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/socket.h>
19 #include <linux/sockios.h>
20 #include <linux/jiffies.h>
21 #include <linux/net.h>
22 #include <linux/list.h>
23 #include <linux/netdevice.h>
24 #include <linux/in6.h>
25 #include <linux/ipv6.h>
26 #include <linux/icmpv6.h>
27 #include <linux/random.h>
28 #include <linux/slab.h>
29 
30 #include <net/sock.h>
31 #include <net/snmp.h>
32 #include <net/ipv6_frag.h>
33 
34 #include <net/protocol.h>
35 #include <net/transp_v6.h>
36 #include <net/rawv6.h>
37 #include <net/ndisc.h>
38 #include <net/addrconf.h>
39 #include <net/inet_ecn.h>
40 #include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
41 #include <linux/sysctl.h>
42 #include <linux/netfilter.h>
43 #include <linux/netfilter_ipv6.h>
44 #include <linux/kernel.h>
45 #include <linux/module.h>
46 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
47 
48 static const char nf_frags_cache_name[] = "nf-frags";
49 
50 static struct inet_frags nf_frags;
51 
52 #ifdef CONFIG_SYSCTL
53 
54 static struct ctl_table nf_ct_frag6_sysctl_table[] = {
55 	{
56 		.procname	= "nf_conntrack_frag6_timeout",
57 		.maxlen		= sizeof(unsigned int),
58 		.mode		= 0644,
59 		.proc_handler	= proc_dointvec_jiffies,
60 	},
61 	{
62 		.procname	= "nf_conntrack_frag6_low_thresh",
63 		.maxlen		= sizeof(unsigned long),
64 		.mode		= 0644,
65 		.proc_handler	= proc_doulongvec_minmax,
66 	},
67 	{
68 		.procname	= "nf_conntrack_frag6_high_thresh",
69 		.maxlen		= sizeof(unsigned long),
70 		.mode		= 0644,
71 		.proc_handler	= proc_doulongvec_minmax,
72 	},
73 	{ }
74 };
75 
76 static int nf_ct_frag6_sysctl_register(struct net *net)
77 {
78 	struct ctl_table *table;
79 	struct ctl_table_header *hdr;
80 
81 	table = nf_ct_frag6_sysctl_table;
82 	if (!net_eq(net, &init_net)) {
83 		table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
84 				GFP_KERNEL);
85 		if (table == NULL)
86 			goto err_alloc;
87 	}
88 
89 	table[0].data	= &net->nf_frag.fqdir->timeout;
90 	table[1].data	= &net->nf_frag.fqdir->low_thresh;
91 	table[1].extra2	= &net->nf_frag.fqdir->high_thresh;
92 	table[2].data	= &net->nf_frag.fqdir->high_thresh;
93 	table[2].extra1	= &net->nf_frag.fqdir->low_thresh;
94 	table[2].extra2	= &init_net.nf_frag.fqdir->high_thresh;
95 
96 	hdr = register_net_sysctl(net, "net/netfilter", table);
97 	if (hdr == NULL)
98 		goto err_reg;
99 
100 	net->nf_frag_frags_hdr = hdr;
101 	return 0;
102 
103 err_reg:
104 	if (!net_eq(net, &init_net))
105 		kfree(table);
106 err_alloc:
107 	return -ENOMEM;
108 }
109 
110 static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
111 {
112 	struct ctl_table *table;
113 
114 	table = net->nf_frag_frags_hdr->ctl_table_arg;
115 	unregister_net_sysctl_table(net->nf_frag_frags_hdr);
116 	if (!net_eq(net, &init_net))
117 		kfree(table);
118 }
119 
120 #else
121 static int nf_ct_frag6_sysctl_register(struct net *net)
122 {
123 	return 0;
124 }
125 static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
126 {
127 }
128 #endif
129 
130 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
131 			     struct sk_buff *prev_tail, struct net_device *dev);
132 
133 static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
134 {
135 	return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
136 }
137 
138 static void nf_ct_frag6_expire(struct timer_list *t)
139 {
140 	struct inet_frag_queue *frag = from_timer(frag, t, timer);
141 	struct frag_queue *fq;
142 
143 	fq = container_of(frag, struct frag_queue, q);
144 
145 	ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
146 }
147 
148 /* Creation primitives. */
149 static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
150 				  const struct ipv6hdr *hdr, int iif)
151 {
152 	struct frag_v6_compare_key key = {
153 		.id = id,
154 		.saddr = hdr->saddr,
155 		.daddr = hdr->daddr,
156 		.user = user,
157 		.iif = iif,
158 	};
159 	struct inet_frag_queue *q;
160 
161 	q = inet_frag_find(net->nf_frag.fqdir, &key);
162 	if (!q)
163 		return NULL;
164 
165 	return container_of(q, struct frag_queue, q);
166 }
167 
168 
169 static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
170 			     const struct frag_hdr *fhdr, int nhoff)
171 {
172 	unsigned int payload_len;
173 	struct net_device *dev;
174 	struct sk_buff *prev;
175 	int offset, end, err;
176 	u8 ecn;
177 
178 	if (fq->q.flags & INET_FRAG_COMPLETE) {
179 		pr_debug("Already completed\n");
180 		goto err;
181 	}
182 
183 	payload_len = ntohs(ipv6_hdr(skb)->payload_len);
184 
185 	offset = ntohs(fhdr->frag_off) & ~0x7;
186 	end = offset + (payload_len -
187 			((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
188 
189 	if ((unsigned int)end > IPV6_MAXPLEN) {
190 		pr_debug("offset is too large.\n");
191 		return -EINVAL;
192 	}
193 
194 	ecn = ip6_frag_ecn(ipv6_hdr(skb));
195 
196 	if (skb->ip_summed == CHECKSUM_COMPLETE) {
197 		const unsigned char *nh = skb_network_header(skb);
198 		skb->csum = csum_sub(skb->csum,
199 				     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
200 						  0));
201 	}
202 
203 	/* Is this the final fragment? */
204 	if (!(fhdr->frag_off & htons(IP6_MF))) {
205 		/* If we already have some bits beyond end
206 		 * or have different end, the segment is corrupted.
207 		 */
208 		if (end < fq->q.len ||
209 		    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len)) {
210 			pr_debug("already received last fragment\n");
211 			goto err;
212 		}
213 		fq->q.flags |= INET_FRAG_LAST_IN;
214 		fq->q.len = end;
215 	} else {
216 		/* Check if the fragment is rounded to 8 bytes.
217 		 * Required by the RFC.
218 		 */
219 		if (end & 0x7) {
220 			/* RFC2460 says always send parameter problem in
221 			 * this case. -DaveM
222 			 */
223 			pr_debug("end of fragment not rounded to 8 bytes.\n");
224 			inet_frag_kill(&fq->q);
225 			return -EPROTO;
226 		}
227 		if (end > fq->q.len) {
228 			/* Some bits beyond end -> corruption. */
229 			if (fq->q.flags & INET_FRAG_LAST_IN) {
230 				pr_debug("last packet already reached.\n");
231 				goto err;
232 			}
233 			fq->q.len = end;
234 		}
235 	}
236 
237 	if (end == offset)
238 		goto err;
239 
240 	/* Point into the IP datagram 'data' part. */
241 	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
242 		pr_debug("queue: message is too short.\n");
243 		goto err;
244 	}
245 	if (pskb_trim_rcsum(skb, end - offset)) {
246 		pr_debug("Can't trim\n");
247 		goto err;
248 	}
249 
250 	/* Note : skb->rbnode and skb->dev share the same location. */
251 	dev = skb->dev;
252 	/* Makes sure compiler wont do silly aliasing games */
253 	barrier();
254 
255 	prev = fq->q.fragments_tail;
256 	err = inet_frag_queue_insert(&fq->q, skb, offset, end);
257 	if (err) {
258 		if (err == IPFRAG_DUP) {
259 			/* No error for duplicates, pretend they got queued. */
260 			kfree_skb(skb);
261 			return -EINPROGRESS;
262 		}
263 		goto insert_error;
264 	}
265 
266 	if (dev)
267 		fq->iif = dev->ifindex;
268 
269 	fq->q.stamp = skb->tstamp;
270 	fq->q.meat += skb->len;
271 	fq->ecn |= ecn;
272 	if (payload_len > fq->q.max_size)
273 		fq->q.max_size = payload_len;
274 	add_frag_mem_limit(fq->q.fqdir, skb->truesize);
275 
276 	/* The first fragment.
277 	 * nhoffset is obtained from the first fragment, of course.
278 	 */
279 	if (offset == 0) {
280 		fq->nhoffset = nhoff;
281 		fq->q.flags |= INET_FRAG_FIRST_IN;
282 	}
283 
284 	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
285 	    fq->q.meat == fq->q.len) {
286 		unsigned long orefdst = skb->_skb_refdst;
287 
288 		skb->_skb_refdst = 0UL;
289 		err = nf_ct_frag6_reasm(fq, skb, prev, dev);
290 		skb->_skb_refdst = orefdst;
291 
292 		/* After queue has assumed skb ownership, only 0 or
293 		 * -EINPROGRESS must be returned.
294 		 */
295 		return err ? -EINPROGRESS : 0;
296 	}
297 
298 	skb_dst_drop(skb);
299 	return -EINPROGRESS;
300 
301 insert_error:
302 	inet_frag_kill(&fq->q);
303 err:
304 	skb_dst_drop(skb);
305 	return -EINVAL;
306 }
307 
308 /*
309  *	Check if this packet is complete.
310  *
311  *	It is called with locked fq, and caller must check that
312  *	queue is eligible for reassembly i.e. it is not COMPLETE,
313  *	the last and the first frames arrived and all the bits are here.
314  */
315 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
316 			     struct sk_buff *prev_tail, struct net_device *dev)
317 {
318 	void *reasm_data;
319 	int payload_len;
320 	u8 ecn;
321 
322 	inet_frag_kill(&fq->q);
323 
324 	ecn = ip_frag_ecn_table[fq->ecn];
325 	if (unlikely(ecn == 0xff))
326 		goto err;
327 
328 	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
329 	if (!reasm_data)
330 		goto err;
331 
332 	payload_len = ((skb->data - skb_network_header(skb)) -
333 		       sizeof(struct ipv6hdr) + fq->q.len -
334 		       sizeof(struct frag_hdr));
335 	if (payload_len > IPV6_MAXPLEN) {
336 		net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
337 				    payload_len);
338 		goto err;
339 	}
340 
341 	/* We have to remove fragment header from datagram and to relocate
342 	 * header in order to calculate ICV correctly. */
343 	skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
344 	memmove(skb->head + sizeof(struct frag_hdr), skb->head,
345 		(skb->data - skb->head) - sizeof(struct frag_hdr));
346 	skb->mac_header += sizeof(struct frag_hdr);
347 	skb->network_header += sizeof(struct frag_hdr);
348 
349 	skb_reset_transport_header(skb);
350 
351 	inet_frag_reasm_finish(&fq->q, skb, reasm_data, false);
352 
353 	skb->ignore_df = 1;
354 	skb->dev = dev;
355 	ipv6_hdr(skb)->payload_len = htons(payload_len);
356 	ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
357 	IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
358 	IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;
359 
360 	/* Yes, and fold redundant checksum back. 8) */
361 	if (skb->ip_summed == CHECKSUM_COMPLETE)
362 		skb->csum = csum_partial(skb_network_header(skb),
363 					 skb_network_header_len(skb),
364 					 skb->csum);
365 
366 	fq->q.rb_fragments = RB_ROOT;
367 	fq->q.fragments_tail = NULL;
368 	fq->q.last_run_head = NULL;
369 
370 	return 0;
371 
372 err:
373 	inet_frag_kill(&fq->q);
374 	return -EINVAL;
375 }
376 
377 /*
378  * find the header just before Fragment Header.
379  *
380  * if success return 0 and set ...
381  * (*prevhdrp): the value of "Next Header Field" in the header
382  *		just before Fragment Header.
383  * (*prevhoff): the offset of "Next Header Field" in the header
384  *		just before Fragment Header.
385  * (*fhoff)   : the offset of Fragment Header.
386  *
387  * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
388  *
389  */
390 static int
391 find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
392 {
393 	u8 nexthdr = ipv6_hdr(skb)->nexthdr;
394 	const int netoff = skb_network_offset(skb);
395 	u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
396 	int start = netoff + sizeof(struct ipv6hdr);
397 	int len = skb->len - start;
398 	u8 prevhdr = NEXTHDR_IPV6;
399 
400 	while (nexthdr != NEXTHDR_FRAGMENT) {
401 		struct ipv6_opt_hdr hdr;
402 		int hdrlen;
403 
404 		if (!ipv6_ext_hdr(nexthdr)) {
405 			return -1;
406 		}
407 		if (nexthdr == NEXTHDR_NONE) {
408 			pr_debug("next header is none\n");
409 			return -1;
410 		}
411 		if (len < (int)sizeof(struct ipv6_opt_hdr)) {
412 			pr_debug("too short\n");
413 			return -1;
414 		}
415 		if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
416 			BUG();
417 		if (nexthdr == NEXTHDR_AUTH)
418 			hdrlen = ipv6_authlen(&hdr);
419 		else
420 			hdrlen = ipv6_optlen(&hdr);
421 
422 		prevhdr = nexthdr;
423 		prev_nhoff = start;
424 
425 		nexthdr = hdr.nexthdr;
426 		len -= hdrlen;
427 		start += hdrlen;
428 	}
429 
430 	if (len < 0)
431 		return -1;
432 
433 	*prevhdrp = prevhdr;
434 	*prevhoff = prev_nhoff;
435 	*fhoff = start;
436 
437 	return 0;
438 }
439 
440 int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
441 {
442 	u16 savethdr = skb->transport_header;
443 	u8 nexthdr = NEXTHDR_FRAGMENT;
444 	int fhoff, nhoff, ret;
445 	struct frag_hdr *fhdr;
446 	struct frag_queue *fq;
447 	struct ipv6hdr *hdr;
448 	u8 prevhdr;
449 
450 	/* Jumbo payload inhibits frag. header */
451 	if (ipv6_hdr(skb)->payload_len == 0) {
452 		pr_debug("payload len = 0\n");
453 		return 0;
454 	}
455 
456 	if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
457 		return 0;
458 
459 	/* Discard the first fragment if it does not include all headers
460 	 * RFC 8200, Section 4.5
461 	 */
462 	if (ipv6frag_thdr_truncated(skb, fhoff, &nexthdr)) {
463 		pr_debug("Drop incomplete fragment\n");
464 		return 0;
465 	}
466 
467 	if (!pskb_may_pull(skb, fhoff + sizeof(*fhdr)))
468 		return -ENOMEM;
469 
470 	skb_set_transport_header(skb, fhoff);
471 	hdr = ipv6_hdr(skb);
472 	fhdr = (struct frag_hdr *)skb_transport_header(skb);
473 
474 	skb_orphan(skb);
475 	fq = fq_find(net, fhdr->identification, user, hdr,
476 		     skb->dev ? skb->dev->ifindex : 0);
477 	if (fq == NULL) {
478 		pr_debug("Can't find and can't create new queue\n");
479 		return -ENOMEM;
480 	}
481 
482 	spin_lock_bh(&fq->q.lock);
483 
484 	ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff);
485 	if (ret == -EPROTO) {
486 		skb->transport_header = savethdr;
487 		ret = 0;
488 	}
489 
490 	spin_unlock_bh(&fq->q.lock);
491 	inet_frag_put(&fq->q);
492 	return ret;
493 }
494 EXPORT_SYMBOL_GPL(nf_ct_frag6_gather);
495 
496 static int nf_ct_net_init(struct net *net)
497 {
498 	int res;
499 
500 	res = fqdir_init(&net->nf_frag.fqdir, &nf_frags, net);
501 	if (res < 0)
502 		return res;
503 
504 	net->nf_frag.fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
505 	net->nf_frag.fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
506 	net->nf_frag.fqdir->timeout = IPV6_FRAG_TIMEOUT;
507 
508 	res = nf_ct_frag6_sysctl_register(net);
509 	if (res < 0)
510 		fqdir_exit(net->nf_frag.fqdir);
511 	return res;
512 }
513 
514 static void nf_ct_net_pre_exit(struct net *net)
515 {
516 	fqdir_pre_exit(net->nf_frag.fqdir);
517 }
518 
519 static void nf_ct_net_exit(struct net *net)
520 {
521 	nf_ct_frags6_sysctl_unregister(net);
522 	fqdir_exit(net->nf_frag.fqdir);
523 }
524 
525 static struct pernet_operations nf_ct_net_ops = {
526 	.init		= nf_ct_net_init,
527 	.pre_exit	= nf_ct_net_pre_exit,
528 	.exit		= nf_ct_net_exit,
529 };
530 
531 static const struct rhashtable_params nfct_rhash_params = {
532 	.head_offset		= offsetof(struct inet_frag_queue, node),
533 	.hashfn			= ip6frag_key_hashfn,
534 	.obj_hashfn		= ip6frag_obj_hashfn,
535 	.obj_cmpfn		= ip6frag_obj_cmpfn,
536 	.automatic_shrinking	= true,
537 };
538 
539 int nf_ct_frag6_init(void)
540 {
541 	int ret = 0;
542 
543 	nf_frags.constructor = ip6frag_init;
544 	nf_frags.destructor = NULL;
545 	nf_frags.qsize = sizeof(struct frag_queue);
546 	nf_frags.frag_expire = nf_ct_frag6_expire;
547 	nf_frags.frags_cache_name = nf_frags_cache_name;
548 	nf_frags.rhash_params = nfct_rhash_params;
549 	ret = inet_frags_init(&nf_frags);
550 	if (ret)
551 		goto out;
552 	ret = register_pernet_subsys(&nf_ct_net_ops);
553 	if (ret)
554 		inet_frags_fini(&nf_frags);
555 
556 out:
557 	return ret;
558 }
559 
560 void nf_ct_frag6_cleanup(void)
561 {
562 	unregister_pernet_subsys(&nf_ct_net_ops);
563 	inet_frags_fini(&nf_frags);
564 }
565