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

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    1 /*-
    2  * Copyright (c) 2001 McAfee, Inc.
    3  * All rights reserved.
    4  *
    5  * This software was developed for the FreeBSD Project by Jonathan Lemon
    6  * and McAfee Research, the Security Research Division of McAfee, Inc. under
    7  * 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  *
   19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  * $FreeBSD: releng/6.4/sys/netinet/tcp_syncache.c 172384 2007-09-28 17:39:45Z maxim $
   32  */
   33 
   34 #include "opt_inet.h"
   35 #include "opt_inet6.h"
   36 #include "opt_ipsec.h"
   37 #include "opt_mac.h"
   38 #include "opt_tcpdebug.h"
   39 #include "opt_tcp_sack.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/malloc.h>
   46 #include <sys/mac.h>
   47 #include <sys/mbuf.h>
   48 #include <sys/md5.h>
   49 #include <sys/proc.h>           /* for proc0 declaration */
   50 #include <sys/random.h>
   51 #include <sys/socket.h>
   52 #include <sys/socketvar.h>
   53 
   54 #include <net/if.h>
   55 #include <net/route.h>
   56 
   57 #include <netinet/in.h>
   58 #include <netinet/in_systm.h>
   59 #include <netinet/ip.h>
   60 #include <netinet/in_var.h>
   61 #include <netinet/in_pcb.h>
   62 #include <netinet/ip_var.h>
   63 #ifdef INET6
   64 #include <netinet/ip6.h>
   65 #include <netinet/icmp6.h>
   66 #include <netinet6/nd6.h>
   67 #include <netinet6/ip6_var.h>
   68 #include <netinet6/in6_pcb.h>
   69 #endif
   70 #include <netinet/tcp.h>
   71 #ifdef TCPDEBUG
   72 #include <netinet/tcpip.h>
   73 #endif
   74 #include <netinet/tcp_fsm.h>
   75 #include <netinet/tcp_seq.h>
   76 #include <netinet/tcp_timer.h>
   77 #include <netinet/tcp_var.h>
   78 #ifdef TCPDEBUG
   79 #include <netinet/tcp_debug.h>
   80 #endif
   81 #ifdef INET6
   82 #include <netinet6/tcp6_var.h>
   83 #endif
   84 
   85 #ifdef IPSEC
   86 #include <netinet6/ipsec.h>
   87 #ifdef INET6
   88 #include <netinet6/ipsec6.h>
   89 #endif
   90 #endif /*IPSEC*/
   91 
   92 #ifdef FAST_IPSEC
   93 #include <netipsec/ipsec.h>
   94 #ifdef INET6
   95 #include <netipsec/ipsec6.h>
   96 #endif
   97 #include <netipsec/key.h>
   98 #endif /*FAST_IPSEC*/
   99 
  100 #include <machine/in_cksum.h>
  101 #include <vm/uma.h>
  102 
  103 static int tcp_syncookies = 1;
  104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  105     &tcp_syncookies, 0,
  106     "Use TCP SYN cookies if the syncache overflows");
  107 
  108 static void      syncache_drop(struct syncache *, struct syncache_head *);
  109 static void      syncache_free(struct syncache *);
  110 static void      syncache_insert(struct syncache *, struct syncache_head *);
  111 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  112 #ifdef TCPDEBUG
  113 static int       syncache_respond(struct syncache *, struct mbuf *, struct socket *);
  114 #else
  115 static int       syncache_respond(struct syncache *, struct mbuf *);
  116 #endif
  117 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  118                     struct mbuf *m);
  119 static void      syncache_timer(void *);
  120 static u_int32_t syncookie_generate(struct syncache *, u_int32_t *);
  121 static struct syncache *syncookie_lookup(struct in_conninfo *,
  122                     struct tcphdr *, struct socket *);
  123 
  124 /*
  125  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  126  * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
  127  * the odds are that the user has given up attempting to connect by then.
  128  */
  129 #define SYNCACHE_MAXREXMTS              3
  130 
  131 /* Arbitrary values */
  132 #define TCP_SYNCACHE_HASHSIZE           512
  133 #define TCP_SYNCACHE_BUCKETLIMIT        30
  134 
  135 struct tcp_syncache {
  136         struct  syncache_head *hashbase;
  137         uma_zone_t zone;
  138         u_int   hashsize;
  139         u_int   hashmask;
  140         u_int   bucket_limit;
  141         u_int   cache_count;
  142         u_int   cache_limit;
  143         u_int   rexmt_limit;
  144         u_int   hash_secret;
  145         TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1];
  146         struct  callout tt_timerq[SYNCACHE_MAXREXMTS + 1];
  147 };
  148 static struct tcp_syncache tcp_syncache;
  149 
  150 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  151 
  152 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  153      &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
  154 
  155 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  156      &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
  157 
  158 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  159      &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
  160 
  161 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  162      &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
  163 
  164 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  165      &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
  166 
  167 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  168 
  169 #define SYNCACHE_HASH(inc, mask)                                        \
  170         ((tcp_syncache.hash_secret ^                                    \
  171           (inc)->inc_faddr.s_addr ^                                     \
  172           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  173           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  174 
  175 #define SYNCACHE_HASH6(inc, mask)                                       \
  176         ((tcp_syncache.hash_secret ^                                    \
  177           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  178           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  179           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  180 
  181 #define ENDPTS_EQ(a, b) (                                               \
  182         (a)->ie_fport == (b)->ie_fport &&                               \
  183         (a)->ie_lport == (b)->ie_lport &&                               \
  184         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  185         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  186 )
  187 
  188 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  189 
  190 #define SYNCACHE_TIMEOUT(sc, slot) do {                         \
  191         sc->sc_rxtslot = (slot);                                        \
  192         sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[(slot)];   \
  193         TAILQ_INSERT_TAIL(&tcp_syncache.timerq[(slot)], sc, sc_timerq); \
  194         if (!callout_active(&tcp_syncache.tt_timerq[(slot)]))           \
  195                 callout_reset(&tcp_syncache.tt_timerq[(slot)],          \
  196                     TCPTV_RTOBASE * tcp_backoff[(slot)],                \
  197                     syncache_timer, (void *)((intptr_t)(slot)));        \
  198 } while (0)
  199 
  200 static void
  201 syncache_free(struct syncache *sc)
  202 {
  203         if (sc->sc_ipopts)
  204                 (void) m_free(sc->sc_ipopts);
  205 
  206         uma_zfree(tcp_syncache.zone, sc);
  207 }
  208 
  209 void
  210 syncache_init(void)
  211 {
  212         int i;
  213 
  214         tcp_syncache.cache_count = 0;
  215         tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  216         tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  217         tcp_syncache.cache_limit =
  218             tcp_syncache.hashsize * tcp_syncache.bucket_limit;
  219         tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  220         tcp_syncache.hash_secret = arc4random();
  221 
  222         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  223             &tcp_syncache.hashsize);
  224         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  225             &tcp_syncache.cache_limit);
  226         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  227             &tcp_syncache.bucket_limit);
  228         if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) {
  229                 printf("WARNING: syncache hash size is not a power of 2.\n");
  230                 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  231         }
  232         tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
  233 
  234         /* Allocate the hash table. */
  235         MALLOC(tcp_syncache.hashbase, struct syncache_head *,
  236             tcp_syncache.hashsize * sizeof(struct syncache_head),
  237             M_SYNCACHE, M_WAITOK);
  238 
  239         /* Initialize the hash buckets. */
  240         for (i = 0; i < tcp_syncache.hashsize; i++) {
  241                 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
  242                 tcp_syncache.hashbase[i].sch_length = 0;
  243         }
  244 
  245         /* Initialize the timer queues. */
  246         for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
  247                 TAILQ_INIT(&tcp_syncache.timerq[i]);
  248                 callout_init(&tcp_syncache.tt_timerq[i], NET_CALLOUT_MPSAFE);
  249         }
  250 
  251         /*
  252          * Allocate the syncache entries.  Allow the zone to allocate one
  253          * more entry than cache limit, so a new entry can bump out an
  254          * older one.
  255          */
  256         tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  257             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  258         uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
  259         tcp_syncache.cache_limit -= 1;
  260 }
  261 
  262 static void
  263 syncache_insert(sc, sch)
  264         struct syncache *sc;
  265         struct syncache_head *sch;
  266 {
  267         struct syncache *sc2;
  268         int i;
  269 
  270         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  271 
  272         /*
  273          * Make sure that we don't overflow the per-bucket
  274          * limit or the total cache size limit.
  275          */
  276         if (sch->sch_length >= tcp_syncache.bucket_limit) {
  277                 /*
  278                  * The bucket is full, toss the oldest element.
  279                  */
  280                 sc2 = TAILQ_FIRST(&sch->sch_bucket);
  281                 sc2->sc_tp->ts_recent = ticks;
  282                 syncache_drop(sc2, sch);
  283                 tcpstat.tcps_sc_bucketoverflow++;
  284         } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) {
  285                 /*
  286                  * The cache is full.  Toss the oldest entry in the
  287                  * entire cache.  This is the front entry in the
  288                  * first non-empty timer queue with the largest
  289                  * timeout value.
  290                  */
  291                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  292                         sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  293                         if (sc2 != NULL)
  294                                 break;
  295                 }
  296                 sc2->sc_tp->ts_recent = ticks;
  297                 syncache_drop(sc2, NULL);
  298                 tcpstat.tcps_sc_cacheoverflow++;
  299         }
  300 
  301         /* Initialize the entry's timer. */
  302         SYNCACHE_TIMEOUT(sc, 0);
  303 
  304         /* Put it into the bucket. */
  305         TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
  306         sch->sch_length++;
  307         tcp_syncache.cache_count++;
  308         tcpstat.tcps_sc_added++;
  309 }
  310 
  311 static void
  312 syncache_drop(sc, sch)
  313         struct syncache *sc;
  314         struct syncache_head *sch;
  315 {
  316         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  317 
  318         if (sch == NULL) {
  319 #ifdef INET6
  320                 if (sc->sc_inc.inc_isipv6) {
  321                         sch = &tcp_syncache.hashbase[
  322                             SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
  323                 } else
  324 #endif
  325                 {
  326                         sch = &tcp_syncache.hashbase[
  327                             SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
  328                 }
  329         }
  330 
  331         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  332         sch->sch_length--;
  333         tcp_syncache.cache_count--;
  334 
  335         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq);
  336         if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot]))
  337                 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]);
  338 
  339         syncache_free(sc);
  340 }
  341 
  342 /*
  343  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  344  * If we have retransmitted an entry the maximum number of times, expire it.
  345  */
  346 static void
  347 syncache_timer(xslot)
  348         void *xslot;
  349 {
  350         intptr_t slot = (intptr_t)xslot;
  351         struct syncache *sc, *nsc;
  352         struct inpcb *inp;
  353 
  354         INP_INFO_WLOCK(&tcbinfo);
  355         if (callout_pending(&tcp_syncache.tt_timerq[slot]) ||
  356             !callout_active(&tcp_syncache.tt_timerq[slot])) {
  357                 /* XXX can this happen? */
  358                 INP_INFO_WUNLOCK(&tcbinfo);
  359                 return;
  360         }
  361         callout_deactivate(&tcp_syncache.tt_timerq[slot]);
  362 
  363         nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]);
  364         while (nsc != NULL) {
  365                 if (ticks < nsc->sc_rxttime)
  366                         break;
  367                 sc = nsc;
  368                 inp = sc->sc_tp->t_inpcb;
  369                 if (slot == SYNCACHE_MAXREXMTS ||
  370                     slot >= tcp_syncache.rexmt_limit ||
  371                     inp == NULL || inp->inp_gencnt != sc->sc_inp_gencnt) {
  372                         nsc = TAILQ_NEXT(sc, sc_timerq);
  373                         syncache_drop(sc, NULL);
  374                         tcpstat.tcps_sc_stale++;
  375                         continue;
  376                 }
  377                 /*
  378                  * syncache_respond() may call back into the syncache to
  379                  * to modify another entry, so do not obtain the next
  380                  * entry on the timer chain until it has completed.
  381                  */
  382 #ifdef TCPDEBUG
  383                 (void) syncache_respond(sc, NULL, NULL);
  384 #else
  385                 (void) syncache_respond(sc, NULL);
  386 #endif
  387                 nsc = TAILQ_NEXT(sc, sc_timerq);
  388                 tcpstat.tcps_sc_retransmitted++;
  389                 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq);
  390                 SYNCACHE_TIMEOUT(sc, slot + 1);
  391         }
  392         if (nsc != NULL)
  393                 callout_reset(&tcp_syncache.tt_timerq[slot],
  394                     nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot));
  395         INP_INFO_WUNLOCK(&tcbinfo);
  396 }
  397 
  398 /*
  399  * Find an entry in the syncache.
  400  */
  401 struct syncache *
  402 syncache_lookup(inc, schp)
  403         struct in_conninfo *inc;
  404         struct syncache_head **schp;
  405 {
  406         struct syncache *sc;
  407         struct syncache_head *sch;
  408 
  409         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  410 
  411 #ifdef INET6
  412         if (inc->inc_isipv6) {
  413                 sch = &tcp_syncache.hashbase[
  414                     SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
  415                 *schp = sch;
  416                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  417                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  418                                 return (sc);
  419                 }
  420         } else
  421 #endif
  422         {
  423                 sch = &tcp_syncache.hashbase[
  424                     SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
  425                 *schp = sch;
  426                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  427 #ifdef INET6
  428                         if (sc->sc_inc.inc_isipv6)
  429                                 continue;
  430 #endif
  431                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  432                                 return (sc);
  433                 }
  434         }
  435         return (NULL);
  436 }
  437 
  438 /*
  439  * This function is called when we get a RST for a
  440  * non-existent connection, so that we can see if the
  441  * connection is in the syn cache.  If it is, zap it.
  442  */
  443 void
  444 syncache_chkrst(inc, th)
  445         struct in_conninfo *inc;
  446         struct tcphdr *th;
  447 {
  448         struct syncache *sc;
  449         struct syncache_head *sch;
  450 
  451         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  452 
  453         sc = syncache_lookup(inc, &sch);
  454         if (sc == NULL)
  455                 return;
  456         /*
  457          * If the RST bit is set, check the sequence number to see
  458          * if this is a valid reset segment.
  459          * RFC 793 page 37:
  460          *   In all states except SYN-SENT, all reset (RST) segments
  461          *   are validated by checking their SEQ-fields.  A reset is
  462          *   valid if its sequence number is in the window.
  463          *
  464          *   The sequence number in the reset segment is normally an
  465          *   echo of our outgoing acknowlegement numbers, but some hosts
  466          *   send a reset with the sequence number at the rightmost edge
  467          *   of our receive window, and we have to handle this case.
  468          */
  469         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  470             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  471                 syncache_drop(sc, sch);
  472                 tcpstat.tcps_sc_reset++;
  473         }
  474 }
  475 
  476 void
  477 syncache_badack(inc)
  478         struct in_conninfo *inc;
  479 {
  480         struct syncache *sc;
  481         struct syncache_head *sch;
  482 
  483         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  484 
  485         sc = syncache_lookup(inc, &sch);
  486         if (sc != NULL) {
  487                 syncache_drop(sc, sch);
  488                 tcpstat.tcps_sc_badack++;
  489         }
  490 }
  491 
  492 void
  493 syncache_unreach(inc, th)
  494         struct in_conninfo *inc;
  495         struct tcphdr *th;
  496 {
  497         struct syncache *sc;
  498         struct syncache_head *sch;
  499 
  500         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  501 
  502         sc = syncache_lookup(inc, &sch);
  503         if (sc == NULL)
  504                 return;
  505 
  506         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  507         if (ntohl(th->th_seq) != sc->sc_iss)
  508                 return;
  509 
  510         /*
  511          * If we've rertransmitted 3 times and this is our second error,
  512          * we remove the entry.  Otherwise, we allow it to continue on.
  513          * This prevents us from incorrectly nuking an entry during a
  514          * spurious network outage.
  515          *
  516          * See tcp_notify().
  517          */
  518         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
  519                 sc->sc_flags |= SCF_UNREACH;
  520                 return;
  521         }
  522         syncache_drop(sc, sch);
  523         tcpstat.tcps_sc_unreach++;
  524 }
  525 
  526 /*
  527  * Build a new TCP socket structure from a syncache entry.
  528  */
  529 static struct socket *
  530 syncache_socket(sc, lso, m)
  531         struct syncache *sc;
  532         struct socket *lso;
  533         struct mbuf *m;
  534 {
  535         struct inpcb *inp = NULL;
  536         struct socket *so;
  537         struct tcpcb *tp;
  538 
  539         NET_ASSERT_GIANT();
  540         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  541 
  542         /*
  543          * Ok, create the full blown connection, and set things up
  544          * as they would have been set up if we had created the
  545          * connection when the SYN arrived.  If we can't create
  546          * the connection, abort it.
  547          */
  548         so = sonewconn(lso, SS_ISCONNECTED);
  549         if (so == NULL) {
  550                 /*
  551                  * Drop the connection; we will send a RST if the peer
  552                  * retransmits the ACK,
  553                  */
  554                 tcpstat.tcps_listendrop++;
  555                 goto abort2;
  556         }
  557 #ifdef MAC
  558         SOCK_LOCK(so);
  559         mac_set_socket_peer_from_mbuf(m, so);
  560         SOCK_UNLOCK(so);
  561 #endif
  562 
  563         inp = sotoinpcb(so);
  564         INP_LOCK(inp);
  565 
  566         /*
  567          * Insert new socket into hash list.
  568          */
  569         inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
  570 #ifdef INET6
  571         if (sc->sc_inc.inc_isipv6) {
  572                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  573         } else {
  574                 inp->inp_vflag &= ~INP_IPV6;
  575                 inp->inp_vflag |= INP_IPV4;
  576 #endif
  577                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  578 #ifdef INET6
  579         }
  580 #endif
  581         inp->inp_lport = sc->sc_inc.inc_lport;
  582         if (in_pcbinshash(inp) != 0) {
  583                 /*
  584                  * Undo the assignments above if we failed to
  585                  * put the PCB on the hash lists.
  586                  */
  587 #ifdef INET6
  588                 if (sc->sc_inc.inc_isipv6)
  589                         inp->in6p_laddr = in6addr_any;
  590                 else
  591 #endif
  592                         inp->inp_laddr.s_addr = INADDR_ANY;
  593                 inp->inp_lport = 0;
  594                 goto abort;
  595         }
  596 #ifdef IPSEC
  597         /* copy old policy into new socket's */
  598         if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  599                 printf("syncache_expand: could not copy policy\n");
  600 #endif
  601 #ifdef FAST_IPSEC
  602         /* copy old policy into new socket's */
  603         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  604                 printf("syncache_expand: could not copy policy\n");
  605 #endif
  606 #ifdef INET6
  607         if (sc->sc_inc.inc_isipv6) {
  608                 struct inpcb *oinp = sotoinpcb(lso);
  609                 struct in6_addr laddr6;
  610                 struct sockaddr_in6 sin6;
  611                 /*
  612                  * Inherit socket options from the listening socket.
  613                  * Note that in6p_inputopts are not (and should not be)
  614                  * copied, since it stores previously received options and is
  615                  * used to detect if each new option is different than the
  616                  * previous one and hence should be passed to a user.
  617                  * If we copied in6p_inputopts, a user would not be able to
  618                  * receive options just after calling the accept system call.
  619                  */
  620                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  621                 if (oinp->in6p_outputopts)
  622                         inp->in6p_outputopts =
  623                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  624 
  625                 sin6.sin6_family = AF_INET6;
  626                 sin6.sin6_len = sizeof(sin6);
  627                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  628                 sin6.sin6_port = sc->sc_inc.inc_fport;
  629                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  630                 laddr6 = inp->in6p_laddr;
  631                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  632                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  633                 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  634                     thread0.td_ucred)) {
  635                         inp->in6p_laddr = laddr6;
  636                         goto abort;
  637                 }
  638                 /* Override flowlabel from in6_pcbconnect. */
  639                 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
  640                 inp->in6p_flowinfo |= sc->sc_flowlabel;
  641         } else
  642 #endif
  643         {
  644                 struct in_addr laddr;
  645                 struct sockaddr_in sin;
  646 
  647                 inp->inp_options = ip_srcroute(m);
  648                 if (inp->inp_options == NULL) {
  649                         inp->inp_options = sc->sc_ipopts;
  650                         sc->sc_ipopts = NULL;
  651                 }
  652 
  653                 sin.sin_family = AF_INET;
  654                 sin.sin_len = sizeof(sin);
  655                 sin.sin_addr = sc->sc_inc.inc_faddr;
  656                 sin.sin_port = sc->sc_inc.inc_fport;
  657                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  658                 laddr = inp->inp_laddr;
  659                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  660                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  661                 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
  662                     thread0.td_ucred)) {
  663                         inp->inp_laddr = laddr;
  664                         goto abort;
  665                 }
  666         }
  667 
  668         tp = intotcpcb(inp);
  669         tp->t_state = TCPS_SYN_RECEIVED;
  670         tp->iss = sc->sc_iss;
  671         tp->irs = sc->sc_irs;
  672         tcp_rcvseqinit(tp);
  673         tcp_sendseqinit(tp);
  674         tp->snd_wl1 = sc->sc_irs;
  675         tp->rcv_up = sc->sc_irs + 1;
  676         tp->rcv_wnd = sc->sc_wnd;
  677         tp->rcv_adv += tp->rcv_wnd;
  678 
  679         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  680         if (sc->sc_flags & SCF_NOOPT)
  681                 tp->t_flags |= TF_NOOPT;
  682         if (sc->sc_flags & SCF_WINSCALE) {
  683                 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  684                 tp->requested_s_scale = sc->sc_requested_s_scale;
  685                 tp->request_r_scale = sc->sc_request_r_scale;
  686         }
  687         if (sc->sc_flags & SCF_TIMESTAMP) {
  688                 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  689                 tp->ts_recent = sc->sc_tsrecent;
  690                 tp->ts_recent_age = ticks;
  691         }
  692 #ifdef TCP_SIGNATURE
  693         if (sc->sc_flags & SCF_SIGNATURE)
  694                 tp->t_flags |= TF_SIGNATURE;
  695 #endif
  696         if (sc->sc_flags & SCF_SACK) {
  697                 tp->sack_enable = 1;
  698                 tp->t_flags |= TF_SACK_PERMIT;
  699         }
  700         /*
  701          * Set up MSS and get cached values from tcp_hostcache.
  702          * This might overwrite some of the defaults we just set.
  703          */
  704         tcp_mss(tp, sc->sc_peer_mss);
  705 
  706         /*
  707          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  708          */
  709         if (sc->sc_rxtslot != 0)
  710                 tp->snd_cwnd = tp->t_maxseg;
  711         callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
  712 
  713         INP_UNLOCK(inp);
  714 
  715         tcpstat.tcps_accepts++;
  716         return (so);
  717 
  718 abort:
  719         INP_UNLOCK(inp);
  720 abort2:
  721         if (so != NULL)
  722                 (void) soabort(so);
  723         return (NULL);
  724 }
  725 
  726 /*
  727  * This function gets called when we receive an ACK for a
  728  * socket in the LISTEN state.  We look up the connection
  729  * in the syncache, and if its there, we pull it out of
  730  * the cache and turn it into a full-blown connection in
  731  * the SYN-RECEIVED state.
  732  */
  733 int
  734 syncache_expand(inc, th, sop, m)
  735         struct in_conninfo *inc;
  736         struct tcphdr *th;
  737         struct socket **sop;
  738         struct mbuf *m;
  739 {
  740         struct syncache *sc;
  741         struct syncache_head *sch;
  742         struct socket *so;
  743 
  744         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  745 
  746         sc = syncache_lookup(inc, &sch);
  747         if (sc == NULL) {
  748                 /*
  749                  * There is no syncache entry, so see if this ACK is
  750                  * a returning syncookie.  To do this, first:
  751                  *  A. See if this socket has had a syncache entry dropped in
  752                  *     the past.  We don't want to accept a bogus syncookie
  753                  *     if we've never received a SYN.
  754                  *  B. check that the syncookie is valid.  If it is, then
  755                  *     cobble up a fake syncache entry, and return.
  756                  */
  757                 if (!tcp_syncookies)
  758                         return (0);
  759                 sc = syncookie_lookup(inc, th, *sop);
  760                 if (sc == NULL)
  761                         return (0);
  762                 sch = NULL;
  763                 tcpstat.tcps_sc_recvcookie++;
  764         }
  765 
  766         /*
  767          * If seg contains an ACK, but not for our SYN/ACK, send a RST.
  768          */
  769         if (th->th_ack != sc->sc_iss + 1) {
  770                 if (sch == NULL)
  771                         syncache_free(sc);
  772                 return (0);
  773         }
  774 
  775         so = syncache_socket(sc, *sop, m);
  776         if (so == NULL) {
  777 #if 0
  778 resetandabort:
  779                 /* XXXjlemon check this - is this correct? */
  780                 (void) tcp_respond(NULL, m, m, th,
  781                     th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
  782 #endif
  783                 m_freem(m);                     /* XXX only needed for above */
  784                 tcpstat.tcps_sc_aborted++;
  785         } else
  786                 tcpstat.tcps_sc_completed++;
  787 
  788         if (sch == NULL)
  789                 syncache_free(sc);
  790         else
  791                 syncache_drop(sc, sch);
  792         *sop = so;
  793         return (1);
  794 }
  795 
  796 /*
  797  * Given a LISTEN socket and an inbound SYN request, add
  798  * this to the syn cache, and send back a segment:
  799  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  800  * to the source.
  801  *
  802  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  803  * Doing so would require that we hold onto the data and deliver it
  804  * to the application.  However, if we are the target of a SYN-flood
  805  * DoS attack, an attacker could send data which would eventually
  806  * consume all available buffer space if it were ACKed.  By not ACKing
  807  * the data, we avoid this DoS scenario.
  808  */
  809 int
  810 syncache_add(inc, to, th, sop, m)
  811         struct in_conninfo *inc;
  812         struct tcpopt *to;
  813         struct tcphdr *th;
  814         struct socket **sop;
  815         struct mbuf *m;
  816 {
  817         struct tcpcb *tp;
  818         struct socket *so;
  819         struct syncache *sc = NULL;
  820         struct syncache_head *sch;
  821         struct mbuf *ipopts = NULL;
  822         u_int32_t flowtmp;
  823         int i, win;
  824 
  825         INP_INFO_WLOCK_ASSERT(&tcbinfo);
  826 
  827         so = *sop;
  828         tp = sototcpcb(so);
  829 
  830         /*
  831          * Remember the IP options, if any.
  832          */
  833 #ifdef INET6
  834         if (!inc->inc_isipv6)
  835 #endif
  836                 ipopts = ip_srcroute(m);
  837 
  838         /*
  839          * See if we already have an entry for this connection.
  840          * If we do, resend the SYN,ACK, and reset the retransmit timer.
  841          *
  842          * XXX
  843          * should the syncache be re-initialized with the contents
  844          * of the new SYN here (which may have different options?)
  845          */
  846         sc = syncache_lookup(inc, &sch);
  847         if (sc != NULL) {
  848                 tcpstat.tcps_sc_dupsyn++;
  849                 if (ipopts) {
  850                         /*
  851                          * If we were remembering a previous source route,
  852                          * forget it and use the new one we've been given.
  853                          */
  854                         if (sc->sc_ipopts)
  855                                 (void) m_free(sc->sc_ipopts);
  856                         sc->sc_ipopts = ipopts;
  857                 }
  858                 /*
  859                  * Update timestamp if present.
  860                  */
  861                 if (sc->sc_flags & SCF_TIMESTAMP)
  862                         sc->sc_tsrecent = to->to_tsval;
  863                 /*
  864                  * PCB may have changed, pick up new values.
  865                  */
  866                 sc->sc_tp = tp;
  867                 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  868 #ifdef TCPDEBUG
  869                 if (syncache_respond(sc, m, so) == 0) {
  870 #else
  871                 if (syncache_respond(sc, m) == 0) {
  872 #endif
  873                         /* NB: guarded by INP_INFO_WLOCK(&tcbinfo) */
  874                         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot],
  875                             sc, sc_timerq);
  876                         SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot);
  877                         tcpstat.tcps_sndacks++;
  878                         tcpstat.tcps_sndtotal++;
  879                 }
  880                 *sop = NULL;
  881                 return (1);
  882         }
  883 
  884         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
  885         if (sc == NULL) {
  886                 /*
  887                  * The zone allocator couldn't provide more entries.
  888                  * Treat this as if the cache was full; drop the oldest
  889                  * entry and insert the new one.
  890                  */
  891                 /* NB: guarded by INP_INFO_WLOCK(&tcbinfo) */
  892                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  893                         sc = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  894                         if (sc != NULL)
  895                                 break;
  896                 }
  897                 sc->sc_tp->ts_recent = ticks;
  898                 syncache_drop(sc, NULL);
  899                 tcpstat.tcps_sc_zonefail++;
  900                 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
  901                 if (sc == NULL) {
  902                         if (ipopts)
  903                                 (void) m_free(ipopts);
  904                         return (0);
  905                 }
  906         }
  907 
  908         /*
  909          * Fill in the syncache values.
  910          */
  911         sc->sc_tp = tp;
  912         sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  913         sc->sc_ipopts = ipopts;
  914         sc->sc_inc.inc_fport = inc->inc_fport;
  915         sc->sc_inc.inc_lport = inc->inc_lport;
  916 #ifdef INET6
  917         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
  918         if (inc->inc_isipv6) {
  919                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
  920                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
  921         } else
  922 #endif
  923         {
  924                 sc->sc_inc.inc_faddr = inc->inc_faddr;
  925                 sc->sc_inc.inc_laddr = inc->inc_laddr;
  926         }
  927         sc->sc_irs = th->th_seq;
  928         sc->sc_flags = 0;
  929         sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
  930         sc->sc_flowlabel = 0;
  931         if (tcp_syncookies) {
  932                 sc->sc_iss = syncookie_generate(sc, &flowtmp);
  933 #ifdef INET6
  934                 if (inc->inc_isipv6 &&
  935                     (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)) {
  936                         sc->sc_flowlabel = flowtmp & IPV6_FLOWLABEL_MASK;
  937                 }
  938 #endif
  939         } else {
  940                 sc->sc_iss = arc4random();
  941 #ifdef INET6
  942                 if (inc->inc_isipv6 &&
  943                     (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)) {
  944                         sc->sc_flowlabel =
  945                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
  946                 }
  947 #endif
  948         }
  949 
  950         /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */
  951         win = sbspace(&so->so_rcv);
  952         win = imax(win, 0);
  953         win = imin(win, TCP_MAXWIN);
  954         sc->sc_wnd = win;
  955 
  956         if (tcp_do_rfc1323) {
  957                 /*
  958                  * A timestamp received in a SYN makes
  959                  * it ok to send timestamp requests and replies.
  960                  */
  961                 if (to->to_flags & TOF_TS) {
  962                         sc->sc_tsrecent = to->to_tsval;
  963                         sc->sc_flags |= SCF_TIMESTAMP;
  964                 }
  965                 if (to->to_flags & TOF_SCALE) {
  966                         int wscale = 0;
  967 
  968                         /* Compute proper scaling value from buffer space */
  969                         while (wscale < TCP_MAX_WINSHIFT &&
  970                             (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat)
  971                                 wscale++;
  972                         sc->sc_request_r_scale = wscale;
  973                         sc->sc_requested_s_scale = to->to_requested_s_scale;
  974                         sc->sc_flags |= SCF_WINSCALE;
  975                 }
  976         }
  977         if (tp->t_flags & TF_NOOPT)
  978                 sc->sc_flags = SCF_NOOPT;
  979 #ifdef TCP_SIGNATURE
  980         /*
  981          * If listening socket requested TCP digests, and received SYN
  982          * contains the option, flag this in the syncache so that
  983          * syncache_respond() will do the right thing with the SYN+ACK.
  984          * XXX Currently we always record the option by default and will
  985          * attempt to use it in syncache_respond().
  986          */
  987         if (to->to_flags & TOF_SIGNATURE)
  988                 sc->sc_flags |= SCF_SIGNATURE;
  989 #endif
  990 
  991         if (to->to_flags & TOF_SACK)
  992                 sc->sc_flags |= SCF_SACK;
  993 
  994         /*
  995          * Do a standard 3-way handshake.
  996          */
  997 #ifdef TCPDEBUG
  998         if (syncache_respond(sc, m, so) == 0) {
  999 #else
 1000         if (syncache_respond(sc, m) == 0) {
 1001 #endif
 1002                 syncache_insert(sc, sch);
 1003                 tcpstat.tcps_sndacks++;
 1004                 tcpstat.tcps_sndtotal++;
 1005         } else {
 1006                 syncache_free(sc);
 1007                 tcpstat.tcps_sc_dropped++;
 1008         }
 1009         *sop = NULL;
 1010         return (1);
 1011 }
 1012 
 1013 #ifdef TCPDEBUG
 1014 static int
 1015 syncache_respond(sc, m, so)
 1016         struct syncache *sc;
 1017         struct mbuf *m;
 1018         struct socket *so;
 1019 #else
 1020 static int
 1021 syncache_respond(sc, m)
 1022         struct syncache *sc;
 1023         struct mbuf *m;
 1024 #endif
 1025 {
 1026         u_int8_t *optp;
 1027         int optlen, error;
 1028         u_int16_t tlen, hlen, mssopt;
 1029         struct ip *ip = NULL;
 1030         struct tcphdr *th;
 1031         struct inpcb *inp;
 1032 #ifdef INET6
 1033         struct ip6_hdr *ip6 = NULL;
 1034 #endif
 1035 
 1036         hlen =
 1037 #ifdef INET6
 1038                (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
 1039 #endif
 1040                 sizeof(struct ip);
 1041 
 1042         KASSERT((&sc->sc_inc) != NULL, ("syncache_respond with NULL in_conninfo pointer"));
 1043 
 1044         /* Determine MSS we advertize to other end of connection */
 1045         mssopt = tcp_mssopt(&sc->sc_inc);
 1046 
 1047         /* Compute the size of the TCP options. */
 1048         if (sc->sc_flags & SCF_NOOPT) {
 1049                 optlen = 0;
 1050         } else {
 1051                 optlen = TCPOLEN_MAXSEG +
 1052                     ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
 1053                     ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0);
 1054 #ifdef TCP_SIGNATURE
 1055                 if (sc->sc_flags & SCF_SIGNATURE)
 1056                         optlen += TCPOLEN_SIGNATURE;
 1057 #endif
 1058                 if (sc->sc_flags & SCF_SACK)
 1059                         optlen += TCPOLEN_SACK_PERMITTED;
 1060                 optlen = roundup2(optlen, 4);
 1061         }
 1062         tlen = hlen + sizeof(struct tcphdr) + optlen;
 1063 
 1064         /*
 1065          * XXX
 1066          * assume that the entire packet will fit in a header mbuf
 1067          */
 1068         KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
 1069 
 1070         /*
 1071          * XXX shouldn't this reuse the mbuf if possible ?
 1072          * Create the IP+TCP header from scratch.
 1073          */
 1074         if (m)
 1075                 m_freem(m);
 1076 
 1077         m = m_gethdr(M_DONTWAIT, MT_HEADER);
 1078         if (m == NULL)
 1079                 return (ENOBUFS);
 1080         m->m_data += max_linkhdr;
 1081         m->m_len = tlen;
 1082         m->m_pkthdr.len = tlen;
 1083         m->m_pkthdr.rcvif = NULL;
 1084         inp = sc->sc_tp->t_inpcb;
 1085         INP_LOCK(inp);
 1086 #ifdef MAC
 1087         mac_create_mbuf_from_inpcb(inp, m);
 1088 #endif
 1089 
 1090 #ifdef INET6
 1091         if (sc->sc_inc.inc_isipv6) {
 1092                 ip6 = mtod(m, struct ip6_hdr *);
 1093                 ip6->ip6_vfc = IPV6_VERSION;
 1094                 ip6->ip6_nxt = IPPROTO_TCP;
 1095                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1096                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1097                 ip6->ip6_plen = htons(tlen - hlen);
 1098                 /* ip6_hlim is set after checksum */
 1099                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1100                 ip6->ip6_flow |= sc->sc_flowlabel;
 1101 
 1102                 th = (struct tcphdr *)(ip6 + 1);
 1103         } else
 1104 #endif
 1105         {
 1106                 ip = mtod(m, struct ip *);
 1107                 ip->ip_v = IPVERSION;
 1108                 ip->ip_hl = sizeof(struct ip) >> 2;
 1109                 ip->ip_len = tlen;
 1110                 ip->ip_id = 0;
 1111                 ip->ip_off = 0;
 1112                 ip->ip_sum = 0;
 1113                 ip->ip_p = IPPROTO_TCP;
 1114                 ip->ip_src = sc->sc_inc.inc_laddr;
 1115                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1116                 ip->ip_ttl = inp->inp_ip_ttl;   /* XXX */
 1117                 ip->ip_tos = inp->inp_ip_tos;   /* XXX */
 1118 
 1119                 /*
 1120                  * See if we should do MTU discovery.  Route lookups are
 1121                  * expensive, so we will only unset the DF bit if:
 1122                  *
 1123                  *      1) path_mtu_discovery is disabled
 1124                  *      2) the SCF_UNREACH flag has been set
 1125                  */
 1126                 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1127                        ip->ip_off |= IP_DF;
 1128 
 1129                 th = (struct tcphdr *)(ip + 1);
 1130         }
 1131         th->th_sport = sc->sc_inc.inc_lport;
 1132         th->th_dport = sc->sc_inc.inc_fport;
 1133 
 1134         th->th_seq = htonl(sc->sc_iss);
 1135         th->th_ack = htonl(sc->sc_irs + 1);
 1136         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1137         th->th_x2 = 0;
 1138         th->th_flags = TH_SYN|TH_ACK;
 1139         th->th_win = htons(sc->sc_wnd);
 1140         th->th_urp = 0;
 1141 
 1142         /* Tack on the TCP options. */
 1143         if (optlen != 0) {
 1144                 optp = (u_int8_t *)(th + 1);
 1145                 *optp++ = TCPOPT_MAXSEG;
 1146                 *optp++ = TCPOLEN_MAXSEG;
 1147                 *optp++ = (mssopt >> 8) & 0xff;
 1148                 *optp++ = mssopt & 0xff;
 1149 
 1150                 if (sc->sc_flags & SCF_WINSCALE) {
 1151                         *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
 1152                             TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
 1153                             sc->sc_request_r_scale);
 1154                         optp += 4;
 1155                 }
 1156 
 1157                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1158                         u_int32_t *lp = (u_int32_t *)(optp);
 1159 
 1160                         /* Form timestamp option per appendix A of RFC 1323. */
 1161                         *lp++ = htonl(TCPOPT_TSTAMP_HDR);
 1162                         *lp++ = htonl(ticks);
 1163                         *lp   = htonl(sc->sc_tsrecent);
 1164                         optp += TCPOLEN_TSTAMP_APPA;
 1165                 }
 1166 
 1167 #ifdef TCP_SIGNATURE
 1168                 /*
 1169                  * Handle TCP-MD5 passive opener response.
 1170                  */
 1171                 if (sc->sc_flags & SCF_SIGNATURE) {
 1172                         u_int8_t *bp = optp;
 1173                         int i;
 1174 
 1175                         *bp++ = TCPOPT_SIGNATURE;
 1176                         *bp++ = TCPOLEN_SIGNATURE;
 1177                         for (i = 0; i < TCP_SIGLEN; i++)
 1178                                 *bp++ = 0;
 1179                         tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
 1180                             optp + 2, IPSEC_DIR_OUTBOUND);
 1181                         optp += TCPOLEN_SIGNATURE;
 1182                 }
 1183 #endif /* TCP_SIGNATURE */
 1184 
 1185                 if (sc->sc_flags & SCF_SACK) {
 1186                         *optp++ = TCPOPT_SACK_PERMITTED;
 1187                         *optp++ = TCPOLEN_SACK_PERMITTED;
 1188                 }
 1189 
 1190                 {
 1191                         /* Pad TCP options to a 4 byte boundary */
 1192                         int padlen = optlen - (optp - (u_int8_t *)(th + 1));
 1193                         while (padlen-- > 0)
 1194                                 *optp++ = TCPOPT_EOL;
 1195                 }
 1196         }
 1197 
 1198 #ifdef INET6
 1199         if (sc->sc_inc.inc_isipv6) {
 1200                 th->th_sum = 0;
 1201                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
 1202                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1203                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, inp);
 1204         } else
 1205 #endif
 1206         {
 1207                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1208                     htons(tlen - hlen + IPPROTO_TCP));
 1209                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1210                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1211 #ifdef TCPDEBUG
 1212                 /*
 1213                  * Trace.
 1214                  */
 1215                 if (so != NULL && so->so_options & SO_DEBUG) {
 1216                         struct tcpcb *tp = sototcpcb(so);
 1217                         tcp_trace(TA_OUTPUT, tp->t_state, tp,
 1218                             mtod(m, void *), th, 0);
 1219                 }
 1220 #endif
 1221                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, inp);
 1222         }
 1223         INP_UNLOCK(inp);
 1224         return (error);
 1225 }
 1226 
 1227 /*
 1228  * cookie layers:
 1229  *
 1230  *      |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
 1231  *      | peer iss                                                      |
 1232  *      | MD5(laddr,faddr,secret,lport,fport)             |. . . . . . .|
 1233  *      |                     0                       |(A)|             |
 1234  * (A): peer mss index
 1235  */
 1236 
 1237 /*
 1238  * The values below are chosen to minimize the size of the tcp_secret
 1239  * table, as well as providing roughly a 16 second lifetime for the cookie.
 1240  */
 1241 
 1242 #define SYNCOOKIE_WNDBITS       5       /* exposed bits for window indexing */
 1243 #define SYNCOOKIE_TIMESHIFT     1       /* scale ticks to window time units */
 1244 
 1245 #define SYNCOOKIE_WNDMASK       ((1 << SYNCOOKIE_WNDBITS) - 1)
 1246 #define SYNCOOKIE_NSECRETS      (1 << SYNCOOKIE_WNDBITS)
 1247 #define SYNCOOKIE_TIMEOUT \
 1248     (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
 1249 #define SYNCOOKIE_DATAMASK      ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
 1250 
 1251 static struct {
 1252         u_int32_t       ts_secbits[4];
 1253         u_int           ts_expire;
 1254 } tcp_secret[SYNCOOKIE_NSECRETS];
 1255 
 1256 static int tcp_msstab[] = { 0, 536, 1460, 8960 };
 1257 
 1258 static MD5_CTX syn_ctx;
 1259 
 1260 #define MD5Add(v)       MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
 1261 
 1262 struct md5_add {
 1263         u_int32_t laddr, faddr;
 1264         u_int32_t secbits[4];
 1265         u_int16_t lport, fport;
 1266 };
 1267 
 1268 #ifdef CTASSERT
 1269 CTASSERT(sizeof(struct md5_add) == 28);
 1270 #endif
 1271 
 1272 /*
 1273  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1274  * original SYN was accepted, the connection is established.  The second
 1275  * SYN is inflight, and if it arrives with an ISN that falls within the
 1276  * receive window, the connection is killed.
 1277  *
 1278  * However, since cookies have other problems, this may not be worth
 1279  * worrying about.
 1280  */
 1281 
 1282 static u_int32_t
 1283 syncookie_generate(struct syncache *sc, u_int32_t *flowid)
 1284 {
 1285         u_int32_t md5_buffer[4];
 1286         u_int32_t data;
 1287         int idx, i;
 1288         struct md5_add add;
 1289 
 1290         /* NB: single threaded; could add INP_INFO_WLOCK_ASSERT(&tcbinfo) */
 1291 
 1292         idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
 1293         if (tcp_secret[idx].ts_expire < ticks) {
 1294                 for (i = 0; i < 4; i++)
 1295                         tcp_secret[idx].ts_secbits[i] = arc4random();
 1296                 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
 1297         }
 1298         for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--)
 1299                 if (tcp_msstab[data] <= sc->sc_peer_mss)
 1300                         break;
 1301         data = (data << SYNCOOKIE_WNDBITS) | idx;
 1302         data ^= sc->sc_irs;                             /* peer's iss */
 1303         MD5Init(&syn_ctx);
 1304 #ifdef INET6
 1305         if (sc->sc_inc.inc_isipv6) {
 1306                 MD5Add(sc->sc_inc.inc6_laddr);
 1307                 MD5Add(sc->sc_inc.inc6_faddr);
 1308                 add.laddr = 0;
 1309                 add.faddr = 0;
 1310         } else
 1311 #endif
 1312         {
 1313                 add.laddr = sc->sc_inc.inc_laddr.s_addr;
 1314                 add.faddr = sc->sc_inc.inc_faddr.s_addr;
 1315         }
 1316         add.lport = sc->sc_inc.inc_lport;
 1317         add.fport = sc->sc_inc.inc_fport;
 1318         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1319         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1320         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1321         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1322         MD5Add(add);
 1323         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1324         data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
 1325         *flowid = md5_buffer[1];
 1326         tcpstat.tcps_sc_sendcookie++;
 1327         return (data);
 1328 }
 1329 
 1330 static struct syncache *
 1331 syncookie_lookup(inc, th, so)
 1332         struct in_conninfo *inc;
 1333         struct tcphdr *th;
 1334         struct socket *so;
 1335 {
 1336         u_int32_t md5_buffer[4];
 1337         struct syncache *sc;
 1338         u_int32_t data;
 1339         int wnd, idx;
 1340         struct md5_add add;
 1341 
 1342         /* NB: single threaded; could add INP_INFO_WLOCK_ASSERT(&tcbinfo) */
 1343 
 1344         data = (th->th_ack - 1) ^ (th->th_seq - 1);     /* remove ISS */
 1345         idx = data & SYNCOOKIE_WNDMASK;
 1346         if (tcp_secret[idx].ts_expire < ticks ||
 1347             sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
 1348                 return (NULL);
 1349         MD5Init(&syn_ctx);
 1350 #ifdef INET6
 1351         if (inc->inc_isipv6) {
 1352                 MD5Add(inc->inc6_laddr);
 1353                 MD5Add(inc->inc6_faddr);
 1354                 add.laddr = 0;
 1355                 add.faddr = 0;
 1356         } else
 1357 #endif
 1358         {
 1359                 add.laddr = inc->inc_laddr.s_addr;
 1360                 add.faddr = inc->inc_faddr.s_addr;
 1361         }
 1362         add.lport = inc->inc_lport;
 1363         add.fport = inc->inc_fport;
 1364         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1365         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1366         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1367         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1368         MD5Add(add);
 1369         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1370         data ^= md5_buffer[0];
 1371         if ((data & ~SYNCOOKIE_DATAMASK) != 0)
 1372                 return (NULL);
 1373         data = data >> SYNCOOKIE_WNDBITS;
 1374 
 1375         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1376         if (sc == NULL)
 1377                 return (NULL);
 1378         /*
 1379          * Fill in the syncache values.
 1380          * XXX duplicate code from syncache_add
 1381          */
 1382         sc->sc_ipopts = NULL;
 1383         sc->sc_inc.inc_fport = inc->inc_fport;
 1384         sc->sc_inc.inc_lport = inc->inc_lport;
 1385         sc->sc_tp = sototcpcb(so);
 1386 #ifdef INET6
 1387         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
 1388         if (inc->inc_isipv6) {
 1389                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
 1390                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
 1391                 if (sc->sc_tp->t_inpcb->in6p_flags & IN6P_AUTOFLOWLABEL)
 1392                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1393         } else
 1394 #endif
 1395         {
 1396                 sc->sc_inc.inc_faddr = inc->inc_faddr;
 1397                 sc->sc_inc.inc_laddr = inc->inc_laddr;
 1398         }
 1399         sc->sc_irs = th->th_seq - 1;
 1400         sc->sc_iss = th->th_ack - 1;
 1401         wnd = sbspace(&so->so_rcv);
 1402         wnd = imax(wnd, 0);
 1403         wnd = imin(wnd, TCP_MAXWIN);
 1404         sc->sc_wnd = wnd;
 1405         sc->sc_flags = 0;
 1406         sc->sc_rxtslot = 0;
 1407         sc->sc_peer_mss = tcp_msstab[data];
 1408         return (sc);
 1409 }

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