sys/netinet6/ip6_forward.c

   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 }