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: releng/6.2/sys/netinet6/frag6.c 158641 2006-05-16 07:27:49Z ps $      */
    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 #include <net/net_osdep.h>
   57 
   58 /*
   59  * Define it to get a correct behavior on per-interface statistics.
   60  * You will need to perform an extra routing table lookup, per fragment,
   61  * to do it.  This may, or may not be, a performance hit.
   62  */
   63 #define IN6_IFSTAT_STRICT
   64 
   65 static void frag6_enq __P((struct ip6asfrag *, struct ip6asfrag *));
   66 static void frag6_deq __P((struct ip6asfrag *));
   67 static void frag6_insque __P((struct ip6q *, struct ip6q *));
   68 static void frag6_remque __P((struct ip6q *));
   69 static void frag6_freef __P((struct ip6q *));
   70 
   71 static struct mtx ip6qlock;
   72 /*
   73  * These fields all protected by ip6qlock.
   74  */
   75 static u_int frag6_nfragpackets;
   76 static u_int frag6_nfrags;
   77 static struct   ip6q ip6q;      /* ip6 reassemble queue */
   78 
   79 #define IP6Q_LOCK_INIT()        mtx_init(&ip6qlock, "ip6qlock", NULL, MTX_DEF);
   80 #define IP6Q_LOCK()             mtx_lock(&ip6qlock)
   81 #define IP6Q_TRYLOCK()          mtx_trylock(&ip6qlock)
   82 #define IP6Q_LOCK_ASSERT()      mtx_assert(&ip6qlock, MA_OWNED)
   83 #define IP6Q_UNLOCK()           mtx_unlock(&ip6qlock)
   84 
   85 static MALLOC_DEFINE(M_FTABLE, "fragment", "fragment reassembly header");
   86 
   87 /*
   88  * Initialise reassembly queue and fragment identifier.
   89  */
   90 static void
   91 frag6_change(void *tag)
   92 {
   93 
   94         ip6_maxfragpackets = nmbclusters / 4;
   95         ip6_maxfrags = nmbclusters / 4;
   96 }
   97 
   98 void
   99 frag6_init()
  100 {
  101 
  102         ip6_maxfragpackets = nmbclusters / 4;
  103         ip6_maxfrags = nmbclusters / 4;
  104         EVENTHANDLER_REGISTER(nmbclusters_change,
  105             frag6_change, NULL, EVENTHANDLER_PRI_ANY);
  106 
  107         IP6Q_LOCK_INIT();
  108 
  109         ip6q.ip6q_next = ip6q.ip6q_prev = &ip6q;
  110 }
  111 
  112 /*
  113  * In RFC2460, fragment and reassembly rule do not agree with each other,
  114  * in terms of next header field handling in fragment header.
  115  * While the sender will use the same value for all of the fragmented packets,
  116  * receiver is suggested not to check the consistency.
  117  *
  118  * fragment rule (p20):
  119  *      (2) A Fragment header containing:
  120  *      The Next Header value that identifies the first header of
  121  *      the Fragmentable Part of the original packet.
  122  *              -> next header field is same for all fragments
  123  *
  124  * reassembly rule (p21):
  125  *      The Next Header field of the last header of the Unfragmentable
  126  *      Part is obtained from the Next Header field of the first
  127  *      fragment's Fragment header.
  128  *              -> should grab it from the first fragment only
  129  *
  130  * The following note also contradicts with fragment rule - noone is going to
  131  * send different fragment with different next header field.
  132  *
  133  * additional note (p22):
  134  *      The Next Header values in the Fragment headers of different
  135  *      fragments of the same original packet may differ.  Only the value
  136  *      from the Offset zero fragment packet is used for reassembly.
  137  *              -> should grab it from the first fragment only
  138  *
  139  * There is no explicit reason given in the RFC.  Historical reason maybe?
  140  */
  141 /*
  142  * Fragment input
  143  */
  144 int
  145 frag6_input(mp, offp, proto)
  146         struct mbuf **mp;
  147         int *offp, proto;
  148 {
  149         struct mbuf *m = *mp, *t;
  150         struct ip6_hdr *ip6;
  151         struct ip6_frag *ip6f;
  152         struct ip6q *q6;
  153         struct ip6asfrag *af6, *ip6af, *af6dwn;
  154 #ifdef IN6_IFSTAT_STRICT
  155         struct in6_ifaddr *ia;
  156 #endif
  157         int offset = *offp, nxt, i, next;
  158         int first_frag = 0;
  159         int fragoff, frgpartlen;        /* must be larger than u_int16_t */
  160         struct ifnet *dstifp;
  161         u_int8_t ecn, ecn0;
  162 
  163         ip6 = mtod(m, struct ip6_hdr *);
  164 #ifndef PULLDOWN_TEST
  165         IP6_EXTHDR_CHECK(m, offset, sizeof(struct ip6_frag), IPPROTO_DONE);
  166         ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);
  167 #else
  168         IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
  169         if (ip6f == NULL)
  170                 return (IPPROTO_DONE);
  171 #endif
  172 
  173         dstifp = NULL;
  174 #ifdef IN6_IFSTAT_STRICT
  175         /* find the destination interface of the packet. */
  176         if ((ia = ip6_getdstifaddr(m)) != NULL)
  177                 dstifp = ia->ia_ifp;
  178 #else
  179         /* we are violating the spec, this is not the destination interface */
  180         if ((m->m_flags & M_PKTHDR) != 0)
  181                 dstifp = m->m_pkthdr.rcvif;
  182 #endif
  183 
  184         /* jumbo payload can't contain a fragment header */
  185         if (ip6->ip6_plen == 0) {
  186                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
  187                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  188                 return IPPROTO_DONE;
  189         }
  190 
  191         /*
  192          * check whether fragment packet's fragment length is
  193          * multiple of 8 octets.
  194          * sizeof(struct ip6_frag) == 8
  195          * sizeof(struct ip6_hdr) = 40
  196          */
  197         if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
  198             (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
  199                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  200                     offsetof(struct ip6_hdr, ip6_plen));
  201                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  202                 return IPPROTO_DONE;
  203         }
  204 
  205         ip6stat.ip6s_fragments++;
  206         in6_ifstat_inc(dstifp, ifs6_reass_reqd);
  207 
  208         /* offset now points to data portion */
  209         offset += sizeof(struct ip6_frag);
  210 
  211         IP6Q_LOCK();
  212 
  213         /*
  214          * Enforce upper bound on number of fragments.
  215          * If maxfrag is 0, never accept fragments.
  216          * If maxfrag is -1, accept all fragments without limitation.
  217          */
  218         if (ip6_maxfrags < 0)
  219                 ;
  220         else if (frag6_nfrags >= (u_int)ip6_maxfrags)
  221                 goto dropfrag;
  222 
  223         for (q6 = ip6q.ip6q_next; q6 != &ip6q; q6 = q6->ip6q_next)
  224                 if (ip6f->ip6f_ident == q6->ip6q_ident &&
  225                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
  226                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst))
  227                         break;
  228 
  229         if (q6 == &ip6q) {
  230                 /*
  231                  * the first fragment to arrive, create a reassembly queue.
  232                  */
  233                 first_frag = 1;
  234 
  235                 /*
  236                  * Enforce upper bound on number of fragmented packets
  237                  * for which we attempt reassembly;
  238                  * If maxfragpackets is 0, never accept fragments.
  239                  * If maxfragpackets is -1, accept all fragments without
  240                  * limitation.
  241                  */
  242                 if (ip6_maxfragpackets < 0)
  243                         ;
  244                 else if (frag6_nfragpackets >= (u_int)ip6_maxfragpackets)
  245                         goto dropfrag;
  246                 frag6_nfragpackets++;
  247                 q6 = (struct ip6q *)malloc(sizeof(struct ip6q), M_FTABLE,
  248                     M_NOWAIT);
  249                 if (q6 == NULL)
  250                         goto dropfrag;
  251                 bzero(q6, sizeof(*q6));
  252 
  253                 frag6_insque(q6, &ip6q);
  254 
  255                 /* ip6q_nxt will be filled afterwards, from 1st fragment */
  256                 q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
  257 #ifdef notyet
  258                 q6->ip6q_nxtp   = (u_char *)nxtp;
  259 #endif
  260                 q6->ip6q_ident  = ip6f->ip6f_ident;
  261                 q6->ip6q_arrive = 0; /* Is it used anywhere? */
  262                 q6->ip6q_ttl    = IPV6_FRAGTTL;
  263                 q6->ip6q_src    = ip6->ip6_src;
  264                 q6->ip6q_dst    = ip6->ip6_dst;
  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_head = ip6->ip6_flow;
  346         ip6af->ip6af_len = ip6->ip6_plen;
  347         ip6af->ip6af_nxt = ip6->ip6_nxt;
  348         ip6af->ip6af_hlim = ip6->ip6_hlim;
  349         ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
  350         ip6af->ip6af_off = fragoff;
  351         ip6af->ip6af_frglen = frgpartlen;
  352         ip6af->ip6af_offset = offset;
  353         IP6_REASS_MBUF(ip6af) = m;
  354 
  355         if (first_frag) {
  356                 af6 = (struct ip6asfrag *)q6;
  357                 goto insert;
  358         }
  359 
  360         /*
  361          * Handle ECN by comparing this segment with the first one;
  362          * if CE is set, do not lose CE.
  363          * drop if CE and not-ECT are mixed for the same packet.
  364          */
  365         ecn = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
  366         ecn0 = (ntohl(q6->ip6q_down->ip6af_head) >> 20) & IPTOS_ECN_MASK;
  367         if (ecn == IPTOS_ECN_CE) {
  368                 if (ecn0 == IPTOS_ECN_NOTECT) {
  369                         free(ip6af, M_FTABLE);
  370                         goto dropfrag;
  371                 }
  372                 if (ecn0 != IPTOS_ECN_CE)
  373                         q6->ip6q_down->ip6af_head |= htonl(IPTOS_ECN_CE << 20);
  374         }
  375         if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
  376                 free(ip6af, M_FTABLE);
  377                 goto dropfrag;
  378         }
  379 
  380         /*
  381          * Find a segment which begins after this one does.
  382          */
  383         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  384              af6 = af6->ip6af_down)
  385                 if (af6->ip6af_off > ip6af->ip6af_off)
  386                         break;
  387 
  388 #if 0
  389         /*
  390          * If there is a preceding segment, it may provide some of
  391          * our data already.  If so, drop the data from the incoming
  392          * segment.  If it provides all of our data, drop us.
  393          */
  394         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  395                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  396                         - ip6af->ip6af_off;
  397                 if (i > 0) {
  398                         if (i >= ip6af->ip6af_frglen)
  399                                 goto dropfrag;
  400                         m_adj(IP6_REASS_MBUF(ip6af), i);
  401                         ip6af->ip6af_off += i;
  402                         ip6af->ip6af_frglen -= i;
  403                 }
  404         }
  405 
  406         /*
  407          * While we overlap succeeding segments trim them or,
  408          * if they are completely covered, dequeue them.
  409          */
  410         while (af6 != (struct ip6asfrag *)q6 &&
  411                ip6af->ip6af_off + ip6af->ip6af_frglen > af6->ip6af_off) {
  412                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  413                 if (i < af6->ip6af_frglen) {
  414                         af6->ip6af_frglen -= i;
  415                         af6->ip6af_off += i;
  416                         m_adj(IP6_REASS_MBUF(af6), i);
  417                         break;
  418                 }
  419                 af6 = af6->ip6af_down;
  420                 m_freem(IP6_REASS_MBUF(af6->ip6af_up));
  421                 frag6_deq(af6->ip6af_up);
  422         }
  423 #else
  424         /*
  425          * If the incoming framgent overlaps some existing fragments in
  426          * the reassembly queue, drop it, since it is dangerous to override
  427          * existing fragments from a security point of view.
  428          * We don't know which fragment is the bad guy - here we trust
  429          * fragment that came in earlier, with no real reason.
  430          */
  431         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  432                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  433                         - ip6af->ip6af_off;
  434                 if (i > 0) {
  435 #if 0                           /* suppress the noisy log */
  436                         log(LOG_ERR, "%d bytes of a fragment from %s "
  437                             "overlaps the previous fragment\n",
  438                             i, ip6_sprintf(&q6->ip6q_src));
  439 #endif
  440                         free(ip6af, M_FTABLE);
  441                         goto dropfrag;
  442                 }
  443         }
  444         if (af6 != (struct ip6asfrag *)q6) {
  445                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  446                 if (i > 0) {
  447 #if 0                           /* suppress the noisy log */
  448                         log(LOG_ERR, "%d bytes of a fragment from %s "
  449                             "overlaps the succeeding fragment",
  450                             i, ip6_sprintf(&q6->ip6q_src));
  451 #endif
  452                         free(ip6af, M_FTABLE);
  453                         goto dropfrag;
  454                 }
  455         }
  456 #endif
  457 
  458 insert:
  459 
  460         /*
  461          * Stick new segment in its place;
  462          * check for complete reassembly.
  463          * Move to front of packet queue, as we are
  464          * the most recently active fragmented packet.
  465          */
  466         frag6_enq(ip6af, af6->ip6af_up);
  467         frag6_nfrags++;
  468         q6->ip6q_nfrag++;
  469 #if 0 /* xxx */
  470         if (q6 != ip6q.ip6q_next) {
  471                 frag6_remque(q6);
  472                 frag6_insque(q6, &ip6q);
  473         }
  474 #endif
  475         next = 0;
  476         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  477              af6 = af6->ip6af_down) {
  478                 if (af6->ip6af_off != next) {
  479                         IP6Q_UNLOCK();
  480                         return IPPROTO_DONE;
  481                 }
  482                 next += af6->ip6af_frglen;
  483         }
  484         if (af6->ip6af_up->ip6af_mff) {
  485                 IP6Q_UNLOCK();
  486                 return IPPROTO_DONE;
  487         }
  488 
  489         /*
  490          * Reassembly is complete; concatenate fragments.
  491          */
  492         ip6af = q6->ip6q_down;
  493         t = m = IP6_REASS_MBUF(ip6af);
  494         af6 = ip6af->ip6af_down;
  495         frag6_deq(ip6af);
  496         while (af6 != (struct ip6asfrag *)q6) {
  497                 af6dwn = af6->ip6af_down;
  498                 frag6_deq(af6);
  499                 while (t->m_next)
  500                         t = t->m_next;
  501                 t->m_next = IP6_REASS_MBUF(af6);
  502                 m_adj(t->m_next, af6->ip6af_offset);
  503                 free(af6, M_FTABLE);
  504                 af6 = af6dwn;
  505         }
  506 
  507         /* adjust offset to point where the original next header starts */
  508         offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
  509         free(ip6af, M_FTABLE);
  510         ip6 = mtod(m, struct ip6_hdr *);
  511         ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
  512         ip6->ip6_src = q6->ip6q_src;
  513         ip6->ip6_dst = q6->ip6q_dst;
  514         nxt = q6->ip6q_nxt;
  515 #ifdef notyet
  516         *q6->ip6q_nxtp = (u_char)(nxt & 0xff);
  517 #endif
  518 
  519         /*
  520          * Delete frag6 header with as a few cost as possible.
  521          */
  522         if (offset < m->m_len) {
  523                 ovbcopy((caddr_t)ip6, (caddr_t)ip6 + sizeof(struct ip6_frag),
  524                         offset);
  525                 m->m_data += sizeof(struct ip6_frag);
  526                 m->m_len -= sizeof(struct ip6_frag);
  527         } else {
  528                 /* this comes with no copy if the boundary is on cluster */
  529                 if ((t = m_split(m, offset, M_DONTWAIT)) == NULL) {
  530                         frag6_remque(q6);
  531                         frag6_nfrags -= q6->ip6q_nfrag;
  532                         free(q6, M_FTABLE);
  533                         frag6_nfragpackets--;
  534                         goto dropfrag;
  535                 }
  536                 m_adj(t, sizeof(struct ip6_frag));
  537                 m_cat(m, t);
  538         }
  539 
  540         /*
  541          * Store NXT to the original.
  542          */
  543         {
  544                 char *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
  545                 *prvnxtp = nxt;
  546         }
  547 
  548         frag6_remque(q6);
  549         frag6_nfrags -= q6->ip6q_nfrag;
  550         free(q6, M_FTABLE);
  551         frag6_nfragpackets--;
  552 
  553         if (m->m_flags & M_PKTHDR) { /* Isn't it always true? */
  554                 int plen = 0;
  555                 for (t = m; t; t = t->m_next)
  556                         plen += t->m_len;
  557                 m->m_pkthdr.len = plen;
  558         }
  559 
  560         ip6stat.ip6s_reassembled++;
  561         in6_ifstat_inc(dstifp, ifs6_reass_ok);
  562 
  563         /*
  564          * Tell launch routine the next header
  565          */
  566 
  567         *mp = m;
  568         *offp = offset;
  569 
  570         IP6Q_UNLOCK();
  571         return nxt;
  572 
  573  dropfrag:
  574         IP6Q_UNLOCK();
  575         in6_ifstat_inc(dstifp, ifs6_reass_fail);
  576         ip6stat.ip6s_fragdropped++;
  577         m_freem(m);
  578         return IPPROTO_DONE;
  579 }
  580 
  581 /*
  582  * Free a fragment reassembly header and all
  583  * associated datagrams.
  584  */
  585 void
  586 frag6_freef(q6)
  587         struct ip6q *q6;
  588 {
  589         struct ip6asfrag *af6, *down6;
  590 
  591         IP6Q_LOCK_ASSERT();
  592 
  593         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  594              af6 = down6) {
  595                 struct mbuf *m = IP6_REASS_MBUF(af6);
  596 
  597                 down6 = af6->ip6af_down;
  598                 frag6_deq(af6);
  599 
  600                 /*
  601                  * Return ICMP time exceeded error for the 1st fragment.
  602                  * Just free other fragments.
  603                  */
  604                 if (af6->ip6af_off == 0) {
  605                         struct ip6_hdr *ip6;
  606 
  607                         /* adjust pointer */
  608                         ip6 = mtod(m, struct ip6_hdr *);
  609 
  610                         /* restore source and destination addresses */
  611                         ip6->ip6_src = q6->ip6q_src;
  612                         ip6->ip6_dst = q6->ip6q_dst;
  613 
  614                         icmp6_error(m, ICMP6_TIME_EXCEEDED,
  615                                     ICMP6_TIME_EXCEED_REASSEMBLY, 0);
  616                 } else
  617                         m_freem(m);
  618                 free(af6, M_FTABLE);
  619         }
  620         frag6_remque(q6);
  621         frag6_nfrags -= q6->ip6q_nfrag;
  622         free(q6, M_FTABLE);
  623         frag6_nfragpackets--;
  624 }
  625 
  626 /*
  627  * Put an ip fragment on a reassembly chain.
  628  * Like insque, but pointers in middle of structure.
  629  */
  630 void
  631 frag6_enq(af6, up6)
  632         struct ip6asfrag *af6, *up6;
  633 {
  634 
  635         IP6Q_LOCK_ASSERT();
  636 
  637         af6->ip6af_up = up6;
  638         af6->ip6af_down = up6->ip6af_down;
  639         up6->ip6af_down->ip6af_up = af6;
  640         up6->ip6af_down = af6;
  641 }
  642 
  643 /*
  644  * To frag6_enq as remque is to insque.
  645  */
  646 void
  647 frag6_deq(af6)
  648         struct ip6asfrag *af6;
  649 {
  650 
  651         IP6Q_LOCK_ASSERT();
  652 
  653         af6->ip6af_up->ip6af_down = af6->ip6af_down;
  654         af6->ip6af_down->ip6af_up = af6->ip6af_up;
  655 }
  656 
  657 void
  658 frag6_insque(new, old)
  659         struct ip6q *new, *old;
  660 {
  661 
  662         IP6Q_LOCK_ASSERT();
  663 
  664         new->ip6q_prev = old;
  665         new->ip6q_next = old->ip6q_next;
  666         old->ip6q_next->ip6q_prev= new;
  667         old->ip6q_next = new;
  668 }
  669 
  670 void
  671 frag6_remque(p6)
  672         struct ip6q *p6;
  673 {
  674 
  675         IP6Q_LOCK_ASSERT();
  676 
  677         p6->ip6q_prev->ip6q_next = p6->ip6q_next;
  678         p6->ip6q_next->ip6q_prev = p6->ip6q_prev;
  679 }
  680 
  681 /*
  682  * IPv6 reassembling timer processing;
  683  * if a timer expires on a reassembly
  684  * queue, discard it.
  685  */
  686 void
  687 frag6_slowtimo()
  688 {
  689         struct ip6q *q6;
  690         int s = splnet();
  691 
  692         IP6Q_LOCK();
  693         q6 = ip6q.ip6q_next;
  694         if (q6)
  695                 while (q6 != &ip6q) {
  696                         --q6->ip6q_ttl;
  697                         q6 = q6->ip6q_next;
  698                         if (q6->ip6q_prev->ip6q_ttl == 0) {
  699                                 ip6stat.ip6s_fragtimeout++;
  700                                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  701                                 frag6_freef(q6->ip6q_prev);
  702                         }
  703                 }
  704         /*
  705          * If we are over the maximum number of fragments
  706          * (due to the limit being lowered), drain off
  707          * enough to get down to the new limit.
  708          */
  709         while (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
  710             ip6q.ip6q_prev) {
  711                 ip6stat.ip6s_fragoverflow++;
  712                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  713                 frag6_freef(ip6q.ip6q_prev);
  714         }
  715         IP6Q_UNLOCK();
  716 
  717 #if 0
  718         /*
  719          * Routing changes might produce a better route than we last used;
  720          * make sure we notice eventually, even if forwarding only for one
  721          * destination and the cache is never replaced.
  722          */
  723         if (ip6_forward_rt.ro_rt) {
  724                 RTFREE(ip6_forward_rt.ro_rt);
  725                 ip6_forward_rt.ro_rt = 0;
  726         }
  727         if (ipsrcchk_rt.ro_rt) {
  728                 RTFREE(ipsrcchk_rt.ro_rt);
  729                 ipsrcchk_rt.ro_rt = 0;
  730         }
  731 #endif
  732 
  733         splx(s);
  734 }
  735 
  736 /*
  737  * Drain off all datagram fragments.
  738  */
  739 void
  740 frag6_drain()
  741 {
  742 
  743         if (IP6Q_TRYLOCK() == 0)
  744                 return;
  745         while (ip6q.ip6q_next != &ip6q) {
  746                 ip6stat.ip6s_fragdropped++;
  747                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  748                 frag6_freef(ip6q.ip6q_next);
  749         }
  750         IP6Q_UNLOCK();
  751 }

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