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) 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
    3  * Copyright (c) 2003, 2004 The DragonFly Project.  All rights reserved.
    4  *
    5  * This code is derived from software contributed to The DragonFly Project
    6  * by Jeffrey M. Hsu.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. Neither the name of The DragonFly Project nor the names of its
   17  *    contributors may be used to endorse or promote products derived
   18  *    from this software without specific, prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
   24  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   25  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
   26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   27  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  */
   33 
   34 /*
   35  * All advertising materials mentioning features or use of this software
   36  * must display the following acknowledgement:
   37  *   This product includes software developed by Jeffrey M. Hsu.
   38  *
   39  * Copyright (c) 2001 Networks Associates Technologies, Inc.
   40  * All rights reserved.
   41  *
   42  * This software was developed for the FreeBSD Project by Jonathan Lemon
   43  * and NAI Labs, the Security Research Division of Network Associates, Inc.
   44  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
   45  * DARPA CHATS research program.
   46  *
   47  * Redistribution and use in source and binary forms, with or without
   48  * modification, are permitted provided that the following conditions
   49  * are met:
   50  * 1. Redistributions of source code must retain the above copyright
   51  *    notice, this list of conditions and the following disclaimer.
   52  * 2. Redistributions in binary form must reproduce the above copyright
   53  *    notice, this list of conditions and the following disclaimer in the
   54  *    documentation and/or other materials provided with the distribution.
   55  * 3. The name of the author may not be used to endorse or promote
   56  *    products derived from this software without specific prior written
   57  *    permission.
   58  *
   59  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   60  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   61  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   62  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   63  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   64  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   65  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   66  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   67  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   68  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   69  * SUCH DAMAGE.
   70  *
   71  * $FreeBSD: src/sys/netinet/tcp_syncache.c,v 1.5.2.14 2003/02/24 04:02:27 silby Exp $
   72  */
   73 
   74 #include "opt_inet.h"
   75 #include "opt_inet6.h"
   76 #include "opt_ipsec.h"
   77 
   78 #include <sys/param.h>
   79 #include <sys/systm.h>
   80 #include <sys/kernel.h>
   81 #include <sys/sysctl.h>
   82 #include <sys/malloc.h>
   83 #include <sys/mbuf.h>
   84 #include <sys/md5.h>
   85 #include <sys/proc.h>           /* for proc0 declaration */
   86 #include <sys/random.h>
   87 #include <sys/socket.h>
   88 #include <sys/socketvar.h>
   89 #include <sys/in_cksum.h>
   90 
   91 #include <sys/msgport2.h>
   92 #include <net/netmsg2.h>
   93 #include <net/netisr2.h>
   94 
   95 #include <net/if.h>
   96 #include <net/route.h>
   97 
   98 #include <netinet/in.h>
   99 #include <netinet/in_systm.h>
  100 #include <netinet/ip.h>
  101 #include <netinet/in_var.h>
  102 #include <netinet/in_pcb.h>
  103 #include <netinet/ip_var.h>
  104 #include <netinet/ip6.h>
  105 #ifdef INET6
  106 #include <netinet/icmp6.h>
  107 #include <netinet6/nd6.h>
  108 #endif
  109 #include <netinet6/ip6_var.h>
  110 #include <netinet6/in6_pcb.h>
  111 #include <netinet/tcp.h>
  112 #include <netinet/tcp_fsm.h>
  113 #include <netinet/tcp_seq.h>
  114 #include <netinet/tcp_timer.h>
  115 #include <netinet/tcp_timer2.h>
  116 #include <netinet/tcp_var.h>
  117 #include <netinet6/tcp6_var.h>
  118 
  119 #ifdef IPSEC
  120 #include <netinet6/ipsec.h>
  121 #ifdef INET6
  122 #include <netinet6/ipsec6.h>
  123 #endif
  124 #include <netproto/key/key.h>
  125 #endif /*IPSEC*/
  126 
  127 #ifdef FAST_IPSEC
  128 #include <netproto/ipsec/ipsec.h>
  129 #ifdef INET6
  130 #include <netproto/ipsec/ipsec6.h>
  131 #endif
  132 #include <netproto/ipsec/key.h>
  133 #define IPSEC
  134 #endif /*FAST_IPSEC*/
  135 
  136 static int tcp_syncookies = 1;
  137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
  138     &tcp_syncookies, 0,
  139     "Use TCP SYN cookies if the syncache overflows");
  140 
  141 static void      syncache_drop(struct syncache *, struct syncache_head *);
  142 static void      syncache_free(struct syncache *);
  143 static void      syncache_insert(struct syncache *, struct syncache_head *);
  144 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
  145 static int       syncache_respond(struct syncache *, struct mbuf *);
  146 static struct    socket *syncache_socket(struct syncache *, struct socket *,
  147                     struct mbuf *);
  148 static void      syncache_timer(void *);
  149 static u_int32_t syncookie_generate(struct syncache *);
  150 static struct syncache *syncookie_lookup(struct in_conninfo *,
  151                     struct tcphdr *, struct socket *);
  152 
  153 /*
  154  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
  155  * 4 retransmits corresponds to a timeout of (3 + 3 + 3 + 3 + 3 == 15) seconds
  156  * or (1 + 1 + 2 + 4 + 8 == 16) seconds if RFC6298 is used, the odds are that
  157  * the user has given up attempting to connect by then.
  158  */
  159 #define SYNCACHE_MAXREXMTS              4
  160 
  161 /* Arbitrary values */
  162 #define TCP_SYNCACHE_HASHSIZE           512
  163 #define TCP_SYNCACHE_BUCKETLIMIT        30
  164 
  165 struct netmsg_sc_timer {
  166         struct netmsg_base base;
  167         struct msgrec *nm_mrec;         /* back pointer to containing msgrec */
  168 };
  169 
  170 struct msgrec {
  171         struct netmsg_sc_timer msg;
  172         lwkt_port_t port;               /* constant after init */
  173         int slot;                       /* constant after init */
  174 };
  175 
  176 static void syncache_timer_handler(netmsg_t);
  177 
  178 struct tcp_syncache {
  179         u_int   hashsize;
  180         u_int   hashmask;
  181         u_int   bucket_limit;
  182         u_int   cache_limit;
  183         u_int   rexmt_limit;
  184         u_int   hash_secret;
  185 };
  186 static struct tcp_syncache tcp_syncache;
  187 
  188 TAILQ_HEAD(syncache_list, syncache);
  189 
  190 struct tcp_syncache_percpu {
  191         struct syncache_head    *hashbase;
  192         u_int                   cache_count;
  193         struct syncache_list    timerq[SYNCACHE_MAXREXMTS + 1];
  194         struct callout          tt_timerq[SYNCACHE_MAXREXMTS + 1];
  195         struct msgrec           mrec[SYNCACHE_MAXREXMTS + 1];
  196 };
  197 static struct tcp_syncache_percpu tcp_syncache_percpu[MAXCPU];
  198 
  199 static struct lwkt_port syncache_null_rport;
  200 
  201 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
  202 
  203 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RD,
  204      &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
  205 
  206 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RD,
  207      &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
  208 
  209 /* XXX JH */
  210 #if 0
  211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
  212      &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
  213 #endif
  214 
  215 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RD,
  216      &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
  217 
  218 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
  219      &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
  220 
  221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
  222 
  223 #define SYNCACHE_HASH(inc, mask)                                        \
  224         ((tcp_syncache.hash_secret ^                                    \
  225           (inc)->inc_faddr.s_addr ^                                     \
  226           ((inc)->inc_faddr.s_addr >> 16) ^                             \
  227           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  228 
  229 #define SYNCACHE_HASH6(inc, mask)                                       \
  230         ((tcp_syncache.hash_secret ^                                    \
  231           (inc)->inc6_faddr.s6_addr32[0] ^                              \
  232           (inc)->inc6_faddr.s6_addr32[3] ^                              \
  233           (inc)->inc_fport ^ (inc)->inc_lport) & mask)
  234 
  235 #define ENDPTS_EQ(a, b) (                                               \
  236         (a)->ie_fport == (b)->ie_fport &&                               \
  237         (a)->ie_lport == (b)->ie_lport &&                               \
  238         (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr &&                 \
  239         (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr                    \
  240 )
  241 
  242 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
  243 
  244 static __inline int
  245 syncache_rto(int slot)
  246 {
  247         if (tcp_low_rtobase)
  248                 return (TCPTV_RTOBASE * tcp_syn_backoff_low[slot]);
  249         else
  250                 return (TCPTV_RTOBASE * tcp_syn_backoff[slot]);
  251 }
  252 
  253 static __inline void
  254 syncache_timeout(struct tcp_syncache_percpu *syncache_percpu,
  255                  struct syncache *sc, int slot)
  256 {
  257         int rto;
  258 
  259         if (slot > 0) {
  260                 /*
  261                  * Record the time that we spent in SYN|ACK
  262                  * retransmition.
  263                  *
  264                  * Needed by RFC3390 and RFC6298.
  265                  */
  266                 sc->sc_rxtused += syncache_rto(slot - 1);
  267         }
  268         sc->sc_rxtslot = slot;
  269 
  270         rto = syncache_rto(slot);
  271         sc->sc_rxttime = ticks + rto;
  272 
  273         TAILQ_INSERT_TAIL(&syncache_percpu->timerq[slot], sc, sc_timerq);
  274         if (!callout_active(&syncache_percpu->tt_timerq[slot])) {
  275                 callout_reset(&syncache_percpu->tt_timerq[slot], rto,
  276                     syncache_timer, &syncache_percpu->mrec[slot]);
  277         }
  278 }
  279 
  280 static void
  281 syncache_free(struct syncache *sc)
  282 {
  283         struct rtentry *rt;
  284 #ifdef INET6
  285         const boolean_t isipv6 = sc->sc_inc.inc_isipv6;
  286 #else
  287         const boolean_t isipv6 = FALSE;
  288 #endif
  289 
  290         if (sc->sc_ipopts)
  291                 m_free(sc->sc_ipopts);
  292 
  293         rt = isipv6 ? sc->sc_route6.ro_rt : sc->sc_route.ro_rt;
  294         if (rt != NULL) {
  295                 /*
  296                  * If this is the only reference to a protocol-cloned
  297                  * route, remove it immediately.
  298                  */
  299                 if ((rt->rt_flags & (RTF_WASCLONED | RTF_LLINFO)) ==
  300                     RTF_WASCLONED && rt->rt_refcnt == 1) {
  301                         rtrequest(RTM_DELETE, rt_key(rt), rt->rt_gateway,
  302                                   rt_mask(rt), rt->rt_flags, NULL);
  303                 }
  304                 RTFREE(rt);
  305         }
  306         kfree(sc, M_SYNCACHE);
  307 }
  308 
  309 void
  310 syncache_init(void)
  311 {
  312         int i, cpu;
  313 
  314         tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
  315         tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
  316         tcp_syncache.cache_limit =
  317             tcp_syncache.hashsize * tcp_syncache.bucket_limit;
  318         tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
  319         tcp_syncache.hash_secret = karc4random();
  320 
  321         TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
  322             &tcp_syncache.hashsize);
  323         TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
  324             &tcp_syncache.cache_limit);
  325         TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
  326             &tcp_syncache.bucket_limit);
  327         if (!powerof2(tcp_syncache.hashsize)) {
  328                 kprintf("WARNING: syncache hash size is not a power of 2.\n");
  329                 tcp_syncache.hashsize = 512;    /* safe default */
  330         }
  331         tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
  332 
  333         lwkt_initport_replyonly_null(&syncache_null_rport);
  334 
  335         for (cpu = 0; cpu < ncpus2; cpu++) {
  336                 struct tcp_syncache_percpu *syncache_percpu;
  337 
  338                 syncache_percpu = &tcp_syncache_percpu[cpu];
  339                 /* Allocate the hash table. */
  340                 syncache_percpu->hashbase = kmalloc(tcp_syncache.hashsize * sizeof(struct syncache_head),
  341                                                     M_SYNCACHE, M_WAITOK);
  342 
  343                 /* Initialize the hash buckets. */
  344                 for (i = 0; i < tcp_syncache.hashsize; i++) {
  345                         struct syncache_head *bucket;
  346 
  347                         bucket = &syncache_percpu->hashbase[i];
  348                         TAILQ_INIT(&bucket->sch_bucket);
  349                         bucket->sch_length = 0;
  350                 }
  351 
  352                 for (i = 0; i <= SYNCACHE_MAXREXMTS; i++) {
  353                         /* Initialize the timer queues. */
  354                         TAILQ_INIT(&syncache_percpu->timerq[i]);
  355                         callout_init_mp(&syncache_percpu->tt_timerq[i]);
  356 
  357                         syncache_percpu->mrec[i].slot = i;
  358                         syncache_percpu->mrec[i].port = netisr_cpuport(cpu);
  359                         syncache_percpu->mrec[i].msg.nm_mrec =
  360                                     &syncache_percpu->mrec[i];
  361                         netmsg_init(&syncache_percpu->mrec[i].msg.base,
  362                                     NULL, &syncache_null_rport,
  363                                     0, syncache_timer_handler);
  364                 }
  365         }
  366 }
  367 
  368 static void
  369 syncache_insert(struct syncache *sc, struct syncache_head *sch)
  370 {
  371         struct tcp_syncache_percpu *syncache_percpu;
  372         struct syncache *sc2;
  373         int i;
  374 
  375         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  376 
  377         /*
  378          * Make sure that we don't overflow the per-bucket
  379          * limit or the total cache size limit.
  380          */
  381         if (sch->sch_length >= tcp_syncache.bucket_limit) {
  382                 /*
  383                  * The bucket is full, toss the oldest element.
  384                  */
  385                 sc2 = TAILQ_FIRST(&sch->sch_bucket);
  386                 if (sc2->sc_tp != NULL)
  387                         sc2->sc_tp->ts_recent = ticks;
  388                 syncache_drop(sc2, sch);
  389                 tcpstat.tcps_sc_bucketoverflow++;
  390         } else if (syncache_percpu->cache_count >= tcp_syncache.cache_limit) {
  391                 /*
  392                  * The cache is full.  Toss the oldest entry in the
  393                  * entire cache.  This is the front entry in the
  394                  * first non-empty timer queue with the largest
  395                  * timeout value.
  396                  */
  397                 for (i = SYNCACHE_MAXREXMTS; i >= 0; i--) {
  398                         sc2 = TAILQ_FIRST(&syncache_percpu->timerq[i]);
  399                         while (sc2 && (sc2->sc_flags & SCF_MARKER))
  400                                 sc2 = TAILQ_NEXT(sc2, sc_timerq);
  401                         if (sc2 != NULL)
  402                                 break;
  403                 }
  404                 if (sc2->sc_tp != NULL)
  405                         sc2->sc_tp->ts_recent = ticks;
  406                 syncache_drop(sc2, NULL);
  407                 tcpstat.tcps_sc_cacheoverflow++;
  408         }
  409 
  410         /* Initialize the entry's timer. */
  411         syncache_timeout(syncache_percpu, sc, 0);
  412 
  413         /* Put it into the bucket. */
  414         TAILQ_INSERT_TAIL(&sch->sch_bucket, sc, sc_hash);
  415         sch->sch_length++;
  416         syncache_percpu->cache_count++;
  417         tcpstat.tcps_sc_added++;
  418 }
  419 
  420 void
  421 syncache_destroy(struct tcpcb *tp, struct tcpcb *tp_inh)
  422 {
  423         struct tcp_syncache_percpu *syncache_percpu;
  424         struct syncache_head *bucket;
  425         struct syncache *sc;
  426         int i;
  427 
  428         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  429         sc = NULL;
  430 
  431         for (i = 0; i < tcp_syncache.hashsize; i++) {
  432                 bucket = &syncache_percpu->hashbase[i];
  433                 TAILQ_FOREACH(sc, &bucket->sch_bucket, sc_hash) {
  434                         if (sc->sc_tp == tp)
  435                                 sc->sc_tp = tp_inh;
  436                 }
  437         }
  438 }
  439 
  440 static void
  441 syncache_drop(struct syncache *sc, struct syncache_head *sch)
  442 {
  443         struct tcp_syncache_percpu *syncache_percpu;
  444 #ifdef INET6
  445         const boolean_t isipv6 = sc->sc_inc.inc_isipv6;
  446 #else
  447         const boolean_t isipv6 = FALSE;
  448 #endif
  449 
  450         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  451 
  452         if (sch == NULL) {
  453                 if (isipv6) {
  454                         sch = &syncache_percpu->hashbase[
  455                             SYNCACHE_HASH6(&sc->sc_inc, tcp_syncache.hashmask)];
  456                 } else {
  457                         sch = &syncache_percpu->hashbase[
  458                             SYNCACHE_HASH(&sc->sc_inc, tcp_syncache.hashmask)];
  459                 }
  460         }
  461 
  462         TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
  463         sch->sch_length--;
  464         syncache_percpu->cache_count--;
  465 
  466         /*
  467          * Cleanup
  468          */
  469         sc->sc_tp = NULL;
  470 
  471         /*
  472          * Remove the entry from the syncache timer/timeout queue.  Note
  473          * that we do not try to stop any running timer since we do not know
  474          * whether the timer's message is in-transit or not.  Since timeouts
  475          * are fairly long, taking an unneeded callout does not detrimentally
  476          * effect performance.
  477          */
  478         TAILQ_REMOVE(&syncache_percpu->timerq[sc->sc_rxtslot], sc, sc_timerq);
  479 
  480         syncache_free(sc);
  481 }
  482 
  483 /*
  484  * Place a timeout message on the TCP thread's message queue.
  485  * This routine runs in soft interrupt context.
  486  *
  487  * An invariant is for this routine to be called, the callout must
  488  * have been active.  Note that the callout is not deactivated until
  489  * after the message has been processed in syncache_timer_handler() below.
  490  */
  491 static void
  492 syncache_timer(void *p)
  493 {
  494         struct netmsg_sc_timer *msg = p;
  495 
  496         lwkt_sendmsg_oncpu(msg->nm_mrec->port, &msg->base.lmsg);
  497 }
  498 
  499 /*
  500  * Service a timer message queued by timer expiration.
  501  * This routine runs in the TCP protocol thread.
  502  *
  503  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
  504  * If we have retransmitted an entry the maximum number of times, expire it.
  505  *
  506  * When we finish processing timed-out entries, we restart the timer if there
  507  * are any entries still on the queue and deactivate it otherwise.  Only after
  508  * a timer has been deactivated here can it be restarted by syncache_timeout().
  509  */
  510 static void
  511 syncache_timer_handler(netmsg_t msg)
  512 {
  513         struct tcp_syncache_percpu *syncache_percpu;
  514         struct syncache *sc;
  515         struct syncache marker;
  516         struct syncache_list *list;
  517         struct inpcb *inp;
  518         int slot;
  519 
  520         slot = ((struct netmsg_sc_timer *)msg)->nm_mrec->slot;
  521         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  522 
  523         list = &syncache_percpu->timerq[slot];
  524 
  525         /*
  526          * Use a marker to keep our place in the scan.  syncache_drop()
  527          * can block and cause any next pointer we cache to become stale.
  528          */
  529         marker.sc_flags = SCF_MARKER;
  530         TAILQ_INSERT_HEAD(list, &marker, sc_timerq);
  531 
  532         while ((sc = TAILQ_NEXT(&marker, sc_timerq)) != NULL) {
  533                 /*
  534                  * Move the marker.
  535                  */
  536                 TAILQ_REMOVE(list, &marker, sc_timerq);
  537                 TAILQ_INSERT_AFTER(list, sc, &marker, sc_timerq);
  538 
  539                 if (sc->sc_flags & SCF_MARKER)
  540                         continue;
  541 
  542                 if (ticks < sc->sc_rxttime)
  543                         break;  /* finished because timerq sorted by time */
  544                 if (sc->sc_tp == NULL) {
  545                         syncache_drop(sc, NULL);
  546                         tcpstat.tcps_sc_stale++;
  547                         continue;
  548                 }
  549                 inp = sc->sc_tp->t_inpcb;
  550                 if (slot == SYNCACHE_MAXREXMTS ||
  551                     slot >= tcp_syncache.rexmt_limit ||
  552                     inp == NULL ||
  553                     inp->inp_gencnt != sc->sc_inp_gencnt) {
  554                         syncache_drop(sc, NULL);
  555                         tcpstat.tcps_sc_stale++;
  556                         continue;
  557                 }
  558                 /*
  559                  * syncache_respond() may call back into the syncache to
  560                  * to modify another entry, so do not obtain the next
  561                  * entry on the timer chain until it has completed.
  562                  */
  563                 syncache_respond(sc, NULL);
  564                 tcpstat.tcps_sc_retransmitted++;
  565                 TAILQ_REMOVE(list, sc, sc_timerq);
  566                 syncache_timeout(syncache_percpu, sc, slot + 1);
  567         }
  568         TAILQ_REMOVE(list, &marker, sc_timerq);
  569 
  570         if (sc != NULL) {
  571                 callout_reset(&syncache_percpu->tt_timerq[slot],
  572                               sc->sc_rxttime - ticks, syncache_timer,
  573                               &syncache_percpu->mrec[slot]);
  574         } else {
  575                 callout_deactivate(&syncache_percpu->tt_timerq[slot]);
  576         }
  577         lwkt_replymsg(&msg->base.lmsg, 0);
  578 }
  579 
  580 /*
  581  * Find an entry in the syncache.
  582  */
  583 struct syncache *
  584 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
  585 {
  586         struct tcp_syncache_percpu *syncache_percpu;
  587         struct syncache *sc;
  588         struct syncache_head *sch;
  589 
  590         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  591 #ifdef INET6
  592         if (inc->inc_isipv6) {
  593                 sch = &syncache_percpu->hashbase[
  594                     SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
  595                 *schp = sch;
  596                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
  597                         if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  598                                 return (sc);
  599         } else
  600 #endif
  601         {
  602                 sch = &syncache_percpu->hashbase[
  603                     SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
  604                 *schp = sch;
  605                 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
  606 #ifdef INET6
  607                         if (sc->sc_inc.inc_isipv6)
  608                                 continue;
  609 #endif
  610                         if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
  611                                 return (sc);
  612                 }
  613         }
  614         return (NULL);
  615 }
  616 
  617 /*
  618  * This function is called when we get a RST for a
  619  * non-existent connection, so that we can see if the
  620  * connection is in the syn cache.  If it is, zap it.
  621  */
  622 void
  623 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
  624 {
  625         struct syncache *sc;
  626         struct syncache_head *sch;
  627 
  628         sc = syncache_lookup(inc, &sch);
  629         if (sc == NULL) {
  630                 return;
  631         }
  632         /*
  633          * If the RST bit is set, check the sequence number to see
  634          * if this is a valid reset segment.
  635          * RFC 793 page 37:
  636          *   In all states except SYN-SENT, all reset (RST) segments
  637          *   are validated by checking their SEQ-fields.  A reset is
  638          *   valid if its sequence number is in the window.
  639          *
  640          *   The sequence number in the reset segment is normally an
  641          *   echo of our outgoing acknowlegement numbers, but some hosts
  642          *   send a reset with the sequence number at the rightmost edge
  643          *   of our receive window, and we have to handle this case.
  644          */
  645         if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
  646             SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
  647                 syncache_drop(sc, sch);
  648                 tcpstat.tcps_sc_reset++;
  649         }
  650 }
  651 
  652 void
  653 syncache_badack(struct in_conninfo *inc)
  654 {
  655         struct syncache *sc;
  656         struct syncache_head *sch;
  657 
  658         sc = syncache_lookup(inc, &sch);
  659         if (sc != NULL) {
  660                 syncache_drop(sc, sch);
  661                 tcpstat.tcps_sc_badack++;
  662         }
  663 }
  664 
  665 void
  666 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
  667 {
  668         struct syncache *sc;
  669         struct syncache_head *sch;
  670 
  671         /* we are called at splnet() here */
  672         sc = syncache_lookup(inc, &sch);
  673         if (sc == NULL)
  674                 return;
  675 
  676         /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
  677         if (ntohl(th->th_seq) != sc->sc_iss)
  678                 return;
  679 
  680         /*
  681          * If we've rertransmitted 3 times and this is our second error,
  682          * we remove the entry.  Otherwise, we allow it to continue on.
  683          * This prevents us from incorrectly nuking an entry during a
  684          * spurious network outage.
  685          *
  686          * See tcp_notify().
  687          */
  688         if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtslot < 3) {
  689                 sc->sc_flags |= SCF_UNREACH;
  690                 return;
  691         }
  692         syncache_drop(sc, sch);
  693         tcpstat.tcps_sc_unreach++;
  694 }
  695 
  696 /*
  697  * Build a new TCP socket structure from a syncache entry.
  698  *
  699  * This is called from the context of the SYN+ACK
  700  */
  701 static struct socket *
  702 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
  703 {
  704         struct inpcb *inp = NULL, *linp;
  705         struct socket *so;
  706         struct tcpcb *tp, *ltp;
  707         lwkt_port_t port;
  708 #ifdef INET6
  709         const boolean_t isipv6 = sc->sc_inc.inc_isipv6;
  710 #else
  711         const boolean_t isipv6 = FALSE;
  712 #endif
  713         struct sockaddr_in sin_faddr;
  714         struct sockaddr_in6 sin6_faddr;
  715         struct sockaddr *faddr;
  716 
  717         if (isipv6) {
  718                 faddr = (struct sockaddr *)&sin6_faddr;
  719                 sin6_faddr.sin6_family = AF_INET6;
  720                 sin6_faddr.sin6_len = sizeof(sin6_faddr);
  721                 sin6_faddr.sin6_addr = sc->sc_inc.inc6_faddr;
  722                 sin6_faddr.sin6_port = sc->sc_inc.inc_fport;
  723                 sin6_faddr.sin6_flowinfo = sin6_faddr.sin6_scope_id = 0;
  724         } else {
  725                 faddr = (struct sockaddr *)&sin_faddr;
  726                 sin_faddr.sin_family = AF_INET;
  727                 sin_faddr.sin_len = sizeof(sin_faddr);
  728                 sin_faddr.sin_addr = sc->sc_inc.inc_faddr;
  729                 sin_faddr.sin_port = sc->sc_inc.inc_fport;
  730                 bzero(sin_faddr.sin_zero, sizeof(sin_faddr.sin_zero));
  731         }
  732 
  733         /*
  734          * Ok, create the full blown connection, and set things up
  735          * as they would have been set up if we had created the
  736          * connection when the SYN arrived.  If we can't create
  737          * the connection, abort it.
  738          *
  739          * Set the protocol processing port for the socket to the current
  740          * port (that the connection came in on).
  741          */
  742         so = sonewconn_faddr(lso, SS_ISCONNECTED, faddr);
  743         if (so == NULL) {
  744                 /*
  745                  * Drop the connection; we will send a RST if the peer
  746                  * retransmits the ACK,
  747                  */
  748                 tcpstat.tcps_listendrop++;
  749                 goto abort;
  750         }
  751 
  752         /*
  753          * Insert new socket into hash list.
  754          */
  755         inp = so->so_pcb;
  756         inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
  757         if (isipv6) {
  758                 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  759         } else {
  760 #ifdef INET6
  761                 inp->inp_vflag &= ~INP_IPV6;
  762                 inp->inp_vflag |= INP_IPV4;
  763                 inp->inp_flags &= ~IN6P_IPV6_V6ONLY;
  764 #endif
  765                 inp->inp_laddr = sc->sc_inc.inc_laddr;
  766         }
  767         inp->inp_lport = sc->sc_inc.inc_lport;
  768         if (in_pcbinsporthash(inp) != 0) {
  769                 /*
  770                  * Undo the assignments above if we failed to
  771                  * put the PCB on the hash lists.
  772                  */
  773                 if (isipv6)
  774                         inp->in6p_laddr = kin6addr_any;
  775                 else
  776                         inp->inp_laddr.s_addr = INADDR_ANY;
  777                 inp->inp_lport = 0;
  778                 goto abort;
  779         }
  780         linp = lso->so_pcb;
  781 #ifdef IPSEC
  782         /* copy old policy into new socket's */
  783         if (ipsec_copy_policy(linp->inp_sp, inp->inp_sp))
  784                 kprintf("syncache_expand: could not copy policy\n");
  785 #endif
  786         if (isipv6) {
  787                 struct in6_addr laddr6;
  788                 /*
  789                  * Inherit socket options from the listening socket.
  790                  * Note that in6p_inputopts are not (and should not be)
  791                  * copied, since it stores previously received options and is
  792                  * used to detect if each new option is different than the
  793                  * previous one and hence should be passed to a user.
  794                  * If we copied in6p_inputopts, a user would not be able to
  795                  * receive options just after calling the accept system call.
  796                  */
  797                 inp->inp_flags |= linp->inp_flags & INP_CONTROLOPTS;
  798                 if (linp->in6p_outputopts)
  799                         inp->in6p_outputopts =
  800                             ip6_copypktopts(linp->in6p_outputopts, M_INTWAIT);
  801                 inp->in6p_route = sc->sc_route6;
  802                 sc->sc_route6.ro_rt = NULL;
  803 
  804                 laddr6 = inp->in6p_laddr;
  805                 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
  806                         inp->in6p_laddr = sc->sc_inc.inc6_laddr;
  807                 if (in6_pcbconnect(inp, faddr, &thread0)) {
  808                         inp->in6p_laddr = laddr6;
  809                         goto abort;
  810                 }
  811         } else {
  812                 struct in_addr laddr;
  813 
  814                 inp->inp_options = ip_srcroute(m);
  815                 if (inp->inp_options == NULL) {
  816                         inp->inp_options = sc->sc_ipopts;
  817                         sc->sc_ipopts = NULL;
  818                 }
  819                 inp->inp_route = sc->sc_route;
  820                 sc->sc_route.ro_rt = NULL;
  821 
  822                 laddr = inp->inp_laddr;
  823                 if (inp->inp_laddr.s_addr == INADDR_ANY)
  824                         inp->inp_laddr = sc->sc_inc.inc_laddr;
  825                 if (in_pcbconnect(inp, faddr, &thread0)) {
  826                         inp->inp_laddr = laddr;
  827                         goto abort;
  828                 }
  829         }
  830 
  831         /*
  832          * The current port should be in the context of the SYN+ACK and
  833          * so should match the tcp address port.
  834          */
  835         if (isipv6) {
  836                 port = tcp6_addrport();
  837         } else {
  838                 port = tcp_addrport(inp->inp_faddr.s_addr, inp->inp_fport,
  839                                     inp->inp_laddr.s_addr, inp->inp_lport);
  840         }
  841         KASSERT(port == &curthread->td_msgport,
  842             ("TCP PORT MISMATCH %p vs %p\n", port, &curthread->td_msgport));
  843 
  844         tp = intotcpcb(inp);
  845         tp->t_state = TCPS_SYN_RECEIVED;
  846         tp->iss = sc->sc_iss;
  847         tp->irs = sc->sc_irs;
  848         tcp_rcvseqinit(tp);
  849         tcp_sendseqinit(tp);
  850         tp->snd_wnd = sc->sc_sndwnd;
  851         tp->snd_wl1 = sc->sc_irs;
  852         tp->rcv_up = sc->sc_irs + 1;
  853         tp->rcv_wnd = sc->sc_wnd;
  854         tp->rcv_adv += tp->rcv_wnd;
  855 
  856         tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH | TF_NODELAY);
  857         if (sc->sc_flags & SCF_NOOPT)
  858                 tp->t_flags |= TF_NOOPT;
  859         if (sc->sc_flags & SCF_WINSCALE) {
  860                 tp->t_flags |= TF_REQ_SCALE | TF_RCVD_SCALE;
  861                 tp->snd_scale = sc->sc_requested_s_scale;
  862                 tp->request_r_scale = sc->sc_request_r_scale;
  863         }
  864         if (sc->sc_flags & SCF_TIMESTAMP) {
  865                 tp->t_flags |= TF_REQ_TSTMP | TF_RCVD_TSTMP;
  866                 tp->ts_recent = sc->sc_tsrecent;
  867                 tp->ts_recent_age = ticks;
  868         }
  869         if (sc->sc_flags & SCF_SACK_PERMITTED)
  870                 tp->t_flags |= TF_SACK_PERMITTED;
  871 
  872 #ifdef TCP_SIGNATURE
  873         if (sc->sc_flags & SCF_SIGNATURE)
  874                 tp->t_flags |= TF_SIGNATURE;
  875 #endif /* TCP_SIGNATURE */
  876 
  877         tp->t_rxtsyn = sc->sc_rxtused;
  878         tcp_mss(tp, sc->sc_peer_mss);
  879 
  880         /*
  881          * Inherit some properties from the listen socket
  882          */
  883         ltp = intotcpcb(linp);
  884         tp->t_keepinit = ltp->t_keepinit;
  885         tp->t_keepidle = ltp->t_keepidle;
  886         tp->t_keepintvl = ltp->t_keepintvl;
  887         tp->t_keepcnt = ltp->t_keepcnt;
  888         tp->t_maxidle = ltp->t_maxidle;
  889 
  890         tcp_create_timermsg(tp, port);
  891         tcp_callout_reset(tp, tp->tt_keep, tp->t_keepinit, tcp_timer_keep);
  892 
  893         tcpstat.tcps_accepts++;
  894         return (so);
  895 
  896 abort:
  897         if (so != NULL)
  898                 soabort_oncpu(so);
  899         return (NULL);
  900 }
  901 
  902 /*
  903  * This function gets called when we receive an ACK for a
  904  * socket in the LISTEN state.  We look up the connection
  905  * in the syncache, and if its there, we pull it out of
  906  * the cache and turn it into a full-blown connection in
  907  * the SYN-RECEIVED state.
  908  */
  909 int
  910 syncache_expand(struct in_conninfo *inc, struct tcphdr *th, struct socket **sop,
  911                 struct mbuf *m)
  912 {
  913         struct syncache *sc;
  914         struct syncache_head *sch;
  915         struct socket *so;
  916 
  917         sc = syncache_lookup(inc, &sch);
  918         if (sc == NULL) {
  919                 /*
  920                  * There is no syncache entry, so see if this ACK is
  921                  * a returning syncookie.  To do this, first:
  922                  *  A. See if this socket has had a syncache entry dropped in
  923                  *     the past.  We don't want to accept a bogus syncookie
  924                  *     if we've never received a SYN.
  925                  *  B. check that the syncookie is valid.  If it is, then
  926                  *     cobble up a fake syncache entry, and return.
  927                  */
  928                 if (!tcp_syncookies)
  929                         return (0);
  930                 sc = syncookie_lookup(inc, th, *sop);
  931                 if (sc == NULL)
  932                         return (0);
  933                 sch = NULL;
  934                 tcpstat.tcps_sc_recvcookie++;
  935         }
  936 
  937         /*
  938          * If seg contains an ACK, but not for our SYN/ACK, send a RST.
  939          */
  940         if (th->th_ack != sc->sc_iss + 1)
  941                 return (0);
  942 
  943         so = syncache_socket(sc, *sop, m);
  944         if (so == NULL) {
  945 #if 0
  946 resetandabort:
  947                 /* XXXjlemon check this - is this correct? */
  948                 tcp_respond(NULL, m, m, th,
  949                     th->th_seq + tlen, (tcp_seq)0, TH_RST | TH_ACK);
  950 #endif
  951                 m_freem(m);                     /* XXX only needed for above */
  952                 tcpstat.tcps_sc_aborted++;
  953         } else {
  954                 tcpstat.tcps_sc_completed++;
  955         }
  956         if (sch == NULL)
  957                 syncache_free(sc);
  958         else
  959                 syncache_drop(sc, sch);
  960         *sop = so;
  961         return (1);
  962 }
  963 
  964 /*
  965  * Given a LISTEN socket and an inbound SYN request, add
  966  * this to the syn cache, and send back a segment:
  967  *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
  968  * to the source.
  969  *
  970  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
  971  * Doing so would require that we hold onto the data and deliver it
  972  * to the application.  However, if we are the target of a SYN-flood
  973  * DoS attack, an attacker could send data which would eventually
  974  * consume all available buffer space if it were ACKed.  By not ACKing
  975  * the data, we avoid this DoS scenario.
  976  */
  977 int
  978 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
  979              struct socket *so, struct mbuf *m)
  980 {
  981         struct tcp_syncache_percpu *syncache_percpu;
  982         struct tcpcb *tp;
  983         struct syncache *sc = NULL;
  984         struct syncache_head *sch;
  985         struct mbuf *ipopts = NULL;
  986         int win;
  987 
  988         syncache_percpu = &tcp_syncache_percpu[mycpu->gd_cpuid];
  989         tp = sototcpcb(so);
  990 
  991         /*
  992          * Remember the IP options, if any.
  993          */
  994 #ifdef INET6
  995         if (!inc->inc_isipv6)
  996 #endif
  997                 ipopts = ip_srcroute(m);
  998 
  999         /*
 1000          * See if we already have an entry for this connection.
 1001          * If we do, resend the SYN,ACK, and reset the retransmit timer.
 1002          *
 1003          * XXX
 1004          * The syncache should be re-initialized with the contents
 1005          * of the new SYN which may have different options.
 1006          */
 1007         sc = syncache_lookup(inc, &sch);
 1008         if (sc != NULL) {
 1009                 tcpstat.tcps_sc_dupsyn++;
 1010                 if (ipopts) {
 1011                         /*
 1012                          * If we were remembering a previous source route,
 1013                          * forget it and use the new one we've been given.
 1014                          */
 1015                         if (sc->sc_ipopts)
 1016                                 m_free(sc->sc_ipopts);
 1017                         sc->sc_ipopts = ipopts;
 1018                 }
 1019                 /*
 1020                  * Update timestamp if present.
 1021                  */
 1022                 if (sc->sc_flags & SCF_TIMESTAMP)
 1023                         sc->sc_tsrecent = to->to_tsval;
 1024 
 1025                 /* Just update the TOF_SACK_PERMITTED for now. */
 1026                 if (tcp_do_sack && (to->to_flags & TOF_SACK_PERMITTED))
 1027                         sc->sc_flags |= SCF_SACK_PERMITTED;
 1028                 else
 1029                         sc->sc_flags &= ~SCF_SACK_PERMITTED;
 1030 
 1031                 /* Update initial send window */
 1032                 sc->sc_sndwnd = th->th_win;
 1033 
 1034                 /*
 1035                  * PCB may have changed, pick up new values.
 1036                  */
 1037                 sc->sc_tp = tp;
 1038                 sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
 1039                 if (syncache_respond(sc, m) == 0) {
 1040                         TAILQ_REMOVE(&syncache_percpu->timerq[sc->sc_rxtslot],
 1041                                      sc, sc_timerq);
 1042                         syncache_timeout(syncache_percpu, sc, sc->sc_rxtslot);
 1043                         tcpstat.tcps_sndacks++;
 1044                         tcpstat.tcps_sndtotal++;
 1045                 }
 1046                 return (1);
 1047         }
 1048 
 1049         /*
 1050          * Fill in the syncache values.
 1051          */
 1052         sc = kmalloc(sizeof(struct syncache), M_SYNCACHE, M_WAITOK|M_ZERO);
 1053         sc->sc_inp_gencnt = tp->t_inpcb->inp_gencnt;
 1054         sc->sc_ipopts = ipopts;
 1055         sc->sc_inc.inc_fport = inc->inc_fport;
 1056         sc->sc_inc.inc_lport = inc->inc_lport;
 1057         sc->sc_tp = tp;
 1058 #ifdef INET6
 1059         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
 1060         if (inc->inc_isipv6) {
 1061                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
 1062                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
 1063                 sc->sc_route6.ro_rt = NULL;
 1064         } else
 1065 #endif
 1066         {
 1067                 sc->sc_inc.inc_faddr = inc->inc_faddr;
 1068                 sc->sc_inc.inc_laddr = inc->inc_laddr;
 1069                 sc->sc_route.ro_rt = NULL;
 1070         }
 1071         sc->sc_irs = th->th_seq;
 1072         sc->sc_flags = 0;
 1073         sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0;
 1074         if (tcp_syncookies)
 1075                 sc->sc_iss = syncookie_generate(sc);
 1076         else
 1077                 sc->sc_iss = karc4random();
 1078 
 1079         /* Initial receive window: clip ssb_space to [0 .. TCP_MAXWIN] */
 1080         win = ssb_space(&so->so_rcv);
 1081         win = imax(win, 0);
 1082         win = imin(win, TCP_MAXWIN);
 1083         sc->sc_wnd = win;
 1084 
 1085         if (tcp_do_rfc1323) {
 1086                 /*
 1087                  * A timestamp received in a SYN makes
 1088                  * it ok to send timestamp requests and replies.
 1089                  */
 1090                 if (to->to_flags & TOF_TS) {
 1091                         sc->sc_tsrecent = to->to_tsval;
 1092                         sc->sc_flags |= SCF_TIMESTAMP;
 1093                 }
 1094                 if (to->to_flags & TOF_SCALE) {
 1095                         int wscale = TCP_MIN_WINSHIFT;
 1096 
 1097                         /* Compute proper scaling value from buffer space */
 1098                         while (wscale < TCP_MAX_WINSHIFT &&
 1099                             (TCP_MAXWIN << wscale) < so->so_rcv.ssb_hiwat) {
 1100                                 wscale++;
 1101                         }
 1102                         sc->sc_request_r_scale = wscale;
 1103                         sc->sc_requested_s_scale = to->to_requested_s_scale;
 1104                         sc->sc_flags |= SCF_WINSCALE;
 1105                 }
 1106         }
 1107         if (tcp_do_sack && (to->to_flags & TOF_SACK_PERMITTED))
 1108                 sc->sc_flags |= SCF_SACK_PERMITTED;
 1109         if (tp->t_flags & TF_NOOPT)
 1110                 sc->sc_flags = SCF_NOOPT;
 1111 #ifdef TCP_SIGNATURE
 1112         /*
 1113          * If listening socket requested TCP digests, and received SYN
 1114          * contains the option, flag this in the syncache so that
 1115          * syncache_respond() will do the right thing with the SYN+ACK.
 1116          * XXX Currently we always record the option by default and will
 1117          * attempt to use it in syncache_respond().
 1118          */
 1119         if (to->to_flags & TOF_SIGNATURE)
 1120                 sc->sc_flags = SCF_SIGNATURE;
 1121 #endif /* TCP_SIGNATURE */
 1122         sc->sc_sndwnd = th->th_win;
 1123 
 1124         if (syncache_respond(sc, m) == 0) {
 1125                 syncache_insert(sc, sch);
 1126                 tcpstat.tcps_sndacks++;
 1127                 tcpstat.tcps_sndtotal++;
 1128         } else {
 1129                 syncache_free(sc);
 1130                 tcpstat.tcps_sc_dropped++;
 1131         }
 1132         return (1);
 1133 }
 1134 
 1135 static int
 1136 syncache_respond(struct syncache *sc, struct mbuf *m)
 1137 {
 1138         u_int8_t *optp;
 1139         int optlen, error;
 1140         u_int16_t tlen, hlen, mssopt;
 1141         struct ip *ip = NULL;
 1142         struct rtentry *rt;
 1143         struct tcphdr *th;
 1144         struct ip6_hdr *ip6 = NULL;
 1145 #ifdef INET6
 1146         const boolean_t isipv6 = sc->sc_inc.inc_isipv6;
 1147 #else
 1148         const boolean_t isipv6 = FALSE;
 1149 #endif
 1150 
 1151         if (isipv6) {
 1152                 rt = tcp_rtlookup6(&sc->sc_inc);
 1153                 if (rt != NULL)
 1154                         mssopt = rt->rt_ifp->if_mtu -
 1155                              (sizeof(struct ip6_hdr) + sizeof(struct tcphdr));
 1156                 else
 1157                         mssopt = tcp_v6mssdflt;
 1158                 hlen = sizeof(struct ip6_hdr);
 1159         } else {
 1160                 rt = tcp_rtlookup(&sc->sc_inc);
 1161                 if (rt != NULL)
 1162                         mssopt = rt->rt_ifp->if_mtu -
 1163                              (sizeof(struct ip) + sizeof(struct tcphdr));
 1164                 else
 1165                         mssopt = tcp_mssdflt;
 1166                 hlen = sizeof(struct ip);
 1167         }
 1168 
 1169         /* Compute the size of the TCP options. */
 1170         if (sc->sc_flags & SCF_NOOPT) {
 1171                 optlen = 0;
 1172         } else {
 1173                 optlen = TCPOLEN_MAXSEG +
 1174                     ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
 1175                     ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0) +
 1176                     ((sc->sc_flags & SCF_SACK_PERMITTED) ?
 1177                         TCPOLEN_SACK_PERMITTED_ALIGNED : 0);
 1178 #ifdef TCP_SIGNATURE
 1179                 optlen += ((sc->sc_flags & SCF_SIGNATURE) ?
 1180                     (TCPOLEN_SIGNATURE + 2) : 0);
 1181 #endif /* TCP_SIGNATURE */
 1182         }
 1183         tlen = hlen + sizeof(struct tcphdr) + optlen;
 1184 
 1185         /*
 1186          * XXX
 1187          * assume that the entire packet will fit in a header mbuf
 1188          */
 1189         KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
 1190 
 1191         /*
 1192          * XXX shouldn't this reuse the mbuf if possible ?
 1193          * Create the IP+TCP header from scratch.
 1194          */
 1195         if (m)
 1196                 m_freem(m);
 1197 
 1198         m = m_gethdr(MB_DONTWAIT, MT_HEADER);
 1199         if (m == NULL)
 1200                 return (ENOBUFS);
 1201         m->m_data += max_linkhdr;
 1202         m->m_len = tlen;
 1203         m->m_pkthdr.len = tlen;
 1204         m->m_pkthdr.rcvif = NULL;
 1205         if (tcp_prio_synack)
 1206                 m->m_flags |= M_PRIO;
 1207 
 1208         if (isipv6) {
 1209                 ip6 = mtod(m, struct ip6_hdr *);
 1210                 ip6->ip6_vfc = IPV6_VERSION;
 1211                 ip6->ip6_nxt = IPPROTO_TCP;
 1212                 ip6->ip6_src = sc->sc_inc.inc6_laddr;
 1213                 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
 1214                 ip6->ip6_plen = htons(tlen - hlen);
 1215                 /* ip6_hlim is set after checksum */
 1216                 /* ip6_flow = ??? */
 1217 
 1218                 th = (struct tcphdr *)(ip6 + 1);
 1219         } else {
 1220                 ip = mtod(m, struct ip *);
 1221                 ip->ip_v = IPVERSION;
 1222                 ip->ip_hl = sizeof(struct ip) >> 2;
 1223                 ip->ip_len = tlen;
 1224                 ip->ip_id = 0;
 1225                 ip->ip_off = 0;
 1226                 ip->ip_sum = 0;
 1227                 ip->ip_p = IPPROTO_TCP;
 1228                 ip->ip_src = sc->sc_inc.inc_laddr;
 1229                 ip->ip_dst = sc->sc_inc.inc_faddr;
 1230                 ip->ip_ttl = sc->sc_tp->t_inpcb->inp_ip_ttl;   /* XXX */
 1231                 ip->ip_tos = sc->sc_tp->t_inpcb->inp_ip_tos;   /* XXX */
 1232 
 1233                 /*
 1234                  * See if we should do MTU discovery.  Route lookups are
 1235                  * expensive, so we will only unset the DF bit if:
 1236                  *
 1237                  *      1) path_mtu_discovery is disabled
 1238                  *      2) the SCF_UNREACH flag has been set
 1239                  */
 1240                 if (path_mtu_discovery
 1241                     && ((sc->sc_flags & SCF_UNREACH) == 0)) {
 1242                        ip->ip_off |= IP_DF;
 1243                 }
 1244 
 1245                 th = (struct tcphdr *)(ip + 1);
 1246         }
 1247         th->th_sport = sc->sc_inc.inc_lport;
 1248         th->th_dport = sc->sc_inc.inc_fport;
 1249 
 1250         th->th_seq = htonl(sc->sc_iss);
 1251         th->th_ack = htonl(sc->sc_irs + 1);
 1252         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 1253         th->th_x2 = 0;
 1254         th->th_flags = TH_SYN | TH_ACK;
 1255         th->th_win = htons(sc->sc_wnd);
 1256         th->th_urp = 0;
 1257 
 1258         /* Tack on the TCP options. */
 1259         if (optlen == 0)
 1260                 goto no_options;
 1261         optp = (u_int8_t *)(th + 1);
 1262         *optp++ = TCPOPT_MAXSEG;
 1263         *optp++ = TCPOLEN_MAXSEG;
 1264         *optp++ = (mssopt >> 8) & 0xff;
 1265         *optp++ = mssopt & 0xff;
 1266 
 1267         if (sc->sc_flags & SCF_WINSCALE) {
 1268                 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
 1269                     TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
 1270                     sc->sc_request_r_scale);
 1271                 optp += 4;
 1272         }
 1273 
 1274         if (sc->sc_flags & SCF_TIMESTAMP) {
 1275                 u_int32_t *lp = (u_int32_t *)(optp);
 1276 
 1277                 /* Form timestamp option as shown in appendix A of RFC 1323. */
 1278                 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
 1279                 *lp++ = htonl(ticks);
 1280                 *lp   = htonl(sc->sc_tsrecent);
 1281                 optp += TCPOLEN_TSTAMP_APPA;
 1282         }
 1283 
 1284 #ifdef TCP_SIGNATURE
 1285         /*
 1286          * Handle TCP-MD5 passive opener response.
 1287          */
 1288         if (sc->sc_flags & SCF_SIGNATURE) {
 1289                 u_int8_t *bp = optp;
 1290                 int i;
 1291 
 1292                 *bp++ = TCPOPT_SIGNATURE;
 1293                 *bp++ = TCPOLEN_SIGNATURE;
 1294                 for (i = 0; i < TCP_SIGLEN; i++)
 1295                         *bp++ = 0;
 1296                 tcpsignature_compute(m, 0, optlen,
 1297                                 optp + 2, IPSEC_DIR_OUTBOUND);
 1298                 *bp++ = TCPOPT_NOP;
 1299                 *bp++ = TCPOPT_EOL;
 1300                 optp += TCPOLEN_SIGNATURE + 2;
 1301         }
 1302 #endif /* TCP_SIGNATURE */
 1303 
 1304         if (sc->sc_flags & SCF_SACK_PERMITTED) {
 1305                 *((u_int32_t *)optp) = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
 1306                 optp += TCPOLEN_SACK_PERMITTED_ALIGNED;
 1307         }
 1308 
 1309 no_options:
 1310         if (isipv6) {
 1311                 struct route_in6 *ro6 = &sc->sc_route6;
 1312 
 1313                 th->th_sum = 0;
 1314                 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
 1315                 ip6->ip6_hlim = in6_selecthlim(NULL,
 1316                     ro6->ro_rt ? ro6->ro_rt->rt_ifp : NULL);
 1317                 error = ip6_output(m, NULL, ro6, 0, NULL, NULL,
 1318                                 sc->sc_tp->t_inpcb);
 1319         } else {
 1320                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1321                                        htons(tlen - hlen + IPPROTO_TCP));
 1322                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1323                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1324                 m->m_pkthdr.csum_thlen = sizeof(struct tcphdr) + optlen;
 1325                 error = ip_output(m, sc->sc_ipopts, &sc->sc_route,
 1326                                   IP_DEBUGROUTE, NULL, sc->sc_tp->t_inpcb);
 1327         }
 1328         return (error);
 1329 }
 1330 
 1331 /*
 1332  * cookie layers:
 1333  *
 1334  *      |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|
 1335  *      | peer iss                                                      |
 1336  *      | MD5(laddr,faddr,secret,lport,fport)             |. . . . . . .|
 1337  *      |                     0                       |(A)|             |
 1338  * (A): peer mss index
 1339  */
 1340 
 1341 /*
 1342  * The values below are chosen to minimize the size of the tcp_secret
 1343  * table, as well as providing roughly a 16 second lifetime for the cookie.
 1344  */
 1345 
 1346 #define SYNCOOKIE_WNDBITS       5       /* exposed bits for window indexing */
 1347 #define SYNCOOKIE_TIMESHIFT     1       /* scale ticks to window time units */
 1348 
 1349 #define SYNCOOKIE_WNDMASK       ((1 << SYNCOOKIE_WNDBITS) - 1)
 1350 #define SYNCOOKIE_NSECRETS      (1 << SYNCOOKIE_WNDBITS)
 1351 #define SYNCOOKIE_TIMEOUT \
 1352     (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT))
 1353 #define SYNCOOKIE_DATAMASK      ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK)
 1354 
 1355 static struct {
 1356         u_int32_t       ts_secbits[4];
 1357         u_int           ts_expire;
 1358 } tcp_secret[SYNCOOKIE_NSECRETS];
 1359 
 1360 static int tcp_msstab[] = { 0, 536, 1460, 8960 };
 1361 
 1362 static MD5_CTX syn_ctx;
 1363 
 1364 #define MD5Add(v)       MD5Update(&syn_ctx, (u_char *)&v, sizeof(v))
 1365 
 1366 struct md5_add {
 1367         u_int32_t laddr, faddr;
 1368         u_int32_t secbits[4];
 1369         u_int16_t lport, fport;
 1370 };
 1371 
 1372 #ifdef CTASSERT
 1373 CTASSERT(sizeof(struct md5_add) == 28);
 1374 #endif
 1375 
 1376 /*
 1377  * Consider the problem of a recreated (and retransmitted) cookie.  If the
 1378  * original SYN was accepted, the connection is established.  The second
 1379  * SYN is inflight, and if it arrives with an ISN that falls within the
 1380  * receive window, the connection is killed.
 1381  *
 1382  * However, since cookies have other problems, this may not be worth
 1383  * worrying about.
 1384  */
 1385 
 1386 static u_int32_t
 1387 syncookie_generate(struct syncache *sc)
 1388 {
 1389         u_int32_t md5_buffer[4];
 1390         u_int32_t data;
 1391         int idx, i;
 1392         struct md5_add add;
 1393 #ifdef INET6
 1394         const boolean_t isipv6 = sc->sc_inc.inc_isipv6;
 1395 #else
 1396         const boolean_t isipv6 = FALSE;
 1397 #endif
 1398 
 1399         idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK;
 1400         if (tcp_secret[idx].ts_expire < ticks) {
 1401                 for (i = 0; i < 4; i++)
 1402                         tcp_secret[idx].ts_secbits[i] = karc4random();
 1403                 tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT;
 1404         }
 1405         for (data = NELEM(tcp_msstab) - 1; data > 0; data--)
 1406                 if (tcp_msstab[data] <= sc->sc_peer_mss)
 1407                         break;
 1408         data = (data << SYNCOOKIE_WNDBITS) | idx;
 1409         data ^= sc->sc_irs;                             /* peer's iss */
 1410         MD5Init(&syn_ctx);
 1411         if (isipv6) {
 1412                 MD5Add(sc->sc_inc.inc6_laddr);
 1413                 MD5Add(sc->sc_inc.inc6_faddr);
 1414                 add.laddr = 0;
 1415                 add.faddr = 0;
 1416         } else {
 1417                 add.laddr = sc->sc_inc.inc_laddr.s_addr;
 1418                 add.faddr = sc->sc_inc.inc_faddr.s_addr;
 1419         }
 1420         add.lport = sc->sc_inc.inc_lport;
 1421         add.fport = sc->sc_inc.inc_fport;
 1422         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1423         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1424         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1425         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1426         MD5Add(add);
 1427         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1428         data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK);
 1429         return (data);
 1430 }
 1431 
 1432 static struct syncache *
 1433 syncookie_lookup(struct in_conninfo *inc, struct tcphdr *th, struct socket *so)
 1434 {
 1435         u_int32_t md5_buffer[4];
 1436         struct syncache *sc;
 1437         u_int32_t data;
 1438         int wnd, idx;
 1439         struct md5_add add;
 1440 
 1441         data = (th->th_ack - 1) ^ (th->th_seq - 1);     /* remove ISS */
 1442         idx = data & SYNCOOKIE_WNDMASK;
 1443         if (tcp_secret[idx].ts_expire < ticks ||
 1444             sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks)
 1445                 return (NULL);
 1446         MD5Init(&syn_ctx);
 1447 #ifdef INET6
 1448         if (inc->inc_isipv6) {
 1449                 MD5Add(inc->inc6_laddr);
 1450                 MD5Add(inc->inc6_faddr);
 1451                 add.laddr = 0;
 1452                 add.faddr = 0;
 1453         } else
 1454 #endif
 1455         {
 1456                 add.laddr = inc->inc_laddr.s_addr;
 1457                 add.faddr = inc->inc_faddr.s_addr;
 1458         }
 1459         add.lport = inc->inc_lport;
 1460         add.fport = inc->inc_fport;
 1461         add.secbits[0] = tcp_secret[idx].ts_secbits[0];
 1462         add.secbits[1] = tcp_secret[idx].ts_secbits[1];
 1463         add.secbits[2] = tcp_secret[idx].ts_secbits[2];
 1464         add.secbits[3] = tcp_secret[idx].ts_secbits[3];
 1465         MD5Add(add);
 1466         MD5Final((u_char *)&md5_buffer, &syn_ctx);
 1467         data ^= md5_buffer[0];
 1468         if (data & ~SYNCOOKIE_DATAMASK)
 1469                 return (NULL);
 1470         data = data >> SYNCOOKIE_WNDBITS;
 1471 
 1472         /*
 1473          * Fill in the syncache values.
 1474          * XXX duplicate code from syncache_add
 1475          */
 1476         sc = kmalloc(sizeof(struct syncache), M_SYNCACHE, M_WAITOK|M_ZERO);
 1477         sc->sc_ipopts = NULL;
 1478         sc->sc_inc.inc_fport = inc->inc_fport;
 1479         sc->sc_inc.inc_lport = inc->inc_lport;
 1480 #ifdef INET6
 1481         sc->sc_inc.inc_isipv6 = inc->inc_isipv6;
 1482         if (inc->inc_isipv6) {
 1483                 sc->sc_inc.inc6_faddr = inc->inc6_faddr;
 1484                 sc->sc_inc.inc6_laddr = inc->inc6_laddr;
 1485                 sc->sc_route6.ro_rt = NULL;
 1486         } else
 1487 #endif
 1488         {
 1489                 sc->sc_inc.inc_faddr = inc->inc_faddr;
 1490                 sc->sc_inc.inc_laddr = inc->inc_laddr;
 1491                 sc->sc_route.ro_rt = NULL;
 1492         }
 1493         sc->sc_irs = th->th_seq - 1;
 1494         sc->sc_iss = th->th_ack - 1;
 1495         wnd = ssb_space(&so->so_rcv);
 1496         wnd = imax(wnd, 0);
 1497         wnd = imin(wnd, TCP_MAXWIN);
 1498         sc->sc_wnd = wnd;
 1499         sc->sc_flags = 0;
 1500         sc->sc_rxtslot = 0;
 1501         sc->sc_peer_mss = tcp_msstab[data];
 1502         return (sc);
 1503 }

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