The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/netinet6/frag6.c

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    1 /*      $FreeBSD$       */
    2 /*      $KAME: frag6.c,v 1.33 2002/01/07 11:34:48 kjc Exp $     */
    3 
    4 /*-
    5  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
    6  * All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. Neither the name of the project nor the names of its contributors
   17  *    may be used to endorse or promote products derived from this software
   18  *    without specific prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  */
   32 
   33 #include <sys/param.h>
   34 #include <sys/systm.h>
   35 #include <sys/malloc.h>
   36 #include <sys/mbuf.h>
   37 #include <sys/domain.h>
   38 #include <sys/protosw.h>
   39 #include <sys/socket.h>
   40 #include <sys/errno.h>
   41 #include <sys/time.h>
   42 #include <sys/kernel.h>
   43 #include <sys/syslog.h>
   44 
   45 #include <net/if.h>
   46 #include <net/route.h>
   47 
   48 #include <netinet/in.h>
   49 #include <netinet/in_var.h>
   50 #include <netinet/ip6.h>
   51 #include <netinet6/ip6_var.h>
   52 #include <netinet/icmp6.h>
   53 #include <netinet/in_systm.h>   /* for ECN definitions */
   54 #include <netinet/ip.h>         /* for ECN definitions */
   55 
   56 /*
   57  * Define it to get a correct behavior on per-interface statistics.
   58  * You will need to perform an extra routing table lookup, per fragment,
   59  * to do it.  This may, or may not be, a performance hit.
   60  */
   61 #define IN6_IFSTAT_STRICT
   62 
   63 static void frag6_enq __P((struct ip6asfrag *, struct ip6asfrag *));
   64 static void frag6_deq __P((struct ip6asfrag *));
   65 static void frag6_insque __P((struct ip6q *, struct ip6q *));
   66 static void frag6_remque __P((struct ip6q *));
   67 static void frag6_freef __P((struct ip6q *));
   68 
   69 static struct mtx ip6qlock;
   70 /*
   71  * These fields all protected by ip6qlock.
   72  */
   73 static u_int frag6_nfragpackets;
   74 static u_int frag6_nfrags;
   75 static struct   ip6q ip6q;      /* ip6 reassemble queue */
   76 
   77 #define IP6Q_LOCK_INIT()        mtx_init(&ip6qlock, "ip6qlock", NULL, MTX_DEF);
   78 #define IP6Q_LOCK()             mtx_lock(&ip6qlock)
   79 #define IP6Q_TRYLOCK()          mtx_trylock(&ip6qlock)
   80 #define IP6Q_LOCK_ASSERT()      mtx_assert(&ip6qlock, MA_OWNED)
   81 #define IP6Q_UNLOCK()           mtx_unlock(&ip6qlock)
   82 
   83 static MALLOC_DEFINE(M_FTABLE, "fragment", "fragment reassembly header");
   84 
   85 /*
   86  * Initialise reassembly queue and fragment identifier.
   87  */
   88 static void
   89 frag6_change(void *tag)
   90 {
   91 
   92         ip6_maxfragpackets = nmbclusters / 4;
   93         ip6_maxfrags = nmbclusters / 4;
   94 }
   95 
   96 void
   97 frag6_init(void)
   98 {
   99 
  100         ip6_maxfragpackets = nmbclusters / 4;
  101         ip6_maxfrags = nmbclusters / 4;
  102         EVENTHANDLER_REGISTER(nmbclusters_change,
  103             frag6_change, NULL, EVENTHANDLER_PRI_ANY);
  104 
  105         IP6Q_LOCK_INIT();
  106 
  107         ip6q.ip6q_next = ip6q.ip6q_prev = &ip6q;
  108 }
  109 
  110 /*
  111  * In RFC2460, fragment and reassembly rule do not agree with each other,
  112  * in terms of next header field handling in fragment header.
  113  * While the sender will use the same value for all of the fragmented packets,
  114  * receiver is suggested not to check the consistency.
  115  *
  116  * fragment rule (p20):
  117  *      (2) A Fragment header containing:
  118  *      The Next Header value that identifies the first header of
  119  *      the Fragmentable Part of the original packet.
  120  *              -> next header field is same for all fragments
  121  *
  122  * reassembly rule (p21):
  123  *      The Next Header field of the last header of the Unfragmentable
  124  *      Part is obtained from the Next Header field of the first
  125  *      fragment's Fragment header.
  126  *              -> should grab it from the first fragment only
  127  *
  128  * The following note also contradicts with fragment rule - noone is going to
  129  * send different fragment with different next header field.
  130  *
  131  * additional note (p22):
  132  *      The Next Header values in the Fragment headers of different
  133  *      fragments of the same original packet may differ.  Only the value
  134  *      from the Offset zero fragment packet is used for reassembly.
  135  *              -> should grab it from the first fragment only
  136  *
  137  * There is no explicit reason given in the RFC.  Historical reason maybe?
  138  */
  139 /*
  140  * Fragment input
  141  */
  142 int
  143 frag6_input(struct mbuf **mp, int *offp, int proto)
  144 {
  145         struct mbuf *m = *mp, *t;
  146         struct ip6_hdr *ip6;
  147         struct ip6_frag *ip6f;
  148         struct ip6q *q6;
  149         struct ip6asfrag *af6, *ip6af, *af6dwn;
  150 #ifdef IN6_IFSTAT_STRICT
  151         struct in6_ifaddr *ia;
  152 #endif
  153         int offset = *offp, nxt, i, next;
  154         int first_frag = 0;
  155         int fragoff, frgpartlen;        /* must be larger than u_int16_t */
  156         struct ifnet *dstifp;
  157         u_int8_t ecn, ecn0;
  158 #if 0
  159         char ip6buf[INET6_ADDRSTRLEN];
  160 #endif
  161 
  162         ip6 = mtod(m, struct ip6_hdr *);
  163 #ifndef PULLDOWN_TEST
  164         IP6_EXTHDR_CHECK(m, offset, sizeof(struct ip6_frag), IPPROTO_DONE);
  165         ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);
  166 #else
  167         IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
  168         if (ip6f == NULL)
  169                 return (IPPROTO_DONE);
  170 #endif
  171 
  172         dstifp = NULL;
  173 #ifdef IN6_IFSTAT_STRICT
  174         /* find the destination interface of the packet. */
  175         if ((ia = ip6_getdstifaddr(m)) != NULL)
  176                 dstifp = ia->ia_ifp;
  177 #else
  178         /* we are violating the spec, this is not the destination interface */
  179         if ((m->m_flags & M_PKTHDR) != 0)
  180                 dstifp = m->m_pkthdr.rcvif;
  181 #endif
  182 
  183         /* jumbo payload can't contain a fragment header */
  184         if (ip6->ip6_plen == 0) {
  185                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
  186                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  187                 return IPPROTO_DONE;
  188         }
  189 
  190         /*
  191          * check whether fragment packet's fragment length is
  192          * multiple of 8 octets.
  193          * sizeof(struct ip6_frag) == 8
  194          * sizeof(struct ip6_hdr) = 40
  195          */
  196         if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
  197             (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
  198                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  199                     offsetof(struct ip6_hdr, ip6_plen));
  200                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  201                 return IPPROTO_DONE;
  202         }
  203 
  204         ip6stat.ip6s_fragments++;
  205         in6_ifstat_inc(dstifp, ifs6_reass_reqd);
  206 
  207         /* offset now points to data portion */
  208         offset += sizeof(struct ip6_frag);
  209 
  210         IP6Q_LOCK();
  211 
  212         /*
  213          * Enforce upper bound on number of fragments.
  214          * If maxfrag is 0, never accept fragments.
  215          * If maxfrag is -1, accept all fragments without limitation.
  216          */
  217         if (ip6_maxfrags < 0)
  218                 ;
  219         else if (frag6_nfrags >= (u_int)ip6_maxfrags)
  220                 goto dropfrag;
  221 
  222         for (q6 = ip6q.ip6q_next; q6 != &ip6q; q6 = q6->ip6q_next)
  223                 if (ip6f->ip6f_ident == q6->ip6q_ident &&
  224                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
  225                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst))
  226                         break;
  227 
  228         if (q6 == &ip6q) {
  229                 /*
  230                  * the first fragment to arrive, create a reassembly queue.
  231                  */
  232                 first_frag = 1;
  233 
  234                 /*
  235                  * Enforce upper bound on number of fragmented packets
  236                  * for which we attempt reassembly;
  237                  * If maxfragpackets is 0, never accept fragments.
  238                  * If maxfragpackets is -1, accept all fragments without
  239                  * limitation.
  240                  */
  241                 if (ip6_maxfragpackets < 0)
  242                         ;
  243                 else if (frag6_nfragpackets >= (u_int)ip6_maxfragpackets)
  244                         goto dropfrag;
  245                 frag6_nfragpackets++;
  246                 q6 = (struct ip6q *)malloc(sizeof(struct ip6q), M_FTABLE,
  247                     M_NOWAIT);
  248                 if (q6 == NULL)
  249                         goto dropfrag;
  250                 bzero(q6, sizeof(*q6));
  251 
  252                 frag6_insque(q6, &ip6q);
  253 
  254                 /* ip6q_nxt will be filled afterwards, from 1st fragment */
  255                 q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
  256 #ifdef notyet
  257                 q6->ip6q_nxtp   = (u_char *)nxtp;
  258 #endif
  259                 q6->ip6q_ident  = ip6f->ip6f_ident;
  260                 q6->ip6q_ttl    = IPV6_FRAGTTL;
  261                 q6->ip6q_src    = ip6->ip6_src;
  262                 q6->ip6q_dst    = ip6->ip6_dst;
  263                 q6->ip6q_ecn    =
  264                     (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
  265                 q6->ip6q_unfrglen = -1; /* The 1st fragment has not arrived. */
  266 
  267                 q6->ip6q_nfrag = 0;
  268         }
  269 
  270         /*
  271          * If it's the 1st fragment, record the length of the
  272          * unfragmentable part and the next header of the fragment header.
  273          */
  274         fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
  275         if (fragoff == 0) {
  276                 q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
  277                     sizeof(struct ip6_frag);
  278                 q6->ip6q_nxt = ip6f->ip6f_nxt;
  279         }
  280 
  281         /*
  282          * Check that the reassembled packet would not exceed 65535 bytes
  283          * in size.
  284          * If it would exceed, discard the fragment and return an ICMP error.
  285          */
  286         frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
  287         if (q6->ip6q_unfrglen >= 0) {
  288                 /* The 1st fragment has already arrived. */
  289                 if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
  290                         icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  291                             offset - sizeof(struct ip6_frag) +
  292                             offsetof(struct ip6_frag, ip6f_offlg));
  293                         IP6Q_UNLOCK();
  294                         return (IPPROTO_DONE);
  295                 }
  296         } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
  297                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  298                     offset - sizeof(struct ip6_frag) +
  299                     offsetof(struct ip6_frag, ip6f_offlg));
  300                 IP6Q_UNLOCK();
  301                 return (IPPROTO_DONE);
  302         }
  303         /*
  304          * If it's the first fragment, do the above check for each
  305          * fragment already stored in the reassembly queue.
  306          */
  307         if (fragoff == 0) {
  308                 for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  309                      af6 = af6dwn) {
  310                         af6dwn = af6->ip6af_down;
  311 
  312                         if (q6->ip6q_unfrglen + af6->ip6af_off + af6->ip6af_frglen >
  313                             IPV6_MAXPACKET) {
  314                                 struct mbuf *merr = IP6_REASS_MBUF(af6);
  315                                 struct ip6_hdr *ip6err;
  316                                 int erroff = af6->ip6af_offset;
  317 
  318                                 /* dequeue the fragment. */
  319                                 frag6_deq(af6);
  320                                 free(af6, M_FTABLE);
  321 
  322                                 /* adjust pointer. */
  323                                 ip6err = mtod(merr, struct ip6_hdr *);
  324 
  325                                 /*
  326                                  * Restore source and destination addresses
  327                                  * in the erroneous IPv6 header.
  328                                  */
  329                                 ip6err->ip6_src = q6->ip6q_src;
  330                                 ip6err->ip6_dst = q6->ip6q_dst;
  331 
  332                                 icmp6_error(merr, ICMP6_PARAM_PROB,
  333                                     ICMP6_PARAMPROB_HEADER,
  334                                     erroff - sizeof(struct ip6_frag) +
  335                                     offsetof(struct ip6_frag, ip6f_offlg));
  336                         }
  337                 }
  338         }
  339 
  340         ip6af = (struct ip6asfrag *)malloc(sizeof(struct ip6asfrag), M_FTABLE,
  341             M_NOWAIT);
  342         if (ip6af == NULL)
  343                 goto dropfrag;
  344         bzero(ip6af, sizeof(*ip6af));
  345         ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
  346         ip6af->ip6af_off = fragoff;
  347         ip6af->ip6af_frglen = frgpartlen;
  348         ip6af->ip6af_offset = offset;
  349         IP6_REASS_MBUF(ip6af) = m;
  350 
  351         if (first_frag) {
  352                 af6 = (struct ip6asfrag *)q6;
  353                 goto insert;
  354         }
  355 
  356         /*
  357          * Handle ECN by comparing this segment with the first one;
  358          * if CE is set, do not lose CE.
  359          * drop if CE and not-ECT are mixed for the same packet.
  360          */
  361         ecn = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
  362         ecn0 = q6->ip6q_ecn;
  363         if (ecn == IPTOS_ECN_CE) {
  364                 if (ecn0 == IPTOS_ECN_NOTECT) {
  365                         free(ip6af, M_FTABLE);
  366                         goto dropfrag;
  367                 }
  368                 if (ecn0 != IPTOS_ECN_CE)
  369                         q6->ip6q_ecn = IPTOS_ECN_CE;
  370         }
  371         if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
  372                 free(ip6af, M_FTABLE);
  373                 goto dropfrag;
  374         }
  375 
  376         /*
  377          * Find a segment which begins after this one does.
  378          */
  379         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  380              af6 = af6->ip6af_down)
  381                 if (af6->ip6af_off > ip6af->ip6af_off)
  382                         break;
  383 
  384 #if 0
  385         /*
  386          * If there is a preceding segment, it may provide some of
  387          * our data already.  If so, drop the data from the incoming
  388          * segment.  If it provides all of our data, drop us.
  389          */
  390         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  391                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  392                         - ip6af->ip6af_off;
  393                 if (i > 0) {
  394                         if (i >= ip6af->ip6af_frglen)
  395                                 goto dropfrag;
  396                         m_adj(IP6_REASS_MBUF(ip6af), i);
  397                         ip6af->ip6af_off += i;
  398                         ip6af->ip6af_frglen -= i;
  399                 }
  400         }
  401 
  402         /*
  403          * While we overlap succeeding segments trim them or,
  404          * if they are completely covered, dequeue them.
  405          */
  406         while (af6 != (struct ip6asfrag *)q6 &&
  407                ip6af->ip6af_off + ip6af->ip6af_frglen > af6->ip6af_off) {
  408                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  409                 if (i < af6->ip6af_frglen) {
  410                         af6->ip6af_frglen -= i;
  411                         af6->ip6af_off += i;
  412                         m_adj(IP6_REASS_MBUF(af6), i);
  413                         break;
  414                 }
  415                 af6 = af6->ip6af_down;
  416                 m_freem(IP6_REASS_MBUF(af6->ip6af_up));
  417                 frag6_deq(af6->ip6af_up);
  418         }
  419 #else
  420         /*
  421          * If the incoming framgent overlaps some existing fragments in
  422          * the reassembly queue, drop it, since it is dangerous to override
  423          * existing fragments from a security point of view.
  424          * We don't know which fragment is the bad guy - here we trust
  425          * fragment that came in earlier, with no real reason.
  426          *
  427          * Note: due to changes after disabling this part, mbuf passed to
  428          * m_adj() below now does not meet the requirement.
  429          */
  430         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  431                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  432                         - ip6af->ip6af_off;
  433                 if (i > 0) {
  434 #if 0                           /* suppress the noisy log */
  435                         log(LOG_ERR, "%d bytes of a fragment from %s "
  436                             "overlaps the previous fragment\n",
  437                             i, ip6_sprintf(ip6buf, &q6->ip6q_src));
  438 #endif
  439                         free(ip6af, M_FTABLE);
  440                         goto dropfrag;
  441                 }
  442         }
  443         if (af6 != (struct ip6asfrag *)q6) {
  444                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  445                 if (i > 0) {
  446 #if 0                           /* suppress the noisy log */
  447                         log(LOG_ERR, "%d bytes of a fragment from %s "
  448                             "overlaps the succeeding fragment",
  449                             i, ip6_sprintf(ip6buf, &q6->ip6q_src));
  450 #endif
  451                         free(ip6af, M_FTABLE);
  452                         goto dropfrag;
  453                 }
  454         }
  455 #endif
  456 
  457 insert:
  458 
  459         /*
  460          * Stick new segment in its place;
  461          * check for complete reassembly.
  462          * Move to front of packet queue, as we are
  463          * the most recently active fragmented packet.
  464          */
  465         frag6_enq(ip6af, af6->ip6af_up);
  466         frag6_nfrags++;
  467         q6->ip6q_nfrag++;
  468 #if 0 /* xxx */
  469         if (q6 != ip6q.ip6q_next) {
  470                 frag6_remque(q6);
  471                 frag6_insque(q6, &ip6q);
  472         }
  473 #endif
  474         next = 0;
  475         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  476              af6 = af6->ip6af_down) {
  477                 if (af6->ip6af_off != next) {
  478                         IP6Q_UNLOCK();
  479                         return IPPROTO_DONE;
  480                 }
  481                 next += af6->ip6af_frglen;
  482         }
  483         if (af6->ip6af_up->ip6af_mff) {
  484                 IP6Q_UNLOCK();
  485                 return IPPROTO_DONE;
  486         }
  487 
  488         /*
  489          * Reassembly is complete; concatenate fragments.
  490          */
  491         ip6af = q6->ip6q_down;
  492         t = m = IP6_REASS_MBUF(ip6af);
  493         af6 = ip6af->ip6af_down;
  494         frag6_deq(ip6af);
  495         while (af6 != (struct ip6asfrag *)q6) {
  496                 af6dwn = af6->ip6af_down;
  497                 frag6_deq(af6);
  498                 while (t->m_next)
  499                         t = t->m_next;
  500                 t->m_next = IP6_REASS_MBUF(af6);
  501                 m_adj(t->m_next, af6->ip6af_offset);
  502                 free(af6, M_FTABLE);
  503                 af6 = af6dwn;
  504         }
  505 
  506         /* adjust offset to point where the original next header starts */
  507         offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
  508         free(ip6af, M_FTABLE);
  509         ip6 = mtod(m, struct ip6_hdr *);
  510         ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
  511         if (q6->ip6q_ecn == IPTOS_ECN_CE)
  512                 ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
  513         nxt = q6->ip6q_nxt;
  514 #ifdef notyet
  515         *q6->ip6q_nxtp = (u_char)(nxt & 0xff);
  516 #endif
  517 
  518         /* Delete frag6 header */
  519         if (m->m_len >= offset + sizeof(struct ip6_frag)) {
  520                 /* This is the only possible case with !PULLDOWN_TEST */
  521                 ovbcopy((caddr_t)ip6, (caddr_t)ip6 + sizeof(struct ip6_frag),
  522                     offset);
  523                 m->m_data += sizeof(struct ip6_frag);
  524                 m->m_len -= sizeof(struct ip6_frag);
  525         } else {
  526                 /* this comes with no copy if the boundary is on cluster */
  527                 if ((t = m_split(m, offset, M_DONTWAIT)) == NULL) {
  528                         frag6_remque(q6);
  529                         frag6_nfrags -= q6->ip6q_nfrag;
  530                         free(q6, M_FTABLE);
  531                         frag6_nfragpackets--;
  532                         goto dropfrag;
  533                 }
  534                 m_adj(t, sizeof(struct ip6_frag));
  535                 m_cat(m, t);
  536         }
  537 
  538         /*
  539          * Store NXT to the original.
  540          */
  541         {
  542                 char *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
  543                 *prvnxtp = nxt;
  544         }
  545 
  546         frag6_remque(q6);
  547         frag6_nfrags -= q6->ip6q_nfrag;
  548         free(q6, M_FTABLE);
  549         frag6_nfragpackets--;
  550 
  551         if (m->m_flags & M_PKTHDR) { /* Isn't it always true? */
  552                 int plen = 0;
  553                 for (t = m; t; t = t->m_next)
  554                         plen += t->m_len;
  555                 m->m_pkthdr.len = plen;
  556         }
  557 
  558         ip6stat.ip6s_reassembled++;
  559         in6_ifstat_inc(dstifp, ifs6_reass_ok);
  560 
  561         /*
  562          * Tell launch routine the next header
  563          */
  564 
  565         *mp = m;
  566         *offp = offset;
  567 
  568         IP6Q_UNLOCK();
  569         return nxt;
  570 
  571  dropfrag:
  572         IP6Q_UNLOCK();
  573         in6_ifstat_inc(dstifp, ifs6_reass_fail);
  574         ip6stat.ip6s_fragdropped++;
  575         m_freem(m);
  576         return IPPROTO_DONE;
  577 }
  578 
  579 /*
  580  * Free a fragment reassembly header and all
  581  * associated datagrams.
  582  */
  583 void
  584 frag6_freef(struct ip6q *q6)
  585 {
  586         struct ip6asfrag *af6, *down6;
  587 
  588         IP6Q_LOCK_ASSERT();
  589 
  590         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  591              af6 = down6) {
  592                 struct mbuf *m = IP6_REASS_MBUF(af6);
  593 
  594                 down6 = af6->ip6af_down;
  595                 frag6_deq(af6);
  596 
  597                 /*
  598                  * Return ICMP time exceeded error for the 1st fragment.
  599                  * Just free other fragments.
  600                  */
  601                 if (af6->ip6af_off == 0) {
  602                         struct ip6_hdr *ip6;
  603 
  604                         /* adjust pointer */
  605                         ip6 = mtod(m, struct ip6_hdr *);
  606 
  607                         /* restore source and destination addresses */
  608                         ip6->ip6_src = q6->ip6q_src;
  609                         ip6->ip6_dst = q6->ip6q_dst;
  610 
  611                         icmp6_error(m, ICMP6_TIME_EXCEEDED,
  612                                     ICMP6_TIME_EXCEED_REASSEMBLY, 0);
  613                 } else
  614                         m_freem(m);
  615                 free(af6, M_FTABLE);
  616         }
  617         frag6_remque(q6);
  618         frag6_nfrags -= q6->ip6q_nfrag;
  619         free(q6, M_FTABLE);
  620         frag6_nfragpackets--;
  621 }
  622 
  623 /*
  624  * Put an ip fragment on a reassembly chain.
  625  * Like insque, but pointers in middle of structure.
  626  */
  627 void
  628 frag6_enq(struct ip6asfrag *af6, struct ip6asfrag *up6)
  629 {
  630 
  631         IP6Q_LOCK_ASSERT();
  632 
  633         af6->ip6af_up = up6;
  634         af6->ip6af_down = up6->ip6af_down;
  635         up6->ip6af_down->ip6af_up = af6;
  636         up6->ip6af_down = af6;
  637 }
  638 
  639 /*
  640  * To frag6_enq as remque is to insque.
  641  */
  642 void
  643 frag6_deq(struct ip6asfrag *af6)
  644 {
  645 
  646         IP6Q_LOCK_ASSERT();
  647 
  648         af6->ip6af_up->ip6af_down = af6->ip6af_down;
  649         af6->ip6af_down->ip6af_up = af6->ip6af_up;
  650 }
  651 
  652 void
  653 frag6_insque(struct ip6q *new, struct ip6q *old)
  654 {
  655 
  656         IP6Q_LOCK_ASSERT();
  657 
  658         new->ip6q_prev = old;
  659         new->ip6q_next = old->ip6q_next;
  660         old->ip6q_next->ip6q_prev= new;
  661         old->ip6q_next = new;
  662 }
  663 
  664 void
  665 frag6_remque(struct ip6q *p6)
  666 {
  667 
  668         IP6Q_LOCK_ASSERT();
  669 
  670         p6->ip6q_prev->ip6q_next = p6->ip6q_next;
  671         p6->ip6q_next->ip6q_prev = p6->ip6q_prev;
  672 }
  673 
  674 /*
  675  * IPv6 reassembling timer processing;
  676  * if a timer expires on a reassembly
  677  * queue, discard it.
  678  */
  679 void
  680 frag6_slowtimo(void)
  681 {
  682         struct ip6q *q6;
  683 
  684 #if 0
  685         GIANT_REQUIRED; /* XXX bz: ip6_forward_rt */
  686 #endif
  687 
  688         IP6Q_LOCK();
  689         q6 = ip6q.ip6q_next;
  690         if (q6)
  691                 while (q6 != &ip6q) {
  692                         --q6->ip6q_ttl;
  693                         q6 = q6->ip6q_next;
  694                         if (q6->ip6q_prev->ip6q_ttl == 0) {
  695                                 ip6stat.ip6s_fragtimeout++;
  696                                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  697                                 frag6_freef(q6->ip6q_prev);
  698                         }
  699                 }
  700         /*
  701          * If we are over the maximum number of fragments
  702          * (due to the limit being lowered), drain off
  703          * enough to get down to the new limit.
  704          */
  705         while (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
  706             ip6q.ip6q_prev) {
  707                 ip6stat.ip6s_fragoverflow++;
  708                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  709                 frag6_freef(ip6q.ip6q_prev);
  710         }
  711         IP6Q_UNLOCK();
  712 
  713 #if 0
  714         /*
  715          * Routing changes might produce a better route than we last used;
  716          * make sure we notice eventually, even if forwarding only for one
  717          * destination and the cache is never replaced.
  718          */
  719         if (ip6_forward_rt.ro_rt) {
  720                 RTFREE(ip6_forward_rt.ro_rt);
  721                 ip6_forward_rt.ro_rt = 0;
  722         }
  723         if (ipsrcchk_rt.ro_rt) {
  724                 RTFREE(ipsrcchk_rt.ro_rt);
  725                 ipsrcchk_rt.ro_rt = 0;
  726         }
  727 #endif
  728 }
  729 
  730 /*
  731  * Drain off all datagram fragments.
  732  */
  733 void
  734 frag6_drain(void)
  735 {
  736 
  737         if (IP6Q_TRYLOCK() == 0)
  738                 return;
  739         while (ip6q.ip6q_next != &ip6q) {
  740                 ip6stat.ip6s_fragdropped++;
  741                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  742                 frag6_freef(ip6q.ip6q_next);
  743         }
  744         IP6Q_UNLOCK();
  745 }

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