bsd/netinet6/ip6_forward.c

   1 /*      $FreeBSD: src/sys/netinet6/ip6_forward.c,v 1.16 2002/10/16 02:25:05 sam Exp $   */
   2 /*      $KAME: ip6_forward.c,v 1.69 2001/05/17 03:48:30 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
  34 #include <sys/param.h>
  35 #include <sys/systm.h>
  36 #include <sys/malloc.h>
  37 #include <sys/mbuf.h>
  38 #include <sys/domain.h>
  39 #include <sys/protosw.h>
  40 #include <sys/socket.h>
  41 #include <sys/errno.h>
  42 #include <sys/time.h>
  43 #include <sys/kernel.h>
  44 #include <sys/syslog.h>
  45
  46 #include <net/if.h>
  47 #include <net/route.h>
  48
  49 #include <netinet/in.h>
  50 #include <netinet/in_var.h>
  51 #include <netinet/in_systm.h>
  52 #include <netinet/ip.h>
  53 #include <netinet/ip_var.h>
  54 #include <netinet6/in6_var.h>
  55 #include <netinet/ip6.h>
  56 #include <netinet6/ip6_var.h>
  57 #include <netinet/icmp6.h>
  58 #include <netinet6/nd6.h>
  59
  60 #include <netinet/in_pcb.h>
  61
  62 #if IPSEC
  63 #include <netinet6/ipsec.h>
  64 #if INET6
  65 #include <netinet6/ipsec6.h>
  66 #endif
  67 #include <netkey/key.h>
  68 extern int ipsec_bypass;
  69 #endif /* IPSEC */
  70 extern lck_mtx_t *ip6_mutex;
  71
  72 #include <netinet6/ip6_fw.h>
  73
  74 #include <net/net_osdep.h>
  75
  76 /*
  77  * Forward a packet.  If some error occurs return the sender
  78  * an icmp packet.  Note we can't always generate a meaningful
  79  * icmp message because icmp doesn't have a large enough repertoire
  80  * of codes and types.
  81  *
  82  * If not forwarding, just drop the packet.  This could be confusing
  83  * if ipforwarding was zero but some routing protocol was advancing
  84  * us as a gateway to somewhere.  However, we must let the routing
  85  * protocol deal with that.
  86  *
  87  */
  88
  89 void
  90 ip6_forward(struct mbuf *m, struct route_in6 *ip6forward_rt,
  91     int srcrt, int locked)
  92 {
  93         struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
  94         struct sockaddr_in6 *dst;
  95         struct rtentry *rt;
  96         int error, type = 0, code = 0;
  97         struct mbuf *mcopy = NULL;
  98         struct ifnet *origifp;  /* maybe unnecessary */
  99 #if IPSEC
 100         struct secpolicy *sp = NULL;
 101 #endif
 102         struct timeval timenow;
 103         int     tunneledv4 = 0;
 104
 105         getmicrotime(&timenow);
 106
 107
 108 #if IPSEC
 109         /*
 110          * Check AH/ESP integrity.
 111          */
 112         /*
 113          * Don't increment ip6s_cantforward because this is the check
 114          * before forwarding packet actually.
 115          */
 116         if (ipsec_bypass == 0) {
 117                 if (ipsec6_in_reject(m, NULL)) {
 118                         IPSEC_STAT_INCREMENT(ipsec6stat.in_polvio);
 119                         m_freem(m);
 120                         return;
 121                 }
 122         }
 123 #endif /*IPSEC*/
 124
 125         /*
 126          * Do not forward packets to multicast destination (should be handled
 127          * by ip6_mforward().
 128          * Do not forward packets with unspecified source.  It was discussed
 129          * in July 2000, on ipngwg mailing list.
 130          */
 131         if ((m->m_flags & (M_BCAST|M_MCAST)) != 0 ||
 132             IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
 133             IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 134                 ip6stat.ip6s_cantforward++;
 135                 /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
 136                 if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
 137                         ip6_log_time = timenow.tv_sec;
 138                         log(LOG_DEBUG,
 139                             "cannot forward "
 140                             "from %s to %s nxt %d received on %s\n",
 141                             ip6_sprintf(&ip6->ip6_src),
 142                             ip6_sprintf(&ip6->ip6_dst),
 143                             ip6->ip6_nxt,
 144                             if_name(m->m_pkthdr.rcvif));
 145                 }
 146                 m_freem(m);
 147                 return;
 148         }
 149
 150         if (ip6->ip6_hlim <= IPV6_HLIMDEC) {
 151                 /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
 152                 if (locked)
 153                         lck_mtx_unlock(ip6_mutex);
 154                 icmp6_error(m, ICMP6_TIME_EXCEEDED,
 155                                 ICMP6_TIME_EXCEED_TRANSIT, 0);
 156                 if (locked)
 157                         lck_mtx_lock(ip6_mutex);
 158                 return;
 159         }
 160         ip6->ip6_hlim -= IPV6_HLIMDEC;
 161
 162         /*
 163          * Save at most ICMPV6_PLD_MAXLEN (= the min IPv6 MTU -
 164          * size of IPv6 + ICMPv6 headers) bytes of the packet in case
 165          * we need to generate an ICMP6 message to the src.
 166          * Thanks to M_EXT, in most cases copy will not occur.
 167          *
 168          * It is important to save it before IPsec processing as IPsec
 169          * processing may modify the mbuf.
 170          */
 171         mcopy = m_copy(m, 0, imin(m->m_pkthdr.len, ICMPV6_PLD_MAXLEN));
 172
 173 #if IPSEC
 174         if (ipsec_bypass != 0)
 175                 goto skip_ipsec;
 176         /* get a security policy for this packet */
 177         sp = ipsec6_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND, IP_FORWARDING,
 178             &error);
 179         if (sp == NULL) {
 180                 IPSEC_STAT_INCREMENT(ipsec6stat.out_inval);
 181                 ip6stat.ip6s_cantforward++;
 182                 if (mcopy) {
 183 #if 0
 184                         /* XXX: what icmp ? */
 185 #else
 186                         m_freem(mcopy);
 187 #endif
 188                 }
 189                 m_freem(m);
 190                 return;
 191         }
 192
 193         error = 0;
 194
 195         /* check policy */
 196         switch (sp->policy) {
 197         case IPSEC_POLICY_DISCARD:
 198         case IPSEC_POLICY_GENERATE:
 199                 /*
 200                  * This packet is just discarded.
 201                  */
 202                 IPSEC_STAT_INCREMENT(ipsec6stat.out_polvio);
 203                 ip6stat.ip6s_cantforward++;
 204                 key_freesp(sp, KEY_SADB_UNLOCKED);
 205                 if (mcopy) {
 206 #if 0
 207                         /* XXX: what icmp ? */
 208 #else
 209                         m_freem(mcopy);
 210 #endif
 211                 }
 212                 m_freem(m);
 213                 return;
 214
 215         case IPSEC_POLICY_BYPASS:
 216         case IPSEC_POLICY_NONE:
 217                 /* no need to do IPsec. */
 218                 key_freesp(sp, KEY_SADB_UNLOCKED);
 219                 goto skip_ipsec;
 220
 221         case IPSEC_POLICY_IPSEC:
 222                 if (sp->req == NULL) {
 223                         /* XXX should be panic ? */
 224                         printf("ip6_forward: No IPsec request specified.\n");
 225                         ip6stat.ip6s_cantforward++;
 226                         key_freesp(sp, KEY_SADB_UNLOCKED);
 227                         if (mcopy) {
 228 #if 0
 229                                 /* XXX: what icmp ? */
 230 #else
 231                                 m_freem(mcopy);
 232 #endif
 233                         }
 234                         m_freem(m);
 235                         return;
 236                 }
 237                 /* do IPsec */
 238                 break;
 239
 240         case IPSEC_POLICY_ENTRUST:
 241         default:
 242                 /* should be panic ?? */
 243                 printf("ip6_forward: Invalid policy found. %d\n", sp->policy);
 244                 key_freesp(sp, KEY_SADB_UNLOCKED);
 245                 goto skip_ipsec;
 246         }
 247
 248     {
 249         struct ipsec_output_state state;
 250
 251         /*
 252          * All the extension headers will become inaccessible
 253          * (since they can be encrypted).
 254          * Don't panic, we need no more updates to extension headers
 255          * on inner IPv6 packet (since they are now encapsulated).
 256          *
 257          * IPv6 [ESP|AH] IPv6 [extension headers] payload
 258          */
 259         bzero(&state, sizeof(state));
 260         state.m = m;
 261         state.ro = NULL;        /* update at ipsec6_output_tunnel() */
 262         state.dst = NULL;       /* update at ipsec6_output_tunnel() */
 263
 264         if (locked)
 265                 lck_mtx_unlock(ip6_mutex);
 266         error = ipsec6_output_tunnel(&state, sp, 0, &tunneledv4);
 267         if (locked)
 268                 lck_mtx_lock(ip6_mutex);
 269         key_freesp(sp, KEY_SADB_UNLOCKED);
 270         if (tunneledv4)
 271                 return;  /* packet is gone - sent over IPv4 */
 272
 273         m = state.m;
 274         if (error) {
 275                 /* mbuf is already reclaimed in ipsec6_output_tunnel. */
 276                 switch (error) {
 277                 case EHOSTUNREACH:
 278                 case ENETUNREACH:
 279                 case EMSGSIZE:
 280                 case ENOBUFS:
 281                 case ENOMEM:
 282                         break;
 283                 default:
 284                         printf("ip6_output (ipsec): error code %d\n", error);
 285                         /* fall through */
 286                 case ENOENT:
 287                         /* don't show these error codes to the user */
 288                         break;
 289                 }
 290                 ip6stat.ip6s_cantforward++;
 291                 if (mcopy) {
 292 #if 0
 293                         /* XXX: what icmp ? */
 294 #else
 295                         m_freem(mcopy);
 296 #endif
 297                 }
 298                 m_freem(m);
 299                 return;
 300         }
 301     }
 302     skip_ipsec:
 303 #endif /* IPSEC */
 304
 305         dst = (struct sockaddr_in6 *)&ip6forward_rt->ro_dst;
 306         if (!srcrt) {
 307                 /*
 308                  * ip6forward_rt->ro_dst.sin6_addr is equal to ip6->ip6_dst
 309                  */
 310                 if (ip6forward_rt->ro_rt == 0 ||
 311                     (ip6forward_rt->ro_rt->rt_flags & RTF_UP) == 0) {
 312                         if (ip6forward_rt->ro_rt) {
 313                                 rtfree(ip6forward_rt->ro_rt);
 314                                 ip6forward_rt->ro_rt = 0;
 315                         }
 316                         /* this probably fails but give it a try again */
 317                         rtalloc_ign((struct route *)ip6forward_rt,
 318                                     RTF_PRCLONING);
 319                 }
 320
 321                 if (ip6forward_rt->ro_rt == 0) {
 322                         ip6stat.ip6s_noroute++;
 323                         in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
 324                         if (mcopy) {
 325                                 if (locked)
 326                                         lck_mtx_unlock(ip6_mutex);
 327                                 icmp6_error(mcopy, ICMP6_DST_UNREACH,
 328                                             ICMP6_DST_UNREACH_NOROUTE, 0);
 329                                 if (locked)
 330                                         lck_mtx_lock(ip6_mutex);
 331                         }
 332                         m_freem(m);
 333                         return;
 334                 }
 335         } else if ((rt = ip6forward_rt->ro_rt) == 0 ||
 336                  !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &dst->sin6_addr)) {
 337                 if (ip6forward_rt->ro_rt) {
 338                         rtfree(ip6forward_rt->ro_rt);
 339                         ip6forward_rt->ro_rt = 0;
 340                 }
 341                 bzero(dst, sizeof(*dst));
 342                 dst->sin6_len = sizeof(struct sockaddr_in6);
 343                 dst->sin6_family = AF_INET6;
 344                 dst->sin6_addr = ip6->ip6_dst;
 345
 346                 rtalloc_ign((struct route *)ip6forward_rt, RTF_PRCLONING);
 347                 if (ip6forward_rt->ro_rt == 0) {
 348                         ip6stat.ip6s_noroute++;
 349                         in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
 350                         if (mcopy) {
 351                                 if (locked)
 352                                         lck_mtx_unlock(ip6_mutex);
 353                                 icmp6_error(mcopy, ICMP6_DST_UNREACH,
 354                                             ICMP6_DST_UNREACH_NOROUTE, 0);
 355                                 if (locked)
 356                                         lck_mtx_lock(ip6_mutex);
 357                         }
 358                         m_freem(m);
 359                         return;
 360                 }
 361         }
 362         rt = ip6forward_rt->ro_rt;
 363
 364         /*
 365          * Scope check: if a packet can't be delivered to its destination
 366          * for the reason that the destination is beyond the scope of the
 367          * source address, discard the packet and return an icmp6 destination
 368          * unreachable error with Code 2 (beyond scope of source address).
 369          * [draft-ietf-ipngwg-icmp-v3-02.txt, Section 3.1]
 370          */
 371         if (in6_addr2scopeid(m->m_pkthdr.rcvif, &ip6->ip6_src) !=
 372             in6_addr2scopeid(rt->rt_ifp, &ip6->ip6_src)) {
 373                 ip6stat.ip6s_cantforward++;
 374                 ip6stat.ip6s_badscope++;
 375                 in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard);
 376
 377                 if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
 378                         ip6_log_time = timenow.tv_sec;
 379                         log(LOG_DEBUG,
 380                             "cannot forward "
 381                             "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
 382                             ip6_sprintf(&ip6->ip6_src),
 383                             ip6_sprintf(&ip6->ip6_dst),
 384                             ip6->ip6_nxt,
 385                             if_name(m->m_pkthdr.rcvif), if_name(rt->rt_ifp));
 386                 }
 387                 if (mcopy) {
 388                         if (locked)
 389                                 lck_mtx_unlock(ip6_mutex);
 390                         icmp6_error(mcopy, ICMP6_DST_UNREACH,
 391                                     ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
 392                         if (locked)
 393                                 lck_mtx_lock(ip6_mutex);
 394                 }
 395                 m_freem(m);
 396                 return;
 397         }
 398
 399         if (m->m_pkthdr.len > rt->rt_ifp->if_mtu) {
 400                 in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);
 401                 if (mcopy) {
 402                         u_long mtu;
 403 #if IPSEC
 404                         struct secpolicy *sp2;
 405                         int ipsecerror;
 406                         size_t ipsechdrsiz;
 407 #endif
 408
 409                         mtu = rt->rt_ifp->if_mtu;
 410 #if IPSEC
 411                         /*
 412                          * When we do IPsec tunnel ingress, we need to play
 413                          * with if_mtu value (decrement IPsec header size
 414                          * from mtu value).  The code is much simpler than v4
 415                          * case, as we have the outgoing interface for
 416                          * encapsulated packet as "rt->rt_ifp".
 417                          */
 418                         sp2 = ipsec6_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,
 419                                 IP_FORWARDING, &ipsecerror);
 420                         if (sp2) {
 421                                 ipsechdrsiz = ipsec6_hdrsiz(mcopy,
 422                                         IPSEC_DIR_OUTBOUND, NULL);
 423                                 if (ipsechdrsiz < mtu)
 424                                         mtu -= ipsechdrsiz;
 425                                 key_freesp(sp2, KEY_SADB_UNLOCKED);
 426                         }
 427                         /*
 428                          * if mtu becomes less than minimum MTU,
 429                          * tell minimum MTU (and I'll need to fragment it).
 430                          */
 431                         if (mtu < IPV6_MMTU)
 432                                 mtu = IPV6_MMTU;
 433 #endif
 434                         if (locked)
 435                                 lck_mtx_unlock(ip6_mutex);
 436                         icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, mtu);
 437                         if (locked)
 438                                 lck_mtx_lock(ip6_mutex);
 439                 }
 440                 m_freem(m);
 441                 return;
 442         }
 443
 444         if (rt->rt_flags & RTF_GATEWAY)
 445                 dst = (struct sockaddr_in6 *)rt->rt_gateway;
 446
 447         /*
 448          * If we are to forward the packet using the same interface
 449          * as one we got the packet from, perhaps we should send a redirect
 450          * to sender to shortcut a hop.
 451          * Only send redirect if source is sending directly to us,
 452          * and if packet was not source routed (or has any options).
 453          * Also, don't send redirect if forwarding using a route
 454          * modified by a redirect.
 455          */
 456         if (rt->rt_ifp == m->m_pkthdr.rcvif && !srcrt &&
 457             (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
 458                 if ((rt->rt_ifp->if_flags & IFF_POINTOPOINT) != 0) {
 459                         /*
 460                          * If the incoming interface is equal to the outgoing
 461                          * one, and the link attached to the interface is
 462                          * point-to-point, then it will be highly probable
 463                          * that a routing loop occurs. Thus, we immediately
 464                          * drop the packet and send an ICMPv6 error message.
 465                          *
 466                          * type/code is based on suggestion by Rich Draves.
 467                          * not sure if it is the best pick.
 468                          */
 469                         if (locked)
 470                                 lck_mtx_unlock(ip6_mutex);
 471                         icmp6_error(mcopy, ICMP6_DST_UNREACH,
 472                                     ICMP6_DST_UNREACH_ADDR, 0);
 473                         if (locked)
 474                                 lck_mtx_lock(ip6_mutex);
 475                         m_freem(m);
 476                         return;
 477                 }
 478                 type = ND_REDIRECT;
 479         }
 480
 481         /*
 482          * Check with the firewall...
 483          */
 484         if (ip6_fw_enable && ip6_fw_chk_ptr) {
 485                 u_short port = 0;
 486                 /* If ipfw says divert, we have to just drop packet */
 487                 if (ip6_fw_chk_ptr(&ip6, rt->rt_ifp, &port, &m)) {
 488                         m_freem(m);
 489                         goto freecopy;
 490                 }
 491                 if (!m)
 492                         goto freecopy;
 493         }
 494
 495         /*
 496          * Fake scoped addresses. Note that even link-local source or
 497          * destinaion can appear, if the originating node just sends the
 498          * packet to us (without address resolution for the destination).
 499          * Since both icmp6_error and icmp6_redirect_output fill the embedded
 500          * link identifiers, we can do this stuff after making a copy for
 501          * returning an error.
 502          */
 503         if ((rt->rt_ifp->if_flags & IFF_LOOPBACK) != 0) {
 504                 /*
 505                  * See corresponding comments in ip6_output.
 506                  * XXX: but is it possible that ip6_forward() sends a packet
 507                  *      to a loopback interface? I don't think so, and thus
 508                  *      I bark here. (jinmei@kame.net)
 509                  * XXX: it is common to route invalid packets to loopback.
 510                  *      also, the codepath will be visited on use of ::1 in
 511                  *      rthdr. (itojun)
 512                  */
 513 #if 1
 514                 if (0)
 515 #else
 516                 if ((rt->rt_flags & (RTF_BLACKHOLE|RTF_REJECT)) == 0)
 517 #endif
 518                 {
 519                         printf("ip6_forward: outgoing interface is loopback. "
 520                                 "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
 521                                 ip6_sprintf(&ip6->ip6_src),
 522                                 ip6_sprintf(&ip6->ip6_dst),
 523                                 ip6->ip6_nxt, if_name(m->m_pkthdr.rcvif),
 524                                 if_name(rt->rt_ifp));
 525                 }
 526
 527                 /* we can just use rcvif in forwarding. */
 528                 origifp = m->m_pkthdr.rcvif;
 529         }
 530         else
 531                 origifp = rt->rt_ifp;
 532 #ifndef SCOPEDROUTING
 533         /*
 534          * clear embedded scope identifiers if necessary.
 535          * in6_clearscope will touch the addresses only when necessary.
 536          */
 537         in6_clearscope(&ip6->ip6_src);
 538         in6_clearscope(&ip6->ip6_dst);
 539 #endif
 540
 541         error = nd6_output(rt->rt_ifp, origifp, m, dst, rt, locked);
 542         if (error) {
 543                 in6_ifstat_inc(rt->rt_ifp, ifs6_out_discard);
 544                 ip6stat.ip6s_cantforward++;
 545         } else {
 546                 ip6stat.ip6s_forward++;
 547                 in6_ifstat_inc(rt->rt_ifp, ifs6_out_forward);
 548                 if (type)
 549                         ip6stat.ip6s_redirectsent++;
 550                 else {
 551                         if (mcopy)
 552                                 goto freecopy;
 553                 }
 554         }
 555         if (mcopy == NULL)
 556                 return;
 557
 558         switch (error) {
 559         case 0:
 560 #if 1
 561                 if (type == ND_REDIRECT) {
 562                         icmp6_redirect_output(mcopy, rt);
 563                         return;
 564                 }
 565 #endif
 566                 goto freecopy;
 567
 568         case EMSGSIZE:
 569                 /* xxx MTU is constant in PPP? */
 570                 goto freecopy;
 571
 572         case ENOBUFS:
 573                 /* Tell source to slow down like source quench in IP? */
 574                 goto freecopy;
 575
 576         case ENETUNREACH:       /* shouldn't happen, checked above */
 577         case EHOSTUNREACH:
 578         case ENETDOWN:
 579         case EHOSTDOWN:
 580         default:
 581                 type = ICMP6_DST_UNREACH;
 582                 code = ICMP6_DST_UNREACH_ADDR;
 583                 break;
 584         }
 585         if (locked)
 586                 lck_mtx_unlock(ip6_mutex);
 587         icmp6_error(mcopy, type, code, 0);
 588         if (locked)
 589                 lck_mtx_lock(ip6_mutex);
 590         return;
 591
 592  freecopy:
 593         m_freem(mcopy);
 594         return;
 595 }