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

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    1 /*-
    2  * Copyright (c) 2001 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/8.0/sys/netinet/tcp_syncache.c 196019 2009-08-01 19:26:27Z rwatson $");
   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(struct tcp_syncache, tcp_syncache);
  101 static VNET_DEFINE(int, tcp_syncookies);
  102 static VNET_DEFINE(int, tcp_syncookiesonly);
  103 VNET_DEFINE(int, tcp_sc_rst_sock_fail);
  104 
  105 #define V_tcp_syncache                  VNET(tcp_syncache)
  106 #define V_tcp_syncookies                VNET(tcp_syncookies)
  107 #define V_tcp_syncookiesonly            VNET(tcp_syncookiesonly)
  108 
  109 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  110     &VNET_NAME(tcp_syncookies), 0,
  111     "Use TCP SYN cookies if the syncache overflows");
  112 
  113 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
  114     &VNET_NAME(tcp_syncookiesonly), 0,
  115     "Use only TCP SYN cookies");
  116 
  117 #ifdef TCP_OFFLOAD_DISABLE
  118 #define TOEPCB_ISSET(sc) (0)
  119 #else
  120 #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL)
  121 #endif
  122 
  123 static void      syncache_drop(struct syncache *, struct syncache_head *);
  124 static void      syncache_free(struct syncache *);
  125 static void      syncache_insert(struct syncache *, struct syncache_head *);
  126 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  127 static int       syncache_respond(struct syncache *);
  128 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  129                     struct mbuf *m);
  130 static void      syncache_timeout(struct syncache *sc, struct syncache_head *sch,
  131                     int docallout);
  132 static void      syncache_timer(void *);
  133 static void      syncookie_generate(struct syncache_head *, struct syncache *,
  134                     u_int32_t *);
  135 static struct syncache
  136                 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
  137                     struct syncache *, struct tcpopt *, struct tcphdr *,
  138                     struct socket *);
  139 
  140 /*
  141  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  142  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
  143  * the odds are that the user has given up attempting to connect by then.
  144  */
  145 #define SYNCACHE_MAXREXMTS              3
  146 
  147 /* Arbitrary values */
  148 #define TCP_SYNCACHE_HASHSIZE           512
  149 #define TCP_SYNCACHE_BUCKETLIMIT        30
  150 
  151 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  152 
  153 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
  154     &VNET_NAME(tcp_syncache.bucket_limit), 0,
  155     "Per-bucket hash limit for syncache");
  156 
  157 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
  158     &VNET_NAME(tcp_syncache.cache_limit), 0,
  159     "Overall entry limit for syncache");
  160 
  161 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  162     &VNET_NAME(tcp_syncache.cache_count), 0,
  163     "Current number of entries in syncache");
  164 
  165 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
  166     &VNET_NAME(tcp_syncache.hashsize), 0,
  167     "Size of TCP syncache hashtable");
  168 
  169 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  170     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
  171     "Limit on SYN/ACK retransmissions");
  172 
  173 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
  174     CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
  175     "Send reset on socket allocation failure");
  176 
  177 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  178 
  179 #define SYNCACHE_HASH(inc, mask)                                        \
  180         ((V_tcp_syncache.hash_secret ^                                  \
  181           (inc)->inc_faddr.s_addr ^                                     \
  182           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  183           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  184 
  185 #define SYNCACHE_HASH6(inc, mask)                                       \
  186         ((V_tcp_syncache.hash_secret ^                                  \
  187           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  188           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  189           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  190 
  191 #define ENDPTS_EQ(a, b) (                                               \
  192         (a)->ie_fport == (b)->ie_fport &&                               \
  193         (a)->ie_lport == (b)->ie_lport &&                               \
  194         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  195         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  196 )
  197 
  198 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  199 
  200 #define SCH_LOCK(sch)           mtx_lock(&(sch)->sch_mtx)
  201 #define SCH_UNLOCK(sch)         mtx_unlock(&(sch)->sch_mtx)
  202 #define SCH_LOCK_ASSERT(sch)    mtx_assert(&(sch)->sch_mtx, MA_OWNED)
  203 
  204 /*
  205  * Requires the syncache entry to be already removed from the bucket list.
  206  */
  207 static void
  208 syncache_free(struct syncache *sc)
  209 {
  210 
  211         if (sc->sc_ipopts)
  212                 (void) m_free(sc->sc_ipopts);
  213         if (sc->sc_cred)
  214                 crfree(sc->sc_cred);
  215 #ifdef MAC
  216         mac_syncache_destroy(&sc->sc_label);
  217 #endif
  218 
  219         uma_zfree(V_tcp_syncache.zone, sc);
  220 }
  221 
  222 void
  223 syncache_init(void)
  224 {
  225         int i;
  226 
  227         V_tcp_syncookies = 1;
  228         V_tcp_syncookiesonly = 0;
  229         V_tcp_sc_rst_sock_fail = 1;
  230 
  231         V_tcp_syncache.cache_count = 0;
  232         V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  233         V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  234         V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  235         V_tcp_syncache.hash_secret = arc4random();
  236 
  237         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  238             &V_tcp_syncache.hashsize);
  239         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  240             &V_tcp_syncache.bucket_limit);
  241         if (!powerof2(V_tcp_syncache.hashsize) ||
  242             V_tcp_syncache.hashsize == 0) {
  243                 printf("WARNING: syncache hash size is not a power of 2.\n");
  244                 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  245         }
  246         V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
  247 
  248         /* Set limits. */
  249         V_tcp_syncache.cache_limit =
  250             V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
  251         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  252             &V_tcp_syncache.cache_limit);
  253 
  254         /* Allocate the hash table. */
  255         V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
  256             sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
  257 
  258         /* Initialize the hash buckets. */
  259         for (i = 0; i < V_tcp_syncache.hashsize; i++) {
  260 #ifdef VIMAGE
  261                 V_tcp_syncache.hashbase[i].sch_vnet = curvnet;
  262 #endif
  263                 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
  264                 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
  265                          NULL, MTX_DEF);
  266                 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
  267                          &V_tcp_syncache.hashbase[i].sch_mtx, 0);
  268                 V_tcp_syncache.hashbase[i].sch_length = 0;
  269         }
  270 
  271         /* Create the syncache entry zone. */
  272         V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  273             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
  274         uma_zone_set_max(V_tcp_syncache.zone, V_tcp_syncache.cache_limit);
  275 }
  276 
  277 #ifdef VIMAGE
  278 void
  279 syncache_destroy(void)
  280 {
  281 
  282         /* XXX walk the cache, free remaining objects, stop timers */
  283 
  284         uma_zdestroy(V_tcp_syncache.zone);
  285         FREE(V_tcp_syncache.hashbase, M_SYNCACHE);
  286 }
  287 #endif
  288 
  289 /*
  290  * Inserts a syncache entry into the specified bucket row.
  291  * Locks and unlocks the syncache_head autonomously.
  292  */
  293 static void
  294 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  295 {
  296         struct syncache *sc2;
  297 
  298         SCH_LOCK(sch);
  299 
  300         /*
  301          * Make sure that we don't overflow the per-bucket limit.
  302          * If the bucket is full, toss the oldest element.
  303          */
  304         if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
  305                 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
  306                         ("sch->sch_length incorrect"));
  307                 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
  308                 syncache_drop(sc2, sch);
  309                 TCPSTAT_INC(tcps_sc_bucketoverflow);
  310         }
  311 
  312         /* Put it into the bucket. */
  313         TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
  314         sch->sch_length++;
  315 
  316         /* Reinitialize the bucket row's timer. */
  317         if (sch->sch_length == 1)
  318                 sch->sch_nextc = ticks + INT_MAX;
  319         syncache_timeout(sc, sch, 1);
  320 
  321         SCH_UNLOCK(sch);
  322 
  323         V_tcp_syncache.cache_count++;
  324         TCPSTAT_INC(tcps_sc_added);
  325 }
  326 
  327 /*
  328  * Remove and free entry from syncache bucket row.
  329  * Expects locked syncache head.
  330  */
  331 static void
  332 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  333 {
  334 
  335         SCH_LOCK_ASSERT(sch);
  336 
  337         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  338         sch->sch_length--;
  339 
  340 #ifndef TCP_OFFLOAD_DISABLE
  341         if (sc->sc_tu)
  342                 sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb);
  343 #endif              
  344         syncache_free(sc);
  345         V_tcp_syncache.cache_count--;
  346 }
  347 
  348 /*
  349  * Engage/reengage time on bucket row.
  350  */
  351 static void
  352 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
  353 {
  354         sc->sc_rxttime = ticks +
  355                 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
  356         sc->sc_rxmits++;
  357         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
  358                 sch->sch_nextc = sc->sc_rxttime;
  359                 if (docallout)
  360                         callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
  361                             syncache_timer, (void *)sch);
  362         }
  363 }
  364 
  365 /*
  366  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  367  * If we have retransmitted an entry the maximum number of times, expire it.
  368  * One separate timer for each bucket row.
  369  */
  370 static void
  371 syncache_timer(void *xsch)
  372 {
  373         struct syncache_head *sch = (struct syncache_head *)xsch;
  374         struct syncache *sc, *nsc;
  375         int tick = ticks;
  376         char *s;
  377 
  378         CURVNET_SET(sch->sch_vnet);
  379 
  380         /* NB: syncache_head has already been locked by the callout. */
  381         SCH_LOCK_ASSERT(sch);
  382 
  383         /*
  384          * In the following cycle we may remove some entries and/or
  385          * advance some timeouts, so re-initialize the bucket timer.
  386          */
  387         sch->sch_nextc = tick + INT_MAX;
  388 
  389         TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
  390                 /*
  391                  * We do not check if the listen socket still exists
  392                  * and accept the case where the listen socket may be
  393                  * gone by the time we resend the SYN/ACK.  We do
  394                  * not expect this to happens often. If it does,
  395                  * then the RST will be sent by the time the remote
  396                  * host does the SYN/ACK->ACK.
  397                  */
  398                 if (TSTMP_GT(sc->sc_rxttime, tick)) {
  399                         if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
  400                                 sch->sch_nextc = sc->sc_rxttime;
  401                         continue;
  402                 }
  403                 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
  404                         if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  405                                 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
  406                                     "giving up and removing syncache entry\n",
  407                                     s, __func__);
  408                                 free(s, M_TCPLOG);
  409                         }
  410                         syncache_drop(sc, sch);
  411                         TCPSTAT_INC(tcps_sc_stale);
  412                         continue;
  413                 }
  414                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  415                         log(LOG_DEBUG, "%s; %s: Response timeout, "
  416                             "retransmitting (%u) SYN|ACK\n",
  417                             s, __func__, sc->sc_rxmits);
  418                         free(s, M_TCPLOG);
  419                 }
  420 
  421                 (void) syncache_respond(sc);
  422                 TCPSTAT_INC(tcps_sc_retransmitted);
  423                 syncache_timeout(sc, sch, 0);
  424         }
  425         if (!TAILQ_EMPTY(&(sch)->sch_bucket))
  426                 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
  427                         syncache_timer, (void *)(sch));
  428         CURVNET_RESTORE();
  429 }
  430 
  431 /*
  432  * Find an entry in the syncache.
  433  * Returns always with locked syncache_head plus a matching entry or NULL.
  434  */
  435 struct syncache *
  436 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  437 {
  438         struct syncache *sc;
  439         struct syncache_head *sch;
  440 
  441 #ifdef INET6
  442         if (inc->inc_flags & INC_ISIPV6) {
  443                 sch = &V_tcp_syncache.hashbase[
  444                     SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
  445                 *schp = sch;
  446 
  447                 SCH_LOCK(sch);
  448 
  449                 /* Circle through bucket row to find matching entry. */
  450                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  451                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  452                                 return (sc);
  453                 }
  454         } else
  455 #endif
  456         {
  457                 sch = &V_tcp_syncache.hashbase[
  458                     SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
  459                 *schp = sch;
  460 
  461                 SCH_LOCK(sch);
  462 
  463                 /* Circle through bucket row to find matching entry. */
  464                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  465 #ifdef INET6
  466                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
  467                                 continue;
  468 #endif
  469                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  470                                 return (sc);
  471                 }
  472         }
  473         SCH_LOCK_ASSERT(*schp);
  474         return (NULL);                  /* always returns with locked sch */
  475 }
  476 
  477 /*
  478  * This function is called when we get a RST for a
  479  * non-existent connection, so that we can see if the
  480  * connection is in the syn cache.  If it is, zap it.
  481  */
  482 void
  483 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  484 {
  485         struct syncache *sc;
  486         struct syncache_head *sch;
  487         char *s = NULL;
  488 
  489         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  490         SCH_LOCK_ASSERT(sch);
  491 
  492         /*
  493          * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
  494          * See RFC 793 page 65, section SEGMENT ARRIVES.
  495          */
  496         if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
  497                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  498                         log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
  499                             "FIN flag set, segment ignored\n", s, __func__);
  500                 TCPSTAT_INC(tcps_badrst);
  501                 goto done;
  502         }
  503 
  504         /*
  505          * No corresponding connection was found in syncache.
  506          * If syncookies are enabled and possibly exclusively
  507          * used, or we are under memory pressure, a valid RST
  508          * may not find a syncache entry.  In that case we're
  509          * done and no SYN|ACK retransmissions will happen.
  510          * Otherwise the the RST was misdirected or spoofed.
  511          */
  512         if (sc == NULL) {
  513                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  514                         log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
  515                             "syncache entry (possibly syncookie only), "
  516                             "segment ignored\n", s, __func__);
  517                 TCPSTAT_INC(tcps_badrst);
  518                 goto done;
  519         }
  520 
  521         /*
  522          * If the RST bit is set, check the sequence number to see
  523          * if this is a valid reset segment.
  524          * RFC 793 page 37:
  525          *   In all states except SYN-SENT, all reset (RST) segments
  526          *   are validated by checking their SEQ-fields.  A reset is
  527          *   valid if its sequence number is in the window.
  528          *
  529          *   The sequence number in the reset segment is normally an
  530          *   echo of our outgoing acknowlegement numbers, but some hosts
  531          *   send a reset with the sequence number at the rightmost edge
  532          *   of our receive window, and we have to handle this case.
  533          */
  534         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  535             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  536                 syncache_drop(sc, sch);
  537                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  538                         log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
  539                             "connection attempt aborted by remote endpoint\n",
  540                             s, __func__);
  541                 TCPSTAT_INC(tcps_sc_reset);
  542         } else {
  543                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  544                         log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
  545                             "IRS %u (+WND %u), segment ignored\n",
  546                             s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
  547                 TCPSTAT_INC(tcps_badrst);
  548         }
  549 
  550 done:
  551         if (s != NULL)
  552                 free(s, M_TCPLOG);
  553         SCH_UNLOCK(sch);
  554 }
  555 
  556 void
  557 syncache_badack(struct in_conninfo *inc)
  558 {
  559         struct syncache *sc;
  560         struct syncache_head *sch;
  561 
  562         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  563         SCH_LOCK_ASSERT(sch);
  564         if (sc != NULL) {
  565                 syncache_drop(sc, sch);
  566                 TCPSTAT_INC(tcps_sc_badack);
  567         }
  568         SCH_UNLOCK(sch);
  569 }
  570 
  571 void
  572 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  573 {
  574         struct syncache *sc;
  575         struct syncache_head *sch;
  576 
  577         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  578         SCH_LOCK_ASSERT(sch);
  579         if (sc == NULL)
  580                 goto done;
  581 
  582         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  583         if (ntohl(th->th_seq) != sc->sc_iss)
  584                 goto done;
  585 
  586         /*
  587          * If we've rertransmitted 3 times and this is our second error,
  588          * we remove the entry.  Otherwise, we allow it to continue on.
  589          * This prevents us from incorrectly nuking an entry during a
  590          * spurious network outage.
  591          *
  592          * See tcp_notify().
  593          */
  594         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
  595                 sc->sc_flags |= SCF_UNREACH;
  596                 goto done;
  597         }
  598         syncache_drop(sc, sch);
  599         TCPSTAT_INC(tcps_sc_unreach);
  600 done:
  601         SCH_UNLOCK(sch);
  602 }
  603 
  604 /*
  605  * Build a new TCP socket structure from a syncache entry.
  606  */
  607 static struct socket *
  608 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  609 {
  610         struct inpcb *inp = NULL;
  611         struct socket *so;
  612         struct tcpcb *tp;
  613         char *s;
  614 
  615         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  616 
  617         /*
  618          * Ok, create the full blown connection, and set things up
  619          * as they would have been set up if we had created the
  620          * connection when the SYN arrived.  If we can't create
  621          * the connection, abort it.
  622          */
  623         so = sonewconn(lso, SS_ISCONNECTED);
  624         if (so == NULL) {
  625                 /*
  626                  * Drop the connection; we will either send a RST or
  627                  * have the peer retransmit its SYN again after its
  628                  * RTO and try again.
  629                  */
  630                 TCPSTAT_INC(tcps_listendrop);
  631                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  632                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  633                             "due to limits or memory shortage\n",
  634                             s, __func__);
  635                         free(s, M_TCPLOG);
  636                 }
  637                 goto abort2;
  638         }
  639 #ifdef MAC
  640         mac_socketpeer_set_from_mbuf(m, so);
  641 #endif
  642 
  643         inp = sotoinpcb(so);
  644         inp->inp_inc.inc_fibnum = so->so_fibnum;
  645         INP_WLOCK(inp);
  646 
  647         /* Insert new socket into PCB hash list. */
  648         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  649 #ifdef INET6
  650         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  651                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  652         } else {
  653                 inp->inp_vflag &= ~INP_IPV6;
  654                 inp->inp_vflag |= INP_IPV4;
  655 #endif
  656                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  657 #ifdef INET6
  658         }
  659 #endif
  660         inp->inp_lport = sc->sc_inc.inc_lport;
  661         if (in_pcbinshash(inp) != 0) {
  662                 /*
  663                  * Undo the assignments above if we failed to
  664                  * put the PCB on the hash lists.
  665                  */
  666 #ifdef INET6
  667                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  668                         inp->in6p_laddr = in6addr_any;
  669                 else
  670 #endif
  671                         inp->inp_laddr.s_addr = INADDR_ANY;
  672                 inp->inp_lport = 0;
  673                 goto abort;
  674         }
  675 #ifdef IPSEC
  676         /* Copy old policy into new socket's. */
  677         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  678                 printf("syncache_socket: could not copy policy\n");
  679 #endif
  680 #ifdef INET6
  681         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  682                 struct inpcb *oinp = sotoinpcb(lso);
  683                 struct in6_addr laddr6;
  684                 struct sockaddr_in6 sin6;
  685                 /*
  686                  * Inherit socket options from the listening socket.
  687                  * Note that in6p_inputopts are not (and should not be)
  688                  * copied, since it stores previously received options and is
  689                  * used to detect if each new option is different than the
  690                  * previous one and hence should be passed to a user.
  691                  * If we copied in6p_inputopts, a user would not be able to
  692                  * receive options just after calling the accept system call.
  693                  */
  694                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  695                 if (oinp->in6p_outputopts)
  696                         inp->in6p_outputopts =
  697                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  698 
  699                 sin6.sin6_family = AF_INET6;
  700                 sin6.sin6_len = sizeof(sin6);
  701                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  702                 sin6.sin6_port = sc->sc_inc.inc_fport;
  703                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  704                 laddr6 = inp->in6p_laddr;
  705                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  706                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  707                 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  708                     thread0.td_ucred)) {
  709                         inp->in6p_laddr = laddr6;
  710                         goto abort;
  711                 }
  712                 /* Override flowlabel from in6_pcbconnect. */
  713                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  714                 inp->inp_flow |= sc->sc_flowlabel;
  715         } else
  716 #endif
  717         {
  718                 struct in_addr laddr;
  719                 struct sockaddr_in sin;
  720 
  721                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  722                 
  723                 if (inp->inp_options == NULL) {
  724                         inp->inp_options = sc->sc_ipopts;
  725                         sc->sc_ipopts = NULL;
  726                 }
  727 
  728                 sin.sin_family = AF_INET;
  729                 sin.sin_len = sizeof(sin);
  730                 sin.sin_addr = sc->sc_inc.inc_faddr;
  731                 sin.sin_port = sc->sc_inc.inc_fport;
  732                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  733                 laddr = inp->inp_laddr;
  734                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  735                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  736                 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
  737                     thread0.td_ucred)) {
  738                         inp->inp_laddr = laddr;
  739                         goto abort;
  740                 }
  741         }
  742         tp = intotcpcb(inp);
  743         tp->t_state = TCPS_SYN_RECEIVED;
  744         tp->iss = sc->sc_iss;
  745         tp->irs = sc->sc_irs;
  746         tcp_rcvseqinit(tp);
  747         tcp_sendseqinit(tp);
  748         tp->snd_wl1 = sc->sc_irs;
  749         tp->snd_max = tp->iss + 1;
  750         tp->snd_nxt = tp->iss + 1;
  751         tp->rcv_up = sc->sc_irs + 1;
  752         tp->rcv_wnd = sc->sc_wnd;
  753         tp->rcv_adv += tp->rcv_wnd;
  754         tp->last_ack_sent = tp->rcv_nxt;
  755 
  756         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  757         if (sc->sc_flags & SCF_NOOPT)
  758                 tp->t_flags |= TF_NOOPT;
  759         else {
  760                 if (sc->sc_flags & SCF_WINSCALE) {
  761                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  762                         tp->snd_scale = sc->sc_requested_s_scale;
  763                         tp->request_r_scale = sc->sc_requested_r_scale;
  764                 }
  765                 if (sc->sc_flags & SCF_TIMESTAMP) {
  766                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  767                         tp->ts_recent = sc->sc_tsreflect;
  768                         tp->ts_recent_age = ticks;
  769                         tp->ts_offset = sc->sc_tsoff;
  770                 }
  771 #ifdef TCP_SIGNATURE
  772                 if (sc->sc_flags & SCF_SIGNATURE)
  773                         tp->t_flags |= TF_SIGNATURE;
  774 #endif
  775                 if (sc->sc_flags & SCF_SACK)
  776                         tp->t_flags |= TF_SACK_PERMIT;
  777         }
  778 
  779         if (sc->sc_flags & SCF_ECN)
  780                 tp->t_flags |= TF_ECN_PERMIT;
  781 
  782         /*
  783          * Set up MSS and get cached values from tcp_hostcache.
  784          * This might overwrite some of the defaults we just set.
  785          */
  786         tcp_mss(tp, sc->sc_peer_mss);
  787 
  788         /*
  789          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  790          */
  791         if (sc->sc_rxmits)
  792                 tp->snd_cwnd = tp->t_maxseg;
  793         tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
  794 
  795         INP_WUNLOCK(inp);
  796 
  797         TCPSTAT_INC(tcps_accepts);
  798         return (so);
  799 
  800 abort:
  801         INP_WUNLOCK(inp);
  802 abort2:
  803         if (so != NULL)
  804                 soabort(so);
  805         return (NULL);
  806 }
  807 
  808 /*
  809  * This function gets called when we receive an ACK for a
  810  * socket in the LISTEN state.  We look up the connection
  811  * in the syncache, and if its there, we pull it out of
  812  * the cache and turn it into a full-blown connection in
  813  * the SYN-RECEIVED state.
  814  */
  815 int
  816 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  817     struct socket **lsop, struct mbuf *m)
  818 {
  819         struct syncache *sc;
  820         struct syncache_head *sch;
  821         struct syncache scs;
  822         char *s;
  823 
  824         /*
  825          * Global TCP locks are held because we manipulate the PCB lists
  826          * and create a new socket.
  827          */
  828         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  829         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  830             ("%s: can handle only ACK", __func__));
  831 
  832         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  833         SCH_LOCK_ASSERT(sch);
  834         if (sc == NULL) {
  835                 /*
  836                  * There is no syncache entry, so see if this ACK is
  837                  * a returning syncookie.  To do this, first:
  838                  *  A. See if this socket has had a syncache entry dropped in
  839                  *     the past.  We don't want to accept a bogus syncookie
  840                  *     if we've never received a SYN.
  841                  *  B. check that the syncookie is valid.  If it is, then
  842                  *     cobble up a fake syncache entry, and return.
  843                  */
  844                 if (!V_tcp_syncookies) {
  845                         SCH_UNLOCK(sch);
  846                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  847                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  848                                     "segment rejected (syncookies disabled)\n",
  849                                     s, __func__);
  850                         goto failed;
  851                 }
  852                 bzero(&scs, sizeof(scs));
  853                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  854                 SCH_UNLOCK(sch);
  855                 if (sc == NULL) {
  856                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  857                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  858                                     "SYNCOOKIE authentication, segment rejected "
  859                                     "(probably spoofed)\n", s, __func__);
  860                         goto failed;
  861                 }
  862         } else {
  863                 /* Pull out the entry to unlock the bucket row. */
  864                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  865                 sch->sch_length--;
  866                 V_tcp_syncache.cache_count--;
  867                 SCH_UNLOCK(sch);
  868         }
  869 
  870         /*
  871          * Segment validation:
  872          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  873          */
  874         if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
  875                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  876                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  877                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  878                 goto failed;
  879         }
  880 
  881         /*
  882          * The SEQ must fall in the window starting at the received
  883          * initial receive sequence number + 1 (the SYN).
  884          */
  885         if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  886             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) &&
  887             !TOEPCB_ISSET(sc)) {
  888                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  889                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  890                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  891                 goto failed;
  892         }
  893 
  894         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  895                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  896                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  897                             "segment rejected\n", s, __func__);
  898                 goto failed;
  899         }
  900         /*
  901          * If timestamps were negotiated the reflected timestamp
  902          * must be equal to what we actually sent in the SYN|ACK.
  903          */
  904         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
  905             !TOEPCB_ISSET(sc)) {
  906                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  907                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
  908                             "segment rejected\n",
  909                             s, __func__, to->to_tsecr, sc->sc_ts);
  910                 goto failed;
  911         }
  912 
  913         *lsop = syncache_socket(sc, *lsop, m);
  914 
  915         if (*lsop == NULL)
  916                 TCPSTAT_INC(tcps_sc_aborted);
  917         else
  918                 TCPSTAT_INC(tcps_sc_completed);
  919 
  920 /* how do we find the inp for the new socket? */
  921         if (sc != &scs)
  922                 syncache_free(sc);
  923         return (1);
  924 failed:
  925         if (sc != NULL && sc != &scs)
  926                 syncache_free(sc);
  927         if (s != NULL)
  928                 free(s, M_TCPLOG);
  929         *lsop = NULL;
  930         return (0);
  931 }
  932 
  933 int
  934 tcp_offload_syncache_expand(struct in_conninfo *inc, struct toeopt *toeo,
  935     struct tcphdr *th, struct socket **lsop, struct mbuf *m)
  936 {
  937         struct tcpopt to;
  938         int rc;
  939 
  940         bzero(&to, sizeof(struct tcpopt));
  941         to.to_mss = toeo->to_mss;
  942         to.to_wscale = toeo->to_wscale;
  943         to.to_flags = toeo->to_flags;
  944         
  945         INP_INFO_WLOCK(&V_tcbinfo);
  946         rc = syncache_expand(inc, &to, th, lsop, m);
  947         INP_INFO_WUNLOCK(&V_tcbinfo);
  948 
  949         return (rc);
  950 }
  951 
  952 /*
  953  * Given a LISTEN socket and an inbound SYN request, add
  954  * this to the syn cache, and send back a segment:
  955  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  956  * to the source.
  957  *
  958  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  959  * Doing so would require that we hold onto the data and deliver it
  960  * to the application.  However, if we are the target of a SYN-flood
  961  * DoS attack, an attacker could send data which would eventually
  962  * consume all available buffer space if it were ACKed.  By not ACKing
  963  * the data, we avoid this DoS scenario.
  964  */
  965 static void
  966 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  967     struct inpcb *inp, struct socket **lsop, struct mbuf *m,
  968     struct toe_usrreqs *tu, void *toepcb)
  969 {
  970         struct tcpcb *tp;
  971         struct socket *so;
  972         struct syncache *sc = NULL;
  973         struct syncache_head *sch;
  974         struct mbuf *ipopts = NULL;
  975         u_int32_t flowtmp;
  976         int win, sb_hiwat, ip_ttl, ip_tos, noopt;
  977         char *s;
  978 #ifdef INET6
  979         int autoflowlabel = 0;
  980 #endif
  981 #ifdef MAC
  982         struct label *maclabel;
  983 #endif
  984         struct syncache scs;
  985         struct ucred *cred;
  986 
  987         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  988         INP_WLOCK_ASSERT(inp);                  /* listen socket */
  989         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
  990             ("%s: unexpected tcp flags", __func__));
  991 
  992         /*
  993          * Combine all so/tp operations very early to drop the INP lock as
  994          * soon as possible.
  995          */
  996         so = *lsop;
  997         tp = sototcpcb(so);
  998         cred = crhold(so->so_cred);
  999 
 1000 #ifdef INET6
 1001         if ((inc->inc_flags & INC_ISIPV6) &&
 1002             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1003                 autoflowlabel = 1;
 1004 #endif
 1005         ip_ttl = inp->inp_ip_ttl;
 1006         ip_tos = inp->inp_ip_tos;
 1007         win = sbspace(&so->so_rcv);
 1008         sb_hiwat = so->so_rcv.sb_hiwat;
 1009         noopt = (tp->t_flags & TF_NOOPT);
 1010 
 1011         /* By the time we drop the lock these should no longer be used. */
 1012         so = NULL;
 1013         tp = NULL;
 1014 
 1015 #ifdef MAC
 1016         if (mac_syncache_init(&maclabel) != 0) {
 1017                 INP_WUNLOCK(inp);
 1018                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1019                 goto done;
 1020         } else
 1021                 mac_syncache_create(maclabel, inp);
 1022 #endif
 1023         INP_WUNLOCK(inp);
 1024         INP_INFO_WUNLOCK(&V_tcbinfo);
 1025 
 1026         /*
 1027          * Remember the IP options, if any.
 1028          */
 1029 #ifdef INET6
 1030         if (!(inc->inc_flags & INC_ISIPV6))
 1031 #endif
 1032                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1033 
 1034         /*
 1035          * See if we already have an entry for this connection.
 1036          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1037          *
 1038          * XXX: should the syncache be re-initialized with the contents
 1039          * of the new SYN here (which may have different options?)
 1040          *
 1041          * XXX: We do not check the sequence number to see if this is a
 1042          * real retransmit or a new connection attempt.  The question is
 1043          * how to handle such a case; either ignore it as spoofed, or
 1044          * drop the current entry and create a new one?
 1045          */
 1046         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1047         SCH_LOCK_ASSERT(sch);
 1048         if (sc != NULL) {
 1049 #ifndef TCP_OFFLOAD_DISABLE
 1050                 if (sc->sc_tu)
 1051                         sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
 1052                             sc->sc_toepcb);
 1053 #endif              
 1054                 TCPSTAT_INC(tcps_sc_dupsyn);
 1055                 if (ipopts) {
 1056                         /*
 1057                          * If we were remembering a previous source route,
 1058                          * forget it and use the new one we've been given.
 1059                          */
 1060                         if (sc->sc_ipopts)
 1061                                 (void) m_free(sc->sc_ipopts);
 1062                         sc->sc_ipopts = ipopts;
 1063                 }
 1064                 /*
 1065                  * Update timestamp if present.
 1066                  */
 1067                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1068                         sc->sc_tsreflect = to->to_tsval;
 1069                 else
 1070                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1071 #ifdef MAC
 1072                 /*
 1073                  * Since we have already unconditionally allocated label
 1074                  * storage, free it up.  The syncache entry will already
 1075                  * have an initialized label we can use.
 1076                  */
 1077                 mac_syncache_destroy(&maclabel);
 1078 #endif
 1079                 /* Retransmit SYN|ACK and reset retransmit count. */
 1080                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1081                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1082                             "resetting timer and retransmitting SYN|ACK\n",
 1083                             s, __func__);
 1084                         free(s, M_TCPLOG);
 1085                 }
 1086                 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
 1087                         sc->sc_rxmits = 0;
 1088                         syncache_timeout(sc, sch, 1);
 1089                         TCPSTAT_INC(tcps_sndacks);
 1090                         TCPSTAT_INC(tcps_sndtotal);
 1091                 }
 1092                 SCH_UNLOCK(sch);
 1093                 goto done;
 1094         }
 1095 
 1096         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1097         if (sc == NULL) {
 1098                 /*
 1099                  * The zone allocator couldn't provide more entries.
 1100                  * Treat this as if the cache was full; drop the oldest
 1101                  * entry and insert the new one.
 1102                  */
 1103                 TCPSTAT_INC(tcps_sc_zonefail);
 1104                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1105                         syncache_drop(sc, sch);
 1106                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1107                 if (sc == NULL) {
 1108                         if (V_tcp_syncookies) {
 1109                                 bzero(&scs, sizeof(scs));
 1110                                 sc = &scs;
 1111                         } else {
 1112                                 SCH_UNLOCK(sch);
 1113                                 if (ipopts)
 1114                                         (void) m_free(ipopts);
 1115                                 goto done;
 1116                         }
 1117                 }
 1118         }
 1119         
 1120         /*
 1121          * Fill in the syncache values.
 1122          */
 1123 #ifdef MAC
 1124         sc->sc_label = maclabel;
 1125 #endif
 1126         sc->sc_cred = cred;
 1127         cred = NULL;
 1128         sc->sc_ipopts = ipopts;
 1129         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1130 #ifdef INET6
 1131         if (!(inc->inc_flags & INC_ISIPV6))
 1132 #endif
 1133         {
 1134                 sc->sc_ip_tos = ip_tos;
 1135                 sc->sc_ip_ttl = ip_ttl;
 1136         }
 1137 #ifndef TCP_OFFLOAD_DISABLE     
 1138         sc->sc_tu = tu;
 1139         sc->sc_toepcb = toepcb;
 1140 #endif
 1141         sc->sc_irs = th->th_seq;
 1142         sc->sc_iss = arc4random();
 1143         sc->sc_flags = 0;
 1144         sc->sc_flowlabel = 0;
 1145 
 1146         /*
 1147          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1148          * win was derived from socket earlier in the function.
 1149          */
 1150         win = imax(win, 0);
 1151         win = imin(win, TCP_MAXWIN);
 1152         sc->sc_wnd = win;
 1153 
 1154         if (V_tcp_do_rfc1323) {
 1155                 /*
 1156                  * A timestamp received in a SYN makes
 1157                  * it ok to send timestamp requests and replies.
 1158                  */
 1159                 if (to->to_flags & TOF_TS) {
 1160                         sc->sc_tsreflect = to->to_tsval;
 1161                         sc->sc_ts = ticks;
 1162                         sc->sc_flags |= SCF_TIMESTAMP;
 1163                 }
 1164                 if (to->to_flags & TOF_SCALE) {
 1165                         int wscale = 0;
 1166 
 1167                         /*
 1168                          * Pick the smallest possible scaling factor that
 1169                          * will still allow us to scale up to sb_max, aka
 1170                          * kern.ipc.maxsockbuf.
 1171                          *
 1172                          * We do this because there are broken firewalls that
 1173                          * will corrupt the window scale option, leading to
 1174                          * the other endpoint believing that our advertised
 1175                          * window is unscaled.  At scale factors larger than
 1176                          * 5 the unscaled window will drop below 1500 bytes,
 1177                          * leading to serious problems when traversing these
 1178                          * broken firewalls.
 1179                          *
 1180                          * With the default maxsockbuf of 256K, a scale factor
 1181                          * of 3 will be chosen by this algorithm.  Those who
 1182                          * choose a larger maxsockbuf should watch out
 1183                          * for the compatiblity problems mentioned above.
 1184                          *
 1185                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1186                          * or <SYN,ACK>) segment itself is never scaled.
 1187                          */
 1188                         while (wscale < TCP_MAX_WINSHIFT &&
 1189                             (TCP_MAXWIN << wscale) < sb_max)
 1190                                 wscale++;
 1191                         sc->sc_requested_r_scale = wscale;
 1192                         sc->sc_requested_s_scale = to->to_wscale;
 1193                         sc->sc_flags |= SCF_WINSCALE;
 1194                 }
 1195         }
 1196 #ifdef TCP_SIGNATURE
 1197         /*
 1198          * If listening socket requested TCP digests, and received SYN
 1199          * contains the option, flag this in the syncache so that
 1200          * syncache_respond() will do the right thing with the SYN+ACK.
 1201          * XXX: Currently we always record the option by default and will
 1202          * attempt to use it in syncache_respond().
 1203          */
 1204         if (to->to_flags & TOF_SIGNATURE)
 1205                 sc->sc_flags |= SCF_SIGNATURE;
 1206 #endif
 1207         if (to->to_flags & TOF_SACKPERM)
 1208                 sc->sc_flags |= SCF_SACK;
 1209         if (to->to_flags & TOF_MSS)
 1210                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1211         if (noopt)
 1212                 sc->sc_flags |= SCF_NOOPT;
 1213         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1214                 sc->sc_flags |= SCF_ECN;
 1215 
 1216         if (V_tcp_syncookies) {
 1217                 syncookie_generate(sch, sc, &flowtmp);
 1218 #ifdef INET6
 1219                 if (autoflowlabel)
 1220                         sc->sc_flowlabel = flowtmp;
 1221 #endif
 1222         } else {
 1223 #ifdef INET6
 1224                 if (autoflowlabel)
 1225                         sc->sc_flowlabel =
 1226                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1227 #endif
 1228         }
 1229         SCH_UNLOCK(sch);
 1230 
 1231         /*
 1232          * Do a standard 3-way handshake.
 1233          */
 1234         if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
 1235                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1236                         syncache_free(sc);
 1237                 else if (sc != &scs)
 1238                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1239                 TCPSTAT_INC(tcps_sndacks);
 1240                 TCPSTAT_INC(tcps_sndtotal);
 1241         } else {
 1242                 if (sc != &scs)
 1243                         syncache_free(sc);
 1244                 TCPSTAT_INC(tcps_sc_dropped);
 1245         }
 1246 
 1247 done:
 1248         if (cred != NULL)
 1249                 crfree(cred);
 1250 #ifdef MAC
 1251         if (sc == &scs)
 1252                 mac_syncache_destroy(&maclabel);
 1253 #endif
 1254         if (m) {
 1255                 
 1256                 *lsop = NULL;
 1257                 m_freem(m);
 1258         }
 1259 }
 1260 
 1261 static int
 1262 syncache_respond(struct syncache *sc)
 1263 {
 1264         struct ip *ip = NULL;
 1265         struct mbuf *m;
 1266         struct tcphdr *th;
 1267         int optlen, error;
 1268         u_int16_t hlen, tlen, mssopt;
 1269         struct tcpopt to;
 1270 #ifdef INET6
 1271         struct ip6_hdr *ip6 = NULL;
 1272 #endif
 1273 
 1274         hlen =
 1275 #ifdef INET6
 1276                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1277 #endif
 1278                 sizeof(struct ip);
 1279         tlen = hlen + sizeof(struct tcphdr);
 1280 
 1281         /* Determine MSS we advertize to other end of connection. */
 1282         mssopt = tcp_mssopt(&sc->sc_inc);
 1283         if (sc->sc_peer_mss)
 1284                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1285 
 1286         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1287         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1288             ("syncache: mbuf too small"));
 1289 
 1290         /* Create the IP+TCP header from scratch. */
 1291         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1292         if (m == NULL)
 1293                 return (ENOBUFS);
 1294 #ifdef MAC
 1295         mac_syncache_create_mbuf(sc->sc_label, m);
 1296 #endif
 1297         m->m_data += max_linkhdr;
 1298         m->m_len = tlen;
 1299         m->m_pkthdr.len = tlen;
 1300         m->m_pkthdr.rcvif = NULL;
 1301 
 1302 #ifdef INET6
 1303         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1304                 ip6 = mtod(m, struct ip6_hdr *);
 1305                 ip6->ip6_vfc = IPV6_VERSION;
 1306                 ip6->ip6_nxt = IPPROTO_TCP;
 1307                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1308                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1309                 ip6->ip6_plen = htons(tlen - hlen);
 1310                 /* ip6_hlim is set after checksum */
 1311                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1312                 ip6->ip6_flow |= sc->sc_flowlabel;
 1313 
 1314                 th = (struct tcphdr *)(ip6 + 1);
 1315         } else
 1316 #endif
 1317         {
 1318                 ip = mtod(m, struct ip *);
 1319                 ip->ip_v = IPVERSION;
 1320                 ip->ip_hl = sizeof(struct ip) >> 2;
 1321                 ip->ip_len = tlen;
 1322                 ip->ip_id = 0;
 1323                 ip->ip_off = 0;
 1324                 ip->ip_sum = 0;
 1325                 ip->ip_p = IPPROTO_TCP;
 1326                 ip->ip_src = sc->sc_inc.inc_laddr;
 1327                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1328                 ip->ip_ttl = sc->sc_ip_ttl;
 1329                 ip->ip_tos = sc->sc_ip_tos;
 1330 
 1331                 /*
 1332                  * See if we should do MTU discovery.  Route lookups are
 1333                  * expensive, so we will only unset the DF bit if:
 1334                  *
 1335                  *      1) path_mtu_discovery is disabled
 1336                  *      2) the SCF_UNREACH flag has been set
 1337                  */
 1338                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1339                        ip->ip_off |= IP_DF;
 1340 
 1341                 th = (struct tcphdr *)(ip + 1);
 1342         }
 1343         th->th_sport = sc->sc_inc.inc_lport;
 1344         th->th_dport = sc->sc_inc.inc_fport;
 1345 
 1346         th->th_seq = htonl(sc->sc_iss);
 1347         th->th_ack = htonl(sc->sc_irs + 1);
 1348         th->th_off = sizeof(struct tcphdr) >> 2;
 1349         th->th_x2 = 0;
 1350         th->th_flags = TH_SYN|TH_ACK;
 1351         th->th_win = htons(sc->sc_wnd);
 1352         th->th_urp = 0;
 1353 
 1354         if (sc->sc_flags & SCF_ECN) {
 1355                 th->th_flags |= TH_ECE;
 1356                 TCPSTAT_INC(tcps_ecn_shs);
 1357         }
 1358 
 1359         /* Tack on the TCP options. */
 1360         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1361                 to.to_flags = 0;
 1362 
 1363                 to.to_mss = mssopt;
 1364                 to.to_flags = TOF_MSS;
 1365                 if (sc->sc_flags & SCF_WINSCALE) {
 1366                         to.to_wscale = sc->sc_requested_r_scale;
 1367                         to.to_flags |= TOF_SCALE;
 1368                 }
 1369                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1370                         /* Virgin timestamp or TCP cookie enhanced one. */
 1371                         to.to_tsval = sc->sc_ts;
 1372                         to.to_tsecr = sc->sc_tsreflect;
 1373                         to.to_flags |= TOF_TS;
 1374                 }
 1375                 if (sc->sc_flags & SCF_SACK)
 1376                         to.to_flags |= TOF_SACKPERM;
 1377 #ifdef TCP_SIGNATURE
 1378                 if (sc->sc_flags & SCF_SIGNATURE)
 1379                         to.to_flags |= TOF_SIGNATURE;
 1380 #endif
 1381                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1382 
 1383                 /* Adjust headers by option size. */
 1384                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1385                 m->m_len += optlen;
 1386                 m->m_pkthdr.len += optlen;
 1387 
 1388 #ifdef TCP_SIGNATURE
 1389                 if (sc->sc_flags & SCF_SIGNATURE)
 1390                         tcp_signature_compute(m, 0, 0, optlen,
 1391                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1392 #endif
 1393 #ifdef INET6
 1394                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1395                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1396                 else
 1397 #endif
 1398                         ip->ip_len += optlen;
 1399         } else
 1400                 optlen = 0;
 1401 
 1402         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1403 #ifdef INET6
 1404         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1405                 th->th_sum = 0;
 1406                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
 1407                                        tlen + optlen - hlen);
 1408                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1409                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1410         } else
 1411 #endif
 1412         {
 1413                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1414                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1415                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1416                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1417                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1418         }
 1419         return (error);
 1420 }
 1421 
 1422 void
 1423 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1424     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1425 {
 1426         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1427 }
 1428 
 1429 void
 1430 tcp_offload_syncache_add(struct in_conninfo *inc, struct toeopt *toeo,
 1431     struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
 1432     struct toe_usrreqs *tu, void *toepcb)
 1433 {
 1434         struct tcpopt to;
 1435 
 1436         bzero(&to, sizeof(struct tcpopt));
 1437         to.to_mss = toeo->to_mss;
 1438         to.to_wscale = toeo->to_wscale;
 1439         to.to_flags = toeo->to_flags;
 1440 
 1441         INP_INFO_WLOCK(&V_tcbinfo);
 1442         INP_WLOCK(inp);
 1443 
 1444         _syncache_add(inc, &to, th, inp, lsop, NULL, tu, toepcb);
 1445 }
 1446 
 1447 /*
 1448  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1449  * receive and to be able to handle SYN floods from bogus source addresses
 1450  * (where we will never receive any reply).  SYN floods try to exhaust all
 1451  * our memory and available slots in the SYN cache table to cause a denial
 1452  * of service to legitimate users of the local host.
 1453  *
 1454  * The idea of SYN cookies is to encode and include all necessary information
 1455  * about the connection setup state within the SYN-ACK we send back and thus
 1456  * to get along without keeping any local state until the ACK to the SYN-ACK
 1457  * arrives (if ever).  Everything we need to know should be available from
 1458  * the information we encoded in the SYN-ACK.
 1459  *
 1460  * More information about the theory behind SYN cookies and its first
 1461  * discussion and specification can be found at:
 1462  *  http://cr.yp.to/syncookies.html    (overview)
 1463  *  http://cr.yp.to/syncookies/archive (gory details)
 1464  *
 1465  * This implementation extends the orginal idea and first implementation
 1466  * of FreeBSD by using not only the initial sequence number field to store
 1467  * information but also the timestamp field if present.  This way we can
 1468  * keep track of the entire state we need to know to recreate the session in
 1469  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1470  * these days.  For those that do not we still have to live with the known
 1471  * shortcomings of the ISN only SYN cookies.
 1472  *
 1473  * Cookie layers:
 1474  *
 1475  * Initial sequence number we send:
 1476  * 31|................................|0
 1477  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1478  *    D = MD5 Digest (first dword)
 1479  *    M = MSS index
 1480  *    R = Rotation of secret
 1481  *    P = Odd or Even secret
 1482  *
 1483  * The MD5 Digest is computed with over following parameters:
 1484  *  a) randomly rotated secret
 1485  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1486  *  c) the received initial sequence number from remote host
 1487  *  d) the rotation offset and odd/even bit
 1488  *
 1489  * Timestamp we send:
 1490  * 31|................................|0
 1491  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1492  *    D = MD5 Digest (third dword) (only as filler)
 1493  *    S = Requested send window scale
 1494  *    R = Requested receive window scale
 1495  *    A = SACK allowed
 1496  *    5 = TCP-MD5 enabled (not implemented yet)
 1497  *    XORed with MD5 Digest (forth dword)
 1498  *
 1499  * The timestamp isn't cryptographically secure and doesn't need to be.
 1500  * The double use of the MD5 digest dwords ties it to a specific remote/
 1501  * local host/port, remote initial sequence number and our local time
 1502  * limited secret.  A received timestamp is reverted (XORed) and then
 1503  * the contained MD5 dword is compared to the computed one to ensure the
 1504  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1505  * have been tampered with but this isn't different from supplying bogus
 1506  * values in the SYN in the first place.
 1507  *
 1508  * Some problems with SYN cookies remain however:
 1509  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1510  * original SYN was accepted, the connection is established.  The second
 1511  * SYN is inflight, and if it arrives with an ISN that falls within the
 1512  * receive window, the connection is killed.
 1513  *
 1514  * Notes:
 1515  * A heuristic to determine when to accept syn cookies is not necessary.
 1516  * An ACK flood would cause the syncookie verification to be attempted,
 1517  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1518  * cost, so there's no point in trying to optimize the ACK flood case.
 1519  * Also, if you don't process certain ACKs for some reason, then all someone
 1520  * would have to do is launch a SYN and ACK flood at the same time, which
 1521  * would stop cookie verification and defeat the entire purpose of syncookies.
 1522  */
 1523 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1524 
 1525 static void
 1526 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1527     u_int32_t *flowlabel)
 1528 {
 1529         MD5_CTX ctx;
 1530         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1531         u_int32_t data;
 1532         u_int32_t *secbits;
 1533         u_int off, pmss, mss;
 1534         int i;
 1535 
 1536         SCH_LOCK_ASSERT(sch);
 1537 
 1538         /* Which of the two secrets to use. */
 1539         secbits = sch->sch_oddeven ?
 1540                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1541 
 1542         /* Reseed secret if too old. */
 1543         if (sch->sch_reseed < time_uptime) {
 1544                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1545                 secbits = sch->sch_oddeven ?
 1546                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1547                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1548                         secbits[i] = arc4random();
 1549                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1550         }
 1551 
 1552         /* Secret rotation offset. */
 1553         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1554 
 1555         /* Maximum segment size calculation. */
 1556         pmss =
 1557             max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), V_tcp_minmss);
 1558         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1559                 if (tcp_sc_msstab[mss] <= pmss)
 1560                         break;
 1561 
 1562         /* Fold parameters and MD5 digest into the ISN we will send. */
 1563         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1564         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1565         data |= mss << 4;       /* mss, 3 bits */
 1566 
 1567         MD5Init(&ctx);
 1568         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1569             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1570         MD5Update(&ctx, secbits, off);
 1571         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1572         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1573         MD5Update(&ctx, &data, sizeof(data));
 1574         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1575 
 1576         data |= (md5_buffer[0] << 7);
 1577         sc->sc_iss = data;
 1578 
 1579 #ifdef INET6
 1580         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1581 #endif
 1582 
 1583         /* Additional parameters are stored in the timestamp if present. */
 1584         if (sc->sc_flags & SCF_TIMESTAMP) {
 1585                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1586                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1587                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1588                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1589                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1590                 data ^= md5_buffer[3];
 1591                 sc->sc_ts = data;
 1592                 sc->sc_tsoff = data - ticks;            /* after XOR */
 1593         }
 1594 
 1595         TCPSTAT_INC(tcps_sc_sendcookie);
 1596 }
 1597 
 1598 static struct syncache *
 1599 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1600     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1601     struct socket *so)
 1602 {
 1603         MD5_CTX ctx;
 1604         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1605         u_int32_t data = 0;
 1606         u_int32_t *secbits;
 1607         tcp_seq ack, seq;
 1608         int off, mss, wnd, flags;
 1609 
 1610         SCH_LOCK_ASSERT(sch);
 1611 
 1612         /*
 1613          * Pull information out of SYN-ACK/ACK and
 1614          * revert sequence number advances.
 1615          */
 1616         ack = th->th_ack - 1;
 1617         seq = th->th_seq - 1;
 1618         off = (ack >> 1) & 0x7;
 1619         mss = (ack >> 4) & 0x7;
 1620         flags = ack & 0x7f;
 1621 
 1622         /* Which of the two secrets to use. */
 1623         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1624 
 1625         /*
 1626          * The secret wasn't updated for the lifetime of a syncookie,
 1627          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1628          */
 1629         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1630                 return (NULL);
 1631         }
 1632 
 1633         /* Recompute the digest so we can compare it. */
 1634         MD5Init(&ctx);
 1635         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1636             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1637         MD5Update(&ctx, secbits, off);
 1638         MD5Update(&ctx, inc, sizeof(*inc));
 1639         MD5Update(&ctx, &seq, sizeof(seq));
 1640         MD5Update(&ctx, &flags, sizeof(flags));
 1641         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1642 
 1643         /* Does the digest part of or ACK'ed ISS match? */
 1644         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1645                 return (NULL);
 1646 
 1647         /* Does the digest part of our reflected timestamp match? */
 1648         if (to->to_flags & TOF_TS) {
 1649                 data = md5_buffer[3] ^ to->to_tsecr;
 1650                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1651                         return (NULL);
 1652         }
 1653 
 1654         /* Fill in the syncache values. */
 1655         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1656         sc->sc_ipopts = NULL;
 1657         
 1658         sc->sc_irs = seq;
 1659         sc->sc_iss = ack;
 1660 
 1661 #ifdef INET6
 1662         if (inc->inc_flags & INC_ISIPV6) {
 1663                 if (sotoinpcb(so)->inp_flags & IN6P_AUTOFLOWLABEL)
 1664                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1665         } else
 1666 #endif
 1667         {
 1668                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1669                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1670         }
 1671 
 1672         /* Additional parameters that were encoded in the timestamp. */
 1673         if (data) {
 1674                 sc->sc_flags |= SCF_TIMESTAMP;
 1675                 sc->sc_tsreflect = to->to_tsval;
 1676                 sc->sc_ts = to->to_tsecr;
 1677                 sc->sc_tsoff = to->to_tsecr - ticks;
 1678                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1679                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1680                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1681                     TCP_MAX_WINSHIFT);
 1682                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1683                     TCP_MAX_WINSHIFT);
 1684                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1685                         sc->sc_flags |= SCF_WINSCALE;
 1686         } else
 1687                 sc->sc_flags |= SCF_NOOPT;
 1688 
 1689         wnd = sbspace(&so->so_rcv);
 1690         wnd = imax(wnd, 0);
 1691         wnd = imin(wnd, TCP_MAXWIN);
 1692         sc->sc_wnd = wnd;
 1693 
 1694         sc->sc_rxmits = 0;
 1695         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1696 
 1697         TCPSTAT_INC(tcps_sc_recvcookie);
 1698         return (sc);
 1699 }
 1700 
 1701 /*
 1702  * Returns the current number of syncache entries.  This number
 1703  * will probably change before you get around to calling 
 1704  * syncache_pcblist.
 1705  */
 1706 
 1707 int
 1708 syncache_pcbcount(void)
 1709 {
 1710         struct syncache_head *sch;
 1711         int count, i;
 1712 
 1713         for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1714                 /* No need to lock for a read. */
 1715                 sch = &V_tcp_syncache.hashbase[i];
 1716                 count += sch->sch_length;
 1717         }
 1718         return count;
 1719 }
 1720 
 1721 /*
 1722  * Exports the syncache entries to userland so that netstat can display
 1723  * them alongside the other sockets.  This function is intended to be
 1724  * called only from tcp_pcblist.
 1725  *
 1726  * Due to concurrency on an active system, the number of pcbs exported
 1727  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1728  * amount of space the caller allocated for this function to use.
 1729  */
 1730 int
 1731 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1732 {
 1733         struct xtcpcb xt;
 1734         struct syncache *sc;
 1735         struct syncache_head *sch;
 1736         int count, error, i;
 1737 
 1738         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1739                 sch = &V_tcp_syncache.hashbase[i];
 1740                 SCH_LOCK(sch);
 1741                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1742                         if (count >= max_pcbs) {
 1743                                 SCH_UNLOCK(sch);
 1744                                 goto exit;
 1745                         }
 1746                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1747                                 continue;
 1748                         bzero(&xt, sizeof(xt));
 1749                         xt.xt_len = sizeof(xt);
 1750                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1751                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1752                         else
 1753                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1754                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1755                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1756                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1757                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1758                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1759                         xt.xt_socket.so_type = SOCK_STREAM;
 1760                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1761                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1762                         if (error) {
 1763                                 SCH_UNLOCK(sch);
 1764                                 goto exit;
 1765                         }
 1766                         count++;
 1767                 }
 1768                 SCH_UNLOCK(sch);
 1769         }
 1770 exit:
 1771         *pcbs_exported = count;
 1772         return error;
 1773 }

Cache object: 3b110e604db658bc72562faedacff737


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