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

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    1 /*-
    2  * Copyright (c) 2001 Networks Associates Technology, Inc.
    3  * All rights reserved.
    4  *
    5  * This software was developed for the FreeBSD Project by Jonathan Lemon
    6  * and NAI Labs, the Security Research Division of Network Associates, Inc.
    7  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    8  * DARPA CHATS research program.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. The name of the author may not be used to endorse or promote
   19  *    products derived from this software without specific prior written
   20  *    permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  * $FreeBSD: releng/5.1/sys/netinet/tcp_syncache.c 111405 2003-02-24 03:15:48Z silby $
   35  */
   36 
   37 #include "opt_inet6.h"
   38 #include "opt_ipsec.h"
   39 #include "opt_mac.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/sysctl.h>
   45 #include <sys/malloc.h>
   46 #include <sys/mac.h>
   47 #include <sys/mbuf.h>
   48 #include <sys/md5.h>
   49 #include <sys/proc.h>           /* for proc0 declaration */
   50 #include <sys/random.h>
   51 #include <sys/socket.h>
   52 #include <sys/socketvar.h>
   53 
   54 #include <net/if.h>
   55 #include <net/route.h>
   56 
   57 #include <netinet/in.h>
   58 #include <netinet/in_systm.h>
   59 #include <netinet/ip.h>
   60 #include <netinet/in_var.h>
   61 #include <netinet/in_pcb.h>
   62 #include <netinet/ip_var.h>
   63 #ifdef INET6
   64 #include <netinet/ip6.h>
   65 #include <netinet/icmp6.h>
   66 #include <netinet6/nd6.h>
   67 #include <netinet6/ip6_var.h>
   68 #include <netinet6/in6_pcb.h>
   69 #endif
   70 #include <netinet/tcp.h>
   71 #include <netinet/tcp_fsm.h>
   72 #include <netinet/tcp_seq.h>
   73 #include <netinet/tcp_timer.h>
   74 #include <netinet/tcp_var.h>
   75 #ifdef INET6
   76 #include <netinet6/tcp6_var.h>
   77 #endif
   78 
   79 #ifdef IPSEC
   80 #include <netinet6/ipsec.h>
   81 #ifdef INET6
   82 #include <netinet6/ipsec6.h>
   83 #endif
   84 #endif /*IPSEC*/
   85 
   86 #ifdef FAST_IPSEC
   87 #include <netipsec/ipsec.h>
   88 #ifdef INET6
   89 #include <netipsec/ipsec6.h>
   90 #endif
   91 #include <netipsec/key.h>
   92 #define IPSEC
   93 #endif /*FAST_IPSEC*/
   94 
   95 #include <machine/in_cksum.h>
   96 #include <vm/uma.h>
   97 
   98 static int tcp_syncookies = 1;
   99 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  100     &tcp_syncookies, 0, 
  101     "Use TCP SYN cookies if the syncache overflows");
  102 
  103 static void      syncache_drop(struct syncache *, struct syncache_head *);
  104 static void      syncache_free(struct syncache *);
  105 static void      syncache_insert(struct syncache *, struct syncache_head *);
  106 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  107 static int       syncache_respond(struct syncache *, struct mbuf *);
  108 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  109                     struct mbuf *m);
  110 static void      syncache_timer(void *);
  111 static u_int32_t syncookie_generate(struct syncache *);
  112 static struct syncache *syncookie_lookup(struct in_conninfo *,
  113                     struct tcphdr *, struct socket *);
  114 
  115 /*
  116  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  117  * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
  118  * the odds are that the user has given up attempting to connect by then.
  119  */
  120 #define SYNCACHE_MAXREXMTS              3
  121 
  122 /* Arbitrary values */
  123 #define TCP_SYNCACHE_HASHSIZE           512
  124 #define TCP_SYNCACHE_BUCKETLIMIT        30
  125 
  126 struct tcp_syncache {
  127         struct  syncache_head *hashbase;
  128         uma_zone_t zone;
  129         u_int   hashsize;
  130         u_int   hashmask;
  131         u_int   bucket_limit;
  132         u_int   cache_count;
  133         u_int   cache_limit;
  134         u_int   rexmt_limit;
  135         u_int   hash_secret;
  136         u_int   next_reseed;
  137         TAILQ_HEAD(, syncache) timerq[SYNCACHE_MAXREXMTS + 1];
  138         struct  callout tt_timerq[SYNCACHE_MAXREXMTS + 1];
  139 };
  140 static struct tcp_syncache tcp_syncache;
  141 
  142 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  143 
  144 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD,
  145      &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
  146 
  147 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD,
  148      &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
  149 
  150 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  151      &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
  152 
  153 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD,
  154      &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
  155 
  156 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  157      &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
  158 
  159 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  160 
  161 #define SYNCACHE_HASH(inc, mask)                                        \
  162         ((tcp_syncache.hash_secret ^                                    \
  163           (inc)->inc_faddr.s_addr ^                                     \
  164           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  165           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  166 
  167 #define SYNCACHE_HASH6(inc, mask)                                       \
  168         ((tcp_syncache.hash_secret ^                                    \
  169           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  170           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  171           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  172 
  173 #define ENDPTS_EQ(a, b) (                                               \
  174         (a)->ie_fport == (b)->ie_fport &&                               \
  175         (a)->ie_lport == (b)->ie_lport &&                               \
  176         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  177         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  178 )
  179 
  180 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  181 
  182 #define SYNCACHE_TIMEOUT(sc, slot) do {                         \
  183         sc->sc_rxtslot = (slot);                                        \
  184         sc->sc_rxttime = ticks + TCPTV_RTOBASE * tcp_backoff[(slot)];   \
  185         TAILQ_INSERT_TAIL(&tcp_syncache.timerq[(slot)], sc, sc_timerq); \
  186         if (!callout_active(&tcp_syncache.tt_timerq[(slot)]))           \
  187                 callout_reset(&tcp_syncache.tt_timerq[(slot)],          \
  188                     TCPTV_RTOBASE * tcp_backoff[(slot)],                \
  189                     syncache_timer, (void *)((intptr_t)(slot)));        \
  190 } while (0)
  191 
  192 static void
  193 syncache_free(struct syncache *sc)
  194 {
  195         struct rtentry *rt;
  196 
  197         if (sc->sc_ipopts)
  198                 (void) m_free(sc->sc_ipopts);
  199 #ifdef INET6
  200         if (sc->sc_inc.inc_isipv6)
  201                 rt = sc->sc_route6.ro_rt;
  202         else
  203 #endif
  204                 rt = sc->sc_route.ro_rt;
  205         if (rt != NULL) {
  206                 /*
  207                  * If this is the only reference to a protocol cloned 
  208                  * route, remove it immediately.
  209                  */
  210                 if (rt->rt_flags & RTF_WASCLONED &&
  211                     (sc->sc_flags & SCF_KEEPROUTE) == 0 &&
  212                     rt->rt_refcnt == 1)
  213                         rtrequest(RTM_DELETE, rt_key(rt),
  214                             rt->rt_gateway, rt_mask(rt),
  215                             rt->rt_flags, NULL);
  216                 RTFREE(rt);
  217         }
  218         uma_zfree(tcp_syncache.zone, sc);
  219 }
  220 
  221 void
  222 syncache_init(void)
  223 {
  224         int i;
  225 
  226         tcp_syncache.cache_count = 0;
  227         tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  228         tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  229         tcp_syncache.cache_limit =
  230             tcp_syncache.hashsize * tcp_syncache.bucket_limit;
  231         tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  232         tcp_syncache.next_reseed = 0;
  233         tcp_syncache.hash_secret = arc4random();
  234 
  235         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  236             &tcp_syncache.hashsize);
  237         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  238             &tcp_syncache.cache_limit);
  239         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  240             &tcp_syncache.bucket_limit);
  241         if (!powerof2(tcp_syncache.hashsize)) {
  242                 printf("WARNING: syncache hash size is not a power of 2.\n");
  243                 tcp_syncache.hashsize = 512;    /* safe default */
  244         }
  245         tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
  246 
  247         /* Allocate the hash table. */
  248         MALLOC(tcp_syncache.hashbase, struct syncache_head *,
  249             tcp_syncache.hashsize * sizeof(struct syncache_head),
  250             M_SYNCACHE, M_WAITOK);
  251 
  252         /* Initialize the hash buckets. */
  253         for (i = 0; i < tcp_syncache.hashsize; i++) {
  254                 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
  255                 tcp_syncache.hashbase[i].sch_length = 0;
  256         }
  257 
  258         /* Initialize the timer queues. */
  259         for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
  260                 TAILQ_INIT(&tcp_syncache.timerq[i]);
  261                 callout_init(&tcp_syncache.tt_timerq[i], 0);
  262         }
  263 
  264         /*
  265          * Allocate the syncache entries.  Allow the zone to allocate one
  266          * more entry than cache limit, so a new entry can bump out an
  267          * older one.
  268          */
  269         tcp_syncache.cache_limit -= 1;
  270         tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
  271             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  272         uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
  273 }
  274 
  275 static void
  276 syncache_insert(sc, sch)
  277         struct syncache *sc;
  278         struct syncache_head *sch;
  279 {
  280         struct syncache *sc2;
  281         int s, i;
  282 
  283         /*
  284          * Make sure that we don't overflow the per-bucket
  285          * limit or the total cache size limit.
  286          */
  287         s = splnet();
  288         if (sch->sch_length >= tcp_syncache.bucket_limit) {
  289                 /*
  290                  * The bucket is full, toss the oldest element.
  291                  */
  292                 sc2 = TAILQ_FIRST(&sch->sch_bucket);
  293                 sc2->sc_tp->ts_recent = ticks;
  294                 syncache_drop(sc2, sch);
  295                 tcpstat.tcps_sc_bucketoverflow++;
  296         } else if (tcp_syncache.cache_count >= tcp_syncache.cache_limit) {
  297                 /*
  298                  * The cache is full.  Toss the oldest entry in the
  299                  * entire cache.  This is the front entry in the
  300                  * first non-empty timer queue with the largest
  301                  * timeout value.
  302                  */
  303                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  304                         sc2 = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  305                         if (sc2 != NULL)
  306                                 break;
  307                 }
  308                 sc2->sc_tp->ts_recent = ticks;
  309                 syncache_drop(sc2, NULL);
  310                 tcpstat.tcps_sc_cacheoverflow++;
  311         }
  312 
  313         /* Initialize the entry's timer. */
  314         SYNCACHE_TIMEOUT(sc, 0);
  315 
  316         /* Put it into the bucket. */
  317         TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
  318         sch->sch_length++;
  319         tcp_syncache.cache_count++;
  320         tcpstat.tcps_sc_added++;
  321         splx(s);
  322 }
  323 
  324 static void
  325 syncache_drop(sc, sch)
  326         struct syncache *sc;
  327         struct syncache_head *sch;
  328 {
  329         int s;
  330 
  331         if (sch == NULL) {
  332 #ifdef INET6
  333                 if (sc->sc_inc.inc_isipv6) {
  334                         sch = &tcp_syncache.hashbase[
  335                             SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
  336                 } else
  337 #endif
  338                 {
  339                         sch = &tcp_syncache.hashbase[
  340                             SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
  341                 }
  342         }
  343 
  344         s = splnet();
  345 
  346         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  347         sch->sch_length--;
  348         tcp_syncache.cache_count--;
  349 
  350         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot], sc, sc_timerq);
  351         if (TAILQ_EMPTY(&tcp_syncache.timerq[sc->sc_rxtslot]))
  352                 callout_stop(&tcp_syncache.tt_timerq[sc->sc_rxtslot]);
  353         splx(s);
  354 
  355         syncache_free(sc);
  356 }
  357 
  358 /*
  359  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  360  * If we have retransmitted an entry the maximum number of times, expire it.
  361  */
  362 static void
  363 syncache_timer(xslot)
  364         void *xslot;
  365 {
  366         intptr_t slot = (intptr_t)xslot;
  367         struct syncache *sc, *nsc;
  368         struct inpcb *inp;
  369         int s;
  370 
  371         s = splnet();
  372         INP_INFO_WLOCK(&tcbinfo);
  373         if (callout_pending(&tcp_syncache.tt_timerq[slot]) ||
  374             !callout_active(&tcp_syncache.tt_timerq[slot])) {
  375                 INP_INFO_WUNLOCK(&tcbinfo);
  376                 splx(s);
  377                 return;
  378         }
  379         callout_deactivate(&tcp_syncache.tt_timerq[slot]);
  380 
  381         nsc = TAILQ_FIRST(&tcp_syncache.timerq[slot]);
  382         while (nsc != NULL) {
  383                 if (ticks < nsc->sc_rxttime)
  384                         break;
  385                 sc = nsc;
  386                 inp = sc->sc_tp->t_inpcb;
  387                 if (slot == SYNCACHE_MAXREXMTS ||
  388                     slot >= tcp_syncache.rexmt_limit ||
  389                     inp == NULL || inp->inp_gencnt != sc->sc_inp_gencnt) {
  390                         nsc = TAILQ_NEXT(sc, sc_timerq);
  391                         syncache_drop(sc, NULL);
  392                         tcpstat.tcps_sc_stale++;
  393                         continue;
  394                 }
  395                 /*
  396                  * syncache_respond() may call back into the syncache to
  397                  * to modify another entry, so do not obtain the next
  398                  * entry on the timer chain until it has completed.
  399                  */
  400                 (void) syncache_respond(sc, NULL);
  401                 nsc = TAILQ_NEXT(sc, sc_timerq);
  402                 tcpstat.tcps_sc_retransmitted++;
  403                 TAILQ_REMOVE(&tcp_syncache.timerq[slot], sc, sc_timerq);
  404                 SYNCACHE_TIMEOUT(sc, slot + 1);
  405         }
  406         if (nsc != NULL)
  407                 callout_reset(&tcp_syncache.tt_timerq[slot],
  408                     nsc->sc_rxttime - ticks, syncache_timer, (void *)(slot));
  409         INP_INFO_WUNLOCK(&tcbinfo);
  410         splx(s);
  411 }
  412 
  413 /*
  414  * Find an entry in the syncache.
  415  */
  416 struct syncache *
  417 syncache_lookup(inc, schp)
  418         struct in_conninfo *inc;
  419         struct syncache_head **schp;
  420 {
  421         struct syncache *sc;
  422         struct syncache_head *sch;
  423         int s;
  424 
  425 #ifdef INET6
  426         if (inc->inc_isipv6) {
  427                 sch = &tcp_syncache.hashbase[
  428                     SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
  429                 *schp = sch;
  430                 s = splnet();
  431                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  432                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
  433                                 splx(s);
  434                                 return (sc);
  435                         }
  436                 }
  437                 splx(s);
  438         } else
  439 #endif
  440         {
  441                 sch = &tcp_syncache.hashbase[
  442                     SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
  443                 *schp = sch;
  444                 s = splnet();
  445                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  446 #ifdef INET6
  447                         if (sc->sc_inc.inc_isipv6)
  448                                 continue;
  449 #endif
  450                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) {
  451                                 splx(s);
  452                                 return (sc);
  453                         }
  454                 }
  455                 splx(s);
  456         }
  457         return (NULL);
  458 }
  459 
  460 /*
  461  * This function is called when we get a RST for a
  462  * non-existent connection, so that we can see if the
  463  * connection is in the syn cache.  If it is, zap it.
  464  */
  465 void
  466 syncache_chkrst(inc, th)
  467         struct in_conninfo *inc;
  468         struct tcphdr *th;
  469 {
  470         struct syncache *sc;
  471         struct syncache_head *sch;
  472 
  473         sc = syncache_lookup(inc, &sch);
  474         if (sc == NULL)
  475                 return;
  476         /*
  477          * If the RST bit is set, check the sequence number to see
  478          * if this is a valid reset segment.
  479          * RFC 793 page 37:
  480          *   In all states except SYN-SENT, all reset (RST) segments
  481          *   are validated by checking their SEQ-fields.  A reset is
  482          *   valid if its sequence number is in the window.
  483          *
  484          *   The sequence number in the reset segment is normally an
  485          *   echo of our outgoing acknowlegement numbers, but some hosts
  486          *   send a reset with the sequence number at the rightmost edge
  487          *   of our receive window, and we have to handle this case.
  488          */
  489         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  490             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  491                 syncache_drop(sc, sch);
  492                 tcpstat.tcps_sc_reset++;
  493         }
  494 }
  495 
  496 void
  497 syncache_badack(inc)
  498         struct in_conninfo *inc;
  499 {
  500         struct syncache *sc;
  501         struct syncache_head *sch;
  502 
  503         sc = syncache_lookup(inc, &sch);
  504         if (sc != NULL) {
  505                 syncache_drop(sc, sch);
  506                 tcpstat.tcps_sc_badack++;
  507         }
  508 }
  509 
  510 void
  511 syncache_unreach(inc, th)
  512         struct in_conninfo *inc;
  513         struct tcphdr *th;
  514 {
  515         struct syncache *sc;
  516         struct syncache_head *sch;
  517 
  518         /* we are called at splnet() here */
  519         sc = syncache_lookup(inc, &sch);
  520         if (sc == NULL)
  521                 return;
  522 
  523         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  524         if (ntohl(th->th_seq) != sc->sc_iss)
  525                 return;
  526 
  527         /*
  528          * If we've rertransmitted 3 times and this is our second error,
  529          * we remove the entry.  Otherwise, we allow it to continue on.
  530          * This prevents us from incorrectly nuking an entry during a
  531          * spurious network outage.
  532          *
  533          * See tcp_notify().
  534          */
  535         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
  536                 sc->sc_flags |= SCF_UNREACH;
  537                 return;
  538         }
  539         syncache_drop(sc, sch);
  540         tcpstat.tcps_sc_unreach++;
  541 }
  542 
  543 /*
  544  * Build a new TCP socket structure from a syncache entry.
  545  */
  546 static struct socket *
  547 syncache_socket(sc, lso, m)
  548         struct syncache *sc;
  549         struct socket *lso;
  550         struct mbuf *m;
  551 {
  552         struct inpcb *inp = NULL;
  553         struct socket *so;
  554         struct tcpcb *tp;
  555 
  556         /*
  557          * Ok, create the full blown connection, and set things up
  558          * as they would have been set up if we had created the
  559          * connection when the SYN arrived.  If we can't create
  560          * the connection, abort it.
  561          */
  562         so = sonewconn(lso, SS_ISCONNECTED);
  563         if (so == NULL) {
  564                 /*
  565                  * Drop the connection; we will send a RST if the peer
  566                  * retransmits the ACK,
  567                  */
  568                 tcpstat.tcps_listendrop++;
  569                 goto abort;
  570         }
  571 #ifdef MAC
  572         mac_set_socket_peer_from_mbuf(m, so);
  573 #endif
  574 
  575         inp = sotoinpcb(so);
  576 
  577         /*
  578          * Insert new socket into hash list.
  579          */
  580         inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
  581 #ifdef INET6
  582         if (sc->sc_inc.inc_isipv6) {
  583                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  584         } else {
  585                 inp->inp_vflag &= ~INP_IPV6;
  586                 inp->inp_vflag |= INP_IPV4;
  587 #endif
  588                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  589 #ifdef INET6
  590         }
  591 #endif
  592         inp->inp_lport = sc->sc_inc.inc_lport;
  593         if (in_pcbinshash(inp) != 0) {
  594                 /*
  595                  * Undo the assignments above if we failed to
  596                  * put the PCB on the hash lists.
  597                  */
  598 #ifdef INET6
  599                 if (sc->sc_inc.inc_isipv6)
  600                         inp->in6p_laddr = in6addr_any;
  601                 else
  602 #endif
  603                         inp->inp_laddr.s_addr = INADDR_ANY;
  604                 inp->inp_lport = 0;
  605                 goto abort;
  606         }
  607 #ifdef IPSEC
  608         /* copy old policy into new socket's */
  609         if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
  610                 printf("syncache_expand: could not copy policy\n");
  611 #endif
  612 #ifdef INET6
  613         if (sc->sc_inc.inc_isipv6) {
  614                 struct inpcb *oinp = sotoinpcb(lso);
  615                 struct in6_addr laddr6;
  616                 struct sockaddr_in6 *sin6;
  617                 /*
  618                  * Inherit socket options from the listening socket.
  619                  * Note that in6p_inputopts are not (and should not be)
  620                  * copied, since it stores previously received options and is
  621                  * used to detect if each new option is different than the
  622                  * previous one and hence should be passed to a user.
  623                  * If we copied in6p_inputopts, a user would not be able to
  624                  * receive options just after calling the accept system call.
  625                  */
  626                 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
  627                 if (oinp->in6p_outputopts)
  628                         inp->in6p_outputopts =
  629                             ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
  630                 inp->in6p_route = sc->sc_route6;
  631                 sc->sc_route6.ro_rt = NULL;
  632 
  633                 MALLOC(sin6, struct sockaddr_in6 *, sizeof *sin6,
  634                     M_SONAME, M_NOWAIT | M_ZERO);
  635                 if (sin6 == NULL)
  636                         goto abort;
  637                 sin6->sin6_family = AF_INET6;
  638                 sin6->sin6_len = sizeof(*sin6);
  639                 sin6->sin6_addr = sc->sc_inc.inc6_faddr;
  640                 sin6->sin6_port = sc->sc_inc.inc_fport;
  641                 laddr6 = inp->in6p_laddr;
  642                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  643                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  644                 if (in6_pcbconnect(inp, (struct sockaddr *)sin6, &thread0)) {
  645                         inp->in6p_laddr = laddr6;
  646                         FREE(sin6, M_SONAME);
  647                         goto abort;
  648                 }
  649                 FREE(sin6, M_SONAME);
  650         } else
  651 #endif
  652         {
  653                 struct in_addr laddr;
  654                 struct sockaddr_in *sin;
  655 
  656                 inp->inp_options = ip_srcroute();
  657                 if (inp->inp_options == NULL) {
  658                         inp->inp_options = sc->sc_ipopts;
  659                         sc->sc_ipopts = NULL;
  660                 }
  661                 inp->inp_route = sc->sc_route;
  662                 sc->sc_route.ro_rt = NULL;
  663 
  664                 MALLOC(sin, struct sockaddr_in *, sizeof *sin,
  665                     M_SONAME, M_NOWAIT | M_ZERO);
  666                 if (sin == NULL)
  667                         goto abort;
  668                 sin->sin_family = AF_INET;
  669                 sin->sin_len = sizeof(*sin);
  670                 sin->sin_addr = sc->sc_inc.inc_faddr;
  671                 sin->sin_port = sc->sc_inc.inc_fport;
  672                 bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
  673                 laddr = inp->inp_laddr;
  674                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  675                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  676                 if (in_pcbconnect(inp, (struct sockaddr *)sin, &thread0)) {
  677                         inp->inp_laddr = laddr;
  678                         FREE(sin, M_SONAME);
  679                         goto abort;
  680                 }
  681                 FREE(sin, M_SONAME);
  682         }
  683 
  684         tp = intotcpcb(inp);
  685         tp->t_state = TCPS_SYN_RECEIVED;
  686         tp->iss = sc->sc_iss;
  687         tp->irs = sc->sc_irs;
  688         tcp_rcvseqinit(tp);
  689         tcp_sendseqinit(tp);
  690         tp->snd_wl1 = sc->sc_irs;
  691         tp->rcv_up = sc->sc_irs + 1;
  692         tp->rcv_wnd = sc->sc_wnd;
  693         tp->rcv_adv += tp->rcv_wnd;
  694 
  695         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
  696         if (sc->sc_flags & SCF_NOOPT)
  697                 tp->t_flags |= TF_NOOPT;
  698         if (sc->sc_flags & SCF_WINSCALE) {
  699                 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
  700                 tp->requested_s_scale = sc->sc_requested_s_scale;
  701                 tp->request_r_scale = sc->sc_request_r_scale;
  702         }
  703         if (sc->sc_flags & SCF_TIMESTAMP) {
  704                 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
  705                 tp->ts_recent = sc->sc_tsrecent;
  706                 tp->ts_recent_age = ticks;
  707         }
  708         if (sc->sc_flags & SCF_CC) {
  709                 /*
  710                  * Initialization of the tcpcb for transaction;
  711                  *   set SND.WND = SEG.WND,
  712                  *   initialize CCsend and CCrecv.
  713                  */
  714                 tp->t_flags |= TF_REQ_CC|TF_RCVD_CC;
  715                 tp->cc_send = sc->sc_cc_send;
  716                 tp->cc_recv = sc->sc_cc_recv;
  717         }
  718 
  719         tcp_mss(tp, sc->sc_peer_mss);
  720 
  721         /*
  722          * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
  723          */
  724         if (sc->sc_rxtslot != 0)
  725                 tp->snd_cwnd = tp->t_maxseg;
  726         callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
  727 
  728         tcpstat.tcps_accepts++;
  729         return (so);
  730 
  731 abort:
  732         if (so != NULL)
  733                 (void) soabort(so);
  734         return (NULL);
  735 }
  736 
  737 /*
  738  * This function gets called when we receive an ACK for a
  739  * socket in the LISTEN state.  We look up the connection
  740  * in the syncache, and if its there, we pull it out of
  741  * the cache and turn it into a full-blown connection in
  742  * the SYN-RECEIVED state.
  743  */
  744 int
  745 syncache_expand(inc, th, sop, m)
  746         struct in_conninfo *inc;
  747         struct tcphdr *th;
  748         struct socket **sop;
  749         struct mbuf *m;
  750 {
  751         struct syncache *sc;
  752         struct syncache_head *sch;
  753         struct socket *so;
  754 
  755         sc = syncache_lookup(inc, &sch);
  756         if (sc == NULL) {
  757                 /*
  758                  * There is no syncache entry, so see if this ACK is 
  759                  * a returning syncookie.  To do this, first:
  760                  *  A. See if this socket has had a syncache entry dropped in
  761                  *     the past.  We don't want to accept a bogus syncookie
  762                  *     if we've never received a SYN.
  763                  *  B. check that the syncookie is valid.  If it is, then
  764                  *     cobble up a fake syncache entry, and return.
  765                  */
  766                 if (!tcp_syncookies)
  767                         return (0);
  768                 sc = syncookie_lookup(inc, th, *sop);
  769                 if (sc == NULL)
  770                         return (0);
  771                 sch = NULL;
  772                 tcpstat.tcps_sc_recvcookie++;
  773         }
  774 
  775         /*
  776          * If seg contains an ACK, but not for our SYN/ACK, send a RST.
  777          */
  778         if (th->th_ack != sc->sc_iss + 1)
  779                 return (0);
  780 
  781         so = syncache_socket(sc, *sop, m);
  782         if (so == NULL) {
  783 #if 0
  784 resetandabort:
  785                 /* XXXjlemon check this - is this correct? */
  786                 (void) tcp_respond(NULL, m, m, th,
  787                     th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
  788 #endif
  789                 m_freem(m);                     /* XXX only needed for above */
  790                 tcpstat.tcps_sc_aborted++;
  791         } else {
  792                 sc->sc_flags |= SCF_KEEPROUTE;
  793                 tcpstat.tcps_sc_completed++;
  794         }
  795         if (sch == NULL)
  796                 syncache_free(sc);
  797         else
  798                 syncache_drop(sc, sch);
  799         *sop = so;
  800         return (1);
  801 }
  802 
  803 /*
  804  * Given a LISTEN socket and an inbound SYN request, add
  805  * this to the syn cache, and send back a segment:
  806  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  807  * to the source.
  808  *
  809  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  810  * Doing so would require that we hold onto the data and deliver it
  811  * to the application.  However, if we are the target of a SYN-flood
  812  * DoS attack, an attacker could send data which would eventually
  813  * consume all available buffer space if it were ACKed.  By not ACKing
  814  * the data, we avoid this DoS scenario.
  815  */
  816 int
  817 syncache_add(inc, to, th, sop, m)
  818         struct in_conninfo *inc;
  819         struct tcpopt *to;
  820         struct tcphdr *th;
  821         struct socket **sop;
  822         struct mbuf *m;
  823 {
  824         struct tcpcb *tp;
  825         struct socket *so;
  826         struct syncache *sc = NULL;
  827         struct syncache_head *sch;
  828         struct mbuf *ipopts = NULL;
  829         struct rmxp_tao *taop;
  830         int i, s, win;
  831 
  832         so = *sop;
  833         tp = sototcpcb(so);
  834 
  835         /*
  836          * Remember the IP options, if any.
  837          */
  838 #ifdef INET6
  839         if (!inc->inc_isipv6)
  840 #endif
  841                 ipopts = ip_srcroute();
  842 
  843         /*
  844          * See if we already have an entry for this connection.
  845          * If we do, resend the SYN,ACK, and reset the retransmit timer.
  846          *
  847          * XXX
  848          * should the syncache be re-initialized with the contents
  849          * of the new SYN here (which may have different options?)
  850          */
  851         sc = syncache_lookup(inc, &sch);
  852         if (sc != NULL) {
  853                 tcpstat.tcps_sc_dupsyn++;
  854                 if (ipopts) {
  855                         /*
  856                          * If we were remembering a previous source route,
  857                          * forget it and use the new one we've been given.
  858                          */
  859                         if (sc->sc_ipopts)
  860                                 (void) m_free(sc->sc_ipopts);
  861                         sc->sc_ipopts = ipopts;
  862                 }
  863                 /*
  864                  * Update timestamp if present.
  865                  */
  866                 if (sc->sc_flags & SCF_TIMESTAMP)
  867                         sc->sc_tsrecent = to->to_tsval;
  868                 /*
  869                  * PCB may have changed, pick up new values.
  870                  */
  871                 sc->sc_tp = tp;
  872                 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  873                 if (syncache_respond(sc, m) == 0) {
  874                         s = splnet();
  875                         TAILQ_REMOVE(&tcp_syncache.timerq[sc->sc_rxtslot],
  876                             sc, sc_timerq);
  877                         SYNCACHE_TIMEOUT(sc, sc->sc_rxtslot);
  878                         splx(s);
  879                         tcpstat.tcps_sndacks++;
  880                         tcpstat.tcps_sndtotal++;
  881                 }
  882                 *sop = NULL;
  883                 return (1);
  884         }
  885 
  886         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
  887         if (sc == NULL) {
  888                 /*
  889                  * The zone allocator couldn't provide more entries.
  890                  * Treat this as if the cache was full; drop the oldest 
  891                  * entry and insert the new one.
  892                  */
  893                 s = splnet();
  894                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  895                         sc = TAILQ_FIRST(&tcp_syncache.timerq[i]);
  896                         if (sc != NULL)
  897                                 break;
  898                 }
  899                 sc->sc_tp->ts_recent = ticks;
  900                 syncache_drop(sc, NULL);
  901                 splx(s);
  902                 tcpstat.tcps_sc_zonefail++;
  903                 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
  904                 if (sc == NULL) {
  905                         if (ipopts)
  906                                 (void) m_free(ipopts);
  907                         return (0);
  908                 }
  909         }
  910 
  911         /*
  912          * Fill in the syncache values.
  913          */
  914         bzero(sc, sizeof(*sc));
  915         sc->sc_tp = tp;
  916         sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
  917         sc->sc_ipopts = ipopts;
  918         sc->sc_inc.inc_fport = inc->inc_fport;
  919         sc->sc_inc.inc_lport = inc->inc_lport;
  920 #ifdef INET6
  921         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
  922         if (inc->inc_isipv6) {
  923                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
  924                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
  925                 sc->sc_route6.ro_rt = NULL;
  926         } else
  927 #endif
  928         {
  929                 sc->sc_inc.inc_faddr = inc->inc_faddr;
  930                 sc->sc_inc.inc_laddr = inc->inc_laddr;
  931                 sc->sc_route.ro_rt = NULL;
  932         }
  933         sc->sc_irs = th->th_seq;
  934         sc->sc_flags = 0;
  935         sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
  936         if (tcp_syncookies)
  937                 sc->sc_iss = syncookie_generate(sc);
  938         else
  939                 sc->sc_iss = arc4random();
  940 
  941         /* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN] */
  942         win = sbspace(&so->so_rcv);
  943         win = imax(win, 0);
  944         win = imin(win, TCP_MAXWIN);
  945         sc->sc_wnd = win;
  946 
  947         if (tcp_do_rfc1323) {
  948                 /*
  949                  * A timestamp received in a SYN makes
  950                  * it ok to send timestamp requests and replies.
  951                  */
  952                 if (to->to_flags & TOF_TS) {
  953                         sc->sc_tsrecent = to->to_tsval;
  954                         sc->sc_flags |= SCF_TIMESTAMP;
  955                 }
  956                 if (to->to_flags & TOF_SCALE) {
  957                         int wscale = 0;
  958 
  959                         /* Compute proper scaling value from buffer space */
  960                         while (wscale < TCP_MAX_WINSHIFT &&
  961                             (TCP_MAXWIN << wscale) < so->so_rcv.sb_hiwat)
  962                                 wscale++;
  963                         sc->sc_request_r_scale = wscale;
  964                         sc->sc_requested_s_scale = to->to_requested_s_scale;
  965                         sc->sc_flags |= SCF_WINSCALE;
  966                 }
  967         }
  968         if (tcp_do_rfc1644) {
  969                 /*
  970                  * A CC or CC.new option received in a SYN makes
  971                  * it ok to send CC in subsequent segments.
  972                  */
  973                 if (to->to_flags & (TOF_CC|TOF_CCNEW)) {
  974                         sc->sc_cc_recv = to->to_cc;
  975                         sc->sc_cc_send = CC_INC(tcp_ccgen);
  976                         sc->sc_flags |= SCF_CC;
  977                 }
  978         }
  979         if (tp->t_flags & TF_NOOPT)
  980                 sc->sc_flags = SCF_NOOPT;
  981 
  982         /*
  983          * XXX
  984          * We have the option here of not doing TAO (even if the segment
  985          * qualifies) and instead fall back to a normal 3WHS via the syncache.
  986          * This allows us to apply synflood protection to TAO-qualifying SYNs
  987          * also. However, there should be a hueristic to determine when to
  988          * do this, and is not present at the moment.
  989          */
  990 
  991         /*
  992          * Perform TAO test on incoming CC (SEG.CC) option, if any.
  993          * - compare SEG.CC against cached CC from the same host, if any.
  994          * - if SEG.CC > chached value, SYN must be new and is accepted
  995          *      immediately: save new CC in the cache, mark the socket
  996          *      connected, enter ESTABLISHED state, turn on flag to
  997          *      send a SYN in the next segment.
  998          *      A virtual advertised window is set in rcv_adv to
  999          *      initialize SWS prevention.  Then enter normal segment
 1000          *      processing: drop SYN, process data and FIN.
 1001          * - otherwise do a normal 3-way handshake.
 1002          */
 1003         taop = tcp_gettaocache(&sc->sc_inc);
 1004         if ((to->to_flags & TOF_CC) != 0) {
 1005                 if (((tp->t_flags & TF_NOPUSH) != 0) &&
 1006                     sc->sc_flags & SCF_CC && 
 1007                     taop != NULL && taop->tao_cc != 0 &&
 1008                     CC_GT(to->to_cc, taop->tao_cc)) {
 1009                         sc->sc_rxtslot = 0;
 1010                         so = syncache_socket(sc, *sop, m);
 1011                         if (so != NULL) {
 1012                                 sc->sc_flags |= SCF_KEEPROUTE;
 1013                                 taop->tao_cc = to->to_cc;
 1014                                 *sop = so;
 1015                         }
 1016                         syncache_free(sc);
 1017                         return (so != NULL);
 1018                 }
 1019         } else {
 1020                 /*
 1021                  * No CC option, but maybe CC.NEW: invalidate cached value.
 1022                  */
 1023                 if (taop != NULL)
 1024                         taop->tao_cc = 0;
 1025         }
 1026         /*
 1027          * TAO test failed or there was no CC option,
 1028          *    do a standard 3-way handshake.
 1029          */
 1030         if (syncache_respond(sc, m) == 0) {
 1031                 syncache_insert(sc, sch);
 1032                 tcpstat.tcps_sndacks++;
 1033                 tcpstat.tcps_sndtotal++;
 1034         } else {
 1035                 syncache_free(sc);
 1036                 tcpstat.tcps_sc_dropped++;
 1037         }
 1038         *sop = NULL;
 1039         return (1);
 1040 }
 1041 
 1042 static int
 1043 syncache_respond(sc, m)
 1044         struct syncache *sc;
 1045         struct mbuf *m;
 1046 {
 1047         u_int8_t *optp;
 1048         int optlen, error;
 1049         u_int16_t tlen, hlen, mssopt;
 1050         struct ip *ip = NULL;
 1051         struct rtentry *rt;
 1052         struct tcphdr *th;
 1053 #ifdef INET6
 1054         struct ip6_hdr *ip6 = NULL;
 1055 #endif
 1056 
 1057 #ifdef INET6
 1058         if (sc->sc_inc.inc_isipv6) {
 1059                 rt = tcp_rtlookup6(&sc->sc_inc);
 1060                 if (rt != NULL)
 1061                         mssopt = rt->rt_ifp->if_mtu -
 1062                              (sizeof(struct ip6_hdr) + sizeof(struct tcphdr));
 1063                 else 
 1064                         mssopt = tcp_v6mssdflt;
 1065                 hlen = sizeof(struct ip6_hdr);
 1066         } else
 1067 #endif
 1068         {
 1069                 rt = tcp_rtlookup(&sc->sc_inc);
 1070                 if (rt != NULL)
 1071                         mssopt = rt->rt_ifp->if_mtu -
 1072                              (sizeof(struct ip) + sizeof(struct tcphdr));
 1073                 else 
 1074                         mssopt = tcp_mssdflt;
 1075                 hlen = sizeof(struct ip);
 1076         }
 1077 
 1078         /* Compute the size of the TCP options. */
 1079         if (sc->sc_flags & SCF_NOOPT) {
 1080                 optlen = 0;
 1081         } else {
 1082                 optlen = TCPOLEN_MAXSEG +
 1083                     ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
 1084                     ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) +
 1085                     ((sc->sc_flags & SCF_CC) ? TCPOLEN_CC_APPA * 2 : 0);
 1086         }
 1087         tlen = hlen + sizeof(struct tcphdr) + optlen;
 1088 
 1089         /*
 1090          * XXX
 1091          * assume that the entire packet will fit in a header mbuf
 1092          */
 1093         KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
 1094 
 1095         /*
 1096          * XXX shouldn't this reuse the mbuf if possible ?
 1097          * Create the IP+TCP header from scratch.
 1098          */
 1099         if (m)
 1100                 m_freem(m);
 1101 
 1102         m = m_gethdr(M_DONTWAIT, MT_HEADER);
 1103         if (m == NULL)
 1104                 return (ENOBUFS);
 1105         m->m_data += max_linkhdr;
 1106         m->m_len = tlen;
 1107         m->m_pkthdr.len = tlen;
 1108         m->m_pkthdr.rcvif = NULL;
 1109 #ifdef MAC
 1110         mac_create_mbuf_from_socket(sc->sc_tp->t_inpcb->inp_socket, m);
 1111 #endif
 1112 
 1113 #ifdef INET6
 1114         if (sc->sc_inc.inc_isipv6) {
 1115                 ip6 = mtod(m, struct ip6_hdr *);
 1116                 ip6->ip6_vfc = IPV6_VERSION;
 1117                 ip6->ip6_nxt = IPPROTO_TCP;
 1118                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1119                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1120                 ip6->ip6_plen = htons(tlen - hlen);
 1121                 /* ip6_hlim is set after checksum */
 1122                 /* ip6_flow = ??? */
 1123 
 1124                 th = (struct tcphdr *)(ip6 + 1);
 1125         } else
 1126 #endif
 1127         {
 1128                 ip = mtod(m, struct ip *);
 1129                 ip->ip_v = IPVERSION;
 1130                 ip->ip_hl = sizeof(struct ip) >> 2;
 1131                 ip->ip_len = tlen;
 1132                 ip->ip_id = 0;
 1133                 ip->ip_off = 0;
 1134                 ip->ip_sum = 0;
 1135                 ip->ip_p = IPPROTO_TCP;
 1136                 ip->ip_src = sc->sc_inc.inc_laddr;
 1137                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1138                 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl;   /* XXX */
 1139                 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos;   /* XXX */
 1140 
 1141                 /*
 1142                  * See if we should do MTU discovery.  Route lookups are
 1143                  * expensive, so we will only unset the DF bit if:
 1144                  *
 1145                  *      1) path_mtu_discovery is disabled
 1146                  *      2) the SCF_UNREACH flag has been set
 1147                  */
 1148                 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
 1149                        ip->ip_off |= IP_DF;
 1150 
 1151                 th = (struct tcphdr *)(ip + 1);
 1152         }
 1153         th->th_sport = sc->sc_inc.inc_lport;
 1154         th->th_dport = sc->sc_inc.inc_fport;
 1155 
 1156         th->th_seq = htonl(sc->sc_iss);
 1157         th->th_ack = htonl(sc->sc_irs + 1);
 1158         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1159         th->th_x2 = 0;
 1160         th->th_flags = TH_SYN|TH_ACK;
 1161         th->th_win = htons(sc->sc_wnd);
 1162         th->th_urp = 0;
 1163 
 1164         /* Tack on the TCP options. */
 1165         if (optlen != 0) {
 1166                 optp = (u_int8_t *)(th + 1);
 1167                 *optp++ = TCPOPT_MAXSEG;
 1168                 *optp++ = TCPOLEN_MAXSEG;
 1169                 *optp++ = (mssopt >> 8) & 0xff;
 1170                 *optp++ = mssopt & 0xff;
 1171 
 1172                 if (sc->sc_flags & SCF_WINSCALE) {
 1173                         *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
 1174                             TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
 1175                             sc->sc_request_r_scale);
 1176                         optp += 4;
 1177                 }
 1178 
 1179                 if (sc->sc_flags & SCF_TIMESTAMP) {
 1180                         u_int32_t *lp = (u_int32_t *)(optp);
 1181 
 1182                         /* Form timestamp option per appendix A of RFC 1323. */
 1183                         *lp++ = htonl(TCPOPT_TSTAMP_HDR);
 1184                         *lp++ = htonl(ticks);
 1185                         *lp   = htonl(sc->sc_tsrecent);
 1186                         optp += TCPOLEN_TSTAMP_APPA;
 1187                 }
 1188 
 1189                 /*
 1190                  * Send CC and CC.echo if we received CC from our peer.
 1191                  */
 1192                 if (sc->sc_flags & SCF_CC) {
 1193                         u_int32_t *lp = (u_int32_t *)(optp);
 1194 
 1195                         *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CC));
 1196                         *lp++ = htonl(sc->sc_cc_send);
 1197                         *lp++ = htonl(TCPOPT_CC_HDR(TCPOPT_CCECHO));
 1198                         *lp   = htonl(sc->sc_cc_recv);
 1199                         optp += TCPOLEN_CC_APPA * 2;
 1200                 }
 1201         }
 1202 
 1203 #ifdef INET6
 1204         if (sc->sc_inc.inc_isipv6) {
 1205                 struct route_in6 *ro6 = &sc->sc_route6;
 1206 
 1207                 th->th_sum = 0;
 1208                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
 1209                 ip6->ip6_hlim = in6_selecthlim(NULL,
 1210                     ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL);
 1211                 error = ip6_output(m, NULL, ro6, 0, NULL, NULL,
 1212                                 sc->sc_tp->t_inpcb);
 1213         } else
 1214 #endif
 1215         {
 1216                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1217                     htons(tlen - hlen + IPPROTO_TCP));
 1218                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1219                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1220                 error = ip_output(m, sc->sc_ipopts, &sc->sc_route, 0, NULL,
 1221                                 sc->sc_tp->t_inpcb);
 1222         }
 1223         return (error);
 1224 }
 1225 
 1226 /*
 1227  * cookie layers:
 1228  *
 1229  *      |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
 1230  *      | peer iss                                                      |
 1231  *      | MD5(laddr,faddr,secret,lport,fport)             |. . . . . . .|
 1232  *      |                     0                       |(A)|             |
 1233  * (A): peer mss index
 1234  */
 1235 
 1236 /*
 1237  * The values below are chosen to minimize the size of the tcp_secret
 1238  * table, as well as providing roughly a 16 second lifetime for the cookie.
 1239  */
 1240 
 1241 #define SYNCOOKIE_WNDBITS       5       /* exposed bits for window indexing */
 1242 #define SYNCOOKIE_TIMESHIFT     1       /* scale ticks to window time units */
 1243 
 1244 #define SYNCOOKIE_WNDMASK       ((1 << SYNCOOKIE_WNDBITS) - 1)
 1245 #define SYNCOOKIE_NSECRETS      (1 << SYNCOOKIE_WNDBITS)
 1246 #define SYNCOOKIE_TIMEOUT \
 1247     (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
 1248 #define SYNCOOKIE_DATAMASK      ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
 1249 
 1250 static struct {
 1251         u_int32_t       ts_secbits[4];
 1252         u_int           ts_expire;
 1253 } tcp_secret[SYNCOOKIE_NSECRETS];
 1254 
 1255 static int tcp_msstab[] = { 0, 536, 1460, 8960 };
 1256 
 1257 static MD5_CTX syn_ctx;
 1258 
 1259 #define MD5Add(v)       MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
 1260 
 1261 struct md5_add {
 1262         u_int32_t laddr, faddr;
 1263         u_int32_t secbits[4];
 1264         u_int16_t lport, fport;
 1265 };
 1266 
 1267 #ifdef CTASSERT
 1268 CTASSERT(sizeof(struct md5_add) == 28);
 1269 #endif
 1270 
 1271 /*
 1272  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1273  * original SYN was accepted, the connection is established.  The second 
 1274  * SYN is inflight, and if it arrives with an ISN that falls within the 
 1275  * receive window, the connection is killed.  
 1276  *
 1277  * However, since cookies have other problems, this may not be worth
 1278  * worrying about.
 1279  */
 1280 
 1281 static u_int32_t
 1282 syncookie_generate(struct syncache *sc)
 1283 {
 1284         u_int32_t md5_buffer[4];
 1285         u_int32_t data;
 1286         int idx, i;
 1287         struct md5_add add;
 1288 
 1289         idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
 1290         if (tcp_secret[idx].ts_expire < ticks) {
 1291                 for (i = 0; i < 4; i++)
 1292                         tcp_secret[idx].ts_secbits[i] = arc4random();
 1293                 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
 1294         }
 1295         for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--)
 1296                 if (tcp_msstab[data] <= sc->sc_peer_mss)
 1297                         break;
 1298         data = (data << SYNCOOKIE_WNDBITS) | idx;
 1299         data ^= sc->sc_irs;                             /* peer's iss */
 1300         MD5Init(&syn_ctx);
 1301 #ifdef INET6
 1302         if (sc->sc_inc.inc_isipv6) {
 1303                 MD5Add(sc->sc_inc.inc6_laddr);
 1304                 MD5Add(sc->sc_inc.inc6_faddr);
 1305                 add.laddr = 0;
 1306                 add.faddr = 0;
 1307         } else
 1308 #endif
 1309         {
 1310                 add.laddr = sc->sc_inc.inc_laddr.s_addr;
 1311                 add.faddr = sc->sc_inc.inc_faddr.s_addr;
 1312         }
 1313         add.lport = sc->sc_inc.inc_lport;
 1314         add.fport = sc->sc_inc.inc_fport;
 1315         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1316         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1317         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1318         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1319         MD5Add(add);
 1320         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1321         data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
 1322         return (data);
 1323 }
 1324 
 1325 static struct syncache *
 1326 syncookie_lookup(inc, th, so)
 1327         struct in_conninfo *inc;
 1328         struct tcphdr *th;
 1329         struct socket *so;
 1330 {
 1331         u_int32_t md5_buffer[4];
 1332         struct syncache *sc;
 1333         u_int32_t data;
 1334         int wnd, idx;
 1335         struct md5_add add;
 1336 
 1337         data = (th->th_ack - 1) ^ (th->th_seq - 1);     /* remove ISS */
 1338         idx = data & SYNCOOKIE_WNDMASK;
 1339         if (tcp_secret[idx].ts_expire < ticks ||
 1340             sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
 1341                 return (NULL);
 1342         MD5Init(&syn_ctx);
 1343 #ifdef INET6
 1344         if (inc->inc_isipv6) {
 1345                 MD5Add(inc->inc6_laddr);
 1346                 MD5Add(inc->inc6_faddr);
 1347                 add.laddr = 0;
 1348                 add.faddr = 0;
 1349         } else
 1350 #endif
 1351         {
 1352                 add.laddr = inc->inc_laddr.s_addr;
 1353                 add.faddr = inc->inc_faddr.s_addr;
 1354         }
 1355         add.lport = inc->inc_lport;
 1356         add.fport = inc->inc_fport;
 1357         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1358         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1359         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1360         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1361         MD5Add(add);
 1362         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1363         data ^= md5_buffer[0];
 1364         if ((data & ~SYNCOOKIE_DATAMASK) != 0)
 1365                 return (NULL);
 1366         data = data >> SYNCOOKIE_WNDBITS;
 1367 
 1368         sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT);
 1369         if (sc == NULL)
 1370                 return (NULL);
 1371         /*
 1372          * Fill in the syncache values.
 1373          * XXX duplicate code from syncache_add
 1374          */
 1375         sc->sc_ipopts = NULL;
 1376         sc->sc_inc.inc_fport = inc->inc_fport;
 1377         sc->sc_inc.inc_lport = inc->inc_lport;
 1378 #ifdef INET6
 1379         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
 1380         if (inc->inc_isipv6) {
 1381                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
 1382                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
 1383                 sc->sc_route6.ro_rt = NULL;
 1384         } else
 1385 #endif
 1386         {
 1387                 sc->sc_inc.inc_faddr = inc->inc_faddr;
 1388                 sc->sc_inc.inc_laddr = inc->inc_laddr;
 1389                 sc->sc_route.ro_rt = NULL;
 1390         }
 1391         sc->sc_irs = th->th_seq - 1;
 1392         sc->sc_iss = th->th_ack - 1;
 1393         wnd = sbspace(&so->so_rcv);
 1394         wnd = imax(wnd, 0);
 1395         wnd = imin(wnd, TCP_MAXWIN);
 1396         sc->sc_wnd = wnd;
 1397         sc->sc_flags = 0;
 1398         sc->sc_rxtslot = 0;
 1399         sc->sc_peer_mss = tcp_msstab[data];
 1400         return (sc);
 1401 }

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