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  * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG
    4  * All rights reserved.
    5  *
    6  * This software was developed for the FreeBSD Project by Jonathan Lemon
    7  * and McAfee Research, the Security Research Division of McAfee, Inc. under
    8  * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    9  * DARPA CHATS research program.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  */
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: releng/8.2/sys/netinet/tcp_syncache.c 211600 2010-08-22 08:47:00Z andre $");
   35 
   36 #include "opt_inet.h"
   37 #include "opt_inet6.h"
   38 #include "opt_ipsec.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/kernel.h>
   43 #include <sys/sysctl.h>
   44 #include <sys/limits.h>
   45 #include <sys/lock.h>
   46 #include <sys/mutex.h>
   47 #include <sys/malloc.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 #include <sys/syslog.h>
   55 #include <sys/ucred.h>
   56 
   57 #include <vm/uma.h>
   58 
   59 #include <net/if.h>
   60 #include <net/route.h>
   61 #include <net/vnet.h>
   62 
   63 #include <netinet/in.h>
   64 #include <netinet/in_systm.h>
   65 #include <netinet/ip.h>
   66 #include <netinet/in_var.h>
   67 #include <netinet/in_pcb.h>
   68 #include <netinet/ip_var.h>
   69 #include <netinet/ip_options.h>
   70 #ifdef INET6
   71 #include <netinet/ip6.h>
   72 #include <netinet/icmp6.h>
   73 #include <netinet6/nd6.h>
   74 #include <netinet6/ip6_var.h>
   75 #include <netinet6/in6_pcb.h>
   76 #endif
   77 #include <netinet/tcp.h>
   78 #include <netinet/tcp_fsm.h>
   79 #include <netinet/tcp_seq.h>
   80 #include <netinet/tcp_timer.h>
   81 #include <netinet/tcp_var.h>
   82 #include <netinet/tcp_syncache.h>
   83 #include <netinet/tcp_offload.h>
   84 #ifdef INET6
   85 #include <netinet6/tcp6_var.h>
   86 #endif
   87 
   88 #ifdef IPSEC
   89 #include <netipsec/ipsec.h>
   90 #ifdef INET6
   91 #include <netipsec/ipsec6.h>
   92 #endif
   93 #include <netipsec/key.h>
   94 #endif /*IPSEC*/
   95 
   96 #include <machine/in_cksum.h>
   97 
   98 #include <security/mac/mac_framework.h>
   99 
  100 static VNET_DEFINE(int, tcp_syncookies) = 1;
  101 #define V_tcp_syncookies                VNET(tcp_syncookies)
  102 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  103     &VNET_NAME(tcp_syncookies), 0,
  104     "Use TCP SYN cookies if the syncache overflows");
  105 
  106 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
  107 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  108 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
  109     &VNET_NAME(tcp_syncookiesonly), 0,
  110     "Use only TCP SYN cookies");
  111 
  112 #ifdef TCP_OFFLOAD_DISABLE
  113 #define TOEPCB_ISSET(sc) (0)
  114 #else
  115 #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL)
  116 #endif
  117 
  118 static void      syncache_drop(struct syncache *, struct syncache_head *);
  119 static void      syncache_free(struct syncache *);
  120 static void      syncache_insert(struct syncache *, struct syncache_head *);
  121 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  122 static int       syncache_respond(struct syncache *);
  123 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  124                     struct mbuf *m);
  125 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  126                     int docallout);
  127 static void      syncache_timer(void *);
  128 static void      syncookie_generate(struct syncache_head *, struct syncache *,
  129                     u_int32_t *);
  130 static struct syncache
  131                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  132                     struct syncache *, struct tcpopt *, struct tcphdr *,
  133                     struct socket *);
  134 
  135 /*
  136  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  137  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  138  * the odds are that the user has given up attempting to connect by then.
  139  */
  140 #define SYNCACHE_MAXREXMTS              3
  141 
  142 /* Arbitrary values */
  143 #define TCP_SYNCACHE_HASHSIZE           512
  144 #define TCP_SYNCACHE_BUCKETLIMIT        30
  145 
  146 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
  147 #define V_tcp_syncache                  VNET(tcp_syncache)
  148 
  149 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  150 
  151 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  152     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  153     "Per-bucket hash limit for syncache");
  154 
  155 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  156     &VNET_NAME(tcp_syncache.cache_limit), 0,
  157     "Overall entry limit for syncache");
  158 
  159 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  160     &VNET_NAME(tcp_syncache.cache_count), 0,
  161     "Current number of entries in syncache");
  162 
  163 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  164     &VNET_NAME(tcp_syncache.hashsize), 0,
  165     "Size of TCP syncache hashtable");
  166 
  167 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  168     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  169     "Limit on SYN/ACK retransmissions");
  170 
  171 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
  172 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  173     CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  174     "Send reset on socket allocation failure");
  175 
  176 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  177 
  178 #define SYNCACHE_HASH(inc, mask)                                        \
  179         ((V_tcp_syncache.hash_secret ^                                  \
  180           (inc)->inc_faddr.s_addr ^                                     \
  181           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  182           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  183 
  184 #define SYNCACHE_HASH6(inc, mask)                                       \
  185         ((V_tcp_syncache.hash_secret ^                                  \
  186           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  187           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  188           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  189 
  190 #define ENDPTS_EQ(a, b) (                                               \
  191         (a)->ie_fport == (b)->ie_fport &&                               \
  192         (a)->ie_lport == (b)->ie_lport &&                               \
  193         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  194         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  195 )
  196 
  197 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  198 
  199 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  200 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  201 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  202 
  203 /*
  204  * Requires the syncache entry to be already removed from the bucket list.
  205  */
  206 static void
  207 syncache_free(struct syncache *sc)
  208 {
  209 
  210         if (sc->sc_ipopts)
  211                 (void) m_free(sc->sc_ipopts);
  212         if (sc->sc_cred)
  213                 crfree(sc->sc_cred);
  214 #ifdef MAC
  215         mac_syncache_destroy(&sc->sc_label);
  216 #endif
  217 
  218         uma_zfree(V_tcp_syncache.zone, sc);
  219 }
  220 
  221 void
  222 syncache_init(void)
  223 {
  224         int i;
  225 
  226         V_tcp_syncache.cache_count = 0;
  227         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  228         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  229         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  230         V_tcp_syncache.hash_secret = arc4random();
  231 
  232         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  233             &V_tcp_syncache.hashsize);
  234         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  235             &V_tcp_syncache.bucket_limit);
  236         if (!powerof2(V_tcp_syncache.hashsize) ||
  237             V_tcp_syncache.hashsize == 0) {
  238                 printf("WARNING: syncache hash size is not a power of 2.\n");
  239                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  240         }
  241         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  242 
  243         /* Set limits. */
  244         V_tcp_syncache.cache_limit =
  245             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  246         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  247             &V_tcp_syncache.cache_limit);
  248 
  249         /* Allocate the hash table. */
  250         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  251             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  252 
  253         /* Initialize the hash buckets. */
  254         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  255 #ifdef VIMAGE
  256                 V_tcp_syncache.hashbase[i].sch_vnet = curvnet;
  257 #endif
  258                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  259                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  260                          NULL, MTX_DEF);
  261                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  262                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  263                 V_tcp_syncache.hashbase[i].sch_length = 0;
  264         }
  265 
  266         /* Create the syncache entry zone. */
  267         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  268             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  269         uma_zone_set_max(V_tcp_syncache.zone, V_tcp_syncache.cache_limit);
  270 }
  271 
  272 #ifdef VIMAGE
  273 void
  274 syncache_destroy(void)
  275 {
  276         struct syncache_head *sch;
  277         struct syncache *sc, *nsc;
  278         int i;
  279 
  280         /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
  281         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  282 
  283                 sch = &V_tcp_syncache.hashbase[i];
  284                 callout_drain(&sch->sch_timer);
  285 
  286                 SCH_LOCK(sch);
  287                 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
  288                         syncache_drop(sc, sch);
  289                 SCH_UNLOCK(sch);
  290                 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
  291                     ("%s: sch->sch_bucket not empty", __func__));
  292                 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
  293                     __func__, sch->sch_length));
  294                 mtx_destroy(&sch->sch_mtx);
  295         }
  296 
  297         KASSERT(V_tcp_syncache.cache_count == 0, ("%s: cache_count %d not 0",
  298             __func__, V_tcp_syncache.cache_count));
  299 
  300         /* Free the allocated global resources. */
  301         uma_zdestroy(V_tcp_syncache.zone);
  302         free(V_tcp_syncache.hashbase, M_SYNCACHE);
  303 }
  304 #endif
  305 
  306 /*
  307  * Inserts a syncache entry into the specified bucket row.
  308  * Locks and unlocks the syncache_head autonomously.
  309  */
  310 static void
  311 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  312 {
  313         struct syncache *sc2;
  314 
  315         SCH_LOCK(sch);
  316 
  317         /*
  318          * Make sure that we don't overflow the per-bucket limit.
  319          * If the bucket is full, toss the oldest element.
  320          */
  321         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  322                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  323                         ("sch->sch_length incorrect"));
  324                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  325                 syncache_drop(sc2, sch);
  326                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  327         }
  328 
  329         /* Put it into the bucket. */
  330         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  331         sch->sch_length++;
  332 
  333         /* Reinitialize the bucket row's timer. */
  334         if (sch->sch_length == 1)
  335                 sch->sch_nextc = ticks + INT_MAX;
  336         syncache_timeout(sc, sch, 1);
  337 
  338         SCH_UNLOCK(sch);
  339 
  340         V_tcp_syncache.cache_count++;
  341         TCPSTAT_INC(tcps_sc_added);
  342 }
  343 
  344 /*
  345  * Remove and free entry from syncache bucket row.
  346  * Expects locked syncache head.
  347  */
  348 static void
  349 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  350 {
  351 
  352         SCH_LOCK_ASSERT(sch);
  353 
  354         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  355         sch->sch_length--;
  356 
  357 #ifndef TCP_OFFLOAD_DISABLE
  358         if (sc->sc_tu)
  359                 sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb);
  360 #endif              
  361         syncache_free(sc);
  362         V_tcp_syncache.cache_count--;
  363 }
  364 
  365 /*
  366  * Engage/reengage time on bucket row.
  367  */
  368 static void
  369 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  370 {
  371         sc->sc_rxttime = ticks +
  372                 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
  373         sc->sc_rxmits++;
  374         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  375                 sch->sch_nextc = sc->sc_rxttime;
  376                 if (docallout)
  377                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  378                             syncache_timer, (void *)sch);
  379         }
  380 }
  381 
  382 /*
  383  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  384  * If we have retransmitted an entry the maximum number of times, expire it.
  385  * One separate timer for each bucket row.
  386  */
  387 static void
  388 syncache_timer(void *xsch)
  389 {
  390         struct syncache_head *sch = (struct syncache_head *)xsch;
  391         struct syncache *sc, *nsc;
  392         int tick = ticks;
  393         char *s;
  394 
  395         CURVNET_SET(sch->sch_vnet);
  396 
  397         /* NB: syncache_head has already been locked by the callout. */
  398         SCH_LOCK_ASSERT(sch);
  399 
  400         /*
  401          * In the following cycle we may remove some entries and/or
  402          * advance some timeouts, so re-initialize the bucket timer.
  403          */
  404         sch->sch_nextc = tick + INT_MAX;
  405 
  406         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  407                 /*
  408                  * We do not check if the listen socket still exists
  409                  * and accept the case where the listen socket may be
  410                  * gone by the time we resend the SYN/ACK.  We do
  411                  * not expect this to happens often. If it does,
  412                  * then the RST will be sent by the time the remote
  413                  * host does the SYN/ACK->ACK.
  414                  */
  415                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  416                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  417                                 sch->sch_nextc = sc->sc_rxttime;
  418                         continue;
  419                 }
  420                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  421                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  422                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  423                                     "giving up and removing syncache entry\n",
  424                                     s, __func__);
  425                                 free(s, M_TCPLOG);
  426                         }
  427                         syncache_drop(sc, sch);
  428                         TCPSTAT_INC(tcps_sc_stale);
  429                         continue;
  430                 }
  431                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  432                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  433                             "retransmitting (%u) SYN|ACK\n",
  434                             s, __func__, sc->sc_rxmits);
  435                         free(s, M_TCPLOG);
  436                 }
  437 
  438                 (void) syncache_respond(sc);
  439                 TCPSTAT_INC(tcps_sc_retransmitted);
  440                 syncache_timeout(sc, sch, 0);
  441         }
  442         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  443                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  444                         syncache_timer, (void *)(sch));
  445         CURVNET_RESTORE();
  446 }
  447 
  448 /*
  449  * Find an entry in the syncache.
  450  * Returns always with locked syncache_head plus a matching entry or NULL.
  451  */
  452 struct syncache *
  453 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  454 {
  455         struct syncache *sc;
  456         struct syncache_head *sch;
  457 
  458 #ifdef INET6
  459         if (inc->inc_flags & INC_ISIPV6) {
  460                 sch = &V_tcp_syncache.hashbase[
  461                     SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
  462                 *schp = sch;
  463 
  464                 SCH_LOCK(sch);
  465 
  466                 /* Circle through bucket row to find matching entry. */
  467                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  468                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  469                                 return (sc);
  470                 }
  471         } else
  472 #endif
  473         {
  474                 sch = &V_tcp_syncache.hashbase[
  475                     SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
  476                 *schp = sch;
  477 
  478                 SCH_LOCK(sch);
  479 
  480                 /* Circle through bucket row to find matching entry. */
  481                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  482 #ifdef INET6
  483                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
  484                                 continue;
  485 #endif
  486                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  487                                 return (sc);
  488                 }
  489         }
  490         SCH_LOCK_ASSERT(*schp);
  491         return (NULL);                  /* always returns with locked sch */
  492 }
  493 
  494 /*
  495  * This function is called when we get a RST for a
  496  * non-existent connection, so that we can see if the
  497  * connection is in the syn cache.  If it is, zap it.
  498  */
  499 void
  500 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  501 {
  502         struct syncache *sc;
  503         struct syncache_head *sch;
  504         char *s = NULL;
  505 
  506         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  507         SCH_LOCK_ASSERT(sch);
  508 
  509         /*
  510          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  511          * See RFC 793 page 65, section SEGMENT ARRIVES.
  512          */
  513         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  514                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  515                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  516                             "FIN flag set, segment ignored\n", s, __func__);
  517                 TCPSTAT_INC(tcps_badrst);
  518                 goto done;
  519         }
  520 
  521         /*
  522          * No corresponding connection was found in syncache.
  523          * If syncookies are enabled and possibly exclusively
  524          * used, or we are under memory pressure, a valid RST
  525          * may not find a syncache entry.  In that case we're
  526          * done and no SYN|ACK retransmissions will happen.
  527          * Otherwise the the RST was misdirected or spoofed.
  528          */
  529         if (sc == NULL) {
  530                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  531                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  532                             "syncache entry (possibly syncookie only), "
  533                             "segment ignored\n", s, __func__);
  534                 TCPSTAT_INC(tcps_badrst);
  535                 goto done;
  536         }
  537 
  538         /*
  539          * If the RST bit is set, check the sequence number to see
  540          * if this is a valid reset segment.
  541          * RFC 793 page 37:
  542          *   In all states except SYN-SENT, all reset (RST) segments
  543          *   are validated by checking their SEQ-fields.  A reset is
  544          *   valid if its sequence number is in the window.
  545          *
  546          *   The sequence number in the reset segment is normally an
  547          *   echo of our outgoing acknowlegement numbers, but some hosts
  548          *   send a reset with the sequence number at the rightmost edge
  549          *   of our receive window, and we have to handle this case.
  550          */
  551         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  552             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  553                 syncache_drop(sc, sch);
  554                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  555                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  556                             "connection attempt aborted by remote endpoint\n",
  557                             s, __func__);
  558                 TCPSTAT_INC(tcps_sc_reset);
  559         } else {
  560                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  561                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  562                             "IRS %u (+WND %u), segment ignored\n",
  563                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  564                 TCPSTAT_INC(tcps_badrst);
  565         }
  566 
  567 done:
  568         if (s != NULL)
  569                 free(s, M_TCPLOG);
  570         SCH_UNLOCK(sch);
  571 }
  572 
  573 void
  574 syncache_badack(struct in_conninfo *inc)
  575 {
  576         struct syncache *sc;
  577         struct syncache_head *sch;
  578 
  579         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  580         SCH_LOCK_ASSERT(sch);
  581         if (sc != NULL) {
  582                 syncache_drop(sc, sch);
  583                 TCPSTAT_INC(tcps_sc_badack);
  584         }
  585         SCH_UNLOCK(sch);
  586 }
  587 
  588 void
  589 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  590 {
  591         struct syncache *sc;
  592         struct syncache_head *sch;
  593 
  594         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  595         SCH_LOCK_ASSERT(sch);
  596         if (sc == NULL)
  597                 goto done;
  598 
  599         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  600         if (ntohl(th->th_seq) != sc->sc_iss)
  601                 goto done;
  602 
  603         /*
  604          * If we've rertransmitted 3 times and this is our second error,
  605          * we remove the entry.  Otherwise, we allow it to continue on.
  606          * This prevents us from incorrectly nuking an entry during a
  607          * spurious network outage.
  608          *
  609          * See tcp_notify().
  610          */
  611         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  612                 sc->sc_flags |= SCF_UNREACH;
  613                 goto done;
  614         }
  615         syncache_drop(sc, sch);
  616         TCPSTAT_INC(tcps_sc_unreach);
  617 done:
  618         SCH_UNLOCK(sch);
  619 }
  620 
  621 /*
  622  * Build a new TCP socket structure from a syncache entry.
  623  */
  624 static struct socket *
  625 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  626 {
  627         struct inpcb *inp = NULL;
  628         struct socket *so;
  629         struct tcpcb *tp;
  630         int error = 0;
  631         char *s;
  632 
  633         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  634 
  635         /*
  636          * Ok, create the full blown connection, and set things up
  637          * as they would have been set up if we had created the
  638          * connection when the SYN arrived.  If we can't create
  639          * the connection, abort it.
  640          */
  641         so = sonewconn(lso, SS_ISCONNECTED);
  642         if (so == NULL) {
  643                 /*
  644                  * Drop the connection; we will either send a RST or
  645                  * have the peer retransmit its SYN again after its
  646                  * RTO and try again.
  647                  */
  648                 TCPSTAT_INC(tcps_listendrop);
  649                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  650                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  651                             "due to limits or memory shortage\n",
  652                             s, __func__);
  653                         free(s, M_TCPLOG);
  654                 }
  655                 goto abort2;
  656         }
  657 #ifdef MAC
  658         mac_socketpeer_set_from_mbuf(m, so);
  659 #endif
  660 
  661         inp = sotoinpcb(so);
  662         inp->inp_inc.inc_fibnum = so->so_fibnum;
  663         INP_WLOCK(inp);
  664 
  665         /* Insert new socket into PCB hash list. */
  666         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  667 #ifdef INET6
  668         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  669                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  670         } else {
  671                 inp->inp_vflag &= ~INP_IPV6;
  672                 inp->inp_vflag |= INP_IPV4;
  673 #endif
  674                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  675 #ifdef INET6
  676         }
  677 #endif
  678         inp->inp_lport = sc->sc_inc.inc_lport;
  679         if ((error = in_pcbinshash(inp)) != 0) {
  680                 /*
  681                  * Undo the assignments above if we failed to
  682                  * put the PCB on the hash lists.
  683                  */
  684 #ifdef INET6
  685                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  686                         inp->in6p_laddr = in6addr_any;
  687                 else
  688 #endif
  689                         inp->inp_laddr.s_addr = INADDR_ANY;
  690                 inp->inp_lport = 0;
  691                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  692                         log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
  693                             "with error %i\n",
  694                             s, __func__, error);
  695                         free(s, M_TCPLOG);
  696                 }
  697                 goto abort;
  698         }
  699 #ifdef IPSEC
  700         /* Copy old policy into new socket's. */
  701         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  702                 printf("syncache_socket: could not copy policy\n");
  703 #endif
  704 #ifdef INET6
  705         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  706                 struct inpcb *oinp = sotoinpcb(lso);
  707                 struct in6_addr laddr6;
  708                 struct sockaddr_in6 sin6;
  709                 /*
  710                  * Inherit socket options from the listening socket.
  711                  * Note that in6p_inputopts are not (and should not be)
  712                  * copied, since it stores previously received options and is
  713                  * used to detect if each new option is different than the
  714                  * previous one and hence should be passed to a user.
  715                  * If we copied in6p_inputopts, a user would not be able to
  716                  * receive options just after calling the accept system call.
  717                  */
  718                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  719                 if (oinp->in6p_outputopts)
  720                         inp->in6p_outputopts =
  721                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  722 
  723                 sin6.sin6_family = AF_INET6;
  724                 sin6.sin6_len = sizeof(sin6);
  725                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  726                 sin6.sin6_port = sc->sc_inc.inc_fport;
  727                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  728                 laddr6 = inp->in6p_laddr;
  729                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  730                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  731                 if ((error = in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  732                     thread0.td_ucred)) != 0) {
  733                         inp->in6p_laddr = laddr6;
  734                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  735                                 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
  736                                     "with error %i\n",
  737                                     s, __func__, error);
  738                                 free(s, M_TCPLOG);
  739                         }
  740                         goto abort;
  741                 }
  742                 /* Override flowlabel from in6_pcbconnect. */
  743                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  744                 inp->inp_flow |= sc->sc_flowlabel;
  745         } else
  746 #endif
  747         {
  748                 struct in_addr laddr;
  749                 struct sockaddr_in sin;
  750 
  751                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  752                 
  753                 if (inp->inp_options == NULL) {
  754                         inp->inp_options = sc->sc_ipopts;
  755                         sc->sc_ipopts = NULL;
  756                 }
  757 
  758                 sin.sin_family = AF_INET;
  759                 sin.sin_len = sizeof(sin);
  760                 sin.sin_addr = sc->sc_inc.inc_faddr;
  761                 sin.sin_port = sc->sc_inc.inc_fport;
  762                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  763                 laddr = inp->inp_laddr;
  764                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  765                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  766                 if ((error = in_pcbconnect(inp, (struct sockaddr *)&sin,
  767                     thread0.td_ucred)) != 0) {
  768                         inp->inp_laddr = laddr;
  769                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  770                                 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
  771                                     "with error %i\n",
  772                                     s, __func__, error);
  773                                 free(s, M_TCPLOG);
  774                         }
  775                         goto abort;
  776                 }
  777         }
  778         tp = intotcpcb(inp);
  779         tp->t_state = TCPS_SYN_RECEIVED;
  780         tp->iss = sc->sc_iss;
  781         tp->irs = sc->sc_irs;
  782         tcp_rcvseqinit(tp);
  783         tcp_sendseqinit(tp);
  784         tp->snd_wl1 = sc->sc_irs;
  785         tp->snd_max = tp->iss + 1;
  786         tp->snd_nxt = tp->iss + 1;
  787         tp->rcv_up = sc->sc_irs + 1;
  788         tp->rcv_wnd = sc->sc_wnd;
  789         tp->rcv_adv += tp->rcv_wnd;
  790         tp->last_ack_sent = tp->rcv_nxt;
  791 
  792         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  793         if (sc->sc_flags & SCF_NOOPT)
  794                 tp->t_flags |= TF_NOOPT;
  795         else {
  796                 if (sc->sc_flags & SCF_WINSCALE) {
  797                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  798                         tp->snd_scale = sc->sc_requested_s_scale;
  799                         tp->request_r_scale = sc->sc_requested_r_scale;
  800                 }
  801                 if (sc->sc_flags & SCF_TIMESTAMP) {
  802                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  803                         tp->ts_recent = sc->sc_tsreflect;
  804                         tp->ts_recent_age = ticks;
  805                         tp->ts_offset = sc->sc_tsoff;
  806                 }
  807 #ifdef TCP_SIGNATURE
  808                 if (sc->sc_flags & SCF_SIGNATURE)
  809                         tp->t_flags |= TF_SIGNATURE;
  810 #endif
  811                 if (sc->sc_flags & SCF_SACK)
  812                         tp->t_flags |= TF_SACK_PERMIT;
  813         }
  814 
  815         if (sc->sc_flags & SCF_ECN)
  816                 tp->t_flags |= TF_ECN_PERMIT;
  817 
  818         /*
  819          * Set up MSS and get cached values from tcp_hostcache.
  820          * This might overwrite some of the defaults we just set.
  821          */
  822         tcp_mss(tp, sc->sc_peer_mss);
  823 
  824         /*
  825          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  826          * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
  827          */
  828         if (sc->sc_rxmits > 1)
  829                 tp->snd_cwnd = tp->t_maxseg;
  830         tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
  831 
  832         INP_WUNLOCK(inp);
  833 
  834         TCPSTAT_INC(tcps_accepts);
  835         return (so);
  836 
  837 abort:
  838         INP_WUNLOCK(inp);
  839 abort2:
  840         if (so != NULL)
  841                 soabort(so);
  842         return (NULL);
  843 }
  844 
  845 /*
  846  * This function gets called when we receive an ACK for a
  847  * socket in the LISTEN state.  We look up the connection
  848  * in the syncache, and if its there, we pull it out of
  849  * the cache and turn it into a full-blown connection in
  850  * the SYN-RECEIVED state.
  851  */
  852 int
  853 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  854     struct socket **lsop, struct mbuf *m)
  855 {
  856         struct syncache *sc;
  857         struct syncache_head *sch;
  858         struct syncache scs;
  859         char *s;
  860 
  861         /*
  862          * Global TCP locks are held because we manipulate the PCB lists
  863          * and create a new socket.
  864          */
  865         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  866         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  867             ("%s: can handle only ACK", __func__));
  868 
  869         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  870         SCH_LOCK_ASSERT(sch);
  871         if (sc == NULL) {
  872                 /*
  873                  * There is no syncache entry, so see if this ACK is
  874                  * a returning syncookie.  To do this, first:
  875                  *  A. See if this socket has had a syncache entry dropped in
  876                  *     the past.  We don't want to accept a bogus syncookie
  877                  *     if we've never received a SYN.
  878                  *  B. check that the syncookie is valid.  If it is, then
  879                  *     cobble up a fake syncache entry, and return.
  880                  */
  881                 if (!V_tcp_syncookies) {
  882                         SCH_UNLOCK(sch);
  883                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  884                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  885                                     "segment rejected (syncookies disabled)\n",
  886                                     s, __func__);
  887                         goto failed;
  888                 }
  889                 bzero(&scs, sizeof(scs));
  890                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  891                 SCH_UNLOCK(sch);
  892                 if (sc == NULL) {
  893                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  894                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  895                                     "SYNCOOKIE authentication, segment rejected "
  896                                     "(probably spoofed)\n", s, __func__);
  897                         goto failed;
  898                 }
  899         } else {
  900                 /* Pull out the entry to unlock the bucket row. */
  901                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  902                 sch->sch_length--;
  903                 V_tcp_syncache.cache_count--;
  904                 SCH_UNLOCK(sch);
  905         }
  906 
  907         /*
  908          * Segment validation:
  909          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  910          */
  911         if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
  912                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  913                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  914                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  915                 goto failed;
  916         }
  917 
  918         /*
  919          * The SEQ must fall in the window starting at the received
  920          * initial receive sequence number + 1 (the SYN).
  921          */
  922         if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  923             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) &&
  924             !TOEPCB_ISSET(sc)) {
  925                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  926                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  927                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  928                 goto failed;
  929         }
  930 
  931         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  932                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  933                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  934                             "segment rejected\n", s, __func__);
  935                 goto failed;
  936         }
  937         /*
  938          * If timestamps were negotiated the reflected timestamp
  939          * must be equal to what we actually sent in the SYN|ACK.
  940          */
  941         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
  942             !TOEPCB_ISSET(sc)) {
  943                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  944                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
  945                             "segment rejected\n",
  946                             s, __func__, to->to_tsecr, sc->sc_ts);
  947                 goto failed;
  948         }
  949 
  950         *lsop = syncache_socket(sc, *lsop, m);
  951 
  952         if (*lsop == NULL)
  953                 TCPSTAT_INC(tcps_sc_aborted);
  954         else
  955                 TCPSTAT_INC(tcps_sc_completed);
  956 
  957 /* how do we find the inp for the new socket? */
  958         if (sc != &scs)
  959                 syncache_free(sc);
  960         return (1);
  961 failed:
  962         if (sc != NULL && sc != &scs)
  963                 syncache_free(sc);
  964         if (s != NULL)
  965                 free(s, M_TCPLOG);
  966         *lsop = NULL;
  967         return (0);
  968 }
  969 
  970 int
  971 tcp_offload_syncache_expand(struct in_conninfo *inc, struct toeopt *toeo,
  972     struct tcphdr *th, struct socket **lsop, struct mbuf *m)
  973 {
  974         struct tcpopt to;
  975         int rc;
  976 
  977         bzero(&to, sizeof(struct tcpopt));
  978         to.to_mss = toeo->to_mss;
  979         to.to_wscale = toeo->to_wscale;
  980         to.to_flags = toeo->to_flags;
  981         
  982         INP_INFO_WLOCK(&V_tcbinfo);
  983         rc = syncache_expand(inc, &to, th, lsop, m);
  984         INP_INFO_WUNLOCK(&V_tcbinfo);
  985 
  986         return (rc);
  987 }
  988 
  989 /*
  990  * Given a LISTEN socket and an inbound SYN request, add
  991  * this to the syn cache, and send back a segment:
  992  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  993  * to the source.
  994  *
  995  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  996  * Doing so would require that we hold onto the data and deliver it
  997  * to the application.  However, if we are the target of a SYN-flood
  998  * DoS attack, an attacker could send data which would eventually
  999  * consume all available buffer space if it were ACKed.  By not ACKing
 1000  * the data, we avoid this DoS scenario.
 1001  */
 1002 static void
 1003 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1004     struct inpcb *inp, struct socket **lsop, struct mbuf *m,
 1005     struct toe_usrreqs *tu, void *toepcb)
 1006 {
 1007         struct tcpcb *tp;
 1008         struct socket *so;
 1009         struct syncache *sc = NULL;
 1010         struct syncache_head *sch;
 1011         struct mbuf *ipopts = NULL;
 1012         u_int32_t flowtmp;
 1013         int win, sb_hiwat, ip_ttl, ip_tos, noopt;
 1014         char *s;
 1015 #ifdef INET6
 1016         int autoflowlabel = 0;
 1017 #endif
 1018 #ifdef MAC
 1019         struct label *maclabel;
 1020 #endif
 1021         struct syncache scs;
 1022         struct ucred *cred;
 1023 
 1024         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1025         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1026         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1027             ("%s: unexpected tcp flags", __func__));
 1028 
 1029         /*
 1030          * Combine all so/tp operations very early to drop the INP lock as
 1031          * soon as possible.
 1032          */
 1033         so = *lsop;
 1034         tp = sototcpcb(so);
 1035         cred = crhold(so->so_cred);
 1036 
 1037 #ifdef INET6
 1038         if ((inc->inc_flags & INC_ISIPV6) &&
 1039             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1040                 autoflowlabel = 1;
 1041 #endif
 1042         ip_ttl = inp->inp_ip_ttl;
 1043         ip_tos = inp->inp_ip_tos;
 1044         win = sbspace(&so->so_rcv);
 1045         sb_hiwat = so->so_rcv.sb_hiwat;
 1046         noopt = (tp->t_flags & TF_NOOPT);
 1047 
 1048         /* By the time we drop the lock these should no longer be used. */
 1049         so = NULL;
 1050         tp = NULL;
 1051 
 1052 #ifdef MAC
 1053         if (mac_syncache_init(&maclabel) != 0) {
 1054                 INP_WUNLOCK(inp);
 1055                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1056                 goto done;
 1057         } else
 1058                 mac_syncache_create(maclabel, inp);
 1059 #endif
 1060         INP_WUNLOCK(inp);
 1061         INP_INFO_WUNLOCK(&V_tcbinfo);
 1062 
 1063         /*
 1064          * Remember the IP options, if any.
 1065          */
 1066 #ifdef INET6
 1067         if (!(inc->inc_flags & INC_ISIPV6))
 1068 #endif
 1069                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1070 
 1071         /*
 1072          * See if we already have an entry for this connection.
 1073          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1074          *
 1075          * XXX: should the syncache be re-initialized with the contents
 1076          * of the new SYN here (which may have different options?)
 1077          *
 1078          * XXX: We do not check the sequence number to see if this is a
 1079          * real retransmit or a new connection attempt.  The question is
 1080          * how to handle such a case; either ignore it as spoofed, or
 1081          * drop the current entry and create a new one?
 1082          */
 1083         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1084         SCH_LOCK_ASSERT(sch);
 1085         if (sc != NULL) {
 1086 #ifndef TCP_OFFLOAD_DISABLE
 1087                 if (sc->sc_tu)
 1088                         sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
 1089                             sc->sc_toepcb);
 1090 #endif              
 1091                 TCPSTAT_INC(tcps_sc_dupsyn);
 1092                 if (ipopts) {
 1093                         /*
 1094                          * If we were remembering a previous source route,
 1095                          * forget it and use the new one we've been given.
 1096                          */
 1097                         if (sc->sc_ipopts)
 1098                                 (void) m_free(sc->sc_ipopts);
 1099                         sc->sc_ipopts = ipopts;
 1100                 }
 1101                 /*
 1102                  * Update timestamp if present.
 1103                  */
 1104                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1105                         sc->sc_tsreflect = to->to_tsval;
 1106                 else
 1107                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1108 #ifdef MAC
 1109                 /*
 1110                  * Since we have already unconditionally allocated label
 1111                  * storage, free it up.  The syncache entry will already
 1112                  * have an initialized label we can use.
 1113                  */
 1114                 mac_syncache_destroy(&maclabel);
 1115 #endif
 1116                 /* Retransmit SYN|ACK and reset retransmit count. */
 1117                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1118                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1119                             "resetting timer and retransmitting SYN|ACK\n",
 1120                             s, __func__);
 1121                         free(s, M_TCPLOG);
 1122                 }
 1123                 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
 1124                         sc->sc_rxmits = 0;
 1125                         syncache_timeout(sc, sch, 1);
 1126                         TCPSTAT_INC(tcps_sndacks);
 1127                         TCPSTAT_INC(tcps_sndtotal);
 1128                 }
 1129                 SCH_UNLOCK(sch);
 1130                 goto done;
 1131         }
 1132 
 1133         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1134         if (sc == NULL) {
 1135                 /*
 1136                  * The zone allocator couldn't provide more entries.
 1137                  * Treat this as if the cache was full; drop the oldest
 1138                  * entry and insert the new one.
 1139                  */
 1140                 TCPSTAT_INC(tcps_sc_zonefail);
 1141                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1142                         syncache_drop(sc, sch);
 1143                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1144                 if (sc == NULL) {
 1145                         if (V_tcp_syncookies) {
 1146                                 bzero(&scs, sizeof(scs));
 1147                                 sc = &scs;
 1148                         } else {
 1149                                 SCH_UNLOCK(sch);
 1150                                 if (ipopts)
 1151                                         (void) m_free(ipopts);
 1152                                 goto done;
 1153                         }
 1154                 }
 1155         }
 1156         
 1157         /*
 1158          * Fill in the syncache values.
 1159          */
 1160 #ifdef MAC
 1161         sc->sc_label = maclabel;
 1162 #endif
 1163         sc->sc_cred = cred;
 1164         cred = NULL;
 1165         sc->sc_ipopts = ipopts;
 1166         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1167 #ifdef INET6
 1168         if (!(inc->inc_flags & INC_ISIPV6))
 1169 #endif
 1170         {
 1171                 sc->sc_ip_tos = ip_tos;
 1172                 sc->sc_ip_ttl = ip_ttl;
 1173         }
 1174 #ifndef TCP_OFFLOAD_DISABLE     
 1175         sc->sc_tu = tu;
 1176         sc->sc_toepcb = toepcb;
 1177 #endif
 1178         sc->sc_irs = th->th_seq;
 1179         sc->sc_iss = arc4random();
 1180         sc->sc_flags = 0;
 1181         sc->sc_flowlabel = 0;
 1182 
 1183         /*
 1184          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1185          * win was derived from socket earlier in the function.
 1186          */
 1187         win = imax(win, 0);
 1188         win = imin(win, TCP_MAXWIN);
 1189         sc->sc_wnd = win;
 1190 
 1191         if (V_tcp_do_rfc1323) {
 1192                 /*
 1193                  * A timestamp received in a SYN makes
 1194                  * it ok to send timestamp requests and replies.
 1195                  */
 1196                 if (to->to_flags & TOF_TS) {
 1197                         sc->sc_tsreflect = to->to_tsval;
 1198                         sc->sc_ts = ticks;
 1199                         sc->sc_flags |= SCF_TIMESTAMP;
 1200                 }
 1201                 if (to->to_flags & TOF_SCALE) {
 1202                         int wscale = 0;
 1203 
 1204                         /*
 1205                          * Pick the smallest possible scaling factor that
 1206                          * will still allow us to scale up to sb_max, aka
 1207                          * kern.ipc.maxsockbuf.
 1208                          *
 1209                          * We do this because there are broken firewalls that
 1210                          * will corrupt the window scale option, leading to
 1211                          * the other endpoint believing that our advertised
 1212                          * window is unscaled.  At scale factors larger than
 1213                          * 5 the unscaled window will drop below 1500 bytes,
 1214                          * leading to serious problems when traversing these
 1215                          * broken firewalls.
 1216                          *
 1217                          * With the default maxsockbuf of 256K, a scale factor
 1218                          * of 3 will be chosen by this algorithm.  Those who
 1219                          * choose a larger maxsockbuf should watch out
 1220                          * for the compatiblity problems mentioned above.
 1221                          *
 1222                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1223                          * or <SYN,ACK>) segment itself is never scaled.
 1224                          */
 1225                         while (wscale < TCP_MAX_WINSHIFT &&
 1226                             (TCP_MAXWIN << wscale) < sb_max)
 1227                                 wscale++;
 1228                         sc->sc_requested_r_scale = wscale;
 1229                         sc->sc_requested_s_scale = to->to_wscale;
 1230                         sc->sc_flags |= SCF_WINSCALE;
 1231                 }
 1232         }
 1233 #ifdef TCP_SIGNATURE
 1234         /*
 1235          * If listening socket requested TCP digests, and received SYN
 1236          * contains the option, flag this in the syncache so that
 1237          * syncache_respond() will do the right thing with the SYN+ACK.
 1238          * XXX: Currently we always record the option by default and will
 1239          * attempt to use it in syncache_respond().
 1240          */
 1241         if (to->to_flags & TOF_SIGNATURE)
 1242                 sc->sc_flags |= SCF_SIGNATURE;
 1243 #endif
 1244         if (to->to_flags & TOF_SACKPERM)
 1245                 sc->sc_flags |= SCF_SACK;
 1246         if (to->to_flags & TOF_MSS)
 1247                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1248         if (noopt)
 1249                 sc->sc_flags |= SCF_NOOPT;
 1250         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1251                 sc->sc_flags |= SCF_ECN;
 1252 
 1253         if (V_tcp_syncookies) {
 1254                 syncookie_generate(sch, sc, &flowtmp);
 1255 #ifdef INET6
 1256                 if (autoflowlabel)
 1257                         sc->sc_flowlabel = flowtmp;
 1258 #endif
 1259         } else {
 1260 #ifdef INET6
 1261                 if (autoflowlabel)
 1262                         sc->sc_flowlabel =
 1263                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1264 #endif
 1265         }
 1266         SCH_UNLOCK(sch);
 1267 
 1268         /*
 1269          * Do a standard 3-way handshake.
 1270          */
 1271         if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
 1272                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1273                         syncache_free(sc);
 1274                 else if (sc != &scs)
 1275                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1276                 TCPSTAT_INC(tcps_sndacks);
 1277                 TCPSTAT_INC(tcps_sndtotal);
 1278         } else {
 1279                 if (sc != &scs)
 1280                         syncache_free(sc);
 1281                 TCPSTAT_INC(tcps_sc_dropped);
 1282         }
 1283 
 1284 done:
 1285         if (cred != NULL)
 1286                 crfree(cred);
 1287 #ifdef MAC
 1288         if (sc == &scs)
 1289                 mac_syncache_destroy(&maclabel);
 1290 #endif
 1291         if (m) {
 1292                 
 1293                 *lsop = NULL;
 1294                 m_freem(m);
 1295         }
 1296 }
 1297 
 1298 static int
 1299 syncache_respond(struct syncache *sc)
 1300 {
 1301         struct ip *ip = NULL;
 1302         struct mbuf *m;
 1303         struct tcphdr *th;
 1304         int optlen, error;
 1305         u_int16_t hlen, tlen, mssopt;
 1306         struct tcpopt to;
 1307 #ifdef INET6
 1308         struct ip6_hdr *ip6 = NULL;
 1309 #endif
 1310 
 1311         hlen =
 1312 #ifdef INET6
 1313                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1314 #endif
 1315                 sizeof(struct ip);
 1316         tlen = hlen + sizeof(struct tcphdr);
 1317 
 1318         /* Determine MSS we advertize to other end of connection. */
 1319         mssopt = tcp_mssopt(&sc->sc_inc);
 1320         if (sc->sc_peer_mss)
 1321                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1322 
 1323         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1324         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1325             ("syncache: mbuf too small"));
 1326 
 1327         /* Create the IP+TCP header from scratch. */
 1328         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1329         if (m == NULL)
 1330                 return (ENOBUFS);
 1331 #ifdef MAC
 1332         mac_syncache_create_mbuf(sc->sc_label, m);
 1333 #endif
 1334         m->m_data += max_linkhdr;
 1335         m->m_len = tlen;
 1336         m->m_pkthdr.len = tlen;
 1337         m->m_pkthdr.rcvif = NULL;
 1338 
 1339 #ifdef INET6
 1340         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1341                 ip6 = mtod(m, struct ip6_hdr *);
 1342                 ip6->ip6_vfc = IPV6_VERSION;
 1343                 ip6->ip6_nxt = IPPROTO_TCP;
 1344                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1345                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1346                 ip6->ip6_plen = htons(tlen - hlen);
 1347                 /* ip6_hlim is set after checksum */
 1348                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1349                 ip6->ip6_flow |= sc->sc_flowlabel;
 1350 
 1351                 th = (struct tcphdr *)(ip6 + 1);
 1352         } else
 1353 #endif
 1354         {
 1355                 ip = mtod(m, struct ip *);
 1356                 ip->ip_v = IPVERSION;
 1357                 ip->ip_hl = sizeof(struct ip) >> 2;
 1358                 ip->ip_len = tlen;
 1359                 ip->ip_id = 0;
 1360                 ip->ip_off = 0;
 1361                 ip->ip_sum = 0;
 1362                 ip->ip_p = IPPROTO_TCP;
 1363                 ip->ip_src = sc->sc_inc.inc_laddr;
 1364                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1365                 ip->ip_ttl = sc->sc_ip_ttl;
 1366                 ip->ip_tos = sc->sc_ip_tos;
 1367 
 1368                 /*
 1369                  * See if we should do MTU discovery.  Route lookups are
 1370                  * expensive, so we will only unset the DF bit if:
 1371                  *
 1372                  *      1) path_mtu_discovery is disabled
 1373                  *      2) the SCF_UNREACH flag has been set
 1374                  */
 1375                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1376                        ip->ip_off |= IP_DF;
 1377 
 1378                 th = (struct tcphdr *)(ip + 1);
 1379         }
 1380         th->th_sport = sc->sc_inc.inc_lport;
 1381         th->th_dport = sc->sc_inc.inc_fport;
 1382 
 1383         th->th_seq = htonl(sc->sc_iss);
 1384         th->th_ack = htonl(sc->sc_irs + 1);
 1385         th->th_off = sizeof(struct tcphdr) >> 2;
 1386         th->th_x2 = 0;
 1387         th->th_flags = TH_SYN|TH_ACK;
 1388         th->th_win = htons(sc->sc_wnd);
 1389         th->th_urp = 0;
 1390 
 1391         if (sc->sc_flags & SCF_ECN) {
 1392                 th->th_flags |= TH_ECE;
 1393                 TCPSTAT_INC(tcps_ecn_shs);
 1394         }
 1395 
 1396         /* Tack on the TCP options. */
 1397         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1398                 to.to_flags = 0;
 1399 
 1400                 to.to_mss = mssopt;
 1401                 to.to_flags = TOF_MSS;
 1402                 if (sc->sc_flags & SCF_WINSCALE) {
 1403                         to.to_wscale = sc->sc_requested_r_scale;
 1404                         to.to_flags |= TOF_SCALE;
 1405                 }
 1406                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1407                         /* Virgin timestamp or TCP cookie enhanced one. */
 1408                         to.to_tsval = sc->sc_ts;
 1409                         to.to_tsecr = sc->sc_tsreflect;
 1410                         to.to_flags |= TOF_TS;
 1411                 }
 1412                 if (sc->sc_flags & SCF_SACK)
 1413                         to.to_flags |= TOF_SACKPERM;
 1414 #ifdef TCP_SIGNATURE
 1415                 if (sc->sc_flags & SCF_SIGNATURE)
 1416                         to.to_flags |= TOF_SIGNATURE;
 1417 #endif
 1418                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1419 
 1420                 /* Adjust headers by option size. */
 1421                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1422                 m->m_len += optlen;
 1423                 m->m_pkthdr.len += optlen;
 1424 
 1425 #ifdef TCP_SIGNATURE
 1426                 if (sc->sc_flags & SCF_SIGNATURE)
 1427                         tcp_signature_compute(m, 0, 0, optlen,
 1428                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1429 #endif
 1430 #ifdef INET6
 1431                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1432                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1433                 else
 1434 #endif
 1435                         ip->ip_len += optlen;
 1436         } else
 1437                 optlen = 0;
 1438 
 1439         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1440 #ifdef INET6
 1441         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1442                 th->th_sum = 0;
 1443                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
 1444                                        tlen + optlen - hlen);
 1445                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1446                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1447         } else
 1448 #endif
 1449         {
 1450                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1451                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1452                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1453                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1454                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1455         }
 1456         return (error);
 1457 }
 1458 
 1459 void
 1460 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1461     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1462 {
 1463         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1464 }
 1465 
 1466 void
 1467 tcp_offload_syncache_add(struct in_conninfo *inc, struct toeopt *toeo,
 1468     struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
 1469     struct toe_usrreqs *tu, void *toepcb)
 1470 {
 1471         struct tcpopt to;
 1472 
 1473         bzero(&to, sizeof(struct tcpopt));
 1474         to.to_mss = toeo->to_mss;
 1475         to.to_wscale = toeo->to_wscale;
 1476         to.to_flags = toeo->to_flags;
 1477 
 1478         INP_INFO_WLOCK(&V_tcbinfo);
 1479         INP_WLOCK(inp);
 1480 
 1481         _syncache_add(inc, &to, th, inp, lsop, NULL, tu, toepcb);
 1482 }
 1483 
 1484 /*
 1485  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1486  * receive and to be able to handle SYN floods from bogus source addresses
 1487  * (where we will never receive any reply).  SYN floods try to exhaust all
 1488  * our memory and available slots in the SYN cache table to cause a denial
 1489  * of service to legitimate users of the local host.
 1490  *
 1491  * The idea of SYN cookies is to encode and include all necessary information
 1492  * about the connection setup state within the SYN-ACK we send back and thus
 1493  * to get along without keeping any local state until the ACK to the SYN-ACK
 1494  * arrives (if ever).  Everything we need to know should be available from
 1495  * the information we encoded in the SYN-ACK.
 1496  *
 1497  * More information about the theory behind SYN cookies and its first
 1498  * discussion and specification can be found at:
 1499  *  http://cr.yp.to/syncookies.html    (overview)
 1500  *  http://cr.yp.to/syncookies/archive (gory details)
 1501  *
 1502  * This implementation extends the orginal idea and first implementation
 1503  * of FreeBSD by using not only the initial sequence number field to store
 1504  * information but also the timestamp field if present.  This way we can
 1505  * keep track of the entire state we need to know to recreate the session in
 1506  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1507  * these days.  For those that do not we still have to live with the known
 1508  * shortcomings of the ISN only SYN cookies.
 1509  *
 1510  * Cookie layers:
 1511  *
 1512  * Initial sequence number we send:
 1513  * 31|................................|0
 1514  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1515  *    D = MD5 Digest (first dword)
 1516  *    M = MSS index
 1517  *    R = Rotation of secret
 1518  *    P = Odd or Even secret
 1519  *
 1520  * The MD5 Digest is computed with over following parameters:
 1521  *  a) randomly rotated secret
 1522  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1523  *  c) the received initial sequence number from remote host
 1524  *  d) the rotation offset and odd/even bit
 1525  *
 1526  * Timestamp we send:
 1527  * 31|................................|0
 1528  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1529  *    D = MD5 Digest (third dword) (only as filler)
 1530  *    S = Requested send window scale
 1531  *    R = Requested receive window scale
 1532  *    A = SACK allowed
 1533  *    5 = TCP-MD5 enabled (not implemented yet)
 1534  *    XORed with MD5 Digest (forth dword)
 1535  *
 1536  * The timestamp isn't cryptographically secure and doesn't need to be.
 1537  * The double use of the MD5 digest dwords ties it to a specific remote/
 1538  * local host/port, remote initial sequence number and our local time
 1539  * limited secret.  A received timestamp is reverted (XORed) and then
 1540  * the contained MD5 dword is compared to the computed one to ensure the
 1541  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1542  * have been tampered with but this isn't different from supplying bogus
 1543  * values in the SYN in the first place.
 1544  *
 1545  * Some problems with SYN cookies remain however:
 1546  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1547  * original SYN was accepted, the connection is established.  The second
 1548  * SYN is inflight, and if it arrives with an ISN that falls within the
 1549  * receive window, the connection is killed.
 1550  *
 1551  * Notes:
 1552  * A heuristic to determine when to accept syn cookies is not necessary.
 1553  * An ACK flood would cause the syncookie verification to be attempted,
 1554  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1555  * cost, so there's no point in trying to optimize the ACK flood case.
 1556  * Also, if you don't process certain ACKs for some reason, then all someone
 1557  * would have to do is launch a SYN and ACK flood at the same time, which
 1558  * would stop cookie verification and defeat the entire purpose of syncookies.
 1559  */
 1560 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1561 
 1562 static void
 1563 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1564     u_int32_t *flowlabel)
 1565 {
 1566         MD5_CTX ctx;
 1567         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1568         u_int32_t data;
 1569         u_int32_t *secbits;
 1570         u_int off, pmss, mss;
 1571         int i;
 1572 
 1573         SCH_LOCK_ASSERT(sch);
 1574 
 1575         /* Which of the two secrets to use. */
 1576         secbits = sch->sch_oddeven ?
 1577                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1578 
 1579         /* Reseed secret if too old. */
 1580         if (sch->sch_reseed < time_uptime) {
 1581                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1582                 secbits = sch->sch_oddeven ?
 1583                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1584                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1585                         secbits[i] = arc4random();
 1586                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1587         }
 1588 
 1589         /* Secret rotation offset. */
 1590         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1591 
 1592         /* Maximum segment size calculation. */
 1593         pmss =
 1594             max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), V_tcp_minmss);
 1595         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1596                 if (tcp_sc_msstab[mss] <= pmss)
 1597                         break;
 1598 
 1599         /* Fold parameters and MD5 digest into the ISN we will send. */
 1600         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1601         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1602         data |= mss << 4;       /* mss, 3 bits */
 1603 
 1604         MD5Init(&ctx);
 1605         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1606             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1607         MD5Update(&ctx, secbits, off);
 1608         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1609         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1610         MD5Update(&ctx, &data, sizeof(data));
 1611         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1612 
 1613         data |= (md5_buffer[0] << 7);
 1614         sc->sc_iss = data;
 1615 
 1616 #ifdef INET6
 1617         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1618 #endif
 1619 
 1620         /* Additional parameters are stored in the timestamp if present. */
 1621         if (sc->sc_flags & SCF_TIMESTAMP) {
 1622                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1623                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1624                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1625                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1626                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1627                 data ^= md5_buffer[3];
 1628                 sc->sc_ts = data;
 1629                 sc->sc_tsoff = data - ticks;            /* after XOR */
 1630         }
 1631 
 1632         TCPSTAT_INC(tcps_sc_sendcookie);
 1633 }
 1634 
 1635 static struct syncache *
 1636 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1637     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1638     struct socket *so)
 1639 {
 1640         MD5_CTX ctx;
 1641         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1642         u_int32_t data = 0;
 1643         u_int32_t *secbits;
 1644         tcp_seq ack, seq;
 1645         int off, mss, wnd, flags;
 1646 
 1647         SCH_LOCK_ASSERT(sch);
 1648 
 1649         /*
 1650          * Pull information out of SYN-ACK/ACK and
 1651          * revert sequence number advances.
 1652          */
 1653         ack = th->th_ack - 1;
 1654         seq = th->th_seq - 1;
 1655         off = (ack >> 1) & 0x7;
 1656         mss = (ack >> 4) & 0x7;
 1657         flags = ack & 0x7f;
 1658 
 1659         /* Which of the two secrets to use. */
 1660         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1661 
 1662         /*
 1663          * The secret wasn't updated for the lifetime of a syncookie,
 1664          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1665          */
 1666         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1667                 return (NULL);
 1668         }
 1669 
 1670         /* Recompute the digest so we can compare it. */
 1671         MD5Init(&ctx);
 1672         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1673             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1674         MD5Update(&ctx, secbits, off);
 1675         MD5Update(&ctx, inc, sizeof(*inc));
 1676         MD5Update(&ctx, &seq, sizeof(seq));
 1677         MD5Update(&ctx, &flags, sizeof(flags));
 1678         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1679 
 1680         /* Does the digest part of or ACK'ed ISS match? */
 1681         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1682                 return (NULL);
 1683 
 1684         /* Does the digest part of our reflected timestamp match? */
 1685         if (to->to_flags & TOF_TS) {
 1686                 data = md5_buffer[3] ^ to->to_tsecr;
 1687                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1688                         return (NULL);
 1689         }
 1690 
 1691         /* Fill in the syncache values. */
 1692         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1693         sc->sc_ipopts = NULL;
 1694         
 1695         sc->sc_irs = seq;
 1696         sc->sc_iss = ack;
 1697 
 1698 #ifdef INET6
 1699         if (inc->inc_flags & INC_ISIPV6) {
 1700                 if (sotoinpcb(so)->inp_flags & IN6P_AUTOFLOWLABEL)
 1701                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1702         } else
 1703 #endif
 1704         {
 1705                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1706                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1707         }
 1708 
 1709         /* Additional parameters that were encoded in the timestamp. */
 1710         if (data) {
 1711                 sc->sc_flags |= SCF_TIMESTAMP;
 1712                 sc->sc_tsreflect = to->to_tsval;
 1713                 sc->sc_ts = to->to_tsecr;
 1714                 sc->sc_tsoff = to->to_tsecr - ticks;
 1715                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1716                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1717                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1718                     TCP_MAX_WINSHIFT);
 1719                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1720                     TCP_MAX_WINSHIFT);
 1721                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1722                         sc->sc_flags |= SCF_WINSCALE;
 1723         } else
 1724                 sc->sc_flags |= SCF_NOOPT;
 1725 
 1726         wnd = sbspace(&so->so_rcv);
 1727         wnd = imax(wnd, 0);
 1728         wnd = imin(wnd, TCP_MAXWIN);
 1729         sc->sc_wnd = wnd;
 1730 
 1731         sc->sc_rxmits = 0;
 1732         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1733 
 1734         TCPSTAT_INC(tcps_sc_recvcookie);
 1735         return (sc);
 1736 }
 1737 
 1738 /*
 1739  * Returns the current number of syncache entries.  This number
 1740  * will probably change before you get around to calling 
 1741  * syncache_pcblist.
 1742  */
 1743 
 1744 int
 1745 syncache_pcbcount(void)
 1746 {
 1747         struct syncache_head *sch;
 1748         int count, i;
 1749 
 1750         for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1751                 /* No need to lock for a read. */
 1752                 sch = &V_tcp_syncache.hashbase[i];
 1753                 count += sch->sch_length;
 1754         }
 1755         return count;
 1756 }
 1757 
 1758 /*
 1759  * Exports the syncache entries to userland so that netstat can display
 1760  * them alongside the other sockets.  This function is intended to be
 1761  * called only from tcp_pcblist.
 1762  *
 1763  * Due to concurrency on an active system, the number of pcbs exported
 1764  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1765  * amount of space the caller allocated for this function to use.
 1766  */
 1767 int
 1768 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1769 {
 1770         struct xtcpcb xt;
 1771         struct syncache *sc;
 1772         struct syncache_head *sch;
 1773         int count, error, i;
 1774 
 1775         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1776                 sch = &V_tcp_syncache.hashbase[i];
 1777                 SCH_LOCK(sch);
 1778                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1779                         if (count >= max_pcbs) {
 1780                                 SCH_UNLOCK(sch);
 1781                                 goto exit;
 1782                         }
 1783                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1784                                 continue;
 1785                         bzero(&xt, sizeof(xt));
 1786                         xt.xt_len = sizeof(xt);
 1787                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1788                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1789                         else
 1790                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1791                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1792                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1793                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1794                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1795                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1796                         xt.xt_socket.so_type = SOCK_STREAM;
 1797                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1798                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1799                         if (error) {
 1800                                 SCH_UNLOCK(sch);
 1801                                 goto exit;
 1802                         }
 1803                         count++;
 1804                 }
 1805                 SCH_UNLOCK(sch);
 1806         }
 1807 exit:
 1808         *pcbs_exported = count;
 1809         return error;
 1810 }

Cache object: ba3cccc8075f4f318ccc5b78309f808f


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