfree(table);
494 }
495 
496 static struct ctl_table_header *ip6_ctl_header;
497 
498 static int ip6_frags_sysctl_register(void)
499 {
500 	ip6_ctl_header = register_net_sysctl(&init_net, "net/ipv6",
501 			ip6_frags_ctl_table);
502 	return ip6_ctl_header == NULL ? -ENOMEM : 0;
503 }
504 
505 static void ip6_frags_sysctl_unregister(void)
506 {
507 	unregister_net_sysctl_table(ip6_ctl_header);
508 }
509 #else
510 static int ip6_frags_ns_sysctl_register(struct net *net)
511 {
512 	return 0;
513 }
514 
515 static void ip6_frags_ns_sysctl_unregister(struct net *net)
516 {
517 }
518 
519 static int ip6_frags_sysctl_register(void)
520 {
521 	return 0;
522 }
523 
524 static void ip6_frags_sysctl_unregister(void)
525 {
526 }
527 #endif
528 
529 static int __net_init ipv6_frags_init_net(struct net *net)
530 {
531 	int res;
532 
533 	res = fqdir_init(&net->ipv6.fqdir, &ip6_frags, net);
534 	if (res < 0)
535 		return res;
536 
537 	net->ipv6.fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
538 	net->ipv6.fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
539 	net->ipv6.fqdir->timeout = IPV6_FRAG_TIMEOUT;
540 
541 	res = ip6_frags_ns_sysctl_register(net);
542 	if (res < 0)
543 		fqdir_exit(net->ipv6.fqdir);
544 	return res;
545 }
546 
547 static void __net_exit ipv6_frags_pre_exit_net(struct net *net)
548 {
549 	fqdir_pre_exit(net->ipv6.fqdir);
550 }
551 
552 static void __net_exit ipv6_frags_exit_net(struct net *net)
553 {
554 	ip6_frags_ns_sysctl_unregister(net);
555 	fqdir_exit(net->ipv6.fqdir);
556 }
557 
558 static struct pernet_operations ip6_frags_ops = {
559 	.init		= ipv6_frags_init_net,
560 	.pre_exit	= ipv6_frags_pre_exit_net,
561 	.exit		= ipv6_frags_exit_net,
562 };
563 
564 static const struct rhashtable_params ip6_rhash_params = {
565 	.head_offset		= offsetof(struct inet_frag_queue, node),
566 	.hashfn			= ip6frag_key_hashfn,
567 	.obj_hashfn		= ip6frag_obj_hashfn,
568 	.obj_cmpfn		= ip6frag_obj_cmpfn,
569 	.automatic_shrinking	= true,
570 };
571 
572 int __init ipv6_frag_init(void)
573 {
574 	int ret;
575 
576 	ip6_frags.constructor = ip6frag_init;
577 	ip6_frags.destructor = NULL;
578 	ip6_frags.qsize = sizeof(struct frag_queue);
579 	ip6_frags.frag_expire = ip6_frag_expire;
580 	ip6_frags.frags_cache_name = ip6_frag_cache_name;
581 	ip6_frags.rhash_params = ip6_rhash_params;
582 	ret = inet_frags_init(&ip6_frags);
583 	if (ret)
584 		goto out;
585 
586 	ret = inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT);
587 	if (ret)
588 		goto err_protocol;
589 
590 	ret = ip6_frags_sysctl_register();
591 	if (ret)
592 		goto err_sysctl;
593 
594 	ret = register_pernet_subsys(&ip6_frags_ops);
595 	if (ret)
596 		goto err_pernet;
597 
598 out:
599 	return ret;
600 
601 err_pernet:
602 	ip6_frags_sysctl_unregister();
603 err_sysctl:
604 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
605 err_protocol:
606 	inet_frags_fini(&ip6_frags);
607 	goto out;
608 }
609 
610 void ipv6_frag_exit(void)
611 {
612 	ip6_frags_sysctl_unregister();
613 	unregister_pernet_subsys(&ip6_frags_ops);
614 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
615 	inet_frags_fini(&ip6_frags);
616 }
617