xref: /freebsd/sys/netinet6/ip6_forward.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*-
2  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. Neither the name of the project nor the names of its contributors
14  *    may be used to endorse or promote products derived from this software
15  *    without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27  * SUCH DAMAGE.
28  *
29  *	$KAME: ip6_forward.c,v 1.69 2001/05/17 03:48:30 itojun Exp $
30  */
31 
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34 
35 #include "opt_inet.h"
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38 #include "opt_ipstealth.h"
39 
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/malloc.h>
43 #include <sys/mbuf.h>
44 #include <sys/domain.h>
45 #include <sys/protosw.h>
46 #include <sys/socket.h>
47 #include <sys/errno.h>
48 #include <sys/time.h>
49 #include <sys/kernel.h>
50 #include <sys/syslog.h>
51 
52 #include <net/if.h>
53 #include <net/route.h>
54 #include <net/pfil.h>
55 
56 #include <netinet/in.h>
57 #include <netinet/in_var.h>
58 #include <netinet/in_systm.h>
59 #include <netinet/ip.h>
60 #include <netinet/ip_var.h>
61 #include <netinet6/in6_var.h>
62 #include <netinet/ip6.h>
63 #include <netinet6/ip6_var.h>
64 #include <netinet6/scope6_var.h>
65 #include <netinet/icmp6.h>
66 #include <netinet6/nd6.h>
67 
68 #include <netinet/in_pcb.h>
69 
70 #ifdef IPSEC
71 #include <netipsec/ipsec.h>
72 #include <netipsec/ipsec6.h>
73 #include <netipsec/key.h>
74 #endif /* IPSEC */
75 
76 #include <netinet6/ip6protosw.h>
77 
78 struct	route_in6 ip6_forward_rt;
79 
80 /*
81  * Forward a packet.  If some error occurs return the sender
82  * an icmp packet.  Note we can't always generate a meaningful
83  * icmp message because icmp doesn't have a large enough repertoire
84  * of codes and types.
85  *
86  * If not forwarding, just drop the packet.  This could be confusing
87  * if ipforwarding was zero but some routing protocol was advancing
88  * us as a gateway to somewhere.  However, we must let the routing
89  * protocol deal with that.
90  *
91  */
92 void
93 ip6_forward(struct mbuf *m, int srcrt)
94 {
95 	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
96 	struct sockaddr_in6 *dst = NULL;
97 	struct rtentry *rt = NULL;
98 	int error, type = 0, code = 0;
99 	struct mbuf *mcopy = NULL;
100 	struct ifnet *origifp;	/* maybe unnecessary */
101 	u_int32_t inzone, outzone;
102 	struct in6_addr src_in6, dst_in6;
103 #ifdef IPSEC
104 	struct secpolicy *sp = NULL;
105 	int ipsecrt = 0;
106 #endif
107 	char ip6bufs[INET6_ADDRSTRLEN], ip6bufd[INET6_ADDRSTRLEN];
108 
109 	GIANT_REQUIRED; /* XXX bz: ip6_forward_rt */
110 
111 #ifdef IPSEC
112 	/*
113 	 * Check AH/ESP integrity.
114 	 */
115 	/*
116 	 * Don't increment ip6s_cantforward because this is the check
117 	 * before forwarding packet actually.
118 	 */
119 	if (ipsec6_in_reject(m, NULL)) {
120 		ipsec6stat.in_polvio++;
121 		m_freem(m);
122 		return;
123 	}
124 #endif /* IPSEC */
125 
126 	/*
127 	 * Do not forward packets to multicast destination (should be handled
128 	 * by ip6_mforward().
129 	 * Do not forward packets with unspecified source.  It was discussed
130 	 * in July 2000, on the ipngwg mailing list.
131 	 */
132 	if ((m->m_flags & (M_BCAST|M_MCAST)) != 0 ||
133 	    IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
134 	    IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
135 		ip6stat.ip6s_cantforward++;
136 		/* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
137 		if (ip6_log_time + ip6_log_interval < time_second) {
138 			ip6_log_time = time_second;
139 			log(LOG_DEBUG,
140 			    "cannot forward "
141 			    "from %s to %s nxt %d received on %s\n",
142 			    ip6_sprintf(ip6bufs, &ip6->ip6_src),
143 			    ip6_sprintf(ip6bufd, &ip6->ip6_dst),
144 			    ip6->ip6_nxt,
145 			    if_name(m->m_pkthdr.rcvif));
146 		}
147 		m_freem(m);
148 		return;
149 	}
150 
151 #ifdef IPSTEALTH
152 	if (!ip6stealth) {
153 #endif
154 	if (ip6->ip6_hlim <= IPV6_HLIMDEC) {
155 		/* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
156 		icmp6_error(m, ICMP6_TIME_EXCEEDED,
157 				ICMP6_TIME_EXCEED_TRANSIT, 0);
158 		return;
159 	}
160 	ip6->ip6_hlim -= IPV6_HLIMDEC;
161 
162 #ifdef IPSTEALTH
163 	}
164 #endif
165 
166 	/*
167 	 * Save at most ICMPV6_PLD_MAXLEN (= the min IPv6 MTU -
168 	 * size of IPv6 + ICMPv6 headers) bytes of the packet in case
169 	 * we need to generate an ICMP6 message to the src.
170 	 * Thanks to M_EXT, in most cases copy will not occur.
171 	 *
172 	 * It is important to save it before IPsec processing as IPsec
173 	 * processing may modify the mbuf.
174 	 */
175 	mcopy = m_copy(m, 0, imin(m->m_pkthdr.len, ICMPV6_PLD_MAXLEN));
176 
177 #ifdef IPSEC
178 	/* get a security policy for this packet */
179 	sp = ipsec_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND,
180 	    IP_FORWARDING, &error);
181 	if (sp == NULL) {
182 		ipsec6stat.out_inval++;
183 		ip6stat.ip6s_cantforward++;
184 		if (mcopy) {
185 #if 0
186 			/* XXX: what icmp ? */
187 #else
188 			m_freem(mcopy);
189 #endif
190 		}
191 		m_freem(m);
192 		return;
193 	}
194 
195 	error = 0;
196 
197 	/* check policy */
198 	switch (sp->policy) {
199 	case IPSEC_POLICY_DISCARD:
200 		/*
201 		 * This packet is just discarded.
202 		 */
203 		ipsec6stat.out_polvio++;
204 		ip6stat.ip6s_cantforward++;
205 		KEY_FREESP(&sp);
206 		if (mcopy) {
207 #if 0
208 			/* XXX: what icmp ? */
209 #else
210 			m_freem(mcopy);
211 #endif
212 		}
213 		m_freem(m);
214 		return;
215 
216 	case IPSEC_POLICY_BYPASS:
217 	case IPSEC_POLICY_NONE:
218 		/* no need to do IPsec. */
219 		KEY_FREESP(&sp);
220 		goto skip_ipsec;
221 
222 	case IPSEC_POLICY_IPSEC:
223 		if (sp->req == NULL) {
224 			/* XXX should be panic ? */
225 			printf("ip6_forward: No IPsec request specified.\n");
226 			ip6stat.ip6s_cantforward++;
227 			KEY_FREESP(&sp);
228 			if (mcopy) {
229 #if 0
230 				/* XXX: what icmp ? */
231 #else
232 				m_freem(mcopy);
233 #endif
234 			}
235 			m_freem(m);
236 			return;
237 		}
238 		/* do IPsec */
239 		break;
240 
241 	case IPSEC_POLICY_ENTRUST:
242 	default:
243 		/* should be panic ?? */
244 		printf("ip6_forward: Invalid policy found. %d\n", sp->policy);
245 		KEY_FREESP(&sp);
246 		goto skip_ipsec;
247 	}
248 
249     {
250 	struct ipsecrequest *isr = NULL;
251 	struct ipsec_output_state state;
252 
253 	/*
254 	 * when the kernel forwards a packet, it is not proper to apply
255 	 * IPsec transport mode to the packet is not proper.  this check
256 	 * avoid from this.
257 	 * at present, if there is even a transport mode SA request in the
258 	 * security policy, the kernel does not apply IPsec to the packet.
259 	 * this check is not enough because the following case is valid.
260 	 *      ipsec esp/tunnel/xxx-xxx/require esp/transport//require;
261 	 */
262 	for (isr = sp->req; isr; isr = isr->next) {
263 		if (isr->saidx.mode == IPSEC_MODE_ANY)
264 			goto doipsectunnel;
265 		if (isr->saidx.mode == IPSEC_MODE_TUNNEL)
266 			goto doipsectunnel;
267 	}
268 
269 	/*
270 	 * if there's no need for tunnel mode IPsec, skip.
271 	 */
272 	if (!isr)
273 		goto skip_ipsec;
274 
275     doipsectunnel:
276 	/*
277 	 * All the extension headers will become inaccessible
278 	 * (since they can be encrypted).
279 	 * Don't panic, we need no more updates to extension headers
280 	 * on inner IPv6 packet (since they are now encapsulated).
281 	 *
282 	 * IPv6 [ESP|AH] IPv6 [extension headers] payload
283 	 */
284 	bzero(&state, sizeof(state));
285 	state.m = m;
286 	state.ro = NULL;	/* update at ipsec6_output_tunnel() */
287 	state.dst = NULL;	/* update at ipsec6_output_tunnel() */
288 
289 	error = ipsec6_output_tunnel(&state, sp, 0);
290 
291 	m = state.m;
292 	KEY_FREESP(&sp);
293 
294 	if (error) {
295 		/* mbuf is already reclaimed in ipsec6_output_tunnel. */
296 		switch (error) {
297 		case EHOSTUNREACH:
298 		case ENETUNREACH:
299 		case EMSGSIZE:
300 		case ENOBUFS:
301 		case ENOMEM:
302 			break;
303 		default:
304 			printf("ip6_output (ipsec): error code %d\n", error);
305 			/* FALLTHROUGH */
306 		case ENOENT:
307 			/* don't show these error codes to the user */
308 			break;
309 		}
310 		ip6stat.ip6s_cantforward++;
311 		if (mcopy) {
312 #if 0
313 			/* XXX: what icmp ? */
314 #else
315 			m_freem(mcopy);
316 #endif
317 		}
318 		m_freem(m);
319 		return;
320 	} else {
321 		/*
322 		 * In the FAST IPSec case we have already
323 		 * re-injected the packet and it has been freed
324 		 * by the ipsec_done() function.  So, just clean
325 		 * up after ourselves.
326 		 */
327 		m = NULL;
328 		goto freecopy;
329 	}
330 
331 	if ((m != NULL) && (ip6 != mtod(m, struct ip6_hdr *)) ){
332 		/*
333 		 * now tunnel mode headers are added.  we are originating
334 		 * packet instead of forwarding the packet.
335 		 */
336 		ip6_output(m, NULL, NULL, IPV6_FORWARDING/*XXX*/, NULL, NULL,
337 		    NULL);
338 		goto freecopy;
339 	}
340 
341 	/* adjust pointer */
342 	dst = (struct sockaddr_in6 *)state.dst;
343 	rt = state.ro ? state.ro->ro_rt : NULL;
344 	if (dst != NULL && rt != NULL)
345 		ipsecrt = 1;
346     }
347     skip_ipsec:
348 #endif /* IPSEC */
349 
350 #ifdef IPSEC
351 	if (ipsecrt)
352 		goto skip_routing;
353 #endif
354 
355 	dst = (struct sockaddr_in6 *)&ip6_forward_rt.ro_dst;
356 	if (!srcrt) {
357 		/* ip6_forward_rt.ro_dst.sin6_addr is equal to ip6->ip6_dst */
358 		if (ip6_forward_rt.ro_rt == 0 ||
359 		    (ip6_forward_rt.ro_rt->rt_flags & RTF_UP) == 0) {
360 			if (ip6_forward_rt.ro_rt) {
361 				RTFREE(ip6_forward_rt.ro_rt);
362 				ip6_forward_rt.ro_rt = 0;
363 			}
364 
365 			/* this probably fails but give it a try again */
366 			rtalloc((struct route *)&ip6_forward_rt);
367 		}
368 
369 		if (ip6_forward_rt.ro_rt == 0) {
370 			ip6stat.ip6s_noroute++;
371 			in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
372 			if (mcopy) {
373 				icmp6_error(mcopy, ICMP6_DST_UNREACH,
374 					    ICMP6_DST_UNREACH_NOROUTE, 0);
375 			}
376 			m_freem(m);
377 			return;
378 		}
379 	} else if ((rt = ip6_forward_rt.ro_rt) == 0 ||
380 		   !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &dst->sin6_addr)) {
381 		if (ip6_forward_rt.ro_rt) {
382 			RTFREE(ip6_forward_rt.ro_rt);
383 			ip6_forward_rt.ro_rt = 0;
384 		}
385 		bzero(dst, sizeof(*dst));
386 		dst->sin6_len = sizeof(struct sockaddr_in6);
387 		dst->sin6_family = AF_INET6;
388 		dst->sin6_addr = ip6->ip6_dst;
389 
390 		rtalloc((struct route *)&ip6_forward_rt);
391 		if (ip6_forward_rt.ro_rt == 0) {
392 			ip6stat.ip6s_noroute++;
393 			in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
394 			if (mcopy) {
395 				icmp6_error(mcopy, ICMP6_DST_UNREACH,
396 					    ICMP6_DST_UNREACH_NOROUTE, 0);
397 			}
398 			m_freem(m);
399 			return;
400 		}
401 	}
402 	rt = ip6_forward_rt.ro_rt;
403 #ifdef IPSEC
404     skip_routing:;
405 #endif
406 
407 	/*
408 	 * Source scope check: if a packet can't be delivered to its
409 	 * destination for the reason that the destination is beyond the scope
410 	 * of the source address, discard the packet and return an icmp6
411 	 * destination unreachable error with Code 2 (beyond scope of source
412 	 * address).  We use a local copy of ip6_src, since in6_setscope()
413 	 * will possibly modify its first argument.
414 	 * [draft-ietf-ipngwg-icmp-v3-04.txt, Section 3.1]
415 	 */
416 	src_in6 = ip6->ip6_src;
417 	if (in6_setscope(&src_in6, rt->rt_ifp, &outzone)) {
418 		/* XXX: this should not happen */
419 		ip6stat.ip6s_cantforward++;
420 		ip6stat.ip6s_badscope++;
421 		m_freem(m);
422 		return;
423 	}
424 	if (in6_setscope(&src_in6, m->m_pkthdr.rcvif, &inzone)) {
425 		ip6stat.ip6s_cantforward++;
426 		ip6stat.ip6s_badscope++;
427 		m_freem(m);
428 		return;
429 	}
430 	if (inzone != outzone
431 #ifdef IPSEC
432 	    && !ipsecrt
433 #endif
434 	    ) {
435 		ip6stat.ip6s_cantforward++;
436 		ip6stat.ip6s_badscope++;
437 		in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard);
438 
439 		if (ip6_log_time + ip6_log_interval < time_second) {
440 			ip6_log_time = time_second;
441 			log(LOG_DEBUG,
442 			    "cannot forward "
443 			    "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
444 			    ip6_sprintf(ip6bufs, &ip6->ip6_src),
445 			    ip6_sprintf(ip6bufd, &ip6->ip6_dst),
446 			    ip6->ip6_nxt,
447 			    if_name(m->m_pkthdr.rcvif), if_name(rt->rt_ifp));
448 		}
449 		if (mcopy)
450 			icmp6_error(mcopy, ICMP6_DST_UNREACH,
451 				    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
452 		m_freem(m);
453 		return;
454 	}
455 
456 	/*
457 	 * Destination scope check: if a packet is going to break the scope
458 	 * zone of packet's destination address, discard it.  This case should
459 	 * usually be prevented by appropriately-configured routing table, but
460 	 * we need an explicit check because we may mistakenly forward the
461 	 * packet to a different zone by (e.g.) a default route.
462 	 */
463 	dst_in6 = ip6->ip6_dst;
464 	if (in6_setscope(&dst_in6, m->m_pkthdr.rcvif, &inzone) != 0 ||
465 	    in6_setscope(&dst_in6, rt->rt_ifp, &outzone) != 0 ||
466 	    inzone != outzone) {
467 		ip6stat.ip6s_cantforward++;
468 		ip6stat.ip6s_badscope++;
469 		m_freem(m);
470 		return;
471 	}
472 
473 	if (m->m_pkthdr.len > IN6_LINKMTU(rt->rt_ifp)) {
474 		in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);
475 		if (mcopy) {
476 			u_long mtu;
477 #ifdef IPSEC
478 			struct secpolicy *sp;
479 			int ipsecerror;
480 			size_t ipsechdrsiz;
481 #endif /* IPSEC */
482 
483 			mtu = IN6_LINKMTU(rt->rt_ifp);
484 #ifdef IPSEC
485 			/*
486 			 * When we do IPsec tunnel ingress, we need to play
487 			 * with the link value (decrement IPsec header size
488 			 * from mtu value).  The code is much simpler than v4
489 			 * case, as we have the outgoing interface for
490 			 * encapsulated packet as "rt->rt_ifp".
491 			 */
492 			sp = ipsec_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,
493 				IP_FORWARDING, &ipsecerror);
494 			if (sp) {
495 				ipsechdrsiz = ipsec6_hdrsiz(mcopy,
496 					IPSEC_DIR_OUTBOUND, NULL);
497 				if (ipsechdrsiz < mtu)
498 					mtu -= ipsechdrsiz;
499 			}
500 
501 			/*
502 			 * if mtu becomes less than minimum MTU,
503 			 * tell minimum MTU (and I'll need to fragment it).
504 			 */
505 			if (mtu < IPV6_MMTU)
506 				mtu = IPV6_MMTU;
507 #endif /* IPSEC */
508 			icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, mtu);
509 		}
510 		m_freem(m);
511 		return;
512 	}
513 
514 	if (rt->rt_flags & RTF_GATEWAY)
515 		dst = (struct sockaddr_in6 *)rt->rt_gateway;
516 
517 	/*
518 	 * If we are to forward the packet using the same interface
519 	 * as one we got the packet from, perhaps we should send a redirect
520 	 * to sender to shortcut a hop.
521 	 * Only send redirect if source is sending directly to us,
522 	 * and if packet was not source routed (or has any options).
523 	 * Also, don't send redirect if forwarding using a route
524 	 * modified by a redirect.
525 	 */
526 	if (ip6_sendredirects && rt->rt_ifp == m->m_pkthdr.rcvif && !srcrt &&
527 #ifdef IPSEC
528 	    !ipsecrt &&
529 #endif /* IPSEC */
530 	    (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
531 		if ((rt->rt_ifp->if_flags & IFF_POINTOPOINT) != 0) {
532 			/*
533 			 * If the incoming interface is equal to the outgoing
534 			 * one, and the link attached to the interface is
535 			 * point-to-point, then it will be highly probable
536 			 * that a routing loop occurs. Thus, we immediately
537 			 * drop the packet and send an ICMPv6 error message.
538 			 *
539 			 * type/code is based on suggestion by Rich Draves.
540 			 * not sure if it is the best pick.
541 			 */
542 			icmp6_error(mcopy, ICMP6_DST_UNREACH,
543 				    ICMP6_DST_UNREACH_ADDR, 0);
544 			m_freem(m);
545 			return;
546 		}
547 		type = ND_REDIRECT;
548 	}
549 
550 	/*
551 	 * Fake scoped addresses. Note that even link-local source or
552 	 * destinaion can appear, if the originating node just sends the
553 	 * packet to us (without address resolution for the destination).
554 	 * Since both icmp6_error and icmp6_redirect_output fill the embedded
555 	 * link identifiers, we can do this stuff after making a copy for
556 	 * returning an error.
557 	 */
558 	if ((rt->rt_ifp->if_flags & IFF_LOOPBACK) != 0) {
559 		/*
560 		 * See corresponding comments in ip6_output.
561 		 * XXX: but is it possible that ip6_forward() sends a packet
562 		 *      to a loopback interface? I don't think so, and thus
563 		 *      I bark here. (jinmei@kame.net)
564 		 * XXX: it is common to route invalid packets to loopback.
565 		 *	also, the codepath will be visited on use of ::1 in
566 		 *	rthdr. (itojun)
567 		 */
568 #if 1
569 		if (0)
570 #else
571 		if ((rt->rt_flags & (RTF_BLACKHOLE|RTF_REJECT)) == 0)
572 #endif
573 		{
574 			printf("ip6_forward: outgoing interface is loopback. "
575 			       "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
576 			       ip6_sprintf(ip6bufs, &ip6->ip6_src),
577 			       ip6_sprintf(ip6bufd, &ip6->ip6_dst),
578 			       ip6->ip6_nxt, if_name(m->m_pkthdr.rcvif),
579 			       if_name(rt->rt_ifp));
580 		}
581 
582 		/* we can just use rcvif in forwarding. */
583 		origifp = m->m_pkthdr.rcvif;
584 	}
585 	else
586 		origifp = rt->rt_ifp;
587 	/*
588 	 * clear embedded scope identifiers if necessary.
589 	 * in6_clearscope will touch the addresses only when necessary.
590 	 */
591 	in6_clearscope(&ip6->ip6_src);
592 	in6_clearscope(&ip6->ip6_dst);
593 
594 	/* Jump over all PFIL processing if hooks are not active. */
595 	if (!PFIL_HOOKED(&inet6_pfil_hook))
596 		goto pass;
597 
598 	/* Run through list of hooks for output packets. */
599 	error = pfil_run_hooks(&inet6_pfil_hook, &m, rt->rt_ifp, PFIL_OUT, NULL);
600 	if (error != 0)
601 		goto senderr;
602 	if (m == NULL)
603 		goto freecopy;
604 	ip6 = mtod(m, struct ip6_hdr *);
605 
606 pass:
607 	error = nd6_output(rt->rt_ifp, origifp, m, dst, rt);
608 	if (error) {
609 		in6_ifstat_inc(rt->rt_ifp, ifs6_out_discard);
610 		ip6stat.ip6s_cantforward++;
611 	} else {
612 		ip6stat.ip6s_forward++;
613 		in6_ifstat_inc(rt->rt_ifp, ifs6_out_forward);
614 		if (type)
615 			ip6stat.ip6s_redirectsent++;
616 		else {
617 			if (mcopy)
618 				goto freecopy;
619 		}
620 	}
621 
622 senderr:
623 	if (mcopy == NULL)
624 		return;
625 	switch (error) {
626 	case 0:
627 		if (type == ND_REDIRECT) {
628 			icmp6_redirect_output(mcopy, rt);
629 			return;
630 		}
631 		goto freecopy;
632 
633 	case EMSGSIZE:
634 		/* xxx MTU is constant in PPP? */
635 		goto freecopy;
636 
637 	case ENOBUFS:
638 		/* Tell source to slow down like source quench in IP? */
639 		goto freecopy;
640 
641 	case ENETUNREACH:	/* shouldn't happen, checked above */
642 	case EHOSTUNREACH:
643 	case ENETDOWN:
644 	case EHOSTDOWN:
645 	default:
646 		type = ICMP6_DST_UNREACH;
647 		code = ICMP6_DST_UNREACH_ADDR;
648 		break;
649 	}
650 	icmp6_error(mcopy, type, code, 0);
651 	return;
652 
653  freecopy:
654 	m_freem(mcopy);
655 	return;
656 }
657