bsd/netinet6/ip6_forward.c

   1 /*
   2  * Copyright (c) 2009-2011 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 /*      $FreeBSD: src/sys/netinet6/ip6_forward.c,v 1.16 2002/10/16 02:25:05 sam Exp $   */
  30 /*      $KAME: ip6_forward.c,v 1.69 2001/05/17 03:48:30 itojun Exp $    */
  31
  32 /*
  33  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
  34  * All rights reserved.
  35  *
  36  * Redistribution and use in source and binary forms, with or without
  37  * modification, are permitted provided that the following conditions
  38  * are met:
  39  * 1. Redistributions of source code must retain the above copyright
  40  *    notice, this list of conditions and the following disclaimer.
  41  * 2. Redistributions in binary form must reproduce the above copyright
  42  *    notice, this list of conditions and the following disclaimer in the
  43  *    documentation and/or other materials provided with the distribution.
  44  * 3. Neither the name of the project nor the names of its contributors
  45  *    may be used to endorse or promote products derived from this software
  46  *    without specific prior written permission.
  47  *
  48  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
  49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
  52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  58  * SUCH DAMAGE.
  59  */
  60
  61
  62 #include <sys/param.h>
  63 #include <sys/systm.h>
  64 #include <sys/malloc.h>
  65 #include <sys/mbuf.h>
  66 #include <sys/domain.h>
  67 #include <sys/protosw.h>
  68 #include <sys/socket.h>
  69 #include <sys/errno.h>
  70 #include <sys/time.h>
  71 #include <sys/kernel.h>
  72 #include <sys/syslog.h>
  73
  74 #include <net/if.h>
  75 #include <net/route.h>
  76
  77 #include <netinet/in.h>
  78 #include <netinet/in_var.h>
  79 #include <netinet/in_systm.h>
  80 #include <netinet/ip.h>
  81 #include <netinet/ip_var.h>
  82 #include <netinet6/in6_var.h>
  83 #include <netinet/ip6.h>
  84 #include <netinet6/ip6_var.h>
  85 #include <netinet/icmp6.h>
  86 #include <netinet6/nd6.h>
  87 #include <netinet6/scope6_var.h>
  88
  89 #include <netinet/in_pcb.h>
  90
  91 #if IPSEC
  92 #include <netinet6/ipsec.h>
  93 #if INET6
  94 #include <netinet6/ipsec6.h>
  95 #endif
  96 #include <netkey/key.h>
  97 extern int ipsec_bypass;
  98 #endif /* IPSEC */
  99
 100 #include <netinet6/ip6_fw.h>
 101
 102 #include <net/net_osdep.h>
 103
 104 #if PF
 105 #include <net/pfvar.h>
 106 #endif /* PF */
 107
 108 /*
 109  * Forward a packet.  If some error occurs return the sender
 110  * an icmp packet.  Note we can't always generate a meaningful
 111  * icmp message because icmp doesn't have a large enough repertoire
 112  * of codes and types.
 113  *
 114  * If not forwarding, just drop the packet.  This could be confusing
 115  * if ipforwarding was zero but some routing protocol was advancing
 116  * us as a gateway to somewhere.  However, we must let the routing
 117  * protocol deal with that.
 118  *
 119  */
 120
 121 struct mbuf *
 122 ip6_forward(struct mbuf *m, struct route_in6 *ip6forward_rt,
 123     int srcrt)
 124 {
 125         struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
 126         struct sockaddr_in6 *dst;
 127         struct rtentry *rt;
 128         int error, type = 0, code = 0;
 129         boolean_t proxy = FALSE;
 130         struct mbuf *mcopy = NULL;
 131         struct ifnet *ifp, *origifp;    /* maybe unnecessary */
 132         u_int32_t inzone, outzone;
 133         struct in6_addr src_in6, dst_in6;
 134 #if IPSEC
 135         struct secpolicy *sp = NULL;
 136 #endif
 137         struct timeval timenow;
 138         unsigned int ifscope = IFSCOPE_NONE;
 139 #if PF
 140         struct pf_mtag *pf_mtag;
 141 #endif /* PF */
 142
 143         getmicrotime(&timenow);
 144 #if PF
 145         pf_mtag = pf_find_mtag(m);
 146         if (pf_mtag != NULL && pf_mtag->pftag_rtableid != IFSCOPE_NONE)
 147                 ifscope = pf_mtag->pftag_rtableid;
 148
 149         /*
 150          * If the caller provides a route which is on a different interface
 151          * than the one specified for scoped forwarding, discard the route
 152          * and do a lookup below.
 153          */
 154         if (ifscope != IFSCOPE_NONE && (rt = ip6forward_rt->ro_rt) != NULL) {
 155                 RT_LOCK(rt);
 156                 if (rt->rt_ifp->if_index != ifscope) {
 157                         RT_UNLOCK(rt);
 158                         rtfree(rt);
 159                         rt = ip6forward_rt->ro_rt = NULL;
 160                 } else {
 161                         RT_UNLOCK(rt);
 162                 }
 163         }
 164 #endif /* PF */
 165
 166 #if IPSEC
 167         /*
 168          * Check AH/ESP integrity.
 169          */
 170         /*
 171          * Don't increment ip6s_cantforward because this is the check
 172          * before forwarding packet actually.
 173          */
 174         if (ipsec_bypass == 0) {
 175                 if (ipsec6_in_reject(m, NULL)) {
 176                         IPSEC_STAT_INCREMENT(ipsec6stat.in_polvio);
 177                         m_freem(m);
 178                         return (NULL);
 179                 }
 180         }
 181 #endif /*IPSEC*/
 182
 183         /*
 184          * Do not forward packets to multicast destination (should be handled
 185          * by ip6_mforward().
 186          * Do not forward packets with unspecified source.  It was discussed
 187          * in July 2000, on ipngwg mailing list.
 188          */
 189         if ((m->m_flags & (M_BCAST|M_MCAST)) != 0 ||
 190             IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 191             IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 192                 ip6stat.ip6s_cantforward++;
 193                 /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
 194                 if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
 195                         ip6_log_time = timenow.tv_sec;
 196                         log(LOG_DEBUG,
 197                             "cannot forward "
 198                             "from %s to %s nxt %d received on %s\n",
 199                             ip6_sprintf(&ip6->ip6_src),
 200                             ip6_sprintf(&ip6->ip6_dst),
 201                             ip6->ip6_nxt,
 202                             if_name(m->m_pkthdr.rcvif));
 203                 }
 204                 m_freem(m);
 205                 return (NULL);
 206         }
 207
 208         if (ip6->ip6_hlim <= IPV6_HLIMDEC) {
 209                 /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
 210                 icmp6_error(m, ICMP6_TIME_EXCEEDED,
 211                                 ICMP6_TIME_EXCEED_TRANSIT, 0);
 212                 return (NULL);
 213         }
 214
 215         /*
 216          * See if the destination is a proxied address, and if so pretend
 217          * that it's for us.  This is mostly to handle NUD probes against
 218          * the proxied addresses.  We filter for ICMPv6 here and will let
 219          * icmp6_input handle the rest.
 220          */
 221         if (!srcrt && nd6_prproxy) {
 222                 VERIFY(!IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst));
 223                 proxy = nd6_prproxy_isours(m, ip6, ip6forward_rt, ifscope);
 224                 /*
 225                  * Don't update hop limit while proxying; RFC 4389 4.1.
 226                  * Also skip IPsec forwarding path processing as this
 227                  * packet is not to be forwarded.
 228                  */
 229                 if (proxy)
 230                         goto skip_ipsec;
 231         }
 232
 233         ip6->ip6_hlim -= IPV6_HLIMDEC;
 234
 235         /*
 236          * Save at most ICMPV6_PLD_MAXLEN (= the min IPv6 MTU -
 237          * size of IPv6 + ICMPv6 headers) bytes of the packet in case
 238          * we need to generate an ICMP6 message to the src.
 239          * Thanks to M_EXT, in most cases copy will not occur.
 240          *
 241          * It is important to save it before IPsec processing as IPsec
 242          * processing may modify the mbuf.
 243          */
 244         mcopy = m_copy(m, 0, imin(m->m_pkthdr.len, ICMPV6_PLD_MAXLEN));
 245
 246 #if IPSEC
 247         if (ipsec_bypass != 0)
 248                 goto skip_ipsec;
 249         /* get a security policy for this packet */
 250         sp = ipsec6_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND, IP_FORWARDING,
 251             &error);
 252         if (sp == NULL) {
 253                 IPSEC_STAT_INCREMENT(ipsec6stat.out_inval);
 254                 ip6stat.ip6s_cantforward++;
 255                 if (mcopy) {
 256 #if 0
 257                         /* XXX: what icmp ? */
 258 #else
 259                         m_freem(mcopy);
 260 #endif
 261                 }
 262                 m_freem(m);
 263                 return (NULL);
 264         }
 265
 266         error = 0;
 267
 268         /* check policy */
 269         switch (sp->policy) {
 270         case IPSEC_POLICY_DISCARD:
 271         case IPSEC_POLICY_GENERATE:
 272                 /*
 273                  * This packet is just discarded.
 274                  */
 275                 IPSEC_STAT_INCREMENT(ipsec6stat.out_polvio);
 276                 ip6stat.ip6s_cantforward++;
 277                 key_freesp(sp, KEY_SADB_UNLOCKED);
 278                 if (mcopy) {
 279 #if 0
 280                         /* XXX: what icmp ? */
 281 #else
 282                         m_freem(mcopy);
 283 #endif
 284                 }
 285                 m_freem(m);
 286                 return (NULL);
 287
 288         case IPSEC_POLICY_BYPASS:
 289         case IPSEC_POLICY_NONE:
 290                 /* no need to do IPsec. */
 291                 key_freesp(sp, KEY_SADB_UNLOCKED);
 292                 goto skip_ipsec;
 293
 294         case IPSEC_POLICY_IPSEC:
 295                 if (sp->req == NULL) {
 296                         /* XXX should be panic ? */
 297                         printf("ip6_forward: No IPsec request specified.\n");
 298                         ip6stat.ip6s_cantforward++;
 299                         key_freesp(sp, KEY_SADB_UNLOCKED);
 300                         if (mcopy) {
 301 #if 0
 302                                 /* XXX: what icmp ? */
 303 #else
 304                                 m_freem(mcopy);
 305 #endif
 306                         }
 307                         m_freem(m);
 308                         return (NULL);
 309                 }
 310                 /* do IPsec */
 311                 break;
 312
 313         case IPSEC_POLICY_ENTRUST:
 314         default:
 315                 /* should be panic ?? */
 316                 printf("ip6_forward: Invalid policy found. %d\n", sp->policy);
 317                 key_freesp(sp, KEY_SADB_UNLOCKED);
 318                 goto skip_ipsec;
 319         }
 320
 321     {
 322         struct ipsec_output_state state;
 323
 324         /*
 325          * All the extension headers will become inaccessible
 326          * (since they can be encrypted).
 327          * Don't panic, we need no more updates to extension headers
 328          * on inner IPv6 packet (since they are now encapsulated).
 329          *
 330          * IPv6 [ESP|AH] IPv6 [extension headers] payload
 331          */
 332         bzero(&state, sizeof(state));
 333         state.m = m;
 334         state.dst = NULL;       /* update at ipsec6_output_tunnel() */
 335
 336         error = ipsec6_output_tunnel(&state, sp, 0);
 337         key_freesp(sp, KEY_SADB_UNLOCKED);
 338         if (state.tunneled == 4)
 339                 return (NULL);  /* packet is gone - sent over IPv4 */
 340
 341         m = state.m;
 342         if (state.ro.ro_rt) {
 343                 rtfree(state.ro.ro_rt);
 344                 state.ro.ro_rt = NULL;
 345         }
 346         if (error) {
 347                 /* mbuf is already reclaimed in ipsec6_output_tunnel. */
 348                 switch (error) {
 349                 case EHOSTUNREACH:
 350                 case ENETUNREACH:
 351                 case EMSGSIZE:
 352                 case ENOBUFS:
 353                 case ENOMEM:
 354                         break;
 355                 default:
 356                         printf("ip6_output (ipsec): error code %d\n", error);
 357                         /* fall through */
 358                 case ENOENT:
 359                         /* don't show these error codes to the user */
 360                         break;
 361                 }
 362                 ip6stat.ip6s_cantforward++;
 363                 if (mcopy) {
 364 #if 0
 365                         /* XXX: what icmp ? */
 366 #else
 367                         m_freem(mcopy);
 368 #endif
 369                 }
 370                 m_freem(m);
 371                 return (NULL);
 372         }
 373     }
 374     skip_ipsec:
 375 #endif /* IPSEC */
 376
 377         dst = (struct sockaddr_in6 *)&ip6forward_rt->ro_dst;
 378         if ((rt = ip6forward_rt->ro_rt) != NULL) {
 379                 RT_LOCK(rt);
 380                 /* Take an extra ref for ourselves */
 381                 RT_ADDREF_LOCKED(rt);
 382         }
 383
 384         if (!srcrt) {
 385                 /*
 386                  * ip6forward_rt->ro_dst.sin6_addr is equal to ip6->ip6_dst
 387                  */
 388                 if (rt == NULL || !(rt->rt_flags & RTF_UP) ||
 389                     rt->generation_id != route_generation) {
 390                         if (rt != NULL) {
 391                                 /* Release extra ref */
 392                                 RT_REMREF_LOCKED(rt);
 393                                 RT_UNLOCK(rt);
 394                                 rtfree(rt);
 395                                 ip6forward_rt->ro_rt = NULL;
 396                         }
 397                         /* this probably fails but give it a try again */
 398                         rtalloc_scoped_ign((struct route *)ip6forward_rt,
 399                             RTF_PRCLONING, ifscope);
 400                         if ((rt = ip6forward_rt->ro_rt) != NULL) {
 401                                 RT_LOCK(rt);
 402                                 /* Take an extra ref for ourselves */
 403                                 RT_ADDREF_LOCKED(rt);
 404                         }
 405                 }
 406
 407                 if (rt == NULL) {
 408                         ip6stat.ip6s_noroute++;
 409                         in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
 410                         if (mcopy)
 411                                 icmp6_error(mcopy, ICMP6_DST_UNREACH,
 412                                             ICMP6_DST_UNREACH_NOROUTE, 0);
 413                         m_freem(m);
 414                         return (NULL);
 415                 }
 416                 RT_LOCK_ASSERT_HELD(rt);
 417         } else if (rt == NULL || !(rt->rt_flags & RTF_UP) ||
 418             !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &dst->sin6_addr) ||
 419             rt->generation_id != route_generation) {
 420                 if (rt != NULL) {
 421                         /* Release extra ref */
 422                         RT_REMREF_LOCKED(rt);
 423                         RT_UNLOCK(rt);
 424                         rtfree(rt);
 425                         ip6forward_rt->ro_rt = NULL;
 426                 }
 427                 bzero(dst, sizeof(*dst));
 428                 dst->sin6_len = sizeof(struct sockaddr_in6);
 429                 dst->sin6_family = AF_INET6;
 430                 dst->sin6_addr = ip6->ip6_dst;
 431
 432                 rtalloc_scoped_ign((struct route *)ip6forward_rt,
 433                     RTF_PRCLONING, ifscope);
 434                 if ((rt = ip6forward_rt->ro_rt) == NULL) {
 435                         ip6stat.ip6s_noroute++;
 436                         in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
 437                         if (mcopy)
 438                                 icmp6_error(mcopy, ICMP6_DST_UNREACH,
 439                                     ICMP6_DST_UNREACH_NOROUTE, 0);
 440                         m_freem(m);
 441                         return (NULL);
 442                 }
 443                 RT_LOCK(rt);
 444                 /* Take an extra ref for ourselves */
 445                 RT_ADDREF_LOCKED(rt);
 446         }
 447
 448         /*
 449          * Source scope check: if a packet can't be delivered to its
 450          * destination for the reason that the destination is beyond the scope
 451          * of the source address, discard the packet and return an icmp6
 452          * destination unreachable error with Code 2 (beyond scope of source
 453          * address) unless we are proxying (source address is link local
 454          * for NUDs.)  We use a local copy of ip6_src, since in6_setscope()
 455          * will possibly modify its first argument.
 456          * [draft-ietf-ipngwg-icmp-v3-04.txt, Section 3.1]
 457          */
 458         src_in6 = ip6->ip6_src;
 459         if (in6_setscope(&src_in6, rt->rt_ifp, &outzone)) {
 460                 /* XXX: this should not happen */
 461                 ip6stat.ip6s_cantforward++;
 462                 ip6stat.ip6s_badscope++;
 463                 m_freem(m);
 464                 return (NULL);
 465         }
 466         if (in6_setscope(&src_in6, m->m_pkthdr.rcvif, &inzone)) {
 467                 ip6stat.ip6s_cantforward++;
 468                 ip6stat.ip6s_badscope++;
 469                 m_freem(m);
 470                 return (NULL);
 471         }
 472
 473         if (inzone != outzone && !proxy) {
 474                 ip6stat.ip6s_cantforward++;
 475                 ip6stat.ip6s_badscope++;
 476                 in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard);
 477
 478                 if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
 479                         ip6_log_time = timenow.tv_sec;
 480                         log(LOG_DEBUG,
 481                             "cannot forward "
 482                             "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
 483                             ip6_sprintf(&ip6->ip6_src),
 484                             ip6_sprintf(&ip6->ip6_dst),
 485                             ip6->ip6_nxt,
 486                             if_name(m->m_pkthdr.rcvif), if_name(rt->rt_ifp));
 487                 }
 488                 /* Release extra ref */
 489                 RT_REMREF_LOCKED(rt);
 490                 RT_UNLOCK(rt);
 491                 if (mcopy) {
 492                         icmp6_error(mcopy, ICMP6_DST_UNREACH,
 493                                     ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
 494                 }
 495                 m_freem(m);
 496                 return (NULL);
 497         }
 498
 499         /*
 500          * Destination scope check: if a packet is going to break the scope
 501          * zone of packet's destination address, discard it.  This case should
 502          * usually be prevented by appropriately-configured routing table, but
 503          * we need an explicit check because we may mistakenly forward the
 504          * packet to a different zone by (e.g.) a default route.
 505          */
 506         dst_in6 = ip6->ip6_dst;
 507         if (in6_setscope(&dst_in6, m->m_pkthdr.rcvif, &inzone) != 0 ||
 508             in6_setscope(&dst_in6, rt->rt_ifp, &outzone) != 0 ||
 509             inzone != outzone) {
 510                 ip6stat.ip6s_cantforward++;
 511                 ip6stat.ip6s_badscope++;
 512                 m_freem(m);
 513                 return (NULL);
 514         }
 515
 516         if (m->m_pkthdr.len > rt->rt_ifp->if_mtu) {
 517                 in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);
 518                 if (mcopy) {
 519                         uint32_t mtu;
 520 #if IPSEC
 521                         struct secpolicy *sp2;
 522                         int ipsecerror;
 523                         size_t ipsechdrsiz;
 524 #endif
 525
 526                         mtu = rt->rt_ifp->if_mtu;
 527 #if IPSEC
 528                         /*
 529                          * When we do IPsec tunnel ingress, we need to play
 530                          * with the link value (decrement IPsec header size
 531                          * from mtu value).  The code is much simpler than v4
 532                          * case, as we have the outgoing interface for
 533                          * encapsulated packet as "rt->rt_ifp".
 534                          */
 535                         sp2 = ipsec6_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,
 536                                 IP_FORWARDING, &ipsecerror);
 537                         if (sp2) {
 538                                 ipsechdrsiz = ipsec6_hdrsiz(mcopy,
 539                                         IPSEC_DIR_OUTBOUND, NULL);
 540                                 if (ipsechdrsiz < mtu)
 541                                         mtu -= ipsechdrsiz;
 542                                 key_freesp(sp2, KEY_SADB_UNLOCKED);
 543                         }
 544                         /*
 545                          * if mtu becomes less than minimum MTU,
 546                          * tell minimum MTU (and I'll need to fragment it).
 547                          */
 548                         if (mtu < IPV6_MMTU)
 549                                 mtu = IPV6_MMTU;
 550 #endif
 551                         /* Release extra ref */
 552                         RT_REMREF_LOCKED(rt);
 553                         RT_UNLOCK(rt);
 554                         icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, mtu);
 555                 } else {
 556                         /* Release extra ref */
 557                         RT_REMREF_LOCKED(rt);
 558                         RT_UNLOCK(rt);
 559                 }
 560                 m_freem(m);
 561                 return (NULL);
 562         }
 563
 564         if (rt->rt_flags & RTF_GATEWAY)
 565                 dst = (struct sockaddr_in6 *)(void *)rt->rt_gateway;
 566
 567         /*
 568          * If we are to forward the packet using the same interface
 569          * as one we got the packet from, perhaps we should send a redirect
 570          * to sender to shortcut a hop.
 571          * Only send redirect if source is sending directly to us,
 572          * and if packet was not source routed (or has any options).
 573          * Also, don't send redirect if forwarding using a route
 574          * modified by a redirect.
 575          */
 576         if (!proxy &&
 577             ip6_sendredirects && rt->rt_ifp == m->m_pkthdr.rcvif && !srcrt &&
 578             (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
 579                 if ((rt->rt_ifp->if_flags & IFF_POINTOPOINT) != 0) {
 580                         /*
 581                          * If the incoming interface is equal to the outgoing
 582                          * one, and the link attached to the interface is
 583                          * point-to-point, then it will be highly probable
 584                          * that a routing loop occurs. Thus, we immediately
 585                          * drop the packet and send an ICMPv6 error message.
 586                          *
 587                          * type/code is based on suggestion by Rich Draves.
 588                          * not sure if it is the best pick.
 589                          */
 590                         RT_REMREF_LOCKED(rt);   /* Release extra ref */
 591                         RT_UNLOCK(rt);
 592                         icmp6_error(mcopy, ICMP6_DST_UNREACH,
 593                                     ICMP6_DST_UNREACH_ADDR, 0);
 594                         m_freem(m);
 595                         return (NULL);
 596                 }
 597                 type = ND_REDIRECT;
 598         }
 599
 600 #if IPFW2
 601         /*
 602          * Check with the firewall...
 603          */
 604         if (ip6_fw_enable && ip6_fw_chk_ptr) {
 605                 u_short port = 0;
 606                 ifp = rt->rt_ifp;
 607                 /* Drop the lock but retain the extra ref */
 608                 RT_UNLOCK(rt);
 609                 /* If ipfw says divert, we have to just drop packet */
 610                 if (ip6_fw_chk_ptr(&ip6, ifp, &port, &m)) {
 611                         m_freem(m);
 612                         goto freecopy;
 613                 }
 614                 if (!m) {
 615                         goto freecopy;
 616                 }
 617                 /* We still have the extra ref on rt */
 618                 RT_LOCK(rt);
 619         }
 620 #endif
 621
 622         /*
 623          * Fake scoped addresses. Note that even link-local source or
 624          * destinaion can appear, if the originating node just sends the
 625          * packet to us (without address resolution for the destination).
 626          * Since both icmp6_error and icmp6_redirect_output fill the embedded
 627          * link identifiers, we can do this stuff after making a copy for
 628          * returning an error.
 629          */
 630         if ((rt->rt_ifp->if_flags & IFF_LOOPBACK) != 0) {
 631                 /*
 632                  * See corresponding comments in ip6_output.
 633                  * XXX: but is it possible that ip6_forward() sends a packet
 634                  *      to a loopback interface? I don't think so, and thus
 635                  *      I bark here. (jinmei@kame.net)
 636                  * XXX: it is common to route invalid packets to loopback.
 637                  *      also, the codepath will be visited on use of ::1 in
 638                  *      rthdr. (itojun)
 639                  */
 640 #if 1
 641                 if (0)
 642 #else
 643                 if ((rt->rt_flags & (RTF_BLACKHOLE|RTF_REJECT)) == 0)
 644 #endif
 645                 {
 646                         printf("ip6_forward: outgoing interface is loopback. "
 647                                 "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
 648                                 ip6_sprintf(&ip6->ip6_src),
 649                                 ip6_sprintf(&ip6->ip6_dst),
 650                                 ip6->ip6_nxt, if_name(m->m_pkthdr.rcvif),
 651                                 if_name(rt->rt_ifp));
 652                 }
 653
 654                 /* we can just use rcvif in forwarding. */
 655                 origifp = m->m_pkthdr.rcvif;
 656         }
 657         else
 658                 origifp = rt->rt_ifp;
 659         /*
 660          * clear embedded scope identifiers if necessary.
 661          * in6_clearscope will touch the addresses only when necessary.
 662          */
 663         in6_clearscope(&ip6->ip6_src);
 664         in6_clearscope(&ip6->ip6_dst);
 665
 666         ifp = rt->rt_ifp;
 667         /* Drop the lock but retain the extra ref */
 668         RT_UNLOCK(rt);
 669
 670         /*
 671          * If this is to be processed locally, let ip6_input have it.
 672          */
 673         if (proxy) {
 674                 VERIFY(m->m_pkthdr.aux_flags & MAUXF_PROXY_DST);
 675                 /* Release extra ref */
 676                 RT_REMREF(rt);
 677                 if (mcopy != NULL)
 678                         m_freem(mcopy);
 679                 return (m);
 680         }
 681
 682 #if PF
 683         /* Invoke outbound packet filter */
 684         error = pf_af_hook(ifp, NULL, &m, AF_INET6, FALSE, NULL);
 685
 686         if (error != 0 || m == NULL) {
 687                 if (m != NULL) {
 688                         panic("%s: unexpected packet %p\n", __func__, m);
 689                         /* NOTREACHED */
 690                 }
 691                 /* Already freed by callee */
 692                 goto senderr;
 693         }
 694         ip6 = mtod(m, struct ip6_hdr *);
 695 #endif /* PF */
 696
 697         error = nd6_output(ifp, origifp, m, dst, rt, NULL);
 698         if (error) {
 699                 in6_ifstat_inc(ifp, ifs6_out_discard);
 700                 ip6stat.ip6s_cantforward++;
 701         } else {
 702                 ip6stat.ip6s_forward++;
 703                 in6_ifstat_inc(ifp, ifs6_out_forward);
 704                 if (type)
 705                         ip6stat.ip6s_redirectsent++;
 706                 else {
 707                         if (mcopy) {
 708                                 goto freecopy;
 709                         }
 710                 }
 711         }
 712 #if PF
 713 senderr:
 714 #endif /* PF */
 715         if (mcopy == NULL) {
 716                 /* Release extra ref */
 717                 RT_REMREF(rt);
 718                 return (NULL);
 719         }
 720         switch (error) {
 721         case 0:
 722 #if 1
 723                 if (type == ND_REDIRECT) {
 724                         icmp6_redirect_output(mcopy, rt);
 725                         /* Release extra ref */
 726                         RT_REMREF(rt);
 727                         return (NULL);
 728                 }
 729 #endif
 730                 goto freecopy;
 731
 732         case EMSGSIZE:
 733                 /* xxx MTU is constant in PPP? */
 734                 goto freecopy;
 735
 736         case ENOBUFS:
 737                 /* Tell source to slow down like source quench in IP? */
 738                 goto freecopy;
 739
 740         case ENETUNREACH:       /* shouldn't happen, checked above */
 741         case EHOSTUNREACH:
 742         case ENETDOWN:
 743         case EHOSTDOWN:
 744         default:
 745                 type = ICMP6_DST_UNREACH;
 746                 code = ICMP6_DST_UNREACH_ADDR;
 747                 break;
 748         }
 749         icmp6_error(mcopy, type, code, 0);
 750         /* Release extra ref */
 751         RT_REMREF(rt);
 752         return (NULL);
 753
 754  freecopy:
 755         m_freem(mcopy);
 756         /* Release extra ref */
 757         RT_REMREF(rt);
 758         return (NULL);
 759 }