xref: /openbsd-src/sys/netinet6/frag6.c (revision f6aab3d83b51b91c24247ad2c2573574de475a82) 
1 /*	$OpenBSD: frag6.c,v 1.87 2022/02/22 01:15:02 guenther Exp $	*/
2 /*	$KAME: frag6.c,v 1.40 2002/05/27 21:40:31 itojun Exp $	*/
3 
4 /*
5  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
6  * All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of the project nor the names of its contributors
17  *    may be used to endorse or promote products derived from this software
18  *    without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  */
32 
33 #include <sys/param.h>
34 #include <sys/systm.h>
35 #include <sys/mbuf.h>
36 #include <sys/socket.h>
37 #include <sys/errno.h>
38 #include <sys/time.h>
39 #include <sys/kernel.h>
40 #include <sys/pool.h>
41 #include <sys/mutex.h>
42 
43 #include <net/if.h>
44 #include <net/if_var.h>
45 #include <net/route.h>
46 
47 #include <netinet/in.h>
48 #include <netinet6/in6_var.h>
49 #include <netinet/ip6.h>
50 #include <netinet6/ip6_var.h>
51 #include <netinet/icmp6.h>
52 #include <netinet/ip.h>		/* for ECN definitions */
53 
54 /* Protects `frag6_queue', `frag6_nfragpackets' and `frag6_nfrags'. */
55 struct mutex frag6_mutex = MUTEX_INITIALIZER(IPL_SOFTNET);
56 
57 u_int frag6_nfragpackets;
58 u_int frag6_nfrags;
59 TAILQ_HEAD(ip6q_head, ip6q) frag6_queue;	/* ip6 reassemble queue */
60 
61 void frag6_freef(struct ip6q *);
62 void frag6_unlink(struct ip6q *, struct ip6q_head *);
63 
64 struct pool ip6af_pool;
65 struct pool ip6q_pool;
66 
67 /*
68  * Initialise reassembly queue and pools.
69  */
70 void
71 frag6_init(void)
72 {
73 	pool_init(&ip6af_pool, sizeof(struct ip6asfrag),
74 	    0, IPL_SOFTNET, 0, "ip6af", NULL);
75 	pool_init(&ip6q_pool, sizeof(struct ip6q),
76 	    0, IPL_SOFTNET, 0, "ip6q", NULL);
77 
78 	TAILQ_INIT(&frag6_queue);
79 }
80 
81 /*
82  * In RFC2460, fragment and reassembly rule do not agree with each other,
83  * in terms of next header field handling in fragment header.
84  * While the sender will use the same value for all of the fragmented packets,
85  * receiver is suggested not to check the consistency.
86  *
87  * fragment rule (p20):
88  *	(2) A Fragment header containing:
89  *	The Next Header value that identifies the first header of
90  *	the Fragmentable Part of the original packet.
91  *		-> next header field is same for all fragments
92  *
93  * reassembly rule (p21):
94  *	The Next Header field of the last header of the Unfragmentable
95  *	Part is obtained from the Next Header field of the first
96  *	fragment's Fragment header.
97  *		-> should grab it from the first fragment only
98  *
99  * The following note also contradicts with fragment rule - noone is going to
100  * send different fragment with different next header field.
101  *
102  * additional note (p22):
103  *	The Next Header values in the Fragment headers of different
104  *	fragments of the same original packet may differ.  Only the value
105  *	from the Offset zero fragment packet is used for reassembly.
106  *		-> should grab it from the first fragment only
107  *
108  * There is no explicit reason given in the RFC.  Historical reason maybe?
109  */
110 /*
111  * Fragment input
112  */
113 int
114 frag6_input(struct mbuf **mp, int *offp, int proto, int af)
115 {
116 	struct mbuf *m = *mp, *t;
117 	struct ip6_hdr *ip6;
118 	struct ip6_frag *ip6f;
119 	struct ip6q *q6;
120 	struct ip6asfrag *af6, *ip6af, *naf6, *paf6;
121 	int offset = *offp, nxt, i, next;
122 	int first_frag = 0;
123 	int fragoff, frgpartlen;	/* must be larger than u_int16_t */
124 	u_int8_t ecn, ecn0;
125 
126 	ip6 = mtod(m, struct ip6_hdr *);
127 	IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
128 	if (ip6f == NULL)
129 		return IPPROTO_DONE;
130 
131 	/* jumbo payload can't contain a fragment header */
132 	if (ip6->ip6_plen == 0) {
133 		icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
134 		return IPPROTO_DONE;
135 	}
136 
137 	/*
138 	 * check whether fragment packet's fragment length is
139 	 * multiple of 8 octets.
140 	 * sizeof(struct ip6_frag) == 8
141 	 * sizeof(struct ip6_hdr) = 40
142 	 */
143 	if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
144 	    (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
145 		icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
146 		    offsetof(struct ip6_hdr, ip6_plen));
147 		return IPPROTO_DONE;
148 	}
149 
150 	ip6stat_inc(ip6s_fragments);
151 
152 	/* offset now points to data portion */
153 	offset += sizeof(struct ip6_frag);
154 
155 	/*
156 	 * RFC6946:  A host that receives an IPv6 packet which includes
157 	 * a Fragment Header with the "Fragment Offset" equal to 0 and
158 	 * the "M" bit equal to 0 MUST process such packet in isolation
159 	 * from any other packets/fragments.
160 	 */
161 	fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
162 	if (fragoff == 0 && !(ip6f->ip6f_offlg & IP6F_MORE_FRAG)) {
163 		ip6stat_inc(ip6s_reassembled);
164 		*offp = offset;
165 		return ip6f->ip6f_nxt;
166 	}
167 
168 	/* Ignore empty non atomic fragment, do not classify as overlapping. */
169 	if (sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) <= offset) {
170 		m_freem(m);
171 		return IPPROTO_DONE;
172 	}
173 
174 	mtx_enter(&frag6_mutex);
175 
176 	/*
177 	 * Enforce upper bound on number of fragments.
178 	 * If maxfrag is 0, never accept fragments.
179 	 * If maxfrag is -1, accept all fragments without limitation.
180 	 */
181 	if (ip6_maxfrags >= 0 && frag6_nfrags >= (u_int)ip6_maxfrags) {
182 		mtx_leave(&frag6_mutex);
183 		goto dropfrag;
184 	}
185 
186 	TAILQ_FOREACH(q6, &frag6_queue, ip6q_queue)
187 		if (ip6f->ip6f_ident == q6->ip6q_ident &&
188 		    IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
189 		    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst))
190 			break;
191 
192 	if (q6 == NULL) {
193 		/*
194 		 * the first fragment to arrive, create a reassembly queue.
195 		 */
196 		first_frag = 1;
197 
198 		/*
199 		 * Enforce upper bound on number of fragmented packets
200 		 * for which we attempt reassembly;
201 		 * If maxfragpackets is 0, never accept fragments.
202 		 * If maxfragpackets is -1, accept all fragments without
203 		 * limitation.
204 		 */
205 		if (ip6_maxfragpackets >= 0 &&
206 		    frag6_nfragpackets >= (u_int)ip6_maxfragpackets) {
207 			mtx_leave(&frag6_mutex);
208 			goto dropfrag;
209 		}
210 		frag6_nfragpackets++;
211 		q6 = pool_get(&ip6q_pool, PR_NOWAIT | PR_ZERO);
212 		if (q6 == NULL) {
213 			mtx_leave(&frag6_mutex);
214 			goto dropfrag;
215 		}
216 
217 		TAILQ_INSERT_HEAD(&frag6_queue, q6, ip6q_queue);
218 
219 		/* ip6q_nxt will be filled afterwards, from 1st fragment */
220 		LIST_INIT(&q6->ip6q_asfrag);
221 		q6->ip6q_ident	= ip6f->ip6f_ident;
222 		q6->ip6q_ttl	= IPV6_FRAGTTL;
223 		q6->ip6q_src	= ip6->ip6_src;
224 		q6->ip6q_dst	= ip6->ip6_dst;
225 		q6->ip6q_ecn	= (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
226 		q6->ip6q_unfrglen = -1;	/* The 1st fragment has not arrived. */
227 		q6->ip6q_nfrag = 0;
228 	}
229 
230 	/*
231 	 * If it's the 1st fragment, record the length of the
232 	 * unfragmentable part and the next header of the fragment header.
233 	 */
234 	if (fragoff == 0) {
235 		q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
236 		    sizeof(struct ip6_frag);
237 		q6->ip6q_nxt = ip6f->ip6f_nxt;
238 	}
239 
240 	/*
241 	 * Check that the reassembled packet would not exceed 65535 bytes
242 	 * in size.
243 	 * If it would exceed, discard the fragment and return an ICMP error.
244 	 */
245 	frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
246 	if (q6->ip6q_unfrglen >= 0) {
247 		/* The 1st fragment has already arrived. */
248 		if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
249 			mtx_leave(&frag6_mutex);
250 			icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
251 			    offset - sizeof(struct ip6_frag) +
252 			    offsetof(struct ip6_frag, ip6f_offlg));
253 			return (IPPROTO_DONE);
254 		}
255 	} else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
256 		mtx_leave(&frag6_mutex);
257 		icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
258 			    offset - sizeof(struct ip6_frag) +
259 				offsetof(struct ip6_frag, ip6f_offlg));
260 		return (IPPROTO_DONE);
261 	}
262 	/*
263 	 * If it's the first fragment, do the above check for each
264 	 * fragment already stored in the reassembly queue.
265 	 */
266 	if (fragoff == 0) {
267 		LIST_FOREACH_SAFE(af6, &q6->ip6q_asfrag, ip6af_list, naf6) {
268 			if (q6->ip6q_unfrglen + af6->ip6af_off +
269 			    af6->ip6af_frglen > IPV6_MAXPACKET) {
270 				struct mbuf *merr = af6->ip6af_m;
271 				struct ip6_hdr *ip6err;
272 				int erroff = af6->ip6af_offset;
273 
274 				/* dequeue the fragment. */
275 				LIST_REMOVE(af6, ip6af_list);
276 				pool_put(&ip6af_pool, af6);
277 
278 				/* adjust pointer. */
279 				ip6err = mtod(merr, struct ip6_hdr *);
280 
281 				/*
282 				 * Restore source and destination addresses
283 				 * in the erroneous IPv6 header.
284 				 */
285 				ip6err->ip6_src = q6->ip6q_src;
286 				ip6err->ip6_dst = q6->ip6q_dst;
287 
288 				icmp6_error(merr, ICMP6_PARAM_PROB,
289 				    ICMP6_PARAMPROB_HEADER,
290 				    erroff - sizeof(struct ip6_frag) +
291 				    offsetof(struct ip6_frag, ip6f_offlg));
292 			}
293 		}
294 	}
295 
296 	ip6af = pool_get(&ip6af_pool, PR_NOWAIT | PR_ZERO);
297 	if (ip6af == NULL) {
298 		mtx_leave(&frag6_mutex);
299 		goto dropfrag;
300 	}
301 	ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
302 	ip6af->ip6af_off = fragoff;
303 	ip6af->ip6af_frglen = frgpartlen;
304 	ip6af->ip6af_offset = offset;
305 	ip6af->ip6af_m = m;
306 
307 	if (first_frag) {
308 		paf6 = NULL;
309 		goto insert;
310 	}
311 
312 	/*
313 	 * Handle ECN by comparing this segment with the first one;
314 	 * if CE is set, do not lose CE.
315 	 * drop if CE and not-ECT are mixed for the same packet.
316 	 */
317 	ecn = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
318 	ecn0 = q6->ip6q_ecn;
319 	if (ecn == IPTOS_ECN_CE) {
320 		if (ecn0 == IPTOS_ECN_NOTECT) {
321 			mtx_leave(&frag6_mutex);
322 			pool_put(&ip6af_pool, ip6af);
323 			goto dropfrag;
324 		}
325 		if (ecn0 != IPTOS_ECN_CE)
326 			q6->ip6q_ecn = IPTOS_ECN_CE;
327 	}
328 	if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
329 		mtx_leave(&frag6_mutex);
330 		pool_put(&ip6af_pool, ip6af);
331 		goto dropfrag;
332 	}
333 
334 	/*
335 	 * Find a segment which begins after this one does.
336 	 */
337 	for (paf6 = NULL, af6 = LIST_FIRST(&q6->ip6q_asfrag);
338 	    af6 != NULL;
339 	    paf6 = af6, af6 = LIST_NEXT(af6, ip6af_list))
340 		if (af6->ip6af_off > ip6af->ip6af_off)
341 			break;
342 
343 	/*
344 	 * RFC 5722, Errata 3089:  When reassembling an IPv6 datagram, if one
345 	 * or more its constituent fragments is determined to be an overlapping
346 	 * fragment, the entire datagram (and any constituent fragments) MUST
347 	 * be silently discarded.
348 	 */
349 	if (paf6 != NULL) {
350 		i = (paf6->ip6af_off + paf6->ip6af_frglen) - ip6af->ip6af_off;
351 		if (i > 0)
352 			goto flushfrags;
353 	}
354 	if (af6 != NULL) {
355 		i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
356 		if (i > 0)
357 			goto flushfrags;
358 	}
359 
360  insert:
361 	/*
362 	 * Stick new segment in its place;
363 	 * check for complete reassembly.
364 	 * Move to front of packet queue, as we are
365 	 * the most recently active fragmented packet.
366 	 */
367 	if (paf6 != NULL)
368 		LIST_INSERT_AFTER(paf6, ip6af, ip6af_list);
369 	else
370 		LIST_INSERT_HEAD(&q6->ip6q_asfrag, ip6af, ip6af_list);
371 	frag6_nfrags++;
372 	q6->ip6q_nfrag++;
373 	next = 0;
374 	for (paf6 = NULL, af6 = LIST_FIRST(&q6->ip6q_asfrag);
375 	    af6 != NULL;
376 	    paf6 = af6, af6 = LIST_NEXT(af6, ip6af_list)) {
377 		if (af6->ip6af_off != next) {
378 			mtx_leave(&frag6_mutex);
379 			return IPPROTO_DONE;
380 		}
381 		next += af6->ip6af_frglen;
382 	}
383 	if (paf6->ip6af_mff) {
384 		mtx_leave(&frag6_mutex);
385 		return IPPROTO_DONE;
386 	}
387 
388 	/*
389 	 * Reassembly is complete; concatenate fragments.
390 	 */
391 	ip6af = LIST_FIRST(&q6->ip6q_asfrag);
392 	LIST_REMOVE(ip6af, ip6af_list);
393 	t = m = ip6af->ip6af_m;
394 	while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
395 		LIST_REMOVE(af6, ip6af_list);
396 		while (t->m_next)
397 			t = t->m_next;
398 		t->m_next = af6->ip6af_m;
399 		m_adj(t->m_next, af6->ip6af_offset);
400 		m_removehdr(t->m_next);
401 		pool_put(&ip6af_pool, af6);
402 	}
403 
404 	/* adjust offset to point where the original next header starts */
405 	offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
406 	pool_put(&ip6af_pool, ip6af);
407 	ip6 = mtod(m, struct ip6_hdr *);
408 	ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
409 	ip6->ip6_src = q6->ip6q_src;
410 	ip6->ip6_dst = q6->ip6q_dst;
411 	if (q6->ip6q_ecn == IPTOS_ECN_CE)
412 		ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
413 	nxt = q6->ip6q_nxt;
414 
415 	/* Delete frag6 header */
416 	if (frag6_deletefraghdr(m, offset) != 0) {
417 		TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
418 		frag6_nfrags -= q6->ip6q_nfrag;
419 		frag6_nfragpackets--;
420 		mtx_leave(&frag6_mutex);
421 		pool_put(&ip6q_pool, q6);
422 		goto dropfrag;
423 	}
424 
425 	TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
426 	frag6_nfrags -= q6->ip6q_nfrag;
427 	frag6_nfragpackets--;
428 
429 	mtx_leave(&frag6_mutex);
430 
431 	pool_put(&ip6q_pool, q6);
432 
433 	m_calchdrlen(m);
434 
435 	/*
436 	 * Restore NXT to the original.
437 	 */
438 	{
439 		int prvnxt = ip6_get_prevhdr(m, offset);
440 		uint8_t *prvnxtp;
441 
442 		IP6_EXTHDR_GET(prvnxtp, uint8_t *, m, prvnxt,
443 		    sizeof(*prvnxtp));
444 		if (prvnxtp == NULL)
445 			goto dropfrag;
446 		*prvnxtp = nxt;
447 	}
448 
449 	ip6stat_inc(ip6s_reassembled);
450 
451 	/*
452 	 * Tell launch routine the next header
453 	 */
454 
455 	*mp = m;
456 	*offp = offset;
457 
458 	return nxt;
459 
460  flushfrags:
461 	TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
462 	frag6_nfrags -= q6->ip6q_nfrag;
463 	frag6_nfragpackets--;
464 
465 	mtx_leave(&frag6_mutex);
466 
467 	pool_put(&ip6af_pool, ip6af);
468 
469 	while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
470 		LIST_REMOVE(af6, ip6af_list);
471 		m_freem(af6->ip6af_m);
472 		pool_put(&ip6af_pool, af6);
473 	}
474 	ip6stat_add(ip6s_fragdropped, q6->ip6q_nfrag + 1);
475 	pool_put(&ip6q_pool, q6);
476 	m_freem(m);
477 	return IPPROTO_DONE;
478 
479  dropfrag:
480 	ip6stat_inc(ip6s_fragdropped);
481 	m_freem(m);
482 	return IPPROTO_DONE;
483 }
484 
485 /*
486  * Delete fragment header after the unfragmentable header portions.
487  */
488 int
489 frag6_deletefraghdr(struct mbuf *m, int offset)
490 {
491 	struct mbuf *t;
492 
493 	if (m->m_len >= offset + sizeof(struct ip6_frag)) {
494 		memmove(mtod(m, caddr_t) + sizeof(struct ip6_frag),
495 		    mtod(m, caddr_t), offset);
496 		m->m_data += sizeof(struct ip6_frag);
497 		m->m_len -= sizeof(struct ip6_frag);
498 	} else {
499 		/* this comes with no copy if the boundary is on cluster */
500 		if ((t = m_split(m, offset, M_DONTWAIT)) == NULL)
501 			return (ENOBUFS);
502 		m_adj(t, sizeof(struct ip6_frag));
503 		m_cat(m, t);
504 	}
505 
506 	return (0);
507 }
508 
509 /*
510  * Free a fragment reassembly header and all
511  * associated datagrams.
512  * The header must not be in any queue.
513  */
514 void
515 frag6_freef(struct ip6q *q6)
516 {
517 	struct ip6asfrag *af6;
518 
519 	while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
520 		struct mbuf *m = af6->ip6af_m;
521 
522 		LIST_REMOVE(af6, ip6af_list);
523 
524 		/*
525 		 * Return ICMP time exceeded error for the 1st fragment.
526 		 * Just free other fragments.
527 		 */
528 		if (af6->ip6af_off == 0) {
529 			struct ip6_hdr *ip6;
530 
531 			/* adjust pointer */
532 			ip6 = mtod(m, struct ip6_hdr *);
533 
534 			/* restore source and destination addresses */
535 			ip6->ip6_src = q6->ip6q_src;
536 			ip6->ip6_dst = q6->ip6q_dst;
537 
538 			NET_LOCK();
539 			icmp6_error(m, ICMP6_TIME_EXCEEDED,
540 				    ICMP6_TIME_EXCEED_REASSEMBLY, 0);
541 			NET_UNLOCK();
542 		} else
543 			m_freem(m);
544 		pool_put(&ip6af_pool, af6);
545 	}
546 	pool_put(&ip6q_pool, q6);
547 }
548 
549 /*
550  * Unlinks a fragment reassembly header from the reassembly queue
551  * and inserts it into a given remove queue.
552  */
553 void
554 frag6_unlink(struct ip6q *q6, struct ip6q_head *rmq6)
555 {
556 	MUTEX_ASSERT_LOCKED(&frag6_mutex);
557 
558 	TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
559 	TAILQ_INSERT_HEAD(rmq6, q6, ip6q_queue);
560 	frag6_nfrags -= q6->ip6q_nfrag;
561 	frag6_nfragpackets--;
562 }
563 
564 /*
565  * IPv6 reassembling timer processing;
566  * if a timer expires on a reassembly
567  * queue, discard it.
568  */
569 void
570 frag6_slowtimo(void)
571 {
572 	struct ip6q_head rmq6;
573 	struct ip6q *q6, *nq6;
574 
575 	TAILQ_INIT(&rmq6);
576 
577 	mtx_enter(&frag6_mutex);
578 
579 	TAILQ_FOREACH_SAFE(q6, &frag6_queue, ip6q_queue, nq6) {
580 		if (--q6->ip6q_ttl == 0) {
581 			ip6stat_inc(ip6s_fragtimeout);
582 			frag6_unlink(q6, &rmq6);
583 		}
584 	}
585 
586 	/*
587 	 * If we are over the maximum number of fragments
588 	 * (due to the limit being lowered), drain off
589 	 * enough to get down to the new limit.
590 	 */
591 	while (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
592 	    !TAILQ_EMPTY(&frag6_queue)) {
593 		ip6stat_inc(ip6s_fragoverflow);
594 		frag6_unlink(TAILQ_LAST(&frag6_queue, ip6q_head), &rmq6);
595 	}
596 
597 	mtx_leave(&frag6_mutex);
598 
599 	while ((q6 = TAILQ_FIRST(&rmq6)) != NULL) {
600 		TAILQ_REMOVE(&rmq6, q6, ip6q_queue);
601 		frag6_freef(q6);
602 	}
603 }
604