The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_syncache.c

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    1 /*-
    2  * Copyright (c) 2001 Networks Associates Technology, Inc.
    3  * All rights reserved.
    4  *
    5  * This software was developed for the FreeBSD Project by Jonathan Lemon
    6  * and NAI Labs, the Security Research Division of Network Associates, Inc.
    7  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    8  * DARPA CHATS research program.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. The name of the author may not be used to endorse or promote
   19  *    products derived from this software without specific prior written
   20  *    permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  * $FreeBSD: releng/5.2/sys/netinet/tcp_syncache.c 122922 2003-11-20 20:07:39Z andre $
   35  */
   36 
   37 #include "opt_inet6.h"
   38 #include "opt_ipsec.h"
   39 #include "opt_mac.h"
   40 #include "opt_tcpdebug.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/kernel.h>
   45 #include <sys/sysctl.h>
   46 #include <sys/malloc.h>
   47 #include <sys/mac.h>
   48 #include <sys/mbuf.h>
   49 #include <sys/md5.h>
   50 #include <sys/proc.h>           /* for proc0 declaration */
   51 #include <sys/random.h>
   52 #include <sys/socket.h>
   53 #include <sys/socketvar.h>
   54 
   55 #include <net/if.h>
   56 #include <net/route.h>
   57 
   58 #include <netinet/in.h>
   59 #include <netinet/in_systm.h>
   60 #include <netinet/ip.h>
   61 #include <netinet/in_var.h>
   62 #include <netinet/in_pcb.h>
   63 #include <netinet/ip_var.h>
   64 #ifdef INET6
   65 #include <netinet/ip6.h>
   66 #include <netinet/icmp6.h>
   67 #include <netinet6/nd6.h>
   68 #include <netinet6/ip6_var.h>
   69 #include <netinet6/in6_pcb.h>
   70 #endif
   71 #include <netinet/tcp.h>
   72 #ifdef TCPDEBUG
   73 #include <netinet/tcpip.h>
   74 #endif
   75 #include <netinet/tcp_fsm.h>
   76 #include <netinet/tcp_seq.h>
   77 #include <netinet/tcp_timer.h>
   78 #include <netinet/tcp_var.h>
   79 #ifdef TCPDEBUG
   80 #include <netinet/tcp_debug.h>
   81 #endif
   82 #ifdef INET6
   83 #include <netinet6/tcp6_var.h>
   84 #endif
   85 
   86 #ifdef IPSEC
   87 #include <netinet6/ipsec.h>
   88 #ifdef INET6
   89 #include <netinet6/ipsec6.h>
   90 #endif
   91 #endif /*IPSEC*/
   92 
   93 #ifdef FAST_IPSEC
   94 #include <netipsec/ipsec.h>
   95 #ifdef INET6
   96 #include <netipsec/ipsec6.h>
   97 #endif
   98 #include <netipsec/key.h>
   99 #endif /*FAST_IPSEC*/
  100 
  101 #include <machine/in_cksum.h>
  102 #include <vm/uma.h>
  103 
  104 static int tcp_syncookies = 1;
  105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  106     &tcp_syncookies, 0, 
  107     "Use TCP SYN cookies if the syncache overflows");
  108 
  109 static void      syncache_drop(struct syncache *, struct syncache_head *);
  110 static void      syncache_free(struct syncache *);
  111 static void      syncache_insert(struct syncache *, struct syncache_head *);
  112 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  113 #ifdef TCPDEBUG
  114 static int       syncache_respond(struct syncache *, struct mbuf *, struct socket *);
  115 #else
  116 static int       syncache_respond(struct syncache *, struct mbuf *);
  117 #endif
  118 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  119                     struct mbuf *m);
  120 static void      syncache_timer(void *);
  121 static u_int32_t syncookie_generate(struct syncache *);
  122 static struct syncache *syncookie_lookup(struct in_conninfo *,
  123                     struct tcphdr *, struct socket *);
  124 
  125 /*
  126  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  127  * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
  128  * the odds are that the user has given up attempting to connect by then.
  129  */
  130 #define SYNCACHE_MAXREXMTS              3
  131 
  132 /* Arbitrary values */
  133 #define TCP_SYNCACHE_HASHSIZE           512
  134 #define TCP_SYNCACHE_BUCKETLIMIT        30
  135 
  136 struct tcp_syncache {
  137         struct  syncache_head *hashbase;
  138         uma_zone_t zone;
  139         u_int   hashsize;
  140         u_int   hashmask;
  141         u_int   bucket_limit;
  142         u_int   cache_count;
  143         u_int   cache_limit;
  144         u_int   rexmt_limit;
  145         u_int   hash_secret;
  146         u_int   next_reseed;
  147         TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1];
  148         struct  callout tt_timerq[SYNCACHE_MAXREXMTS + 1];
  149 };
  150 static struct tcp_syncache tcp_syncache;
  151 
  152 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  153 
  154 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  155      &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
  156 
  157 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  158      &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
  159 
  160 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  161      &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
  162 
  163 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  164      &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
  165 
  166 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  167      &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
  168 
  169 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  170 
  171 #define SYNCACHE_HASH(inc, mask)                                        \
  172         ((tcp_syncache.hash_secret ^                                    \
  173           (inc)->inc_faddr.s_addr ^                                     \
  174           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  175           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  176 
  177 #define SYNCACHE_HASH6(inc, mask)                                       \
  178         ((tcp_syncache.hash_secret ^                                    \
  179           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  180           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  181           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  182 
  183 #define ENDPTS_EQ(a, b) (                                               \
  184         (a)->ie_fport == (b)->ie_fport &&                               \
  185         (a)->ie_lport == (b)->ie_lport &&                               \
  186         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  187         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  188 )
  189 
  190 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  191 
  192 #define SYNCACHE_TIMEOUT(sc, slot) do {                         \
  193         sc->sc_rxtslot = (slot);                                        \
  194         sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[(slot)];   \
  195         TAILQ_INSERT_TAIL(&tcp_syncache.timerq[(slot)], sc, sc_timerq); \
  196         if (!callout_active(&tcp_syncache.tt_timerq[(slot)]))           \
  197                 callout_reset(&tcp_syncache.tt_timerq[(slot)],          \
  198                     TCPTV_RTOBASE * tcp_backoff[(slot)],                \
  199                     syncache_timer, (void *)((intptr_t)(slot)));        \
  200 } while (0)
  201 
  202 static void
  203 syncache_free(struct syncache *sc)
  204 {
  205         if (sc->sc_ipopts)
  206                 (void) m_free(sc->sc_ipopts);
  207 
  208         uma_zfree(tcp_syncache.zone, sc);
  209 }
  210 
  211 void
  212 syncache_init(void)
  213 {
  214         int i;
  215 
  216         tcp_syncache.cache_count = 0;
  217         tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  218         tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  219         tcp_syncache.cache_limit =
  220             tcp_syncache.hashsize * tcp_syncache.bucket_limit;
  221         tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  222         tcp_syncache.next_reseed = 0;
  223         tcp_syncache.hash_secret = arc4random();
  224 
  225         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  226             &tcp_syncache.hashsize);
  227         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  228             &tcp_syncache.cache_limit);
  229         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  230             &tcp_syncache.bucket_limit);
  231         if (!powerof2(tcp_syncache.hashsize)) {
  232                 printf("WARNING: syncache hash size is not a power of 2.\n");
  233                 tcp_syncache.hashsize = 512;    /* safe default */
  234         }
  235         tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
  236 
  237         /* Allocate the hash table. */
  238         MALLOC(tcp_syncache.hashbase, struct syncache_head *,
  239             tcp_syncache.hashsize * sizeof(struct syncache_head),
  240             M_SYNCACHE, M_WAITOK);
  241 
  242         /* Initialize the hash buckets. */
  243         for (i = 0; i < tcp_syncache.hashsize; i++) {
  244                 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
  245                 tcp_syncache.hashbase[i].sch_length = 0;
  246         }
  247 
  248         /* Initialize the timer queues. */
  249         for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
  250                 TAILQ_INIT(&tcp_syncache.timerq[i]);
  251                 callout_init(&tcp_syncache.tt_timerq[i],
  252                         debug_mpsafenet ? CALLOUT_MPSAFE : 0);
  253         }
  254 
  255         /*
  256          * Allocate the syncache entries.  Allow the zone to allocate one
  257          * more entry than cache limit, so a new entry can bump out an
  258          * older one.
  259          */
  260         tcp_syncache.cache_limit -= 1;
  261         tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  262             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  263         uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
  264 }
  265 
  266 static void
  267 syncache_insert(sc, sch)
  268         struct syncache *sc;
  269         struct syncache_head *sch;
  270 {
  271         struct syncache *sc2;
  272         int i;
  273 
  274         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  275 
  276         /*
  277          * Make sure that we don't overflow the per-bucket
  278          * limit or the total cache size limit.
  279          */
  280         if (sch->sch_length >= tcp_syncache.bucket_limit) {
  281                 /*
  282                  * The bucket is full, toss the oldest element.
  283                  */
  284                 sc2 = TAILQ_FIRST(&sch->sch_bucket);
  285                 sc2->sc_tp->ts_recent = ticks;
  286                 syncache_drop(sc2, sch);
  287                 tcpstat.tcps_sc_bucketoverflow++;
  288         } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) {
  289                 /*
  290                  * The cache is full.  Toss the oldest entry in the
  291                  * entire cache.  This is the front entry in the
  292                  * first non-empty timer queue with the largest
  293                  * timeout value.
  294                  */
  295                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  296                         sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  297                         if (sc2 != NULL)
  298                                 break;
  299                 }
  300                 sc2->sc_tp->ts_recent = ticks;
  301                 syncache_drop(sc2, NULL);
  302                 tcpstat.tcps_sc_cacheoverflow++;
  303         }
  304 
  305         /* Initialize the entry's timer. */
  306         SYNCACHE_TIMEOUT(sc, 0);
  307 
  308         /* Put it into the bucket. */
  309         TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
  310         sch->sch_length++;
  311         tcp_syncache.cache_count++;
  312         tcpstat.tcps_sc_added++;
  313 }
  314 
  315 static void
  316 syncache_drop(sc, sch)
  317         struct syncache *sc;
  318         struct syncache_head *sch;
  319 {
  320         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  321 
  322         if (sch == NULL) {
  323 #ifdef INET6
  324                 if (sc->sc_inc.inc_isipv6) {
  325                         sch = &tcp_syncache.hashbase[
  326                             SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
  327                 } else
  328 #endif
  329                 {
  330                         sch = &tcp_syncache.hashbase[
  331                             SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
  332                 }
  333         }
  334 
  335         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  336         sch->sch_length--;
  337         tcp_syncache.cache_count--;
  338 
  339         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq);
  340         if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot]))
  341                 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]);
  342 
  343         syncache_free(sc);
  344 }
  345 
  346 /*
  347  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  348  * If we have retransmitted an entry the maximum number of times, expire it.
  349  */
  350 static void
  351 syncache_timer(xslot)
  352         void *xslot;
  353 {
  354         intptr_t slot = (intptr_t)xslot;
  355         struct syncache *sc, *nsc;
  356         struct inpcb *inp;
  357 
  358         INP_INFO_WLOCK(&tcbinfo);
  359         if (callout_pending(&tcp_syncache.tt_timerq[slot]) ||
  360             !callout_active(&tcp_syncache.tt_timerq[slot])) {
  361                 /* XXX can this happen? */
  362                 INP_INFO_WUNLOCK(&tcbinfo);
  363                 return;
  364         }
  365         callout_deactivate(&tcp_syncache.tt_timerq[slot]);
  366 
  367         nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]);
  368         while (nsc != NULL) {
  369                 if (ticks < nsc->sc_rxttime)
  370                         break;
  371                 sc = nsc;
  372                 inp = sc->sc_tp->t_inpcb;
  373                 if (slot == SYNCACHE_MAXREXMTS ||
  374                     slot >= tcp_syncache.rexmt_limit ||
  375                     inp == NULL || inp->inp_gencnt != sc->sc_inp_gencnt) {
  376                         nsc = TAILQ_NEXT(sc, sc_timerq);
  377                         syncache_drop(sc, NULL);
  378                         tcpstat.tcps_sc_stale++;
  379                         continue;
  380                 }
  381                 /*
  382                  * syncache_respond() may call back into the syncache to
  383                  * to modify another entry, so do not obtain the next
  384                  * entry on the timer chain until it has completed.
  385                  */
  386 #ifdef TCPDEBUG
  387                 (void) syncache_respond(sc, NULL, NULL);
  388 #else
  389                 (void) syncache_respond(sc, NULL);
  390 #endif
  391                 nsc = TAILQ_NEXT(sc, sc_timerq);
  392                 tcpstat.tcps_sc_retransmitted++;
  393                 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq);
  394                 SYNCACHE_TIMEOUT(sc, slot + 1);
  395         }
  396         if (nsc != NULL)
  397                 callout_reset(&tcp_syncache.tt_timerq[slot],
  398                     nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot));
  399         INP_INFO_WUNLOCK(&tcbinfo);
  400 }
  401 
  402 /*
  403  * Find an entry in the syncache.
  404  */
  405 struct syncache *
  406 syncache_lookup(inc, schp)
  407         struct in_conninfo *inc;
  408         struct syncache_head **schp;
  409 {
  410         struct syncache *sc;
  411         struct syncache_head *sch;
  412 
  413         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  414 
  415 #ifdef INET6
  416         if (inc->inc_isipv6) {
  417                 sch = &tcp_syncache.hashbase[
  418                     SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
  419                 *schp = sch;
  420                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  421                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  422                                 return (sc);
  423                 }
  424         } else
  425 #endif
  426         {
  427                 sch = &tcp_syncache.hashbase[
  428                     SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
  429                 *schp = sch;
  430                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  431 #ifdef INET6
  432                         if (sc->sc_inc.inc_isipv6)
  433                                 continue;
  434 #endif
  435                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  436                                 return (sc);
  437                 }
  438         }
  439         return (NULL);
  440 }
  441 
  442 /*
  443  * This function is called when we get a RST for a
  444  * non-existent connection, so that we can see if the
  445  * connection is in the syn cache.  If it is, zap it.
  446  */
  447 void
  448 syncache_chkrst(inc, th)
  449         struct in_conninfo *inc;
  450         struct tcphdr *th;
  451 {
  452         struct syncache *sc;
  453         struct syncache_head *sch;
  454 
  455         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  456 
  457         sc = syncache_lookup(inc, &sch);
  458         if (sc == NULL)
  459                 return;
  460         /*
  461          * If the RST bit is set, check the sequence number to see
  462          * if this is a valid reset segment.
  463          * RFC 793 page 37:
  464          *   In all states except SYN-SENT, all reset (RST) segments
  465          *   are validated by checking their SEQ-fields.  A reset is
  466          *   valid if its sequence number is in the window.
  467          *
  468          *   The sequence number in the reset segment is normally an
  469          *   echo of our outgoing acknowlegement numbers, but some hosts
  470          *   send a reset with the sequence number at the rightmost edge
  471          *   of our receive window, and we have to handle this case.
  472          */
  473         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  474             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  475                 syncache_drop(sc, sch);
  476                 tcpstat.tcps_sc_reset++;
  477         }
  478 }
  479 
  480 void
  481 syncache_badack(inc)
  482         struct in_conninfo *inc;
  483 {
  484         struct syncache *sc;
  485         struct syncache_head *sch;
  486 
  487         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  488 
  489         sc = syncache_lookup(inc, &sch);
  490         if (sc != NULL) {
  491                 syncache_drop(sc, sch);
  492                 tcpstat.tcps_sc_badack++;
  493         }
  494 }
  495 
  496 void
  497 syncache_unreach(inc, th)
  498         struct in_conninfo *inc;
  499         struct tcphdr *th;
  500 {
  501         struct syncache *sc;
  502         struct syncache_head *sch;
  503 
  504         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  505 
  506         /* we are called at splnet() here */
  507         sc = syncache_lookup(inc, &sch);
  508         if (sc == NULL)
  509                 return;
  510 
  511         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  512         if (ntohl(th->th_seq) != sc->sc_iss)
  513                 return;
  514 
  515         /*
  516          * If we've rertransmitted 3 times and this is our second error,
  517          * we remove the entry.  Otherwise, we allow it to continue on.
  518          * This prevents us from incorrectly nuking an entry during a
  519          * spurious network outage.
  520          *
  521          * See tcp_notify().
  522          */
  523         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
  524                 sc->sc_flags |= SCF_UNREACH;
  525                 return;
  526         }
  527         syncache_drop(sc, sch);
  528         tcpstat.tcps_sc_unreach++;
  529 }
  530 
  531 /*
  532  * Build a new TCP socket structure from a syncache entry.
  533  */
  534 static struct socket *
  535 syncache_socket(sc, lso, m)
  536         struct syncache *sc;
  537         struct socket *lso;
  538         struct mbuf *m;
  539 {
  540         struct inpcb *inp = NULL;
  541         struct socket *so;
  542         struct tcpcb *tp;
  543 
  544         GIANT_REQUIRED;                 /* XXX until socket locking */
  545         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  546 
  547         /*
  548          * Ok, create the full blown connection, and set things up
  549          * as they would have been set up if we had created the
  550          * connection when the SYN arrived.  If we can't create
  551          * the connection, abort it.
  552          */
  553         so = sonewconn(lso, SS_ISCONNECTED);
  554         if (so == NULL) {
  555                 /*
  556                  * Drop the connection; we will send a RST if the peer
  557                  * retransmits the ACK,
  558                  */
  559                 tcpstat.tcps_listendrop++;
  560                 goto abort2;
  561         }
  562 #ifdef MAC
  563         mac_set_socket_peer_from_mbuf(m, so);
  564 #endif
  565 
  566         inp = sotoinpcb(so);
  567         INP_LOCK(inp);
  568 
  569         /*
  570          * Insert new socket into hash list.
  571          */
  572         inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
  573 #ifdef INET6
  574         if (sc->sc_inc.inc_isipv6) {
  575                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  576         } else {
  577                 inp->inp_vflag &= ~INP_IPV6;
  578                 inp->inp_vflag |= INP_IPV4;
  579 #endif
  580                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  581 #ifdef INET6
  582         }
  583 #endif
  584         inp->inp_lport = sc->sc_inc.inc_lport;
  585         if (in_pcbinshash(inp) != 0) {
  586                 /*
  587                  * Undo the assignments above if we failed to
  588                  * put the PCB on the hash lists.
  589                  */
  590 #ifdef INET6
  591                 if (sc->sc_inc.inc_isipv6)
  592                         inp->in6p_laddr = in6addr_any;
  593                 else
  594 #endif
  595                         inp->inp_laddr.s_addr = INADDR_ANY;
  596                 inp->inp_lport = 0;
  597                 goto abort;
  598         }
  599 #ifdef IPSEC
  600         /* copy old policy into new socket's */
  601         if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  602                 printf("syncache_expand: could not copy policy\n");
  603 #endif
  604 #ifdef FAST_IPSEC
  605         /* copy old policy into new socket's */
  606         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  607                 printf("syncache_expand: could not copy policy\n");
  608 #endif
  609 #ifdef INET6
  610         if (sc->sc_inc.inc_isipv6) {
  611                 struct inpcb *oinp = sotoinpcb(lso);
  612                 struct in6_addr laddr6;
  613                 struct sockaddr_in6 *sin6;
  614                 /*
  615                  * Inherit socket options from the listening socket.
  616                  * Note that in6p_inputopts are not (and should not be)
  617                  * copied, since it stores previously received options and is
  618                  * used to detect if each new option is different than the
  619                  * previous one and hence should be passed to a user.
  620                  * If we copied in6p_inputopts, a user would not be able to
  621                  * receive options just after calling the accept system call.
  622                  */
  623                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  624                 if (oinp->in6p_outputopts)
  625                         inp->in6p_outputopts =
  626                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  627 
  628                 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
  629                     M_SONAME, M_NOWAIT | M_ZERO);
  630                 if (sin6 == NULL)
  631                         goto abort;
  632                 sin6->sin6_family = AF_INET6;
  633                 sin6->sin6_len = sizeof(*sin6);
  634                 sin6->sin6_addr = sc->sc_inc.inc6_faddr;
  635                 sin6->sin6_port = sc->sc_inc.inc_fport;
  636                 laddr6 = inp->in6p_laddr;
  637                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  638                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  639                 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) {
  640                         inp->in6p_laddr = laddr6;
  641                         FREE(sin6, M_SONAME);
  642                         goto abort;
  643                 }
  644                 FREE(sin6, M_SONAME);
  645         } else
  646 #endif
  647         {
  648                 struct in_addr laddr;
  649                 struct sockaddr_in *sin;
  650 
  651                 inp->inp_options = ip_srcroute();
  652                 if (inp->inp_options == NULL) {
  653                         inp->inp_options = sc->sc_ipopts;
  654                         sc->sc_ipopts = NULL;
  655                 }
  656 
  657                 MALLOC(sin, struct sockaddr_in *, sizeof *sin,
  658                     M_SONAME, M_NOWAIT | M_ZERO);
  659                 if (sin == NULL)
  660                         goto abort;
  661                 sin->sin_family = AF_INET;
  662                 sin->sin_len = sizeof(*sin);
  663                 sin->sin_addr = sc->sc_inc.inc_faddr;
  664                 sin->sin_port = sc->sc_inc.inc_fport;
  665                 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
  666                 laddr = inp->inp_laddr;
  667                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  668                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  669                 if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) {
  670                         inp->inp_laddr = laddr;
  671                         FREE(sin, M_SONAME);
  672                         goto abort;
  673                 }
  674                 FREE(sin, M_SONAME);
  675         }
  676 
  677         tp = intotcpcb(inp);
  678         tp->t_state = TCPS_SYN_RECEIVED;
  679         tp->iss = sc->sc_iss;
  680         tp->irs = sc->sc_irs;
  681         tcp_rcvseqinit(tp);
  682         tcp_sendseqinit(tp);
  683         tp->snd_wl1 = sc->sc_irs;
  684         tp->rcv_up = sc->sc_irs + 1;
  685         tp->rcv_wnd = sc->sc_wnd;
  686         tp->rcv_adv += tp->rcv_wnd;
  687 
  688         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  689         if (sc->sc_flags & SCF_NOOPT)
  690                 tp->t_flags |= TF_NOOPT;
  691         if (sc->sc_flags & SCF_WINSCALE) {
  692                 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  693                 tp->requested_s_scale = sc->sc_requested_s_scale;
  694                 tp->request_r_scale = sc->sc_request_r_scale;
  695         }
  696         if (sc->sc_flags & SCF_TIMESTAMP) {
  697                 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  698                 tp->ts_recent = sc->sc_tsrecent;
  699                 tp->ts_recent_age = ticks;
  700         }
  701         if (sc->sc_flags & SCF_CC) {
  702                 /*
  703                  * Initialization of the tcpcb for transaction;
  704                  *   set SND.WND = SEG.WND,
  705                  *   initialize CCsend and CCrecv.
  706                  */
  707                 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC;
  708                 tp->cc_send = sc->sc_cc_send;
  709                 tp->cc_recv = sc->sc_cc_recv;
  710         }
  711 
  712         /*
  713          * Set up MSS and get cached values from tcp_hostcache.
  714          * This might overwrite some of the defaults we just set.
  715          */
  716         tcp_mss(tp, sc->sc_peer_mss);
  717 
  718         /*
  719          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  720          */
  721         if (sc->sc_rxtslot != 0)
  722                 tp->snd_cwnd = tp->t_maxseg;
  723         callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
  724 
  725         INP_UNLOCK(inp);
  726 
  727         tcpstat.tcps_accepts++;
  728         return (so);
  729 
  730 abort:
  731         INP_UNLOCK(inp);
  732 abort2:
  733         if (so != NULL)
  734                 (void) soabort(so);
  735         return (NULL);
  736 }
  737 
  738 /*
  739  * This function gets called when we receive an ACK for a
  740  * socket in the LISTEN state.  We look up the connection
  741  * in the syncache, and if its there, we pull it out of
  742  * the cache and turn it into a full-blown connection in
  743  * the SYN-RECEIVED state.
  744  */
  745 int
  746 syncache_expand(inc, th, sop, m)
  747         struct in_conninfo *inc;
  748         struct tcphdr *th;
  749         struct socket **sop;
  750         struct mbuf *m;
  751 {
  752         struct syncache *sc;
  753         struct syncache_head *sch;
  754         struct socket *so;
  755 
  756         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  757 
  758         sc = syncache_lookup(inc, &sch);
  759         if (sc == NULL) {
  760                 /*
  761                  * There is no syncache entry, so see if this ACK is 
  762                  * a returning syncookie.  To do this, first:
  763                  *  A. See if this socket has had a syncache entry dropped in
  764                  *     the past.  We don't want to accept a bogus syncookie
  765                  *     if we've never received a SYN.
  766                  *  B. check that the syncookie is valid.  If it is, then
  767                  *     cobble up a fake syncache entry, and return.
  768                  */
  769                 if (!tcp_syncookies)
  770                         return (0);
  771                 sc = syncookie_lookup(inc, th, *sop);
  772                 if (sc == NULL)
  773                         return (0);
  774                 sch = NULL;
  775                 tcpstat.tcps_sc_recvcookie++;
  776         }
  777 
  778         /*
  779          * If seg contains an ACK, but not for our SYN/ACK, send a RST.
  780          */
  781         if (th->th_ack != sc->sc_iss + 1)
  782                 return (0);
  783 
  784         so = syncache_socket(sc, *sop, m);
  785         if (so == NULL) {
  786 #if 0
  787 resetandabort:
  788                 /* XXXjlemon check this - is this correct? */
  789                 (void) tcp_respond(NULL, m, m, th,
  790                     th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
  791 #endif
  792                 m_freem(m);                     /* XXX only needed for above */
  793                 tcpstat.tcps_sc_aborted++;
  794         } else
  795                 tcpstat.tcps_sc_completed++;
  796 
  797         if (sch == NULL)
  798                 syncache_free(sc);
  799         else
  800                 syncache_drop(sc, sch);
  801         *sop = so;
  802         return (1);
  803 }
  804 
  805 /*
  806  * Given a LISTEN socket and an inbound SYN request, add
  807  * this to the syn cache, and send back a segment:
  808  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  809  * to the source.
  810  *
  811  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  812  * Doing so would require that we hold onto the data and deliver it
  813  * to the application.  However, if we are the target of a SYN-flood
  814  * DoS attack, an attacker could send data which would eventually
  815  * consume all available buffer space if it were ACKed.  By not ACKing
  816  * the data, we avoid this DoS scenario.
  817  */
  818 int
  819 syncache_add(inc, to, th, sop, m)
  820         struct in_conninfo *inc;
  821         struct tcpopt *to;
  822         struct tcphdr *th;
  823         struct socket **sop;
  824         struct mbuf *m;
  825 {
  826         struct tcpcb *tp;
  827         struct socket *so;
  828         struct syncache *sc = NULL;
  829         struct syncache_head *sch;
  830         struct mbuf *ipopts = NULL;
  831         struct rmxp_tao tao;
  832         int i, win;
  833 
  834         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  835 
  836         so = *sop;
  837         tp = sototcpcb(so);
  838         bzero(&tao, sizeof(tao));
  839 
  840         /*
  841          * Remember the IP options, if any.
  842          */
  843 #ifdef INET6
  844         if (!inc->inc_isipv6)
  845 #endif
  846                 ipopts = ip_srcroute();
  847 
  848         /*
  849          * See if we already have an entry for this connection.
  850          * If we do, resend the SYN,ACK, and reset the retransmit timer.
  851          *
  852          * XXX
  853          * should the syncache be re-initialized with the contents
  854          * of the new SYN here (which may have different options?)
  855          */
  856         sc = syncache_lookup(inc, &sch);
  857         if (sc != NULL) {
  858                 tcpstat.tcps_sc_dupsyn++;
  859                 if (ipopts) {
  860                         /*
  861                          * If we were remembering a previous source route,
  862                          * forget it and use the new one we've been given.
  863                          */
  864                         if (sc->sc_ipopts)
  865                                 (void) m_free(sc->sc_ipopts);
  866                         sc->sc_ipopts = ipopts;
  867                 }
  868                 /*
  869                  * Update timestamp if present.
  870                  */
  871                 if (sc->sc_flags & SCF_TIMESTAMP)
  872                         sc->sc_tsrecent = to->to_tsval;
  873                 /*
  874                  * PCB may have changed, pick up new values.
  875                  */
  876                 sc->sc_tp = tp;
  877                 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  878 #ifdef TCPDEBUG
  879                 if (syncache_respond(sc, m, so) == 0) {
  880 #else
  881                 if (syncache_respond(sc, m) == 0) {
  882 #endif
  883                         /* NB: guarded by INP_INFO_WLOCK(&tcbinfo) */
  884                         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot],
  885                             sc, sc_timerq);
  886                         SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot);
  887                         tcpstat.tcps_sndacks++;
  888                         tcpstat.tcps_sndtotal++;
  889                 }
  890                 *sop = NULL;
  891                 return (1);
  892         }
  893 
  894         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
  895         if (sc == NULL) {
  896                 /*
  897                  * The zone allocator couldn't provide more entries.
  898                  * Treat this as if the cache was full; drop the oldest 
  899                  * entry and insert the new one.
  900                  */
  901                 /* NB: guarded by INP_INFO_WLOCK(&tcbinfo) */
  902                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  903                         sc = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  904                         if (sc != NULL)
  905                                 break;
  906                 }
  907                 sc->sc_tp->ts_recent = ticks;
  908                 syncache_drop(sc, NULL);
  909                 tcpstat.tcps_sc_zonefail++;
  910                 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
  911                 if (sc == NULL) {
  912                         if (ipopts)
  913                                 (void) m_free(ipopts);
  914                         return (0);
  915                 }
  916         }
  917 
  918         /*
  919          * Fill in the syncache values.
  920          */
  921         bzero(sc, sizeof(*sc));
  922         sc->sc_tp = tp;
  923         sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  924         sc->sc_ipopts = ipopts;
  925         sc->sc_inc.inc_fport = inc->inc_fport;
  926         sc->sc_inc.inc_lport = inc->inc_lport;
  927 #ifdef INET6
  928         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
  929         if (inc->inc_isipv6) {
  930                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
  931                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
  932         } else
  933 #endif
  934         {
  935                 sc->sc_inc.inc_faddr = inc->inc_faddr;
  936                 sc->sc_inc.inc_laddr = inc->inc_laddr;
  937         }
  938         sc->sc_irs = th->th_seq;
  939         sc->sc_flags = 0;
  940         sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
  941         if (tcp_syncookies)
  942                 sc->sc_iss = syncookie_generate(sc);
  943         else
  944                 sc->sc_iss = arc4random();
  945 
  946         /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */
  947         win = sbspace(&so->so_rcv);
  948         win = imax(win, 0);
  949         win = imin(win, TCP_MAXWIN);
  950         sc->sc_wnd = win;
  951 
  952         if (tcp_do_rfc1323) {
  953                 /*
  954                  * A timestamp received in a SYN makes
  955                  * it ok to send timestamp requests and replies.
  956                  */
  957                 if (to->to_flags & TOF_TS) {
  958                         sc->sc_tsrecent = to->to_tsval;
  959                         sc->sc_flags |= SCF_TIMESTAMP;
  960                 }
  961                 if (to->to_flags & TOF_SCALE) {
  962                         int wscale = 0;
  963 
  964                         /* Compute proper scaling value from buffer space */
  965                         while (wscale < TCP_MAX_WINSHIFT &&
  966                             (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat)
  967                                 wscale++;
  968                         sc->sc_request_r_scale = wscale;
  969                         sc->sc_requested_s_scale = to->to_requested_s_scale;
  970                         sc->sc_flags |= SCF_WINSCALE;
  971                 }
  972         }
  973         if (tcp_do_rfc1644) {
  974                 /*
  975                  * A CC or CC.new option received in a SYN makes
  976                  * it ok to send CC in subsequent segments.
  977                  */
  978                 if (to->to_flags & (TOF_CC|TOF_CCNEW)) {
  979                         sc->sc_cc_recv = to->to_cc;
  980                         sc->sc_cc_send = CC_INC(tcp_ccgen);
  981                         sc->sc_flags |= SCF_CC;
  982                 }
  983         }
  984         if (tp->t_flags & TF_NOOPT)
  985                 sc->sc_flags = SCF_NOOPT;
  986 
  987         /*
  988          * XXX
  989          * We have the option here of not doing TAO (even if the segment
  990          * qualifies) and instead fall back to a normal 3WHS via the syncache.
  991          * This allows us to apply synflood protection to TAO-qualifying SYNs
  992          * also. However, there should be a hueristic to determine when to
  993          * do this, and is not present at the moment.
  994          */
  995 
  996         /*
  997          * Perform TAO test on incoming CC (SEG.CC) option, if any.
  998          * - compare SEG.CC against cached CC from the same host, if any.
  999          * - if SEG.CC > chached value, SYN must be new and is accepted
 1000          *      immediately: save new CC in the cache, mark the socket
 1001          *      connected, enter ESTABLISHED state, turn on flag to
 1002          *      send a SYN in the next segment.
 1003          *      A virtual advertised window is set in rcv_adv to
 1004          *      initialize SWS prevention.  Then enter normal segment
 1005          *      processing: drop SYN, process data and FIN.
 1006          * - otherwise do a normal 3-way handshake.
 1007          */
 1008         if (tcp_do_rfc1644)
 1009                 tcp_hc_gettao(&sc->sc_inc, &tao);
 1010 
 1011         if ((to->to_flags & TOF_CC) != 0) {
 1012                 if (((tp->t_flags & TF_NOPUSH) != 0) &&
 1013                     sc->sc_flags & SCF_CC && tao.tao_cc != 0 &&
 1014                     CC_GT(to->to_cc, tao.tao_cc)) {
 1015                         sc->sc_rxtslot = 0;
 1016                         so = syncache_socket(sc, *sop, m);
 1017                         if (so != NULL) {
 1018                                 tao.tao_cc = to->to_cc;
 1019                                 tcp_hc_updatetao(&sc->sc_inc, TCP_HC_TAO_CC,
 1020                                                  tao.tao_cc, 0);
 1021                                 *sop = so;
 1022                         }
 1023                         syncache_free(sc);
 1024                         return (so != NULL);
 1025                 }
 1026         } else {
 1027                 /*
 1028                  * No CC option, but maybe CC.NEW: invalidate cached value.
 1029                  */
 1030                 if (tcp_do_rfc1644) {
 1031                         tao.tao_cc = 0;
 1032                         tcp_hc_updatetao(&sc->sc_inc, TCP_HC_TAO_CC,
 1033                                          tao.tao_cc, 0);
 1034                 }
 1035         }
 1036 
 1037         /*
 1038          * TAO test failed or there was no CC option,
 1039          *    do a standard 3-way handshake.
 1040          */
 1041 #ifdef TCPDEBUG
 1042         if (syncache_respond(sc, m, so) == 0) {
 1043 #else
 1044         if (syncache_respond(sc, m) == 0) {
 1045 #endif
 1046                 syncache_insert(sc, sch);
 1047                 tcpstat.tcps_sndacks++;
 1048                 tcpstat.tcps_sndtotal++;
 1049         } else {
 1050                 syncache_free(sc);
 1051                 tcpstat.tcps_sc_dropped++;
 1052         }
 1053         *sop = NULL;
 1054         return (1);
 1055 }
 1056 
 1057 #ifdef TCPDEBUG
 1058 static int
 1059 syncache_respond(sc, m, so)
 1060         struct syncache *sc;
 1061         struct mbuf *m;
 1062         struct socket *so;
 1063 #else
 1064 static int
 1065 syncache_respond(sc, m)
 1066         struct syncache *sc;
 1067         struct mbuf *m;
 1068 #endif
 1069 {
 1070         u_int8_t *optp;
 1071         int optlen, error;
 1072         u_int16_t tlen, hlen, mssopt;
 1073         struct ip *ip = NULL;
 1074         struct tcphdr *th;
 1075         struct inpcb *inp;
 1076 #ifdef INET6
 1077         struct ip6_hdr *ip6 = NULL;
 1078 #endif
 1079 
 1080         hlen =
 1081 #ifdef INET6
 1082                (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 
 1083 #endif
 1084                 sizeof(struct ip);
 1085 
 1086         KASSERT((&sc->sc_inc) != NULL, ("syncache_respond with NULL in_conninfo pointer"));
 1087 
 1088         /* Determine MSS we advertize to other end of connection */
 1089         mssopt = tcp_mssopt(&sc->sc_inc);
 1090 
 1091         /* Compute the size of the TCP options. */
 1092         if (sc->sc_flags & SCF_NOOPT) {
 1093                 optlen = 0;
 1094         } else {
 1095                 optlen = TCPOLEN_MAXSEG +
 1096                     ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
 1097                     ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) +
 1098                     ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0);
 1099         }
 1100         tlen = hlen + sizeof(struct tcphdr) + optlen;
 1101 
 1102         /*
 1103          * XXX
 1104          * assume that the entire packet will fit in a header mbuf
 1105          */
 1106         KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
 1107 
 1108         /*
 1109          * XXX shouldn't this reuse the mbuf if possible ?
 1110          * Create the IP+TCP header from scratch.
 1111          */
 1112         if (m)
 1113                 m_freem(m);
 1114 
 1115         m = m_gethdr(M_DONTWAIT, MT_HEADER);
 1116         if (m == NULL)
 1117                 return (ENOBUFS);
 1118         m->m_data += max_linkhdr;
 1119         m->m_len = tlen;
 1120         m->m_pkthdr.len = tlen;
 1121         m->m_pkthdr.rcvif = NULL;
 1122         inp = sc->sc_tp->t_inpcb;
 1123         INP_LOCK(inp);
 1124 #ifdef MAC
 1125         mac_create_mbuf_from_socket(inp->inp_socket, m);
 1126 #endif
 1127 
 1128 #ifdef INET6
 1129         if (sc->sc_inc.inc_isipv6) {
 1130                 ip6 = mtod(m, struct ip6_hdr *);
 1131                 ip6->ip6_vfc = IPV6_VERSION;
 1132                 ip6->ip6_nxt = IPPROTO_TCP;
 1133                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1134                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1135                 ip6->ip6_plen = htons(tlen - hlen);
 1136                 /* ip6_hlim is set after checksum */
 1137                 /* ip6_flow = ??? */
 1138 
 1139                 th = (struct tcphdr *)(ip6 + 1);
 1140         } else
 1141 #endif
 1142         {
 1143                 ip = mtod(m, struct ip *);
 1144                 ip->ip_v = IPVERSION;
 1145                 ip->ip_hl = sizeof(struct ip) >> 2;
 1146                 ip->ip_len = tlen;
 1147                 ip->ip_id = 0;
 1148                 ip->ip_off = 0;
 1149                 ip->ip_sum = 0;
 1150                 ip->ip_p = IPPROTO_TCP;
 1151                 ip->ip_src = sc->sc_inc.inc_laddr;
 1152                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1153                 ip->ip_ttl = inp->inp_ip_ttl;   /* XXX */
 1154                 ip->ip_tos = inp->inp_ip_tos;   /* XXX */
 1155 
 1156                 /*
 1157                  * See if we should do MTU discovery.  Route lookups are
 1158                  * expensive, so we will only unset the DF bit if:
 1159                  *
 1160                  *      1) path_mtu_discovery is disabled
 1161                  *      2) the SCF_UNREACH flag has been set
 1162                  */
 1163                 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1164                        ip->ip_off |= IP_DF;
 1165 
 1166                 th = (struct tcphdr *)(ip + 1);
 1167         }
 1168         th->th_sport = sc->sc_inc.inc_lport;
 1169         th->th_dport = sc->sc_inc.inc_fport;
 1170 
 1171         th->th_seq = htonl(sc->sc_iss);
 1172         th->th_ack = htonl(sc->sc_irs + 1);
 1173         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1174         th->th_x2 = 0;
 1175         th->th_flags = TH_SYN|TH_ACK;
 1176         th->th_win = htons(sc->sc_wnd);
 1177         th->th_urp = 0;
 1178 
 1179         /* Tack on the TCP options. */
 1180         if (optlen != 0) {
 1181                 optp = (u_int8_t *)(th + 1);
 1182                 *optp++ = TCPOPT_MAXSEG;
 1183                 *optp++ = TCPOLEN_MAXSEG;
 1184                 *optp++ = (mssopt >> 8) & 0xff;
 1185                 *optp++ = mssopt & 0xff;
 1186 
 1187                 if (sc->sc_flags & SCF_WINSCALE) {
 1188                         *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
 1189                             TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
 1190                             sc->sc_request_r_scale);
 1191                         optp += 4;
 1192                 }
 1193 
 1194                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1195                         u_int32_t *lp = (u_int32_t *)(optp);
 1196 
 1197                         /* Form timestamp option per appendix A of RFC 1323. */
 1198                         *lp++ = htonl(TCPOPT_TSTAMP_HDR);
 1199                         *lp++ = htonl(ticks);
 1200                         *lp   = htonl(sc->sc_tsrecent);
 1201                         optp += TCPOLEN_TSTAMP_APPA;
 1202                 }
 1203 
 1204                 /*
 1205                  * Send CC and CC.echo if we received CC from our peer.
 1206                  */
 1207                 if (sc->sc_flags & SCF_CC) {
 1208                         u_int32_t *lp = (u_int32_t *)(optp);
 1209 
 1210                         *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC));
 1211                         *lp++ = htonl(sc->sc_cc_send);
 1212                         *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO));
 1213                         *lp   = htonl(sc->sc_cc_recv);
 1214                         optp += TCPOLEN_CC_APPA * 2;
 1215                 }
 1216         }
 1217 
 1218 #ifdef INET6
 1219         if (sc->sc_inc.inc_isipv6) {
 1220                 th->th_sum = 0;
 1221                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
 1222                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1223                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, inp);
 1224         } else
 1225 #endif
 1226         {
 1227                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1228                     htons(tlen - hlen + IPPROTO_TCP));
 1229                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1230                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1231 #ifdef TCPDEBUG
 1232                 /*
 1233                  * Trace.
 1234                  */
 1235                 if (so != NULL && so->so_options & SO_DEBUG) {
 1236                         struct tcpcb *tp = sototcpcb(so);
 1237                         tcp_trace(TA_OUTPUT, tp->t_state, tp,
 1238                             mtod(m, void *), th, 0);
 1239                 }
 1240 #endif
 1241                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, inp);
 1242         }
 1243         INP_UNLOCK(inp);
 1244         return (error);
 1245 }
 1246 
 1247 /*
 1248  * cookie layers:
 1249  *
 1250  *      |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
 1251  *      | peer iss                                                      |
 1252  *      | MD5(laddr,faddr,secret,lport,fport)             |. . . . . . .|
 1253  *      |                     0                       |(A)|             |
 1254  * (A): peer mss index
 1255  */
 1256 
 1257 /*
 1258  * The values below are chosen to minimize the size of the tcp_secret
 1259  * table, as well as providing roughly a 16 second lifetime for the cookie.
 1260  */
 1261 
 1262 #define SYNCOOKIE_WNDBITS       5       /* exposed bits for window indexing */
 1263 #define SYNCOOKIE_TIMESHIFT     1       /* scale ticks to window time units */
 1264 
 1265 #define SYNCOOKIE_WNDMASK       ((1 << SYNCOOKIE_WNDBITS) - 1)
 1266 #define SYNCOOKIE_NSECRETS      (1 << SYNCOOKIE_WNDBITS)
 1267 #define SYNCOOKIE_TIMEOUT \
 1268     (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
 1269 #define SYNCOOKIE_DATAMASK      ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
 1270 
 1271 static struct {
 1272         u_int32_t       ts_secbits[4];
 1273         u_int           ts_expire;
 1274 } tcp_secret[SYNCOOKIE_NSECRETS];
 1275 
 1276 static int tcp_msstab[] = { 0, 536, 1460, 8960 };
 1277 
 1278 static MD5_CTX syn_ctx;
 1279 
 1280 #define MD5Add(v)       MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
 1281 
 1282 struct md5_add {
 1283         u_int32_t laddr, faddr;
 1284         u_int32_t secbits[4];
 1285         u_int16_t lport, fport;
 1286 };
 1287 
 1288 #ifdef CTASSERT
 1289 CTASSERT(sizeof(struct md5_add) == 28);
 1290 #endif
 1291 
 1292 /*
 1293  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1294  * original SYN was accepted, the connection is established.  The second 
 1295  * SYN is inflight, and if it arrives with an ISN that falls within the 
 1296  * receive window, the connection is killed.  
 1297  *
 1298  * However, since cookies have other problems, this may not be worth
 1299  * worrying about.
 1300  */
 1301 
 1302 static u_int32_t
 1303 syncookie_generate(struct syncache *sc)
 1304 {
 1305         u_int32_t md5_buffer[4];
 1306         u_int32_t data;
 1307         int idx, i;
 1308         struct md5_add add;
 1309 
 1310         /* NB: single threaded; could add INP_INFO_WLOCK_ASSERT(&tcbinfo) */
 1311 
 1312         idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
 1313         if (tcp_secret[idx].ts_expire < ticks) {
 1314                 for (i = 0; i < 4; i++)
 1315                         tcp_secret[idx].ts_secbits[i] = arc4random();
 1316                 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
 1317         }
 1318         for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--)
 1319                 if (tcp_msstab[data] <= sc->sc_peer_mss)
 1320                         break;
 1321         data = (data << SYNCOOKIE_WNDBITS) | idx;
 1322         data ^= sc->sc_irs;                             /* peer's iss */
 1323         MD5Init(&syn_ctx);
 1324 #ifdef INET6
 1325         if (sc->sc_inc.inc_isipv6) {
 1326                 MD5Add(sc->sc_inc.inc6_laddr);
 1327                 MD5Add(sc->sc_inc.inc6_faddr);
 1328                 add.laddr = 0;
 1329                 add.faddr = 0;
 1330         } else
 1331 #endif
 1332         {
 1333                 add.laddr = sc->sc_inc.inc_laddr.s_addr;
 1334                 add.faddr = sc->sc_inc.inc_faddr.s_addr;
 1335         }
 1336         add.lport = sc->sc_inc.inc_lport;
 1337         add.fport = sc->sc_inc.inc_fport;
 1338         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1339         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1340         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1341         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1342         MD5Add(add);
 1343         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1344         data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
 1345         return (data);
 1346 }
 1347 
 1348 static struct syncache *
 1349 syncookie_lookup(inc, th, so)
 1350         struct in_conninfo *inc;
 1351         struct tcphdr *th;
 1352         struct socket *so;
 1353 {
 1354         u_int32_t md5_buffer[4];
 1355         struct syncache *sc;
 1356         u_int32_t data;
 1357         int wnd, idx;
 1358         struct md5_add add;
 1359 
 1360         /* NB: single threaded; could add INP_INFO_WLOCK_ASSERT(&tcbinfo) */
 1361 
 1362         data = (th->th_ack - 1) ^ (th->th_seq - 1);     /* remove ISS */
 1363         idx = data & SYNCOOKIE_WNDMASK;
 1364         if (tcp_secret[idx].ts_expire < ticks ||
 1365             sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
 1366                 return (NULL);
 1367         MD5Init(&syn_ctx);
 1368 #ifdef INET6
 1369         if (inc->inc_isipv6) {
 1370                 MD5Add(inc->inc6_laddr);
 1371                 MD5Add(inc->inc6_faddr);
 1372                 add.laddr = 0;
 1373                 add.faddr = 0;
 1374         } else
 1375 #endif
 1376         {
 1377                 add.laddr = inc->inc_laddr.s_addr;
 1378                 add.faddr = inc->inc_faddr.s_addr;
 1379         }
 1380         add.lport = inc->inc_lport;
 1381         add.fport = inc->inc_fport;
 1382         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1383         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1384         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1385         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1386         MD5Add(add);
 1387         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1388         data ^= md5_buffer[0];
 1389         if ((data & ~SYNCOOKIE_DATAMASK) != 0)
 1390                 return (NULL);
 1391         data = data >> SYNCOOKIE_WNDBITS;
 1392 
 1393         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
 1394         if (sc == NULL)
 1395                 return (NULL);
 1396         /*
 1397          * Fill in the syncache values.
 1398          * XXX duplicate code from syncache_add
 1399          */
 1400         sc->sc_ipopts = NULL;
 1401         sc->sc_inc.inc_fport = inc->inc_fport;
 1402         sc->sc_inc.inc_lport = inc->inc_lport;
 1403 #ifdef INET6
 1404         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
 1405         if (inc->inc_isipv6) {
 1406                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
 1407                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
 1408         } else
 1409 #endif
 1410         {
 1411                 sc->sc_inc.inc_faddr = inc->inc_faddr;
 1412                 sc->sc_inc.inc_laddr = inc->inc_laddr;
 1413         }
 1414         sc->sc_irs = th->th_seq - 1;
 1415         sc->sc_iss = th->th_ack - 1;
 1416         wnd = sbspace(&so->so_rcv);
 1417         wnd = imax(wnd, 0);
 1418         wnd = imin(wnd, TCP_MAXWIN);
 1419         sc->sc_wnd = wnd;
 1420         sc->sc_flags = 0;
 1421         sc->sc_rxtslot = 0;
 1422         sc->sc_peer_mss = tcp_msstab[data];
 1423         return (sc);
 1424 }

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