The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_syncache.c

Version: -  FREEBSD  -  FREEBSD-12-STABLE  -  FREEBSD-12-0  -  FREEBSD-11-STABLE  -  FREEBSD-11-2  -  FREEBSD-11-1  -  FREEBSD-11-0  -  FREEBSD-10-STABLE  -  FREEBSD-10-4  -  FREEBSD-10-3  -  FREEBSD-10-2  -  FREEBSD-10-1  -  FREEBSD-10-0  -  FREEBSD-9-STABLE  -  FREEBSD-9-3  -  FREEBSD-9-2  -  FREEBSD-9-1  -  FREEBSD-9-0  -  FREEBSD-8-STABLE  -  FREEBSD-8-4  -  FREEBSD-8-3  -  FREEBSD-8-2  -  FREEBSD-8-1  -  FREEBSD-8-0  -  FREEBSD-7-STABLE  -  FREEBSD-7-4  -  FREEBSD-7-3  -  FREEBSD-7-2  -  FREEBSD-7-1  -  FREEBSD-7-0  -  FREEBSD-6-STABLE  -  FREEBSD-6-4  -  FREEBSD-6-3  -  FREEBSD-6-2  -  FREEBSD-6-1  -  FREEBSD-6-0  -  FREEBSD-5-STABLE  -  FREEBSD-5-5  -  FREEBSD-5-4  -  FREEBSD-5-3  -  FREEBSD-5-2  -  FREEBSD-5-1  -  FREEBSD-5-0  -  FREEBSD-4-STABLE  -  FREEBSD-3-STABLE  -  FREEBSD22  -  linux-2.6  -  linux-2.4.22  -  MK83  -  MK84  -  PLAN9  -  DFBSD  -  NETBSD  -  NETBSD5  -  NETBSD4  -  NETBSD3  -  NETBSD20  -  OPENBSD  -  xnu-517  -  xnu-792  -  xnu-792.6.70  -  xnu-1228  -  xnu-1456.1.26  -  xnu-1699.24.8  -  xnu-2050.18.24  -  OPENSOLARIS  -  minix-3-1-1 
SearchContext: -  none  -  3  -  10 

    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/8.1/sys/netinet/tcp_syncache.c 207695 2010-05-06 06:44:19Z bz $");
   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         char *s;
  631 
  632         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  633 
  634         /*
  635          * Ok, create the full blown connection, and set things up
  636          * as they would have been set up if we had created the
  637          * connection when the SYN arrived.  If we can't create
  638          * the connection, abort it.
  639          */
  640         so = sonewconn(lso, SS_ISCONNECTED);
  641         if (so == NULL) {
  642                 /*
  643                  * Drop the connection; we will either send a RST or
  644                  * have the peer retransmit its SYN again after its
  645                  * RTO and try again.
  646                  */
  647                 TCPSTAT_INC(tcps_listendrop);
  648                 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
  649                         log(LOG_DEBUG, "%s; %s: Socket create failed "
  650                             "due to limits or memory shortage\n",
  651                             s, __func__);
  652                         free(s, M_TCPLOG);
  653                 }
  654                 goto abort2;
  655         }
  656 #ifdef MAC
  657         mac_socketpeer_set_from_mbuf(m, so);
  658 #endif
  659 
  660         inp = sotoinpcb(so);
  661         inp->inp_inc.inc_fibnum = so->so_fibnum;
  662         INP_WLOCK(inp);
  663 
  664         /* Insert new socket into PCB hash list. */
  665         inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
  666 #ifdef INET6
  667         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  668                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  669         } else {
  670                 inp->inp_vflag &= ~INP_IPV6;
  671                 inp->inp_vflag |= INP_IPV4;
  672 #endif
  673                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  674 #ifdef INET6
  675         }
  676 #endif
  677         inp->inp_lport = sc->sc_inc.inc_lport;
  678         if (in_pcbinshash(inp) != 0) {
  679                 /*
  680                  * Undo the assignments above if we failed to
  681                  * put the PCB on the hash lists.
  682                  */
  683 #ifdef INET6
  684                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
  685                         inp->in6p_laddr = in6addr_any;
  686                 else
  687 #endif
  688                         inp->inp_laddr.s_addr = INADDR_ANY;
  689                 inp->inp_lport = 0;
  690                 goto abort;
  691         }
  692 #ifdef IPSEC
  693         /* Copy old policy into new socket's. */
  694         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  695                 printf("syncache_socket: could not copy policy\n");
  696 #endif
  697 #ifdef INET6
  698         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
  699                 struct inpcb *oinp = sotoinpcb(lso);
  700                 struct in6_addr laddr6;
  701                 struct sockaddr_in6 sin6;
  702                 /*
  703                  * Inherit socket options from the listening socket.
  704                  * Note that in6p_inputopts are not (and should not be)
  705                  * copied, since it stores previously received options and is
  706                  * used to detect if each new option is different than the
  707                  * previous one and hence should be passed to a user.
  708                  * If we copied in6p_inputopts, a user would not be able to
  709                  * receive options just after calling the accept system call.
  710                  */
  711                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  712                 if (oinp->in6p_outputopts)
  713                         inp->in6p_outputopts =
  714                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  715 
  716                 sin6.sin6_family = AF_INET6;
  717                 sin6.sin6_len = sizeof(sin6);
  718                 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
  719                 sin6.sin6_port = sc->sc_inc.inc_fport;
  720                 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
  721                 laddr6 = inp->in6p_laddr;
  722                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  723                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  724                 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
  725                     thread0.td_ucred)) {
  726                         inp->in6p_laddr = laddr6;
  727                         goto abort;
  728                 }
  729                 /* Override flowlabel from in6_pcbconnect. */
  730                 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
  731                 inp->inp_flow |= sc->sc_flowlabel;
  732         } else
  733 #endif
  734         {
  735                 struct in_addr laddr;
  736                 struct sockaddr_in sin;
  737 
  738                 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
  739                 
  740                 if (inp->inp_options == NULL) {
  741                         inp->inp_options = sc->sc_ipopts;
  742                         sc->sc_ipopts = NULL;
  743                 }
  744 
  745                 sin.sin_family = AF_INET;
  746                 sin.sin_len = sizeof(sin);
  747                 sin.sin_addr = sc->sc_inc.inc_faddr;
  748                 sin.sin_port = sc->sc_inc.inc_fport;
  749                 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
  750                 laddr = inp->inp_laddr;
  751                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  752                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  753                 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
  754                     thread0.td_ucred)) {
  755                         inp->inp_laddr = laddr;
  756                         goto abort;
  757                 }
  758         }
  759         tp = intotcpcb(inp);
  760         tp->t_state = TCPS_SYN_RECEIVED;
  761         tp->iss = sc->sc_iss;
  762         tp->irs = sc->sc_irs;
  763         tcp_rcvseqinit(tp);
  764         tcp_sendseqinit(tp);
  765         tp->snd_wl1 = sc->sc_irs;
  766         tp->snd_max = tp->iss + 1;
  767         tp->snd_nxt = tp->iss + 1;
  768         tp->rcv_up = sc->sc_irs + 1;
  769         tp->rcv_wnd = sc->sc_wnd;
  770         tp->rcv_adv += tp->rcv_wnd;
  771         tp->last_ack_sent = tp->rcv_nxt;
  772 
  773         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  774         if (sc->sc_flags & SCF_NOOPT)
  775                 tp->t_flags |= TF_NOOPT;
  776         else {
  777                 if (sc->sc_flags & SCF_WINSCALE) {
  778                         tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  779                         tp->snd_scale = sc->sc_requested_s_scale;
  780                         tp->request_r_scale = sc->sc_requested_r_scale;
  781                 }
  782                 if (sc->sc_flags & SCF_TIMESTAMP) {
  783                         tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  784                         tp->ts_recent = sc->sc_tsreflect;
  785                         tp->ts_recent_age = ticks;
  786                         tp->ts_offset = sc->sc_tsoff;
  787                 }
  788 #ifdef TCP_SIGNATURE
  789                 if (sc->sc_flags & SCF_SIGNATURE)
  790                         tp->t_flags |= TF_SIGNATURE;
  791 #endif
  792                 if (sc->sc_flags & SCF_SACK)
  793                         tp->t_flags |= TF_SACK_PERMIT;
  794         }
  795 
  796         if (sc->sc_flags & SCF_ECN)
  797                 tp->t_flags |= TF_ECN_PERMIT;
  798 
  799         /*
  800          * Set up MSS and get cached values from tcp_hostcache.
  801          * This might overwrite some of the defaults we just set.
  802          */
  803         tcp_mss(tp, sc->sc_peer_mss);
  804 
  805         /*
  806          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  807          */
  808         if (sc->sc_rxmits)
  809                 tp->snd_cwnd = tp->t_maxseg;
  810         tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
  811 
  812         INP_WUNLOCK(inp);
  813 
  814         TCPSTAT_INC(tcps_accepts);
  815         return (so);
  816 
  817 abort:
  818         INP_WUNLOCK(inp);
  819 abort2:
  820         if (so != NULL)
  821                 soabort(so);
  822         return (NULL);
  823 }
  824 
  825 /*
  826  * This function gets called when we receive an ACK for a
  827  * socket in the LISTEN state.  We look up the connection
  828  * in the syncache, and if its there, we pull it out of
  829  * the cache and turn it into a full-blown connection in
  830  * the SYN-RECEIVED state.
  831  */
  832 int
  833 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  834     struct socket **lsop, struct mbuf *m)
  835 {
  836         struct syncache *sc;
  837         struct syncache_head *sch;
  838         struct syncache scs;
  839         char *s;
  840 
  841         /*
  842          * Global TCP locks are held because we manipulate the PCB lists
  843          * and create a new socket.
  844          */
  845         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  846         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
  847             ("%s: can handle only ACK", __func__));
  848 
  849         sc = syncache_lookup(inc, &sch);        /* returns locked sch */
  850         SCH_LOCK_ASSERT(sch);
  851         if (sc == NULL) {
  852                 /*
  853                  * There is no syncache entry, so see if this ACK is
  854                  * a returning syncookie.  To do this, first:
  855                  *  A. See if this socket has had a syncache entry dropped in
  856                  *     the past.  We don't want to accept a bogus syncookie
  857                  *     if we've never received a SYN.
  858                  *  B. check that the syncookie is valid.  If it is, then
  859                  *     cobble up a fake syncache entry, and return.
  860                  */
  861                 if (!V_tcp_syncookies) {
  862                         SCH_UNLOCK(sch);
  863                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  864                                 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
  865                                     "segment rejected (syncookies disabled)\n",
  866                                     s, __func__);
  867                         goto failed;
  868                 }
  869                 bzero(&scs, sizeof(scs));
  870                 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
  871                 SCH_UNLOCK(sch);
  872                 if (sc == NULL) {
  873                         if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  874                                 log(LOG_DEBUG, "%s; %s: Segment failed "
  875                                     "SYNCOOKIE authentication, segment rejected "
  876                                     "(probably spoofed)\n", s, __func__);
  877                         goto failed;
  878                 }
  879         } else {
  880                 /* Pull out the entry to unlock the bucket row. */
  881                 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  882                 sch->sch_length--;
  883                 V_tcp_syncache.cache_count--;
  884                 SCH_UNLOCK(sch);
  885         }
  886 
  887         /*
  888          * Segment validation:
  889          * ACK must match our initial sequence number + 1 (the SYN|ACK).
  890          */
  891         if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) {
  892                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  893                         log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
  894                             "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
  895                 goto failed;
  896         }
  897 
  898         /*
  899          * The SEQ must fall in the window starting at the received
  900          * initial receive sequence number + 1 (the SYN).
  901          */
  902         if ((SEQ_LEQ(th->th_seq, sc->sc_irs) ||
  903             SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) &&
  904             !TOEPCB_ISSET(sc)) {
  905                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  906                         log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
  907                             "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
  908                 goto failed;
  909         }
  910 
  911         if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
  912                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  913                         log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
  914                             "segment rejected\n", s, __func__);
  915                 goto failed;
  916         }
  917         /*
  918          * If timestamps were negotiated the reflected timestamp
  919          * must be equal to what we actually sent in the SYN|ACK.
  920          */
  921         if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts &&
  922             !TOEPCB_ISSET(sc)) {
  923                 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
  924                         log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
  925                             "segment rejected\n",
  926                             s, __func__, to->to_tsecr, sc->sc_ts);
  927                 goto failed;
  928         }
  929 
  930         *lsop = syncache_socket(sc, *lsop, m);
  931 
  932         if (*lsop == NULL)
  933                 TCPSTAT_INC(tcps_sc_aborted);
  934         else
  935                 TCPSTAT_INC(tcps_sc_completed);
  936 
  937 /* how do we find the inp for the new socket? */
  938         if (sc != &scs)
  939                 syncache_free(sc);
  940         return (1);
  941 failed:
  942         if (sc != NULL && sc != &scs)
  943                 syncache_free(sc);
  944         if (s != NULL)
  945                 free(s, M_TCPLOG);
  946         *lsop = NULL;
  947         return (0);
  948 }
  949 
  950 int
  951 tcp_offload_syncache_expand(struct in_conninfo *inc, struct toeopt *toeo,
  952     struct tcphdr *th, struct socket **lsop, struct mbuf *m)
  953 {
  954         struct tcpopt to;
  955         int rc;
  956 
  957         bzero(&to, sizeof(struct tcpopt));
  958         to.to_mss = toeo->to_mss;
  959         to.to_wscale = toeo->to_wscale;
  960         to.to_flags = toeo->to_flags;
  961         
  962         INP_INFO_WLOCK(&V_tcbinfo);
  963         rc = syncache_expand(inc, &to, th, lsop, m);
  964         INP_INFO_WUNLOCK(&V_tcbinfo);
  965 
  966         return (rc);
  967 }
  968 
  969 /*
  970  * Given a LISTEN socket and an inbound SYN request, add
  971  * this to the syn cache, and send back a segment:
  972  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  973  * to the source.
  974  *
  975  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  976  * Doing so would require that we hold onto the data and deliver it
  977  * to the application.  However, if we are the target of a SYN-flood
  978  * DoS attack, an attacker could send data which would eventually
  979  * consume all available buffer space if it were ACKed.  By not ACKing
  980  * the data, we avoid this DoS scenario.
  981  */
  982 static void
  983 _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  984     struct inpcb *inp, struct socket **lsop, struct mbuf *m,
  985     struct toe_usrreqs *tu, void *toepcb)
  986 {
  987         struct tcpcb *tp;
  988         struct socket *so;
  989         struct syncache *sc = NULL;
  990         struct syncache_head *sch;
  991         struct mbuf *ipopts = NULL;
  992         u_int32_t flowtmp;
  993         int win, sb_hiwat, ip_ttl, ip_tos, noopt;
  994         char *s;
  995 #ifdef INET6
  996         int autoflowlabel = 0;
  997 #endif
  998 #ifdef MAC
  999         struct label *maclabel;
 1000 #endif
 1001         struct syncache scs;
 1002         struct ucred *cred;
 1003 
 1004         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
 1005         INP_WLOCK_ASSERT(inp);                  /* listen socket */
 1006         KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 1007             ("%s: unexpected tcp flags", __func__));
 1008 
 1009         /*
 1010          * Combine all so/tp operations very early to drop the INP lock as
 1011          * soon as possible.
 1012          */
 1013         so = *lsop;
 1014         tp = sototcpcb(so);
 1015         cred = crhold(so->so_cred);
 1016 
 1017 #ifdef INET6
 1018         if ((inc->inc_flags & INC_ISIPV6) &&
 1019             (inp->inp_flags & IN6P_AUTOFLOWLABEL))
 1020                 autoflowlabel = 1;
 1021 #endif
 1022         ip_ttl = inp->inp_ip_ttl;
 1023         ip_tos = inp->inp_ip_tos;
 1024         win = sbspace(&so->so_rcv);
 1025         sb_hiwat = so->so_rcv.sb_hiwat;
 1026         noopt = (tp->t_flags & TF_NOOPT);
 1027 
 1028         /* By the time we drop the lock these should no longer be used. */
 1029         so = NULL;
 1030         tp = NULL;
 1031 
 1032 #ifdef MAC
 1033         if (mac_syncache_init(&maclabel) != 0) {
 1034                 INP_WUNLOCK(inp);
 1035                 INP_INFO_WUNLOCK(&V_tcbinfo);
 1036                 goto done;
 1037         } else
 1038                 mac_syncache_create(maclabel, inp);
 1039 #endif
 1040         INP_WUNLOCK(inp);
 1041         INP_INFO_WUNLOCK(&V_tcbinfo);
 1042 
 1043         /*
 1044          * Remember the IP options, if any.
 1045          */
 1046 #ifdef INET6
 1047         if (!(inc->inc_flags & INC_ISIPV6))
 1048 #endif
 1049                 ipopts = (m) ? ip_srcroute(m) : NULL;
 1050 
 1051         /*
 1052          * See if we already have an entry for this connection.
 1053          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1054          *
 1055          * XXX: should the syncache be re-initialized with the contents
 1056          * of the new SYN here (which may have different options?)
 1057          *
 1058          * XXX: We do not check the sequence number to see if this is a
 1059          * real retransmit or a new connection attempt.  The question is
 1060          * how to handle such a case; either ignore it as spoofed, or
 1061          * drop the current entry and create a new one?
 1062          */
 1063         sc = syncache_lookup(inc, &sch);        /* returns locked entry */
 1064         SCH_LOCK_ASSERT(sch);
 1065         if (sc != NULL) {
 1066 #ifndef TCP_OFFLOAD_DISABLE
 1067                 if (sc->sc_tu)
 1068                         sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT,
 1069                             sc->sc_toepcb);
 1070 #endif              
 1071                 TCPSTAT_INC(tcps_sc_dupsyn);
 1072                 if (ipopts) {
 1073                         /*
 1074                          * If we were remembering a previous source route,
 1075                          * forget it and use the new one we've been given.
 1076                          */
 1077                         if (sc->sc_ipopts)
 1078                                 (void) m_free(sc->sc_ipopts);
 1079                         sc->sc_ipopts = ipopts;
 1080                 }
 1081                 /*
 1082                  * Update timestamp if present.
 1083                  */
 1084                 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
 1085                         sc->sc_tsreflect = to->to_tsval;
 1086                 else
 1087                         sc->sc_flags &= ~SCF_TIMESTAMP;
 1088 #ifdef MAC
 1089                 /*
 1090                  * Since we have already unconditionally allocated label
 1091                  * storage, free it up.  The syncache entry will already
 1092                  * have an initialized label we can use.
 1093                  */
 1094                 mac_syncache_destroy(&maclabel);
 1095 #endif
 1096                 /* Retransmit SYN|ACK and reset retransmit count. */
 1097                 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
 1098                         log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
 1099                             "resetting timer and retransmitting SYN|ACK\n",
 1100                             s, __func__);
 1101                         free(s, M_TCPLOG);
 1102                 }
 1103                 if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) {
 1104                         sc->sc_rxmits = 0;
 1105                         syncache_timeout(sc, sch, 1);
 1106                         TCPSTAT_INC(tcps_sndacks);
 1107                         TCPSTAT_INC(tcps_sndtotal);
 1108                 }
 1109                 SCH_UNLOCK(sch);
 1110                 goto done;
 1111         }
 1112 
 1113         sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1114         if (sc == NULL) {
 1115                 /*
 1116                  * The zone allocator couldn't provide more entries.
 1117                  * Treat this as if the cache was full; drop the oldest
 1118                  * entry and insert the new one.
 1119                  */
 1120                 TCPSTAT_INC(tcps_sc_zonefail);
 1121                 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
 1122                         syncache_drop(sc, sch);
 1123                 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
 1124                 if (sc == NULL) {
 1125                         if (V_tcp_syncookies) {
 1126                                 bzero(&scs, sizeof(scs));
 1127                                 sc = &scs;
 1128                         } else {
 1129                                 SCH_UNLOCK(sch);
 1130                                 if (ipopts)
 1131                                         (void) m_free(ipopts);
 1132                                 goto done;
 1133                         }
 1134                 }
 1135         }
 1136         
 1137         /*
 1138          * Fill in the syncache values.
 1139          */
 1140 #ifdef MAC
 1141         sc->sc_label = maclabel;
 1142 #endif
 1143         sc->sc_cred = cred;
 1144         cred = NULL;
 1145         sc->sc_ipopts = ipopts;
 1146         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1147 #ifdef INET6
 1148         if (!(inc->inc_flags & INC_ISIPV6))
 1149 #endif
 1150         {
 1151                 sc->sc_ip_tos = ip_tos;
 1152                 sc->sc_ip_ttl = ip_ttl;
 1153         }
 1154 #ifndef TCP_OFFLOAD_DISABLE     
 1155         sc->sc_tu = tu;
 1156         sc->sc_toepcb = toepcb;
 1157 #endif
 1158         sc->sc_irs = th->th_seq;
 1159         sc->sc_iss = arc4random();
 1160         sc->sc_flags = 0;
 1161         sc->sc_flowlabel = 0;
 1162 
 1163         /*
 1164          * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
 1165          * win was derived from socket earlier in the function.
 1166          */
 1167         win = imax(win, 0);
 1168         win = imin(win, TCP_MAXWIN);
 1169         sc->sc_wnd = win;
 1170 
 1171         if (V_tcp_do_rfc1323) {
 1172                 /*
 1173                  * A timestamp received in a SYN makes
 1174                  * it ok to send timestamp requests and replies.
 1175                  */
 1176                 if (to->to_flags & TOF_TS) {
 1177                         sc->sc_tsreflect = to->to_tsval;
 1178                         sc->sc_ts = ticks;
 1179                         sc->sc_flags |= SCF_TIMESTAMP;
 1180                 }
 1181                 if (to->to_flags & TOF_SCALE) {
 1182                         int wscale = 0;
 1183 
 1184                         /*
 1185                          * Pick the smallest possible scaling factor that
 1186                          * will still allow us to scale up to sb_max, aka
 1187                          * kern.ipc.maxsockbuf.
 1188                          *
 1189                          * We do this because there are broken firewalls that
 1190                          * will corrupt the window scale option, leading to
 1191                          * the other endpoint believing that our advertised
 1192                          * window is unscaled.  At scale factors larger than
 1193                          * 5 the unscaled window will drop below 1500 bytes,
 1194                          * leading to serious problems when traversing these
 1195                          * broken firewalls.
 1196                          *
 1197                          * With the default maxsockbuf of 256K, a scale factor
 1198                          * of 3 will be chosen by this algorithm.  Those who
 1199                          * choose a larger maxsockbuf should watch out
 1200                          * for the compatiblity problems mentioned above.
 1201                          *
 1202                          * RFC1323: The Window field in a SYN (i.e., a <SYN>
 1203                          * or <SYN,ACK>) segment itself is never scaled.
 1204                          */
 1205                         while (wscale < TCP_MAX_WINSHIFT &&
 1206                             (TCP_MAXWIN << wscale) < sb_max)
 1207                                 wscale++;
 1208                         sc->sc_requested_r_scale = wscale;
 1209                         sc->sc_requested_s_scale = to->to_wscale;
 1210                         sc->sc_flags |= SCF_WINSCALE;
 1211                 }
 1212         }
 1213 #ifdef TCP_SIGNATURE
 1214         /*
 1215          * If listening socket requested TCP digests, and received SYN
 1216          * contains the option, flag this in the syncache so that
 1217          * syncache_respond() will do the right thing with the SYN+ACK.
 1218          * XXX: Currently we always record the option by default and will
 1219          * attempt to use it in syncache_respond().
 1220          */
 1221         if (to->to_flags & TOF_SIGNATURE)
 1222                 sc->sc_flags |= SCF_SIGNATURE;
 1223 #endif
 1224         if (to->to_flags & TOF_SACKPERM)
 1225                 sc->sc_flags |= SCF_SACK;
 1226         if (to->to_flags & TOF_MSS)
 1227                 sc->sc_peer_mss = to->to_mss;   /* peer mss may be zero */
 1228         if (noopt)
 1229                 sc->sc_flags |= SCF_NOOPT;
 1230         if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
 1231                 sc->sc_flags |= SCF_ECN;
 1232 
 1233         if (V_tcp_syncookies) {
 1234                 syncookie_generate(sch, sc, &flowtmp);
 1235 #ifdef INET6
 1236                 if (autoflowlabel)
 1237                         sc->sc_flowlabel = flowtmp;
 1238 #endif
 1239         } else {
 1240 #ifdef INET6
 1241                 if (autoflowlabel)
 1242                         sc->sc_flowlabel =
 1243                             (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
 1244 #endif
 1245         }
 1246         SCH_UNLOCK(sch);
 1247 
 1248         /*
 1249          * Do a standard 3-way handshake.
 1250          */
 1251         if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) {
 1252                 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
 1253                         syncache_free(sc);
 1254                 else if (sc != &scs)
 1255                         syncache_insert(sc, sch);   /* locks and unlocks sch */
 1256                 TCPSTAT_INC(tcps_sndacks);
 1257                 TCPSTAT_INC(tcps_sndtotal);
 1258         } else {
 1259                 if (sc != &scs)
 1260                         syncache_free(sc);
 1261                 TCPSTAT_INC(tcps_sc_dropped);
 1262         }
 1263 
 1264 done:
 1265         if (cred != NULL)
 1266                 crfree(cred);
 1267 #ifdef MAC
 1268         if (sc == &scs)
 1269                 mac_syncache_destroy(&maclabel);
 1270 #endif
 1271         if (m) {
 1272                 
 1273                 *lsop = NULL;
 1274                 m_freem(m);
 1275         }
 1276 }
 1277 
 1278 static int
 1279 syncache_respond(struct syncache *sc)
 1280 {
 1281         struct ip *ip = NULL;
 1282         struct mbuf *m;
 1283         struct tcphdr *th;
 1284         int optlen, error;
 1285         u_int16_t hlen, tlen, mssopt;
 1286         struct tcpopt to;
 1287 #ifdef INET6
 1288         struct ip6_hdr *ip6 = NULL;
 1289 #endif
 1290 
 1291         hlen =
 1292 #ifdef INET6
 1293                (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
 1294 #endif
 1295                 sizeof(struct ip);
 1296         tlen = hlen + sizeof(struct tcphdr);
 1297 
 1298         /* Determine MSS we advertize to other end of connection. */
 1299         mssopt = tcp_mssopt(&sc->sc_inc);
 1300         if (sc->sc_peer_mss)
 1301                 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
 1302 
 1303         /* XXX: Assume that the entire packet will fit in a header mbuf. */
 1304         KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
 1305             ("syncache: mbuf too small"));
 1306 
 1307         /* Create the IP+TCP header from scratch. */
 1308         m = m_gethdr(M_DONTWAIT, MT_DATA);
 1309         if (m == NULL)
 1310                 return (ENOBUFS);
 1311 #ifdef MAC
 1312         mac_syncache_create_mbuf(sc->sc_label, m);
 1313 #endif
 1314         m->m_data += max_linkhdr;
 1315         m->m_len = tlen;
 1316         m->m_pkthdr.len = tlen;
 1317         m->m_pkthdr.rcvif = NULL;
 1318 
 1319 #ifdef INET6
 1320         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1321                 ip6 = mtod(m, struct ip6_hdr *);
 1322                 ip6->ip6_vfc = IPV6_VERSION;
 1323                 ip6->ip6_nxt = IPPROTO_TCP;
 1324                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1325                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1326                 ip6->ip6_plen = htons(tlen - hlen);
 1327                 /* ip6_hlim is set after checksum */
 1328                 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
 1329                 ip6->ip6_flow |= sc->sc_flowlabel;
 1330 
 1331                 th = (struct tcphdr *)(ip6 + 1);
 1332         } else
 1333 #endif
 1334         {
 1335                 ip = mtod(m, struct ip *);
 1336                 ip->ip_v = IPVERSION;
 1337                 ip->ip_hl = sizeof(struct ip) >> 2;
 1338                 ip->ip_len = tlen;
 1339                 ip->ip_id = 0;
 1340                 ip->ip_off = 0;
 1341                 ip->ip_sum = 0;
 1342                 ip->ip_p = IPPROTO_TCP;
 1343                 ip->ip_src = sc->sc_inc.inc_laddr;
 1344                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1345                 ip->ip_ttl = sc->sc_ip_ttl;
 1346                 ip->ip_tos = sc->sc_ip_tos;
 1347 
 1348                 /*
 1349                  * See if we should do MTU discovery.  Route lookups are
 1350                  * expensive, so we will only unset the DF bit if:
 1351                  *
 1352                  *      1) path_mtu_discovery is disabled
 1353                  *      2) the SCF_UNREACH flag has been set
 1354                  */
 1355                 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1356                        ip->ip_off |= IP_DF;
 1357 
 1358                 th = (struct tcphdr *)(ip + 1);
 1359         }
 1360         th->th_sport = sc->sc_inc.inc_lport;
 1361         th->th_dport = sc->sc_inc.inc_fport;
 1362 
 1363         th->th_seq = htonl(sc->sc_iss);
 1364         th->th_ack = htonl(sc->sc_irs + 1);
 1365         th->th_off = sizeof(struct tcphdr) >> 2;
 1366         th->th_x2 = 0;
 1367         th->th_flags = TH_SYN|TH_ACK;
 1368         th->th_win = htons(sc->sc_wnd);
 1369         th->th_urp = 0;
 1370 
 1371         if (sc->sc_flags & SCF_ECN) {
 1372                 th->th_flags |= TH_ECE;
 1373                 TCPSTAT_INC(tcps_ecn_shs);
 1374         }
 1375 
 1376         /* Tack on the TCP options. */
 1377         if ((sc->sc_flags & SCF_NOOPT) == 0) {
 1378                 to.to_flags = 0;
 1379 
 1380                 to.to_mss = mssopt;
 1381                 to.to_flags = TOF_MSS;
 1382                 if (sc->sc_flags & SCF_WINSCALE) {
 1383                         to.to_wscale = sc->sc_requested_r_scale;
 1384                         to.to_flags |= TOF_SCALE;
 1385                 }
 1386                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1387                         /* Virgin timestamp or TCP cookie enhanced one. */
 1388                         to.to_tsval = sc->sc_ts;
 1389                         to.to_tsecr = sc->sc_tsreflect;
 1390                         to.to_flags |= TOF_TS;
 1391                 }
 1392                 if (sc->sc_flags & SCF_SACK)
 1393                         to.to_flags |= TOF_SACKPERM;
 1394 #ifdef TCP_SIGNATURE
 1395                 if (sc->sc_flags & SCF_SIGNATURE)
 1396                         to.to_flags |= TOF_SIGNATURE;
 1397 #endif
 1398                 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 1399 
 1400                 /* Adjust headers by option size. */
 1401                 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1402                 m->m_len += optlen;
 1403                 m->m_pkthdr.len += optlen;
 1404 
 1405 #ifdef TCP_SIGNATURE
 1406                 if (sc->sc_flags & SCF_SIGNATURE)
 1407                         tcp_signature_compute(m, 0, 0, optlen,
 1408                             to.to_signature, IPSEC_DIR_OUTBOUND);
 1409 #endif
 1410 #ifdef INET6
 1411                 if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1412                         ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
 1413                 else
 1414 #endif
 1415                         ip->ip_len += optlen;
 1416         } else
 1417                 optlen = 0;
 1418 
 1419         M_SETFIB(m, sc->sc_inc.inc_fibnum);
 1420 #ifdef INET6
 1421         if (sc->sc_inc.inc_flags & INC_ISIPV6) {
 1422                 th->th_sum = 0;
 1423                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
 1424                                        tlen + optlen - hlen);
 1425                 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
 1426                 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
 1427         } else
 1428 #endif
 1429         {
 1430                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1431                     htons(tlen + optlen - hlen + IPPROTO_TCP));
 1432                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1433                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1434                 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
 1435         }
 1436         return (error);
 1437 }
 1438 
 1439 void
 1440 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 1441     struct inpcb *inp, struct socket **lsop, struct mbuf *m)
 1442 {
 1443         _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL);
 1444 }
 1445 
 1446 void
 1447 tcp_offload_syncache_add(struct in_conninfo *inc, struct toeopt *toeo,
 1448     struct tcphdr *th, struct inpcb *inp, struct socket **lsop,
 1449     struct toe_usrreqs *tu, void *toepcb)
 1450 {
 1451         struct tcpopt to;
 1452 
 1453         bzero(&to, sizeof(struct tcpopt));
 1454         to.to_mss = toeo->to_mss;
 1455         to.to_wscale = toeo->to_wscale;
 1456         to.to_flags = toeo->to_flags;
 1457 
 1458         INP_INFO_WLOCK(&V_tcbinfo);
 1459         INP_WLOCK(inp);
 1460 
 1461         _syncache_add(inc, &to, th, inp, lsop, NULL, tu, toepcb);
 1462 }
 1463 
 1464 /*
 1465  * The purpose of SYN cookies is to avoid keeping track of all SYN's we
 1466  * receive and to be able to handle SYN floods from bogus source addresses
 1467  * (where we will never receive any reply).  SYN floods try to exhaust all
 1468  * our memory and available slots in the SYN cache table to cause a denial
 1469  * of service to legitimate users of the local host.
 1470  *
 1471  * The idea of SYN cookies is to encode and include all necessary information
 1472  * about the connection setup state within the SYN-ACK we send back and thus
 1473  * to get along without keeping any local state until the ACK to the SYN-ACK
 1474  * arrives (if ever).  Everything we need to know should be available from
 1475  * the information we encoded in the SYN-ACK.
 1476  *
 1477  * More information about the theory behind SYN cookies and its first
 1478  * discussion and specification can be found at:
 1479  *  http://cr.yp.to/syncookies.html    (overview)
 1480  *  http://cr.yp.to/syncookies/archive (gory details)
 1481  *
 1482  * This implementation extends the orginal idea and first implementation
 1483  * of FreeBSD by using not only the initial sequence number field to store
 1484  * information but also the timestamp field if present.  This way we can
 1485  * keep track of the entire state we need to know to recreate the session in
 1486  * its original form.  Almost all TCP speakers implement RFC1323 timestamps
 1487  * these days.  For those that do not we still have to live with the known
 1488  * shortcomings of the ISN only SYN cookies.
 1489  *
 1490  * Cookie layers:
 1491  *
 1492  * Initial sequence number we send:
 1493  * 31|................................|0
 1494  *    DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
 1495  *    D = MD5 Digest (first dword)
 1496  *    M = MSS index
 1497  *    R = Rotation of secret
 1498  *    P = Odd or Even secret
 1499  *
 1500  * The MD5 Digest is computed with over following parameters:
 1501  *  a) randomly rotated secret
 1502  *  b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
 1503  *  c) the received initial sequence number from remote host
 1504  *  d) the rotation offset and odd/even bit
 1505  *
 1506  * Timestamp we send:
 1507  * 31|................................|0
 1508  *    DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
 1509  *    D = MD5 Digest (third dword) (only as filler)
 1510  *    S = Requested send window scale
 1511  *    R = Requested receive window scale
 1512  *    A = SACK allowed
 1513  *    5 = TCP-MD5 enabled (not implemented yet)
 1514  *    XORed with MD5 Digest (forth dword)
 1515  *
 1516  * The timestamp isn't cryptographically secure and doesn't need to be.
 1517  * The double use of the MD5 digest dwords ties it to a specific remote/
 1518  * local host/port, remote initial sequence number and our local time
 1519  * limited secret.  A received timestamp is reverted (XORed) and then
 1520  * the contained MD5 dword is compared to the computed one to ensure the
 1521  * timestamp belongs to the SYN-ACK we sent.  The other parameters may
 1522  * have been tampered with but this isn't different from supplying bogus
 1523  * values in the SYN in the first place.
 1524  *
 1525  * Some problems with SYN cookies remain however:
 1526  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1527  * original SYN was accepted, the connection is established.  The second
 1528  * SYN is inflight, and if it arrives with an ISN that falls within the
 1529  * receive window, the connection is killed.
 1530  *
 1531  * Notes:
 1532  * A heuristic to determine when to accept syn cookies is not necessary.
 1533  * An ACK flood would cause the syncookie verification to be attempted,
 1534  * but a SYN flood causes syncookies to be generated.  Both are of equal
 1535  * cost, so there's no point in trying to optimize the ACK flood case.
 1536  * Also, if you don't process certain ACKs for some reason, then all someone
 1537  * would have to do is launch a SYN and ACK flood at the same time, which
 1538  * would stop cookie verification and defeat the entire purpose of syncookies.
 1539  */
 1540 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
 1541 
 1542 static void
 1543 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
 1544     u_int32_t *flowlabel)
 1545 {
 1546         MD5_CTX ctx;
 1547         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1548         u_int32_t data;
 1549         u_int32_t *secbits;
 1550         u_int off, pmss, mss;
 1551         int i;
 1552 
 1553         SCH_LOCK_ASSERT(sch);
 1554 
 1555         /* Which of the two secrets to use. */
 1556         secbits = sch->sch_oddeven ?
 1557                         sch->sch_secbits_odd : sch->sch_secbits_even;
 1558 
 1559         /* Reseed secret if too old. */
 1560         if (sch->sch_reseed < time_uptime) {
 1561                 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1;    /* toggle */
 1562                 secbits = sch->sch_oddeven ?
 1563                                 sch->sch_secbits_odd : sch->sch_secbits_even;
 1564                 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
 1565                         secbits[i] = arc4random();
 1566                 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
 1567         }
 1568 
 1569         /* Secret rotation offset. */
 1570         off = sc->sc_iss & 0x7;                 /* iss was randomized before */
 1571 
 1572         /* Maximum segment size calculation. */
 1573         pmss =
 1574             max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), V_tcp_minmss);
 1575         for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
 1576                 if (tcp_sc_msstab[mss] <= pmss)
 1577                         break;
 1578 
 1579         /* Fold parameters and MD5 digest into the ISN we will send. */
 1580         data = sch->sch_oddeven;/* odd or even secret, 1 bit */
 1581         data |= off << 1;       /* secret offset, derived from iss, 3 bits */
 1582         data |= mss << 4;       /* mss, 3 bits */
 1583 
 1584         MD5Init(&ctx);
 1585         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1586             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1587         MD5Update(&ctx, secbits, off);
 1588         MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
 1589         MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
 1590         MD5Update(&ctx, &data, sizeof(data));
 1591         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1592 
 1593         data |= (md5_buffer[0] << 7);
 1594         sc->sc_iss = data;
 1595 
 1596 #ifdef INET6
 1597         *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1598 #endif
 1599 
 1600         /* Additional parameters are stored in the timestamp if present. */
 1601         if (sc->sc_flags & SCF_TIMESTAMP) {
 1602                 data =  ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
 1603                 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
 1604                 data |= sc->sc_requested_s_scale << 2;  /* SWIN scale, 4 bits */
 1605                 data |= sc->sc_requested_r_scale << 6;  /* RWIN scale, 4 bits */
 1606                 data |= md5_buffer[2] << 10;            /* more digest bits */
 1607                 data ^= md5_buffer[3];
 1608                 sc->sc_ts = data;
 1609                 sc->sc_tsoff = data - ticks;            /* after XOR */
 1610         }
 1611 
 1612         TCPSTAT_INC(tcps_sc_sendcookie);
 1613 }
 1614 
 1615 static struct syncache *
 1616 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 
 1617     struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
 1618     struct socket *so)
 1619 {
 1620         MD5_CTX ctx;
 1621         u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
 1622         u_int32_t data = 0;
 1623         u_int32_t *secbits;
 1624         tcp_seq ack, seq;
 1625         int off, mss, wnd, flags;
 1626 
 1627         SCH_LOCK_ASSERT(sch);
 1628 
 1629         /*
 1630          * Pull information out of SYN-ACK/ACK and
 1631          * revert sequence number advances.
 1632          */
 1633         ack = th->th_ack - 1;
 1634         seq = th->th_seq - 1;
 1635         off = (ack >> 1) & 0x7;
 1636         mss = (ack >> 4) & 0x7;
 1637         flags = ack & 0x7f;
 1638 
 1639         /* Which of the two secrets to use. */
 1640         secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
 1641 
 1642         /*
 1643          * The secret wasn't updated for the lifetime of a syncookie,
 1644          * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
 1645          */
 1646         if (sch->sch_reseed + SYNCOOKIE_LIFETIME < time_uptime) {
 1647                 return (NULL);
 1648         }
 1649 
 1650         /* Recompute the digest so we can compare it. */
 1651         MD5Init(&ctx);
 1652         MD5Update(&ctx, ((u_int8_t *)secbits) + off,
 1653             SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
 1654         MD5Update(&ctx, secbits, off);
 1655         MD5Update(&ctx, inc, sizeof(*inc));
 1656         MD5Update(&ctx, &seq, sizeof(seq));
 1657         MD5Update(&ctx, &flags, sizeof(flags));
 1658         MD5Final((u_int8_t *)&md5_buffer, &ctx);
 1659 
 1660         /* Does the digest part of or ACK'ed ISS match? */
 1661         if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
 1662                 return (NULL);
 1663 
 1664         /* Does the digest part of our reflected timestamp match? */
 1665         if (to->to_flags & TOF_TS) {
 1666                 data = md5_buffer[3] ^ to->to_tsecr;
 1667                 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
 1668                         return (NULL);
 1669         }
 1670 
 1671         /* Fill in the syncache values. */
 1672         bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
 1673         sc->sc_ipopts = NULL;
 1674         
 1675         sc->sc_irs = seq;
 1676         sc->sc_iss = ack;
 1677 
 1678 #ifdef INET6
 1679         if (inc->inc_flags & INC_ISIPV6) {
 1680                 if (sotoinpcb(so)->inp_flags & IN6P_AUTOFLOWLABEL)
 1681                         sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
 1682         } else
 1683 #endif
 1684         {
 1685                 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
 1686                 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
 1687         }
 1688 
 1689         /* Additional parameters that were encoded in the timestamp. */
 1690         if (data) {
 1691                 sc->sc_flags |= SCF_TIMESTAMP;
 1692                 sc->sc_tsreflect = to->to_tsval;
 1693                 sc->sc_ts = to->to_tsecr;
 1694                 sc->sc_tsoff = to->to_tsecr - ticks;
 1695                 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
 1696                 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
 1697                 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
 1698                     TCP_MAX_WINSHIFT);
 1699                 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
 1700                     TCP_MAX_WINSHIFT);
 1701                 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
 1702                         sc->sc_flags |= SCF_WINSCALE;
 1703         } else
 1704                 sc->sc_flags |= SCF_NOOPT;
 1705 
 1706         wnd = sbspace(&so->so_rcv);
 1707         wnd = imax(wnd, 0);
 1708         wnd = imin(wnd, TCP_MAXWIN);
 1709         sc->sc_wnd = wnd;
 1710 
 1711         sc->sc_rxmits = 0;
 1712         sc->sc_peer_mss = tcp_sc_msstab[mss];
 1713 
 1714         TCPSTAT_INC(tcps_sc_recvcookie);
 1715         return (sc);
 1716 }
 1717 
 1718 /*
 1719  * Returns the current number of syncache entries.  This number
 1720  * will probably change before you get around to calling 
 1721  * syncache_pcblist.
 1722  */
 1723 
 1724 int
 1725 syncache_pcbcount(void)
 1726 {
 1727         struct syncache_head *sch;
 1728         int count, i;
 1729 
 1730         for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1731                 /* No need to lock for a read. */
 1732                 sch = &V_tcp_syncache.hashbase[i];
 1733                 count += sch->sch_length;
 1734         }
 1735         return count;
 1736 }
 1737 
 1738 /*
 1739  * Exports the syncache entries to userland so that netstat can display
 1740  * them alongside the other sockets.  This function is intended to be
 1741  * called only from tcp_pcblist.
 1742  *
 1743  * Due to concurrency on an active system, the number of pcbs exported
 1744  * may have no relation to max_pcbs.  max_pcbs merely indicates the
 1745  * amount of space the caller allocated for this function to use.
 1746  */
 1747 int
 1748 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
 1749 {
 1750         struct xtcpcb xt;
 1751         struct syncache *sc;
 1752         struct syncache_head *sch;
 1753         int count, error, i;
 1754 
 1755         for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
 1756                 sch = &V_tcp_syncache.hashbase[i];
 1757                 SCH_LOCK(sch);
 1758                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
 1759                         if (count >= max_pcbs) {
 1760                                 SCH_UNLOCK(sch);
 1761                                 goto exit;
 1762                         }
 1763                         if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
 1764                                 continue;
 1765                         bzero(&xt, sizeof(xt));
 1766                         xt.xt_len = sizeof(xt);
 1767                         if (sc->sc_inc.inc_flags & INC_ISIPV6)
 1768                                 xt.xt_inp.inp_vflag = INP_IPV6;
 1769                         else
 1770                                 xt.xt_inp.inp_vflag = INP_IPV4;
 1771                         bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
 1772                         xt.xt_tp.t_inpcb = &xt.xt_inp;
 1773                         xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
 1774                         xt.xt_socket.xso_protocol = IPPROTO_TCP;
 1775                         xt.xt_socket.xso_len = sizeof (struct xsocket);
 1776                         xt.xt_socket.so_type = SOCK_STREAM;
 1777                         xt.xt_socket.so_state = SS_ISCONNECTING;
 1778                         error = SYSCTL_OUT(req, &xt, sizeof xt);
 1779                         if (error) {
 1780                                 SCH_UNLOCK(sch);
 1781                                 goto exit;
 1782                         }
 1783                         count++;
 1784                 }
 1785                 SCH_UNLOCK(sch);
 1786         }
 1787 exit:
 1788         *pcbs_exported = count;
 1789         return error;
 1790 }

Cache object: 2319b1a965fe32a581ffb42c6d061715


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.