2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * This software was developed for the FreeBSD Project by Jonathan Lemon
7 * and McAfee Research, the Security Research Division of McAfee, Inc. under
8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
9 * DARPA CHATS research program. [2001 McAfee, Inc.]
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39 #include "opt_pcbgroup.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
44 #include <sys/refcount.h>
45 #include <sys/kernel.h>
46 #include <sys/sysctl.h>
47 #include <sys/limits.h>
49 #include <sys/mutex.h>
50 #include <sys/malloc.h>
52 #include <sys/proc.h> /* for proc0 declaration */
53 #include <sys/random.h>
54 #include <sys/socket.h>
55 #include <sys/socketvar.h>
56 #include <sys/syslog.h>
57 #include <sys/ucred.h>
60 #include <crypto/siphash/siphash.h>
65 #include <net/if_var.h>
66 #include <net/route.h>
69 #include <netinet/in.h>
70 #include <netinet/in_systm.h>
71 #include <netinet/ip.h>
72 #include <netinet/in_var.h>
73 #include <netinet/in_pcb.h>
74 #include <netinet/ip_var.h>
75 #include <netinet/ip_options.h>
77 #include <netinet/ip6.h>
78 #include <netinet/icmp6.h>
79 #include <netinet6/nd6.h>
80 #include <netinet6/ip6_var.h>
81 #include <netinet6/in6_pcb.h>
83 #include <netinet/tcp.h>
85 #include <netinet/tcp_fastopen.h>
87 #include <netinet/tcp_fsm.h>
88 #include <netinet/tcp_seq.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcp_var.h>
91 #include <netinet/tcp_syncache.h>
93 #include <netinet6/tcp6_var.h>
96 #include <netinet/toecore.h>
100 #include <netipsec/ipsec.h>
102 #include <netipsec/ipsec6.h>
104 #include <netipsec/key.h>
107 #include <machine/in_cksum.h>
109 #include <security/mac/mac_framework.h>
111 static VNET_DEFINE(int, tcp_syncookies) = 1;
112 #define V_tcp_syncookies VNET(tcp_syncookies)
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookies), 0,
115 "Use TCP SYN cookies if the syncache overflows");
117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
118 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
120 &VNET_NAME(tcp_syncookiesonly), 0,
121 "Use only TCP SYN cookies");
124 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
127 static void syncache_drop(struct syncache *, struct syncache_head *);
128 static void syncache_free(struct syncache *);
129 static void syncache_insert(struct syncache *, struct syncache_head *);
130 static int syncache_respond(struct syncache *, struct syncache_head *, int);
131 static struct socket *syncache_socket(struct syncache *, struct socket *,
133 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
135 static void syncache_timer(void *);
137 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
138 uint8_t *, uintptr_t);
139 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
140 static struct syncache
141 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
142 struct syncache *, struct tcphdr *, struct tcpopt *,
144 static void syncookie_reseed(void *);
146 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
147 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
152 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
153 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
154 * the odds are that the user has given up attempting to connect by then.
156 #define SYNCACHE_MAXREXMTS 3
158 /* Arbitrary values */
159 #define TCP_SYNCACHE_HASHSIZE 512
160 #define TCP_SYNCACHE_BUCKETLIMIT 30
162 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
163 #define V_tcp_syncache VNET(tcp_syncache)
165 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
168 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
169 &VNET_NAME(tcp_syncache.bucket_limit), 0,
170 "Per-bucket hash limit for syncache");
172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
173 &VNET_NAME(tcp_syncache.cache_limit), 0,
174 "Overall entry limit for syncache");
176 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
177 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
180 &VNET_NAME(tcp_syncache.hashsize), 0,
181 "Size of TCP syncache hashtable");
183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
184 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
185 "Limit on SYN/ACK retransmissions");
187 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
188 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
189 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
190 "Send reset on socket allocation failure");
192 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
194 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
195 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
196 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
199 * Requires the syncache entry to be already removed from the bucket list.
202 syncache_free(struct syncache *sc)
206 (void) m_free(sc->sc_ipopts);
210 mac_syncache_destroy(&sc->sc_label);
213 uma_zfree(V_tcp_syncache.zone, sc);
221 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
222 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
223 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
224 V_tcp_syncache.hash_secret = arc4random();
226 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
227 &V_tcp_syncache.hashsize);
228 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
229 &V_tcp_syncache.bucket_limit);
230 if (!powerof2(V_tcp_syncache.hashsize) ||
231 V_tcp_syncache.hashsize == 0) {
232 printf("WARNING: syncache hash size is not a power of 2.\n");
233 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
235 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
238 V_tcp_syncache.cache_limit =
239 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
240 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
241 &V_tcp_syncache.cache_limit);
243 /* Allocate the hash table. */
244 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
245 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
248 V_tcp_syncache.vnet = curvnet;
251 /* Initialize the hash buckets. */
252 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
253 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
254 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
256 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
257 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
258 V_tcp_syncache.hashbase[i].sch_length = 0;
259 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
262 /* Create the syncache entry zone. */
263 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
264 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
265 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
266 V_tcp_syncache.cache_limit);
268 /* Start the SYN cookie reseeder callout. */
269 callout_init(&V_tcp_syncache.secret.reseed, 1);
270 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
271 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
272 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
273 syncookie_reseed, &V_tcp_syncache);
278 syncache_destroy(void)
280 struct syncache_head *sch;
281 struct syncache *sc, *nsc;
285 * Stop the re-seed timer before freeing resources. No need to
286 * possibly schedule it another time.
288 callout_drain(&V_tcp_syncache.secret.reseed);
290 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
291 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
293 sch = &V_tcp_syncache.hashbase[i];
294 callout_drain(&sch->sch_timer);
297 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
298 syncache_drop(sc, sch);
300 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
301 ("%s: sch->sch_bucket not empty", __func__));
302 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
303 __func__, sch->sch_length));
304 mtx_destroy(&sch->sch_mtx);
307 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
308 ("%s: cache_count not 0", __func__));
310 /* Free the allocated global resources. */
311 uma_zdestroy(V_tcp_syncache.zone);
312 free(V_tcp_syncache.hashbase, M_SYNCACHE);
317 * Inserts a syncache entry into the specified bucket row.
318 * Locks and unlocks the syncache_head autonomously.
321 syncache_insert(struct syncache *sc, struct syncache_head *sch)
323 struct syncache *sc2;
328 * Make sure that we don't overflow the per-bucket limit.
329 * If the bucket is full, toss the oldest element.
331 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
332 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
333 ("sch->sch_length incorrect"));
334 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
335 syncache_drop(sc2, sch);
336 TCPSTAT_INC(tcps_sc_bucketoverflow);
339 /* Put it into the bucket. */
340 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
344 if (ADDED_BY_TOE(sc)) {
345 struct toedev *tod = sc->sc_tod;
347 tod->tod_syncache_added(tod, sc->sc_todctx);
351 /* Reinitialize the bucket row's timer. */
352 if (sch->sch_length == 1)
353 sch->sch_nextc = ticks + INT_MAX;
354 syncache_timeout(sc, sch, 1);
358 TCPSTATES_INC(TCPS_SYN_RECEIVED);
359 TCPSTAT_INC(tcps_sc_added);
363 * Remove and free entry from syncache bucket row.
364 * Expects locked syncache head.
367 syncache_drop(struct syncache *sc, struct syncache_head *sch)
370 SCH_LOCK_ASSERT(sch);
372 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
373 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
377 if (ADDED_BY_TOE(sc)) {
378 struct toedev *tod = sc->sc_tod;
380 tod->tod_syncache_removed(tod, sc->sc_todctx);
388 * Engage/reengage time on bucket row.
391 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
393 sc->sc_rxttime = ticks +
394 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
396 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
397 sch->sch_nextc = sc->sc_rxttime;
399 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
400 syncache_timer, (void *)sch);
405 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
406 * If we have retransmitted an entry the maximum number of times, expire it.
407 * One separate timer for each bucket row.
410 syncache_timer(void *xsch)
412 struct syncache_head *sch = (struct syncache_head *)xsch;
413 struct syncache *sc, *nsc;
417 CURVNET_SET(sch->sch_sc->vnet);
419 /* NB: syncache_head has already been locked by the callout. */
420 SCH_LOCK_ASSERT(sch);
423 * In the following cycle we may remove some entries and/or
424 * advance some timeouts, so re-initialize the bucket timer.
426 sch->sch_nextc = tick + INT_MAX;
428 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
430 * We do not check if the listen socket still exists
431 * and accept the case where the listen socket may be
432 * gone by the time we resend the SYN/ACK. We do
433 * not expect this to happens often. If it does,
434 * then the RST will be sent by the time the remote
435 * host does the SYN/ACK->ACK.
437 if (TSTMP_GT(sc->sc_rxttime, tick)) {
438 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
439 sch->sch_nextc = sc->sc_rxttime;
442 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
443 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
444 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
445 "giving up and removing syncache entry\n",
449 syncache_drop(sc, sch);
450 TCPSTAT_INC(tcps_sc_stale);
453 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
454 log(LOG_DEBUG, "%s; %s: Response timeout, "
455 "retransmitting (%u) SYN|ACK\n",
456 s, __func__, sc->sc_rxmits);
460 syncache_respond(sc, sch, 1);
461 TCPSTAT_INC(tcps_sc_retransmitted);
462 syncache_timeout(sc, sch, 0);
464 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
465 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
466 syncache_timer, (void *)(sch));
471 * Find an entry in the syncache.
472 * Returns always with locked syncache_head plus a matching entry or NULL.
474 static struct syncache *
475 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
478 struct syncache_head *sch;
482 * The hash is built on foreign port + local port + foreign address.
483 * We rely on the fact that struct in_conninfo starts with 16 bits
484 * of foreign port, then 16 bits of local port then followed by 128
485 * bits of foreign address. In case of IPv4 address, the first 3
486 * 32-bit words of the address always are zeroes.
488 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
489 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
491 sch = &V_tcp_syncache.hashbase[hash];
495 /* Circle through bucket row to find matching entry. */
496 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
497 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
498 sizeof(struct in_endpoints)) == 0)
501 return (sc); /* Always returns with locked sch. */
505 * This function is called when we get a RST for a
506 * non-existent connection, so that we can see if the
507 * connection is in the syn cache. If it is, zap it.
510 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
513 struct syncache_head *sch;
516 sc = syncache_lookup(inc, &sch); /* returns locked sch */
517 SCH_LOCK_ASSERT(sch);
520 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
521 * See RFC 793 page 65, section SEGMENT ARRIVES.
523 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
524 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
525 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
526 "FIN flag set, segment ignored\n", s, __func__);
527 TCPSTAT_INC(tcps_badrst);
532 * No corresponding connection was found in syncache.
533 * If syncookies are enabled and possibly exclusively
534 * used, or we are under memory pressure, a valid RST
535 * may not find a syncache entry. In that case we're
536 * done and no SYN|ACK retransmissions will happen.
537 * Otherwise the RST was misdirected or spoofed.
540 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
541 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
542 "syncache entry (possibly syncookie only), "
543 "segment ignored\n", s, __func__);
544 TCPSTAT_INC(tcps_badrst);
549 * If the RST bit is set, check the sequence number to see
550 * if this is a valid reset segment.
552 * In all states except SYN-SENT, all reset (RST) segments
553 * are validated by checking their SEQ-fields. A reset is
554 * valid if its sequence number is in the window.
556 * The sequence number in the reset segment is normally an
557 * echo of our outgoing acknowlegement numbers, but some hosts
558 * send a reset with the sequence number at the rightmost edge
559 * of our receive window, and we have to handle this case.
561 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
562 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
563 syncache_drop(sc, sch);
564 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
565 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
566 "connection attempt aborted by remote endpoint\n",
568 TCPSTAT_INC(tcps_sc_reset);
570 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
571 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
572 "IRS %u (+WND %u), segment ignored\n",
573 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
574 TCPSTAT_INC(tcps_badrst);
584 syncache_badack(struct in_conninfo *inc)
587 struct syncache_head *sch;
589 sc = syncache_lookup(inc, &sch); /* returns locked sch */
590 SCH_LOCK_ASSERT(sch);
592 syncache_drop(sc, sch);
593 TCPSTAT_INC(tcps_sc_badack);
599 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
602 struct syncache_head *sch;
604 sc = syncache_lookup(inc, &sch); /* returns locked sch */
605 SCH_LOCK_ASSERT(sch);
609 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
610 if (ntohl(th->th_seq) != sc->sc_iss)
614 * If we've rertransmitted 3 times and this is our second error,
615 * we remove the entry. Otherwise, we allow it to continue on.
616 * This prevents us from incorrectly nuking an entry during a
617 * spurious network outage.
621 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
622 sc->sc_flags |= SCF_UNREACH;
625 syncache_drop(sc, sch);
626 TCPSTAT_INC(tcps_sc_unreach);
632 * Build a new TCP socket structure from a syncache entry.
634 * On success return the newly created socket with its underlying inp locked.
636 static struct socket *
637 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
639 struct tcp_function_block *blk;
640 struct inpcb *inp = NULL;
646 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
649 * Ok, create the full blown connection, and set things up
650 * as they would have been set up if we had created the
651 * connection when the SYN arrived. If we can't create
652 * the connection, abort it.
654 so = sonewconn(lso, 0);
657 * Drop the connection; we will either send a RST or
658 * have the peer retransmit its SYN again after its
661 TCPSTAT_INC(tcps_listendrop);
662 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
663 log(LOG_DEBUG, "%s; %s: Socket create failed "
664 "due to limits or memory shortage\n",
671 mac_socketpeer_set_from_mbuf(m, so);
675 inp->inp_inc.inc_fibnum = so->so_fibnum;
678 * Exclusive pcbinfo lock is not required in syncache socket case even
679 * if two inpcb locks can be acquired simultaneously:
680 * - the inpcb in LISTEN state,
681 * - the newly created inp.
683 * In this case, an inp cannot be at same time in LISTEN state and
684 * just created by an accept() call.
686 INP_HASH_WLOCK(&V_tcbinfo);
688 /* Insert new socket into PCB hash list. */
689 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
691 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
692 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
694 inp->inp_vflag &= ~INP_IPV6;
695 inp->inp_vflag |= INP_IPV4;
697 inp->inp_laddr = sc->sc_inc.inc_laddr;
703 * If there's an mbuf and it has a flowid, then let's initialise the
704 * inp with that particular flowid.
706 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
707 inp->inp_flowid = m->m_pkthdr.flowid;
708 inp->inp_flowtype = M_HASHTYPE_GET(m);
712 * Install in the reservation hash table for now, but don't yet
713 * install a connection group since the full 4-tuple isn't yet
716 inp->inp_lport = sc->sc_inc.inc_lport;
717 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
719 * Undo the assignments above if we failed to
720 * put the PCB on the hash lists.
723 if (sc->sc_inc.inc_flags & INC_ISIPV6)
724 inp->in6p_laddr = in6addr_any;
727 inp->inp_laddr.s_addr = INADDR_ANY;
729 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
730 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
735 INP_HASH_WUNLOCK(&V_tcbinfo);
739 /* Copy old policy into new socket's. */
740 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
741 printf("syncache_socket: could not copy policy\n");
744 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
745 struct inpcb *oinp = sotoinpcb(lso);
746 struct in6_addr laddr6;
747 struct sockaddr_in6 sin6;
749 * Inherit socket options from the listening socket.
750 * Note that in6p_inputopts are not (and should not be)
751 * copied, since it stores previously received options and is
752 * used to detect if each new option is different than the
753 * previous one and hence should be passed to a user.
754 * If we copied in6p_inputopts, a user would not be able to
755 * receive options just after calling the accept system call.
757 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
758 if (oinp->in6p_outputopts)
759 inp->in6p_outputopts =
760 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
762 sin6.sin6_family = AF_INET6;
763 sin6.sin6_len = sizeof(sin6);
764 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
765 sin6.sin6_port = sc->sc_inc.inc_fport;
766 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
767 laddr6 = inp->in6p_laddr;
768 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
769 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
770 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
771 thread0.td_ucred, m)) != 0) {
772 inp->in6p_laddr = laddr6;
773 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
774 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
779 INP_HASH_WUNLOCK(&V_tcbinfo);
782 /* Override flowlabel from in6_pcbconnect. */
783 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
784 inp->inp_flow |= sc->sc_flowlabel;
787 #if defined(INET) && defined(INET6)
792 struct in_addr laddr;
793 struct sockaddr_in sin;
795 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
797 if (inp->inp_options == NULL) {
798 inp->inp_options = sc->sc_ipopts;
799 sc->sc_ipopts = NULL;
802 sin.sin_family = AF_INET;
803 sin.sin_len = sizeof(sin);
804 sin.sin_addr = sc->sc_inc.inc_faddr;
805 sin.sin_port = sc->sc_inc.inc_fport;
806 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
807 laddr = inp->inp_laddr;
808 if (inp->inp_laddr.s_addr == INADDR_ANY)
809 inp->inp_laddr = sc->sc_inc.inc_laddr;
810 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
811 thread0.td_ucred, m)) != 0) {
812 inp->inp_laddr = laddr;
813 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
814 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
819 INP_HASH_WUNLOCK(&V_tcbinfo);
824 INP_HASH_WUNLOCK(&V_tcbinfo);
826 tcp_state_change(tp, TCPS_SYN_RECEIVED);
827 tp->iss = sc->sc_iss;
828 tp->irs = sc->sc_irs;
831 blk = sototcpcb(lso)->t_fb;
832 if (blk != tp->t_fb) {
834 * Our parents t_fb was not the default,
835 * we need to release our ref on tp->t_fb and
836 * pickup one on the new entry.
838 struct tcp_function_block *rblk;
840 rblk = find_and_ref_tcp_fb(blk);
841 KASSERT(rblk != NULL,
842 ("cannot find blk %p out of syncache?", blk));
843 if (tp->t_fb->tfb_tcp_fb_fini)
844 (*tp->t_fb->tfb_tcp_fb_fini)(tp);
845 refcount_release(&tp->t_fb->tfb_refcnt);
847 if (tp->t_fb->tfb_tcp_fb_init) {
848 (*tp->t_fb->tfb_tcp_fb_init)(tp);
851 tp->snd_wl1 = sc->sc_irs;
852 tp->snd_max = tp->iss + 1;
853 tp->snd_nxt = tp->iss + 1;
854 tp->rcv_up = sc->sc_irs + 1;
855 tp->rcv_wnd = sc->sc_wnd;
856 tp->rcv_adv += tp->rcv_wnd;
857 tp->last_ack_sent = tp->rcv_nxt;
859 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
860 if (sc->sc_flags & SCF_NOOPT)
861 tp->t_flags |= TF_NOOPT;
863 if (sc->sc_flags & SCF_WINSCALE) {
864 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
865 tp->snd_scale = sc->sc_requested_s_scale;
866 tp->request_r_scale = sc->sc_requested_r_scale;
868 if (sc->sc_flags & SCF_TIMESTAMP) {
869 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
870 tp->ts_recent = sc->sc_tsreflect;
871 tp->ts_recent_age = tcp_ts_getticks();
872 tp->ts_offset = sc->sc_tsoff;
875 if (sc->sc_flags & SCF_SIGNATURE)
876 tp->t_flags |= TF_SIGNATURE;
878 if (sc->sc_flags & SCF_SACK)
879 tp->t_flags |= TF_SACK_PERMIT;
882 if (sc->sc_flags & SCF_ECN)
883 tp->t_flags |= TF_ECN_PERMIT;
886 * Set up MSS and get cached values from tcp_hostcache.
887 * This might overwrite some of the defaults we just set.
889 tcp_mss(tp, sc->sc_peer_mss);
892 * If the SYN,ACK was retransmitted, indicate that CWND to be
893 * limited to one segment in cc_conn_init().
894 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
896 if (sc->sc_rxmits > 1)
901 * Allow a TOE driver to install its hooks. Note that we hold the
902 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
903 * new connection before the TOE driver has done its thing.
905 if (ADDED_BY_TOE(sc)) {
906 struct toedev *tod = sc->sc_tod;
908 tod->tod_offload_socket(tod, sc->sc_todctx, so);
912 * Copy and activate timers.
914 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
915 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
916 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
917 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
918 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
922 TCPSTAT_INC(tcps_accepts);
934 * This function gets called when we receive an ACK for a
935 * socket in the LISTEN state. We look up the connection
936 * in the syncache, and if its there, we pull it out of
937 * the cache and turn it into a full-blown connection in
938 * the SYN-RECEIVED state.
940 * On syncache_socket() success the newly created socket
941 * has its underlying inp locked.
944 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
945 struct socket **lsop, struct mbuf *m)
948 struct syncache_head *sch;
953 * Global TCP locks are held because we manipulate the PCB lists
954 * and create a new socket.
956 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
957 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
958 ("%s: can handle only ACK", __func__));
960 sc = syncache_lookup(inc, &sch); /* returns locked sch */
961 SCH_LOCK_ASSERT(sch);
965 * Test code for syncookies comparing the syncache stored
966 * values with the reconstructed values from the cookie.
969 syncookie_cmp(inc, sch, sc, th, to, *lsop);
974 * There is no syncache entry, so see if this ACK is
975 * a returning syncookie. To do this, first:
976 * A. See if this socket has had a syncache entry dropped in
977 * the past. We don't want to accept a bogus syncookie
978 * if we've never received a SYN.
979 * B. check that the syncookie is valid. If it is, then
980 * cobble up a fake syncache entry, and return.
982 if (!V_tcp_syncookies) {
984 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
985 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
986 "segment rejected (syncookies disabled)\n",
990 bzero(&scs, sizeof(scs));
991 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
994 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
995 log(LOG_DEBUG, "%s; %s: Segment failed "
996 "SYNCOOKIE authentication, segment rejected "
997 "(probably spoofed)\n", s, __func__);
1002 * Pull out the entry to unlock the bucket row.
1004 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1005 * tcp_state_change(). The tcpcb is not existent at this
1006 * moment. A new one will be allocated via syncache_socket->
1007 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1008 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1010 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1011 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1014 if (ADDED_BY_TOE(sc)) {
1015 struct toedev *tod = sc->sc_tod;
1017 tod->tod_syncache_removed(tod, sc->sc_todctx);
1024 * Segment validation:
1025 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1027 if (th->th_ack != sc->sc_iss + 1) {
1028 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1029 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1030 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1035 * The SEQ must fall in the window starting at the received
1036 * initial receive sequence number + 1 (the SYN).
1038 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1039 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1040 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1041 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1042 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1047 * If timestamps were not negotiated during SYN/ACK they
1048 * must not appear on any segment during this session.
1050 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1051 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1052 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1053 "segment rejected\n", s, __func__);
1058 * If timestamps were negotiated during SYN/ACK they should
1059 * appear on every segment during this session.
1060 * XXXAO: This is only informal as there have been unverified
1061 * reports of non-compliants stacks.
1063 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1064 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1065 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1066 "no action\n", s, __func__);
1073 * If timestamps were negotiated the reflected timestamp
1074 * must be equal to what we actually sent in the SYN|ACK.
1076 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1077 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1078 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1079 "segment rejected\n",
1080 s, __func__, to->to_tsecr, sc->sc_ts);
1084 *lsop = syncache_socket(sc, *lsop, m);
1087 TCPSTAT_INC(tcps_sc_aborted);
1089 TCPSTAT_INC(tcps_sc_completed);
1091 /* how do we find the inp for the new socket? */
1096 if (sc != NULL && sc != &scs)
1106 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1107 uint64_t response_cookie)
1111 unsigned int *pending_counter;
1114 * Global TCP locks are held because we manipulate the PCB lists
1115 * and create a new socket.
1117 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1119 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1120 *lsop = syncache_socket(sc, *lsop, m);
1121 if (*lsop == NULL) {
1122 TCPSTAT_INC(tcps_sc_aborted);
1123 atomic_subtract_int(pending_counter, 1);
1125 inp = sotoinpcb(*lsop);
1126 tp = intotcpcb(inp);
1127 tp->t_flags |= TF_FASTOPEN;
1128 tp->t_tfo_cookie = response_cookie;
1129 tp->snd_max = tp->iss;
1130 tp->snd_nxt = tp->iss;
1131 tp->t_tfo_pending = pending_counter;
1132 TCPSTAT_INC(tcps_sc_completed);
1135 #endif /* TCP_RFC7413 */
1138 * Given a LISTEN socket and an inbound SYN request, add
1139 * this to the syn cache, and send back a segment:
1140 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1143 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1144 * Doing so would require that we hold onto the data and deliver it
1145 * to the application. However, if we are the target of a SYN-flood
1146 * DoS attack, an attacker could send data which would eventually
1147 * consume all available buffer space if it were ACKed. By not ACKing
1148 * the data, we avoid this DoS scenario.
1150 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1151 * cookie is processed, V_tcp_fastopen_enabled set to true, and the
1152 * TCP_FASTOPEN socket option is set. In this case, a new socket is created
1153 * and returned via lsop, the mbuf is not freed so that tcp_input() can
1154 * queue its data to the socket, and 1 is returned to indicate the
1155 * TFO-socket-creation path was taken.
1158 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1159 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1164 struct syncache *sc = NULL;
1165 struct syncache_head *sch;
1166 struct mbuf *ipopts = NULL;
1168 int win, sb_hiwat, ip_ttl, ip_tos;
1172 int autoflowlabel = 0;
1175 struct label *maclabel;
1177 struct syncache scs;
1180 uint64_t tfo_response_cookie;
1181 int tfo_cookie_valid = 0;
1182 int tfo_response_cookie_valid = 0;
1185 INP_WLOCK_ASSERT(inp); /* listen socket */
1186 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1187 ("%s: unexpected tcp flags", __func__));
1190 * Combine all so/tp operations very early to drop the INP lock as
1195 cred = crhold(so->so_cred);
1198 if ((inc->inc_flags & INC_ISIPV6) &&
1199 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1202 ip_ttl = inp->inp_ip_ttl;
1203 ip_tos = inp->inp_ip_tos;
1204 win = sbspace(&so->so_rcv);
1205 sb_hiwat = so->so_rcv.sb_hiwat;
1206 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1209 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
1210 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1212 * Limit the number of pending TFO connections to
1213 * approximately half of the queue limit. This prevents TFO
1214 * SYN floods from starving the service by filling the
1215 * listen queue with bogus TFO connections.
1217 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1218 (so->so_qlimit / 2)) {
1221 result = tcp_fastopen_check_cookie(inc,
1222 to->to_tfo_cookie, to->to_tfo_len,
1223 &tfo_response_cookie);
1224 tfo_cookie_valid = (result > 0);
1225 tfo_response_cookie_valid = (result >= 0);
1227 atomic_subtract_int(tp->t_tfo_pending, 1);
1231 /* By the time we drop the lock these should no longer be used. */
1236 if (mac_syncache_init(&maclabel) != 0) {
1240 mac_syncache_create(maclabel, inp);
1243 if (!tfo_cookie_valid)
1248 * Remember the IP options, if any.
1251 if (!(inc->inc_flags & INC_ISIPV6))
1254 ipopts = (m) ? ip_srcroute(m) : NULL;
1260 * See if we already have an entry for this connection.
1261 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1263 * XXX: should the syncache be re-initialized with the contents
1264 * of the new SYN here (which may have different options?)
1266 * XXX: We do not check the sequence number to see if this is a
1267 * real retransmit or a new connection attempt. The question is
1268 * how to handle such a case; either ignore it as spoofed, or
1269 * drop the current entry and create a new one?
1271 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1272 SCH_LOCK_ASSERT(sch);
1275 if (tfo_cookie_valid)
1278 TCPSTAT_INC(tcps_sc_dupsyn);
1281 * If we were remembering a previous source route,
1282 * forget it and use the new one we've been given.
1285 (void) m_free(sc->sc_ipopts);
1286 sc->sc_ipopts = ipopts;
1289 * Update timestamp if present.
1291 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1292 sc->sc_tsreflect = to->to_tsval;
1294 sc->sc_flags &= ~SCF_TIMESTAMP;
1297 * Since we have already unconditionally allocated label
1298 * storage, free it up. The syncache entry will already
1299 * have an initialized label we can use.
1301 mac_syncache_destroy(&maclabel);
1303 /* Retransmit SYN|ACK and reset retransmit count. */
1304 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1305 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1306 "resetting timer and retransmitting SYN|ACK\n",
1310 if (syncache_respond(sc, sch, 1) == 0) {
1312 syncache_timeout(sc, sch, 1);
1313 TCPSTAT_INC(tcps_sndacks);
1314 TCPSTAT_INC(tcps_sndtotal);
1321 if (tfo_cookie_valid) {
1322 bzero(&scs, sizeof(scs));
1328 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1331 * The zone allocator couldn't provide more entries.
1332 * Treat this as if the cache was full; drop the oldest
1333 * entry and insert the new one.
1335 TCPSTAT_INC(tcps_sc_zonefail);
1336 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1337 syncache_drop(sc, sch);
1338 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1340 if (V_tcp_syncookies) {
1341 bzero(&scs, sizeof(scs));
1346 (void) m_free(ipopts);
1354 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1355 sc->sc_tfo_cookie = &tfo_response_cookie;
1359 * Fill in the syncache values.
1362 sc->sc_label = maclabel;
1366 sc->sc_ipopts = ipopts;
1367 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1369 if (!(inc->inc_flags & INC_ISIPV6))
1372 sc->sc_ip_tos = ip_tos;
1373 sc->sc_ip_ttl = ip_ttl;
1377 sc->sc_todctx = todctx;
1379 sc->sc_irs = th->th_seq;
1380 sc->sc_iss = arc4random();
1382 sc->sc_flowlabel = 0;
1385 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1386 * win was derived from socket earlier in the function.
1389 win = imin(win, TCP_MAXWIN);
1392 if (V_tcp_do_rfc1323) {
1394 * A timestamp received in a SYN makes
1395 * it ok to send timestamp requests and replies.
1397 if (to->to_flags & TOF_TS) {
1398 sc->sc_tsreflect = to->to_tsval;
1399 sc->sc_ts = tcp_ts_getticks();
1400 sc->sc_flags |= SCF_TIMESTAMP;
1402 if (to->to_flags & TOF_SCALE) {
1406 * Pick the smallest possible scaling factor that
1407 * will still allow us to scale up to sb_max, aka
1408 * kern.ipc.maxsockbuf.
1410 * We do this because there are broken firewalls that
1411 * will corrupt the window scale option, leading to
1412 * the other endpoint believing that our advertised
1413 * window is unscaled. At scale factors larger than
1414 * 5 the unscaled window will drop below 1500 bytes,
1415 * leading to serious problems when traversing these
1418 * With the default maxsockbuf of 256K, a scale factor
1419 * of 3 will be chosen by this algorithm. Those who
1420 * choose a larger maxsockbuf should watch out
1421 * for the compatiblity problems mentioned above.
1423 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1424 * or <SYN,ACK>) segment itself is never scaled.
1426 while (wscale < TCP_MAX_WINSHIFT &&
1427 (TCP_MAXWIN << wscale) < sb_max)
1429 sc->sc_requested_r_scale = wscale;
1430 sc->sc_requested_s_scale = to->to_wscale;
1431 sc->sc_flags |= SCF_WINSCALE;
1434 #ifdef TCP_SIGNATURE
1436 * If listening socket requested TCP digests, OR received SYN
1437 * contains the option, flag this in the syncache so that
1438 * syncache_respond() will do the right thing with the SYN+ACK.
1440 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1441 sc->sc_flags |= SCF_SIGNATURE;
1443 if (to->to_flags & TOF_SACKPERM)
1444 sc->sc_flags |= SCF_SACK;
1445 if (to->to_flags & TOF_MSS)
1446 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1447 if (ltflags & TF_NOOPT)
1448 sc->sc_flags |= SCF_NOOPT;
1449 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1450 sc->sc_flags |= SCF_ECN;
1452 if (V_tcp_syncookies)
1453 sc->sc_iss = syncookie_generate(sch, sc);
1455 if (autoflowlabel) {
1456 if (V_tcp_syncookies)
1457 sc->sc_flowlabel = sc->sc_iss;
1459 sc->sc_flowlabel = ip6_randomflowlabel();
1460 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1466 if (tfo_cookie_valid) {
1467 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1468 /* INP_WUNLOCK(inp) will be performed by the called */
1475 * Do a standard 3-way handshake.
1477 if (syncache_respond(sc, sch, 0) == 0) {
1478 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1480 else if (sc != &scs)
1481 syncache_insert(sc, sch); /* locks and unlocks sch */
1482 TCPSTAT_INC(tcps_sndacks);
1483 TCPSTAT_INC(tcps_sndtotal);
1487 TCPSTAT_INC(tcps_sc_dropped);
1502 mac_syncache_destroy(&maclabel);
1508 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked)
1510 struct ip *ip = NULL;
1512 struct tcphdr *th = NULL;
1513 int optlen, error = 0; /* Make compiler happy */
1514 u_int16_t hlen, tlen, mssopt;
1517 struct ip6_hdr *ip6 = NULL;
1519 #ifdef TCP_SIGNATURE
1520 struct secasvar *sav;
1525 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1528 tlen = hlen + sizeof(struct tcphdr);
1530 /* Determine MSS we advertize to other end of connection. */
1531 mssopt = tcp_mssopt(&sc->sc_inc);
1532 if (sc->sc_peer_mss)
1533 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1535 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1536 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1537 ("syncache: mbuf too small"));
1539 /* Create the IP+TCP header from scratch. */
1540 m = m_gethdr(M_NOWAIT, MT_DATA);
1544 mac_syncache_create_mbuf(sc->sc_label, m);
1546 m->m_data += max_linkhdr;
1548 m->m_pkthdr.len = tlen;
1549 m->m_pkthdr.rcvif = NULL;
1552 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1553 ip6 = mtod(m, struct ip6_hdr *);
1554 ip6->ip6_vfc = IPV6_VERSION;
1555 ip6->ip6_nxt = IPPROTO_TCP;
1556 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1557 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1558 ip6->ip6_plen = htons(tlen - hlen);
1559 /* ip6_hlim is set after checksum */
1560 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1561 ip6->ip6_flow |= sc->sc_flowlabel;
1563 th = (struct tcphdr *)(ip6 + 1);
1566 #if defined(INET6) && defined(INET)
1571 ip = mtod(m, struct ip *);
1572 ip->ip_v = IPVERSION;
1573 ip->ip_hl = sizeof(struct ip) >> 2;
1574 ip->ip_len = htons(tlen);
1578 ip->ip_p = IPPROTO_TCP;
1579 ip->ip_src = sc->sc_inc.inc_laddr;
1580 ip->ip_dst = sc->sc_inc.inc_faddr;
1581 ip->ip_ttl = sc->sc_ip_ttl;
1582 ip->ip_tos = sc->sc_ip_tos;
1585 * See if we should do MTU discovery. Route lookups are
1586 * expensive, so we will only unset the DF bit if:
1588 * 1) path_mtu_discovery is disabled
1589 * 2) the SCF_UNREACH flag has been set
1591 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1592 ip->ip_off |= htons(IP_DF);
1594 th = (struct tcphdr *)(ip + 1);
1597 th->th_sport = sc->sc_inc.inc_lport;
1598 th->th_dport = sc->sc_inc.inc_fport;
1600 th->th_seq = htonl(sc->sc_iss);
1601 th->th_ack = htonl(sc->sc_irs + 1);
1602 th->th_off = sizeof(struct tcphdr) >> 2;
1604 th->th_flags = TH_SYN|TH_ACK;
1605 th->th_win = htons(sc->sc_wnd);
1608 if (sc->sc_flags & SCF_ECN) {
1609 th->th_flags |= TH_ECE;
1610 TCPSTAT_INC(tcps_ecn_shs);
1613 /* Tack on the TCP options. */
1614 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1618 to.to_flags = TOF_MSS;
1619 if (sc->sc_flags & SCF_WINSCALE) {
1620 to.to_wscale = sc->sc_requested_r_scale;
1621 to.to_flags |= TOF_SCALE;
1623 if (sc->sc_flags & SCF_TIMESTAMP) {
1624 /* Virgin timestamp or TCP cookie enhanced one. */
1625 to.to_tsval = sc->sc_ts;
1626 to.to_tsecr = sc->sc_tsreflect;
1627 to.to_flags |= TOF_TS;
1629 if (sc->sc_flags & SCF_SACK)
1630 to.to_flags |= TOF_SACKPERM;
1631 #ifdef TCP_SIGNATURE
1633 if (sc->sc_flags & SCF_SIGNATURE) {
1634 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1636 to.to_flags |= TOF_SIGNATURE;
1640 * We've got SCF_SIGNATURE flag
1641 * inherited from listening socket,
1642 * but no SADB key for given source
1643 * address. Assume signature is not
1644 * required and remove signature flag
1645 * instead of silently dropping
1650 sc->sc_flags &= ~SCF_SIGNATURE;
1658 if (sc->sc_tfo_cookie) {
1659 to.to_flags |= TOF_FASTOPEN;
1660 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1661 to.to_tfo_cookie = sc->sc_tfo_cookie;
1662 /* don't send cookie again when retransmitting response */
1663 sc->sc_tfo_cookie = NULL;
1666 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1668 /* Adjust headers by option size. */
1669 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1671 m->m_pkthdr.len += optlen;
1673 #ifdef TCP_SIGNATURE
1674 if (sc->sc_flags & SCF_SIGNATURE)
1675 tcp_signature_do_compute(m, 0, optlen,
1676 to.to_signature, sav);
1679 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1680 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1683 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1687 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1688 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1690 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1691 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1692 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1694 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1696 if (ADDED_BY_TOE(sc)) {
1697 struct toedev *tod = sc->sc_tod;
1699 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1704 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1707 #if defined(INET6) && defined(INET)
1712 m->m_pkthdr.csum_flags = CSUM_TCP;
1713 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1714 htons(tlen + optlen - hlen + IPPROTO_TCP));
1716 if (ADDED_BY_TOE(sc)) {
1717 struct toedev *tod = sc->sc_tod;
1719 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1724 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1731 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1732 * that exceed the capacity of the syncache by avoiding the storage of any
1733 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1734 * attacks where the attacker does not have access to our responses.
1736 * Syncookies encode and include all necessary information about the
1737 * connection setup within the SYN|ACK that we send back. That way we
1738 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1739 * (if ever). Normally the syncache and syncookies are running in parallel
1740 * with the latter taking over when the former is exhausted. When matching
1741 * syncache entry is found the syncookie is ignored.
1743 * The only reliable information persisting the 3WHS is our inital sequence
1744 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1745 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1746 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1747 * returns and signifies a legitimate connection if it matches the ACK.
1749 * The available space of 32 bits to store the hash and to encode the SYN
1750 * option information is very tight and we should have at least 24 bits for
1751 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1753 * SYN option information we have to encode to fully restore a connection:
1754 * MSS: is imporant to chose an optimal segment size to avoid IP level
1755 * fragmentation along the path. The common MSS values can be encoded
1756 * in a 3-bit table. Uncommon values are captured by the next lower value
1757 * in the table leading to a slight increase in packetization overhead.
1758 * WSCALE: is necessary to allow large windows to be used for high delay-
1759 * bandwidth product links. Not scaling the window when it was initially
1760 * negotiated is bad for performance as lack of scaling further decreases
1761 * the apparent available send window. We only need to encode the WSCALE
1762 * we received from the remote end. Our end can be recalculated at any
1763 * time. The common WSCALE values can be encoded in a 3-bit table.
1764 * Uncommon values are captured by the next lower value in the table
1765 * making us under-estimate the available window size halving our
1766 * theoretically possible maximum throughput for that connection.
1767 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1768 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1769 * that are included in all segments on a connection. We enable them when
1772 * Security of syncookies and attack vectors:
1774 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1775 * together with the gloabl secret to make it unique per connection attempt.
1776 * Thus any change of any of those parameters results in a different MAC output
1777 * in an unpredictable way unless a collision is encountered. 24 bits of the
1778 * MAC are embedded into the ISS.
1780 * To prevent replay attacks two rotating global secrets are updated with a
1781 * new random value every 15 seconds. The life-time of a syncookie is thus
1784 * Vector 1: Attacking the secret. This requires finding a weakness in the
1785 * MAC itself or the way it is used here. The attacker can do a chosen plain
1786 * text attack by varying and testing the all parameters under his control.
1787 * The strength depends on the size and randomness of the secret, and the
1788 * cryptographic security of the MAC function. Due to the constant updating
1789 * of the secret the attacker has at most 29.999 seconds to find the secret
1790 * and launch spoofed connections. After that he has to start all over again.
1792 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1793 * size an average of 4,823 attempts are required for a 50% chance of success
1794 * to spoof a single syncookie (birthday collision paradox). However the
1795 * attacker is blind and doesn't know if one of his attempts succeeded unless
1796 * he has a side channel to interfere success from. A single connection setup
1797 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1798 * This many attempts are required for each one blind spoofed connection. For
1799 * every additional spoofed connection he has to launch another N attempts.
1800 * Thus for a sustained rate 100 spoofed connections per second approximately
1801 * 1,800,000 packets per second would have to be sent.
1803 * NB: The MAC function should be fast so that it doesn't become a CPU
1804 * exhaustion attack vector itself.
1807 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1808 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1809 * http://cr.yp.to/syncookies.html (overview)
1810 * http://cr.yp.to/syncookies/archive (details)
1813 * Schematic construction of a syncookie enabled Initial Sequence Number:
1815 * 12345678901234567890123456789012
1816 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1818 * x 24 MAC (truncated)
1819 * W 3 Send Window Scale index
1821 * S 1 SACK permitted
1822 * P 1 Odd/even secret
1826 * Distribution and probability of certain MSS values. Those in between are
1827 * rounded down to the next lower one.
1828 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1829 * .2% .3% 5% 7% 7% 20% 15% 45%
1831 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1834 * Distribution and probability of certain WSCALE values. We have to map the
1835 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1836 * bits based on prevalence of certain values. Where we don't have an exact
1837 * match for are rounded down to the next lower one letting us under-estimate
1838 * the true available window. At the moment this would happen only for the
1839 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1840 * and window size). The absence of the WSCALE option (no scaling in either
1841 * direction) is encoded with index zero.
1842 * [WSCALE values histograms, Allman, 2012]
1843 * X 10 10 35 5 6 14 10% by host
1844 * X 11 4 5 5 18 49 3% by connections
1846 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1849 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1850 * and good cryptographic properties.
1853 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1854 uint8_t *secbits, uintptr_t secmod)
1857 uint32_t siphash[2];
1859 SipHash24_Init(&ctx);
1860 SipHash_SetKey(&ctx, secbits);
1861 switch (inc->inc_flags & INC_ISIPV6) {
1864 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1865 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1870 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1871 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1875 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1876 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1877 SipHash_Update(&ctx, &irs, sizeof(irs));
1878 SipHash_Update(&ctx, &flags, sizeof(flags));
1879 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1880 SipHash_Final((u_int8_t *)&siphash, &ctx);
1882 return (siphash[0] ^ siphash[1]);
1886 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1888 u_int i, mss, secbit, wscale;
1891 union syncookie cookie;
1893 SCH_LOCK_ASSERT(sch);
1897 /* Map our computed MSS into the 3-bit index. */
1898 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1899 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
1902 cookie.flags.mss_idx = i;
1905 * Map the send window scale into the 3-bit index but only if
1906 * the wscale option was received.
1908 if (sc->sc_flags & SCF_WINSCALE) {
1909 wscale = sc->sc_requested_s_scale;
1910 for (i = nitems(tcp_sc_wstab) - 1;
1911 tcp_sc_wstab[i] > wscale && i > 0;
1914 cookie.flags.wscale_idx = i;
1917 /* Can we do SACK? */
1918 if (sc->sc_flags & SCF_SACK)
1919 cookie.flags.sack_ok = 1;
1921 /* Which of the two secrets to use. */
1922 secbit = sch->sch_sc->secret.oddeven & 0x1;
1923 cookie.flags.odd_even = secbit;
1925 secbits = sch->sch_sc->secret.key[secbit];
1926 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1930 * Put the flags into the hash and XOR them to get better ISS number
1931 * variance. This doesn't enhance the cryptographic strength and is
1932 * done to prevent the 8 cookie bits from showing up directly on the
1936 iss |= cookie.cookie ^ (hash >> 24);
1938 /* Randomize the timestamp. */
1939 if (sc->sc_flags & SCF_TIMESTAMP) {
1940 sc->sc_ts = arc4random();
1941 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1944 TCPSTAT_INC(tcps_sc_sendcookie);
1948 static struct syncache *
1949 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1950 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1956 int wnd, wscale = 0;
1957 union syncookie cookie;
1959 SCH_LOCK_ASSERT(sch);
1962 * Pull information out of SYN-ACK/ACK and revert sequence number
1965 ack = th->th_ack - 1;
1966 seq = th->th_seq - 1;
1969 * Unpack the flags containing enough information to restore the
1972 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1974 /* Which of the two secrets to use. */
1975 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1977 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1979 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1980 if ((ack & ~0xff) != (hash & ~0xff))
1983 /* Fill in the syncache values. */
1985 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1986 sc->sc_ipopts = NULL;
1991 switch (inc->inc_flags & INC_ISIPV6) {
1994 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1995 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2000 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2001 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2006 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2008 /* We can simply recompute receive window scale we sent earlier. */
2009 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2012 /* Only use wscale if it was enabled in the orignal SYN. */
2013 if (cookie.flags.wscale_idx > 0) {
2014 sc->sc_requested_r_scale = wscale;
2015 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2016 sc->sc_flags |= SCF_WINSCALE;
2019 wnd = sbspace(&lso->so_rcv);
2021 wnd = imin(wnd, TCP_MAXWIN);
2024 if (cookie.flags.sack_ok)
2025 sc->sc_flags |= SCF_SACK;
2027 if (to->to_flags & TOF_TS) {
2028 sc->sc_flags |= SCF_TIMESTAMP;
2029 sc->sc_tsreflect = to->to_tsval;
2030 sc->sc_ts = to->to_tsecr;
2031 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2034 if (to->to_flags & TOF_SIGNATURE)
2035 sc->sc_flags |= SCF_SIGNATURE;
2039 TCPSTAT_INC(tcps_sc_recvcookie);
2045 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2046 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2049 struct syncache scs, *scx;
2052 bzero(&scs, sizeof(scs));
2053 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2055 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2059 if (sc->sc_peer_mss != scx->sc_peer_mss)
2060 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2061 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2063 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2064 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2065 s, __func__, sc->sc_requested_r_scale,
2066 scx->sc_requested_r_scale);
2068 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2069 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2070 s, __func__, sc->sc_requested_s_scale,
2071 scx->sc_requested_s_scale);
2073 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2074 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2081 #endif /* INVARIANTS */
2084 syncookie_reseed(void *arg)
2086 struct tcp_syncache *sc = arg;
2091 * Reseeding the secret doesn't have to be protected by a lock.
2092 * It only must be ensured that the new random values are visible
2093 * to all CPUs in a SMP environment. The atomic with release
2094 * semantics ensures that.
2096 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2097 secbits = sc->secret.key[secbit];
2098 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2099 atomic_add_rel_int(&sc->secret.oddeven, 1);
2101 /* Reschedule ourself. */
2102 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2106 * Exports the syncache entries to userland so that netstat can display
2107 * them alongside the other sockets. This function is intended to be
2108 * called only from tcp_pcblist.
2110 * Due to concurrency on an active system, the number of pcbs exported
2111 * may have no relation to max_pcbs. max_pcbs merely indicates the
2112 * amount of space the caller allocated for this function to use.
2115 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2118 struct syncache *sc;
2119 struct syncache_head *sch;
2120 int count, error, i;
2122 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2123 sch = &V_tcp_syncache.hashbase[i];
2125 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2126 if (count >= max_pcbs) {
2130 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2132 bzero(&xt, sizeof(xt));
2133 xt.xt_len = sizeof(xt);
2134 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2135 xt.xt_inp.inp_vflag = INP_IPV6;
2137 xt.xt_inp.inp_vflag = INP_IPV4;
2138 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2139 xt.xt_tp.t_inpcb = &xt.xt_inp;
2140 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2141 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2142 xt.xt_socket.xso_len = sizeof (struct xsocket);
2143 xt.xt_socket.so_type = SOCK_STREAM;
2144 xt.xt_socket.so_state = SS_ISCONNECTING;
2145 error = SYSCTL_OUT(req, &xt, sizeof xt);
2155 *pcbs_exported = count;