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;
284 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
285 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
287 sch = &V_tcp_syncache.hashbase[i];
288 callout_drain(&sch->sch_timer);
291 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
292 syncache_drop(sc, sch);
294 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
295 ("%s: sch->sch_bucket not empty", __func__));
296 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
297 __func__, sch->sch_length));
298 mtx_destroy(&sch->sch_mtx);
301 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
302 ("%s: cache_count not 0", __func__));
304 /* Free the allocated global resources. */
305 uma_zdestroy(V_tcp_syncache.zone);
306 free(V_tcp_syncache.hashbase, M_SYNCACHE);
308 callout_drain(&V_tcp_syncache.secret.reseed);
313 * Inserts a syncache entry into the specified bucket row.
314 * Locks and unlocks the syncache_head autonomously.
317 syncache_insert(struct syncache *sc, struct syncache_head *sch)
319 struct syncache *sc2;
324 * Make sure that we don't overflow the per-bucket limit.
325 * If the bucket is full, toss the oldest element.
327 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
328 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
329 ("sch->sch_length incorrect"));
330 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
331 syncache_drop(sc2, sch);
332 TCPSTAT_INC(tcps_sc_bucketoverflow);
335 /* Put it into the bucket. */
336 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
340 if (ADDED_BY_TOE(sc)) {
341 struct toedev *tod = sc->sc_tod;
343 tod->tod_syncache_added(tod, sc->sc_todctx);
347 /* Reinitialize the bucket row's timer. */
348 if (sch->sch_length == 1)
349 sch->sch_nextc = ticks + INT_MAX;
350 syncache_timeout(sc, sch, 1);
354 TCPSTATES_INC(TCPS_SYN_RECEIVED);
355 TCPSTAT_INC(tcps_sc_added);
359 * Remove and free entry from syncache bucket row.
360 * Expects locked syncache head.
363 syncache_drop(struct syncache *sc, struct syncache_head *sch)
366 SCH_LOCK_ASSERT(sch);
368 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
369 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
373 if (ADDED_BY_TOE(sc)) {
374 struct toedev *tod = sc->sc_tod;
376 tod->tod_syncache_removed(tod, sc->sc_todctx);
384 * Engage/reengage time on bucket row.
387 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
389 sc->sc_rxttime = ticks +
390 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
392 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
393 sch->sch_nextc = sc->sc_rxttime;
395 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
396 syncache_timer, (void *)sch);
401 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
402 * If we have retransmitted an entry the maximum number of times, expire it.
403 * One separate timer for each bucket row.
406 syncache_timer(void *xsch)
408 struct syncache_head *sch = (struct syncache_head *)xsch;
409 struct syncache *sc, *nsc;
413 CURVNET_SET(sch->sch_sc->vnet);
415 /* NB: syncache_head has already been locked by the callout. */
416 SCH_LOCK_ASSERT(sch);
419 * In the following cycle we may remove some entries and/or
420 * advance some timeouts, so re-initialize the bucket timer.
422 sch->sch_nextc = tick + INT_MAX;
424 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
426 * We do not check if the listen socket still exists
427 * and accept the case where the listen socket may be
428 * gone by the time we resend the SYN/ACK. We do
429 * not expect this to happens often. If it does,
430 * then the RST will be sent by the time the remote
431 * host does the SYN/ACK->ACK.
433 if (TSTMP_GT(sc->sc_rxttime, tick)) {
434 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
435 sch->sch_nextc = sc->sc_rxttime;
438 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
439 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
440 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
441 "giving up and removing syncache entry\n",
445 syncache_drop(sc, sch);
446 TCPSTAT_INC(tcps_sc_stale);
449 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
450 log(LOG_DEBUG, "%s; %s: Response timeout, "
451 "retransmitting (%u) SYN|ACK\n",
452 s, __func__, sc->sc_rxmits);
456 syncache_respond(sc, sch, 1);
457 TCPSTAT_INC(tcps_sc_retransmitted);
458 syncache_timeout(sc, sch, 0);
460 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
461 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
462 syncache_timer, (void *)(sch));
467 * Find an entry in the syncache.
468 * Returns always with locked syncache_head plus a matching entry or NULL.
470 static struct syncache *
471 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
474 struct syncache_head *sch;
478 * The hash is built on foreign port + local port + foreign address.
479 * We rely on the fact that struct in_conninfo starts with 16 bits
480 * of foreign port, then 16 bits of local port then followed by 128
481 * bits of foreign address. In case of IPv4 address, the first 3
482 * 32-bit words of the address always are zeroes.
484 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
485 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
487 sch = &V_tcp_syncache.hashbase[hash];
491 /* Circle through bucket row to find matching entry. */
492 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
493 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
494 sizeof(struct in_endpoints)) == 0)
497 return (sc); /* Always returns with locked sch. */
501 * This function is called when we get a RST for a
502 * non-existent connection, so that we can see if the
503 * connection is in the syn cache. If it is, zap it.
506 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
509 struct syncache_head *sch;
512 sc = syncache_lookup(inc, &sch); /* returns locked sch */
513 SCH_LOCK_ASSERT(sch);
516 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
517 * See RFC 793 page 65, section SEGMENT ARRIVES.
519 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
520 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
521 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
522 "FIN flag set, segment ignored\n", s, __func__);
523 TCPSTAT_INC(tcps_badrst);
528 * No corresponding connection was found in syncache.
529 * If syncookies are enabled and possibly exclusively
530 * used, or we are under memory pressure, a valid RST
531 * may not find a syncache entry. In that case we're
532 * done and no SYN|ACK retransmissions will happen.
533 * Otherwise the RST was misdirected or spoofed.
536 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
537 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
538 "syncache entry (possibly syncookie only), "
539 "segment ignored\n", s, __func__);
540 TCPSTAT_INC(tcps_badrst);
545 * If the RST bit is set, check the sequence number to see
546 * if this is a valid reset segment.
548 * In all states except SYN-SENT, all reset (RST) segments
549 * are validated by checking their SEQ-fields. A reset is
550 * valid if its sequence number is in the window.
552 * The sequence number in the reset segment is normally an
553 * echo of our outgoing acknowlegement numbers, but some hosts
554 * send a reset with the sequence number at the rightmost edge
555 * of our receive window, and we have to handle this case.
557 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
558 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
559 syncache_drop(sc, sch);
560 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
561 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
562 "connection attempt aborted by remote endpoint\n",
564 TCPSTAT_INC(tcps_sc_reset);
566 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
567 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
568 "IRS %u (+WND %u), segment ignored\n",
569 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
570 TCPSTAT_INC(tcps_badrst);
580 syncache_badack(struct in_conninfo *inc)
583 struct syncache_head *sch;
585 sc = syncache_lookup(inc, &sch); /* returns locked sch */
586 SCH_LOCK_ASSERT(sch);
588 syncache_drop(sc, sch);
589 TCPSTAT_INC(tcps_sc_badack);
595 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
598 struct syncache_head *sch;
600 sc = syncache_lookup(inc, &sch); /* returns locked sch */
601 SCH_LOCK_ASSERT(sch);
605 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
606 if (ntohl(th->th_seq) != sc->sc_iss)
610 * If we've rertransmitted 3 times and this is our second error,
611 * we remove the entry. Otherwise, we allow it to continue on.
612 * This prevents us from incorrectly nuking an entry during a
613 * spurious network outage.
617 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
618 sc->sc_flags |= SCF_UNREACH;
621 syncache_drop(sc, sch);
622 TCPSTAT_INC(tcps_sc_unreach);
628 * Build a new TCP socket structure from a syncache entry.
630 * On success return the newly created socket with its underlying inp locked.
632 static struct socket *
633 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
635 struct tcp_function_block *blk;
636 struct inpcb *inp = NULL;
642 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
645 * Ok, create the full blown connection, and set things up
646 * as they would have been set up if we had created the
647 * connection when the SYN arrived. If we can't create
648 * the connection, abort it.
650 so = sonewconn(lso, 0);
653 * Drop the connection; we will either send a RST or
654 * have the peer retransmit its SYN again after its
657 TCPSTAT_INC(tcps_listendrop);
658 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
659 log(LOG_DEBUG, "%s; %s: Socket create failed "
660 "due to limits or memory shortage\n",
667 mac_socketpeer_set_from_mbuf(m, so);
671 inp->inp_inc.inc_fibnum = so->so_fibnum;
674 * Exclusive pcbinfo lock is not required in syncache socket case even
675 * if two inpcb locks can be acquired simultaneously:
676 * - the inpcb in LISTEN state,
677 * - the newly created inp.
679 * In this case, an inp cannot be at same time in LISTEN state and
680 * just created by an accept() call.
682 INP_HASH_WLOCK(&V_tcbinfo);
684 /* Insert new socket into PCB hash list. */
685 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
687 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
688 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
690 inp->inp_vflag &= ~INP_IPV6;
691 inp->inp_vflag |= INP_IPV4;
693 inp->inp_laddr = sc->sc_inc.inc_laddr;
699 * If there's an mbuf and it has a flowid, then let's initialise the
700 * inp with that particular flowid.
702 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
703 inp->inp_flowid = m->m_pkthdr.flowid;
704 inp->inp_flowtype = M_HASHTYPE_GET(m);
708 * Install in the reservation hash table for now, but don't yet
709 * install a connection group since the full 4-tuple isn't yet
712 inp->inp_lport = sc->sc_inc.inc_lport;
713 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
715 * Undo the assignments above if we failed to
716 * put the PCB on the hash lists.
719 if (sc->sc_inc.inc_flags & INC_ISIPV6)
720 inp->in6p_laddr = in6addr_any;
723 inp->inp_laddr.s_addr = INADDR_ANY;
725 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
726 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
731 INP_HASH_WUNLOCK(&V_tcbinfo);
735 /* Copy old policy into new socket's. */
736 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
737 printf("syncache_socket: could not copy policy\n");
740 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
741 struct inpcb *oinp = sotoinpcb(lso);
742 struct in6_addr laddr6;
743 struct sockaddr_in6 sin6;
745 * Inherit socket options from the listening socket.
746 * Note that in6p_inputopts are not (and should not be)
747 * copied, since it stores previously received options and is
748 * used to detect if each new option is different than the
749 * previous one and hence should be passed to a user.
750 * If we copied in6p_inputopts, a user would not be able to
751 * receive options just after calling the accept system call.
753 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
754 if (oinp->in6p_outputopts)
755 inp->in6p_outputopts =
756 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
758 sin6.sin6_family = AF_INET6;
759 sin6.sin6_len = sizeof(sin6);
760 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
761 sin6.sin6_port = sc->sc_inc.inc_fport;
762 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
763 laddr6 = inp->in6p_laddr;
764 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
765 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
766 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
767 thread0.td_ucred, m)) != 0) {
768 inp->in6p_laddr = laddr6;
769 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
770 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
775 INP_HASH_WUNLOCK(&V_tcbinfo);
778 /* Override flowlabel from in6_pcbconnect. */
779 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
780 inp->inp_flow |= sc->sc_flowlabel;
783 #if defined(INET) && defined(INET6)
788 struct in_addr laddr;
789 struct sockaddr_in sin;
791 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
793 if (inp->inp_options == NULL) {
794 inp->inp_options = sc->sc_ipopts;
795 sc->sc_ipopts = NULL;
798 sin.sin_family = AF_INET;
799 sin.sin_len = sizeof(sin);
800 sin.sin_addr = sc->sc_inc.inc_faddr;
801 sin.sin_port = sc->sc_inc.inc_fport;
802 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
803 laddr = inp->inp_laddr;
804 if (inp->inp_laddr.s_addr == INADDR_ANY)
805 inp->inp_laddr = sc->sc_inc.inc_laddr;
806 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
807 thread0.td_ucred, m)) != 0) {
808 inp->inp_laddr = laddr;
809 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
810 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
815 INP_HASH_WUNLOCK(&V_tcbinfo);
820 INP_HASH_WUNLOCK(&V_tcbinfo);
822 tcp_state_change(tp, TCPS_SYN_RECEIVED);
823 tp->iss = sc->sc_iss;
824 tp->irs = sc->sc_irs;
827 blk = sototcpcb(lso)->t_fb;
828 if (blk != tp->t_fb) {
830 * Our parents t_fb was not the default,
831 * we need to release our ref on tp->t_fb and
832 * pickup one on the new entry.
834 struct tcp_function_block *rblk;
836 rblk = find_and_ref_tcp_fb(blk);
837 KASSERT(rblk != NULL,
838 ("cannot find blk %p out of syncache?", blk));
839 if (tp->t_fb->tfb_tcp_fb_fini)
840 (*tp->t_fb->tfb_tcp_fb_fini)(tp);
841 refcount_release(&tp->t_fb->tfb_refcnt);
843 if (tp->t_fb->tfb_tcp_fb_init) {
844 (*tp->t_fb->tfb_tcp_fb_init)(tp);
847 tp->snd_wl1 = sc->sc_irs;
848 tp->snd_max = tp->iss + 1;
849 tp->snd_nxt = tp->iss + 1;
850 tp->rcv_up = sc->sc_irs + 1;
851 tp->rcv_wnd = sc->sc_wnd;
852 tp->rcv_adv += tp->rcv_wnd;
853 tp->last_ack_sent = tp->rcv_nxt;
855 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
856 if (sc->sc_flags & SCF_NOOPT)
857 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_requested_r_scale;
864 if (sc->sc_flags & SCF_TIMESTAMP) {
865 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
866 tp->ts_recent = sc->sc_tsreflect;
867 tp->ts_recent_age = tcp_ts_getticks();
868 tp->ts_offset = sc->sc_tsoff;
871 if (sc->sc_flags & SCF_SIGNATURE)
872 tp->t_flags |= TF_SIGNATURE;
874 if (sc->sc_flags & SCF_SACK)
875 tp->t_flags |= TF_SACK_PERMIT;
878 if (sc->sc_flags & SCF_ECN)
879 tp->t_flags |= TF_ECN_PERMIT;
882 * Set up MSS and get cached values from tcp_hostcache.
883 * This might overwrite some of the defaults we just set.
885 tcp_mss(tp, sc->sc_peer_mss);
888 * If the SYN,ACK was retransmitted, indicate that CWND to be
889 * limited to one segment in cc_conn_init().
890 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
892 if (sc->sc_rxmits > 1)
897 * Allow a TOE driver to install its hooks. Note that we hold the
898 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
899 * new connection before the TOE driver has done its thing.
901 if (ADDED_BY_TOE(sc)) {
902 struct toedev *tod = sc->sc_tod;
904 tod->tod_offload_socket(tod, sc->sc_todctx, so);
908 * Copy and activate timers.
910 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
911 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
912 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
913 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
914 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
918 TCPSTAT_INC(tcps_accepts);
930 * This function gets called when we receive an ACK for a
931 * socket in the LISTEN state. We look up the connection
932 * in the syncache, and if its there, we pull it out of
933 * the cache and turn it into a full-blown connection in
934 * the SYN-RECEIVED state.
936 * On syncache_socket() success the newly created socket
937 * has its underlying inp locked.
940 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
941 struct socket **lsop, struct mbuf *m)
944 struct syncache_head *sch;
949 * Global TCP locks are held because we manipulate the PCB lists
950 * and create a new socket.
952 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
953 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
954 ("%s: can handle only ACK", __func__));
956 sc = syncache_lookup(inc, &sch); /* returns locked sch */
957 SCH_LOCK_ASSERT(sch);
961 * Test code for syncookies comparing the syncache stored
962 * values with the reconstructed values from the cookie.
965 syncookie_cmp(inc, sch, sc, th, to, *lsop);
970 * There is no syncache entry, so see if this ACK is
971 * a returning syncookie. To do this, first:
972 * A. See if this socket has had a syncache entry dropped in
973 * the past. We don't want to accept a bogus syncookie
974 * if we've never received a SYN.
975 * B. check that the syncookie is valid. If it is, then
976 * cobble up a fake syncache entry, and return.
978 if (!V_tcp_syncookies) {
980 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
981 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
982 "segment rejected (syncookies disabled)\n",
986 bzero(&scs, sizeof(scs));
987 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
990 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
991 log(LOG_DEBUG, "%s; %s: Segment failed "
992 "SYNCOOKIE authentication, segment rejected "
993 "(probably spoofed)\n", s, __func__);
998 * Pull out the entry to unlock the bucket row.
1000 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1001 * tcp_state_change(). The tcpcb is not existent at this
1002 * moment. A new one will be allocated via syncache_socket->
1003 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1004 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1006 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1007 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1010 if (ADDED_BY_TOE(sc)) {
1011 struct toedev *tod = sc->sc_tod;
1013 tod->tod_syncache_removed(tod, sc->sc_todctx);
1020 * Segment validation:
1021 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1023 if (th->th_ack != sc->sc_iss + 1) {
1024 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1025 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1026 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1031 * The SEQ must fall in the window starting at the received
1032 * initial receive sequence number + 1 (the SYN).
1034 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1035 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1036 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1037 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1038 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1043 * If timestamps were not negotiated during SYN/ACK they
1044 * must not appear on any segment during this session.
1046 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1047 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1048 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1049 "segment rejected\n", s, __func__);
1054 * If timestamps were negotiated during SYN/ACK they should
1055 * appear on every segment during this session.
1056 * XXXAO: This is only informal as there have been unverified
1057 * reports of non-compliants stacks.
1059 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1060 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1061 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1062 "no action\n", s, __func__);
1069 * If timestamps were negotiated the reflected timestamp
1070 * must be equal to what we actually sent in the SYN|ACK.
1072 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1073 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1074 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1075 "segment rejected\n",
1076 s, __func__, to->to_tsecr, sc->sc_ts);
1080 *lsop = syncache_socket(sc, *lsop, m);
1083 TCPSTAT_INC(tcps_sc_aborted);
1085 TCPSTAT_INC(tcps_sc_completed);
1087 /* how do we find the inp for the new socket? */
1092 if (sc != NULL && sc != &scs)
1102 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1103 uint64_t response_cookie)
1107 unsigned int *pending_counter;
1110 * Global TCP locks are held because we manipulate the PCB lists
1111 * and create a new socket.
1113 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1115 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1116 *lsop = syncache_socket(sc, *lsop, m);
1117 if (*lsop == NULL) {
1118 TCPSTAT_INC(tcps_sc_aborted);
1119 atomic_subtract_int(pending_counter, 1);
1121 inp = sotoinpcb(*lsop);
1122 tp = intotcpcb(inp);
1123 tp->t_flags |= TF_FASTOPEN;
1124 tp->t_tfo_cookie = response_cookie;
1125 tp->snd_max = tp->iss;
1126 tp->snd_nxt = tp->iss;
1127 tp->t_tfo_pending = pending_counter;
1128 TCPSTAT_INC(tcps_sc_completed);
1131 #endif /* TCP_RFC7413 */
1134 * Given a LISTEN socket and an inbound SYN request, add
1135 * this to the syn cache, and send back a segment:
1136 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1139 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1140 * Doing so would require that we hold onto the data and deliver it
1141 * to the application. However, if we are the target of a SYN-flood
1142 * DoS attack, an attacker could send data which would eventually
1143 * consume all available buffer space if it were ACKed. By not ACKing
1144 * the data, we avoid this DoS scenario.
1146 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1147 * cookie is processed, V_tcp_fastopen_enabled set to true, and the
1148 * TCP_FASTOPEN socket option is set. In this case, a new socket is created
1149 * and returned via lsop, the mbuf is not freed so that tcp_input() can
1150 * queue its data to the socket, and 1 is returned to indicate the
1151 * TFO-socket-creation path was taken.
1154 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1155 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1160 struct syncache *sc = NULL;
1161 struct syncache_head *sch;
1162 struct mbuf *ipopts = NULL;
1164 int win, sb_hiwat, ip_ttl, ip_tos;
1168 int autoflowlabel = 0;
1171 struct label *maclabel;
1173 struct syncache scs;
1176 uint64_t tfo_response_cookie;
1177 int tfo_cookie_valid = 0;
1178 int tfo_response_cookie_valid = 0;
1181 INP_WLOCK_ASSERT(inp); /* listen socket */
1182 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1183 ("%s: unexpected tcp flags", __func__));
1186 * Combine all so/tp operations very early to drop the INP lock as
1191 cred = crhold(so->so_cred);
1194 if ((inc->inc_flags & INC_ISIPV6) &&
1195 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1198 ip_ttl = inp->inp_ip_ttl;
1199 ip_tos = inp->inp_ip_tos;
1200 win = sbspace(&so->so_rcv);
1201 sb_hiwat = so->so_rcv.sb_hiwat;
1202 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1205 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
1206 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1208 * Limit the number of pending TFO connections to
1209 * approximately half of the queue limit. This prevents TFO
1210 * SYN floods from starving the service by filling the
1211 * listen queue with bogus TFO connections.
1213 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1214 (so->so_qlimit / 2)) {
1217 result = tcp_fastopen_check_cookie(inc,
1218 to->to_tfo_cookie, to->to_tfo_len,
1219 &tfo_response_cookie);
1220 tfo_cookie_valid = (result > 0);
1221 tfo_response_cookie_valid = (result >= 0);
1223 atomic_subtract_int(tp->t_tfo_pending, 1);
1227 /* By the time we drop the lock these should no longer be used. */
1232 if (mac_syncache_init(&maclabel) != 0) {
1236 mac_syncache_create(maclabel, inp);
1239 if (!tfo_cookie_valid)
1244 * Remember the IP options, if any.
1247 if (!(inc->inc_flags & INC_ISIPV6))
1250 ipopts = (m) ? ip_srcroute(m) : NULL;
1256 * See if we already have an entry for this connection.
1257 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1259 * XXX: should the syncache be re-initialized with the contents
1260 * of the new SYN here (which may have different options?)
1262 * XXX: We do not check the sequence number to see if this is a
1263 * real retransmit or a new connection attempt. The question is
1264 * how to handle such a case; either ignore it as spoofed, or
1265 * drop the current entry and create a new one?
1267 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1268 SCH_LOCK_ASSERT(sch);
1271 if (tfo_cookie_valid)
1274 TCPSTAT_INC(tcps_sc_dupsyn);
1277 * If we were remembering a previous source route,
1278 * forget it and use the new one we've been given.
1281 (void) m_free(sc->sc_ipopts);
1282 sc->sc_ipopts = ipopts;
1285 * Update timestamp if present.
1287 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1288 sc->sc_tsreflect = to->to_tsval;
1290 sc->sc_flags &= ~SCF_TIMESTAMP;
1293 * Since we have already unconditionally allocated label
1294 * storage, free it up. The syncache entry will already
1295 * have an initialized label we can use.
1297 mac_syncache_destroy(&maclabel);
1299 /* Retransmit SYN|ACK and reset retransmit count. */
1300 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1301 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1302 "resetting timer and retransmitting SYN|ACK\n",
1306 if (syncache_respond(sc, sch, 1) == 0) {
1308 syncache_timeout(sc, sch, 1);
1309 TCPSTAT_INC(tcps_sndacks);
1310 TCPSTAT_INC(tcps_sndtotal);
1317 if (tfo_cookie_valid) {
1318 bzero(&scs, sizeof(scs));
1324 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1327 * The zone allocator couldn't provide more entries.
1328 * Treat this as if the cache was full; drop the oldest
1329 * entry and insert the new one.
1331 TCPSTAT_INC(tcps_sc_zonefail);
1332 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1333 syncache_drop(sc, sch);
1334 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1336 if (V_tcp_syncookies) {
1337 bzero(&scs, sizeof(scs));
1342 (void) m_free(ipopts);
1350 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1351 sc->sc_tfo_cookie = &tfo_response_cookie;
1355 * Fill in the syncache values.
1358 sc->sc_label = maclabel;
1362 sc->sc_ipopts = ipopts;
1363 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1365 if (!(inc->inc_flags & INC_ISIPV6))
1368 sc->sc_ip_tos = ip_tos;
1369 sc->sc_ip_ttl = ip_ttl;
1373 sc->sc_todctx = todctx;
1375 sc->sc_irs = th->th_seq;
1376 sc->sc_iss = arc4random();
1378 sc->sc_flowlabel = 0;
1381 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1382 * win was derived from socket earlier in the function.
1385 win = imin(win, TCP_MAXWIN);
1388 if (V_tcp_do_rfc1323) {
1390 * A timestamp received in a SYN makes
1391 * it ok to send timestamp requests and replies.
1393 if (to->to_flags & TOF_TS) {
1394 sc->sc_tsreflect = to->to_tsval;
1395 sc->sc_ts = tcp_ts_getticks();
1396 sc->sc_flags |= SCF_TIMESTAMP;
1398 if (to->to_flags & TOF_SCALE) {
1402 * Pick the smallest possible scaling factor that
1403 * will still allow us to scale up to sb_max, aka
1404 * kern.ipc.maxsockbuf.
1406 * We do this because there are broken firewalls that
1407 * will corrupt the window scale option, leading to
1408 * the other endpoint believing that our advertised
1409 * window is unscaled. At scale factors larger than
1410 * 5 the unscaled window will drop below 1500 bytes,
1411 * leading to serious problems when traversing these
1414 * With the default maxsockbuf of 256K, a scale factor
1415 * of 3 will be chosen by this algorithm. Those who
1416 * choose a larger maxsockbuf should watch out
1417 * for the compatiblity problems mentioned above.
1419 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1420 * or <SYN,ACK>) segment itself is never scaled.
1422 while (wscale < TCP_MAX_WINSHIFT &&
1423 (TCP_MAXWIN << wscale) < sb_max)
1425 sc->sc_requested_r_scale = wscale;
1426 sc->sc_requested_s_scale = to->to_wscale;
1427 sc->sc_flags |= SCF_WINSCALE;
1430 #ifdef TCP_SIGNATURE
1432 * If listening socket requested TCP digests, OR received SYN
1433 * contains the option, flag this in the syncache so that
1434 * syncache_respond() will do the right thing with the SYN+ACK.
1436 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1437 sc->sc_flags |= SCF_SIGNATURE;
1439 if (to->to_flags & TOF_SACKPERM)
1440 sc->sc_flags |= SCF_SACK;
1441 if (to->to_flags & TOF_MSS)
1442 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1443 if (ltflags & TF_NOOPT)
1444 sc->sc_flags |= SCF_NOOPT;
1445 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1446 sc->sc_flags |= SCF_ECN;
1448 if (V_tcp_syncookies)
1449 sc->sc_iss = syncookie_generate(sch, sc);
1451 if (autoflowlabel) {
1452 if (V_tcp_syncookies)
1453 sc->sc_flowlabel = sc->sc_iss;
1455 sc->sc_flowlabel = ip6_randomflowlabel();
1456 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1462 if (tfo_cookie_valid) {
1463 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1464 /* INP_WUNLOCK(inp) will be performed by the called */
1471 * Do a standard 3-way handshake.
1473 if (syncache_respond(sc, sch, 0) == 0) {
1474 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1476 else if (sc != &scs)
1477 syncache_insert(sc, sch); /* locks and unlocks sch */
1478 TCPSTAT_INC(tcps_sndacks);
1479 TCPSTAT_INC(tcps_sndtotal);
1483 TCPSTAT_INC(tcps_sc_dropped);
1498 mac_syncache_destroy(&maclabel);
1504 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked)
1506 struct ip *ip = NULL;
1508 struct tcphdr *th = NULL;
1509 int optlen, error = 0; /* Make compiler happy */
1510 u_int16_t hlen, tlen, mssopt;
1513 struct ip6_hdr *ip6 = NULL;
1515 #ifdef TCP_SIGNATURE
1516 struct secasvar *sav;
1521 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1524 tlen = hlen + sizeof(struct tcphdr);
1526 /* Determine MSS we advertize to other end of connection. */
1527 mssopt = tcp_mssopt(&sc->sc_inc);
1528 if (sc->sc_peer_mss)
1529 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1531 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1532 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1533 ("syncache: mbuf too small"));
1535 /* Create the IP+TCP header from scratch. */
1536 m = m_gethdr(M_NOWAIT, MT_DATA);
1540 mac_syncache_create_mbuf(sc->sc_label, m);
1542 m->m_data += max_linkhdr;
1544 m->m_pkthdr.len = tlen;
1545 m->m_pkthdr.rcvif = NULL;
1548 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1549 ip6 = mtod(m, struct ip6_hdr *);
1550 ip6->ip6_vfc = IPV6_VERSION;
1551 ip6->ip6_nxt = IPPROTO_TCP;
1552 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1553 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1554 ip6->ip6_plen = htons(tlen - hlen);
1555 /* ip6_hlim is set after checksum */
1556 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1557 ip6->ip6_flow |= sc->sc_flowlabel;
1559 th = (struct tcphdr *)(ip6 + 1);
1562 #if defined(INET6) && defined(INET)
1567 ip = mtod(m, struct ip *);
1568 ip->ip_v = IPVERSION;
1569 ip->ip_hl = sizeof(struct ip) >> 2;
1570 ip->ip_len = htons(tlen);
1574 ip->ip_p = IPPROTO_TCP;
1575 ip->ip_src = sc->sc_inc.inc_laddr;
1576 ip->ip_dst = sc->sc_inc.inc_faddr;
1577 ip->ip_ttl = sc->sc_ip_ttl;
1578 ip->ip_tos = sc->sc_ip_tos;
1581 * See if we should do MTU discovery. Route lookups are
1582 * expensive, so we will only unset the DF bit if:
1584 * 1) path_mtu_discovery is disabled
1585 * 2) the SCF_UNREACH flag has been set
1587 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1588 ip->ip_off |= htons(IP_DF);
1590 th = (struct tcphdr *)(ip + 1);
1593 th->th_sport = sc->sc_inc.inc_lport;
1594 th->th_dport = sc->sc_inc.inc_fport;
1596 th->th_seq = htonl(sc->sc_iss);
1597 th->th_ack = htonl(sc->sc_irs + 1);
1598 th->th_off = sizeof(struct tcphdr) >> 2;
1600 th->th_flags = TH_SYN|TH_ACK;
1601 th->th_win = htons(sc->sc_wnd);
1604 if (sc->sc_flags & SCF_ECN) {
1605 th->th_flags |= TH_ECE;
1606 TCPSTAT_INC(tcps_ecn_shs);
1609 /* Tack on the TCP options. */
1610 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1614 to.to_flags = TOF_MSS;
1615 if (sc->sc_flags & SCF_WINSCALE) {
1616 to.to_wscale = sc->sc_requested_r_scale;
1617 to.to_flags |= TOF_SCALE;
1619 if (sc->sc_flags & SCF_TIMESTAMP) {
1620 /* Virgin timestamp or TCP cookie enhanced one. */
1621 to.to_tsval = sc->sc_ts;
1622 to.to_tsecr = sc->sc_tsreflect;
1623 to.to_flags |= TOF_TS;
1625 if (sc->sc_flags & SCF_SACK)
1626 to.to_flags |= TOF_SACKPERM;
1627 #ifdef TCP_SIGNATURE
1629 if (sc->sc_flags & SCF_SIGNATURE) {
1630 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1632 to.to_flags |= TOF_SIGNATURE;
1636 * We've got SCF_SIGNATURE flag
1637 * inherited from listening socket,
1638 * but no SADB key for given source
1639 * address. Assume signature is not
1640 * required and remove signature flag
1641 * instead of silently dropping
1646 sc->sc_flags &= ~SCF_SIGNATURE;
1654 if (sc->sc_tfo_cookie) {
1655 to.to_flags |= TOF_FASTOPEN;
1656 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1657 to.to_tfo_cookie = sc->sc_tfo_cookie;
1658 /* don't send cookie again when retransmitting response */
1659 sc->sc_tfo_cookie = NULL;
1662 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1664 /* Adjust headers by option size. */
1665 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1667 m->m_pkthdr.len += optlen;
1669 #ifdef TCP_SIGNATURE
1670 if (sc->sc_flags & SCF_SIGNATURE)
1671 tcp_signature_do_compute(m, 0, optlen,
1672 to.to_signature, sav);
1675 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1676 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1679 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1683 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1684 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1686 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1687 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1688 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1690 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1692 if (ADDED_BY_TOE(sc)) {
1693 struct toedev *tod = sc->sc_tod;
1695 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1700 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1703 #if defined(INET6) && defined(INET)
1708 m->m_pkthdr.csum_flags = CSUM_TCP;
1709 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1710 htons(tlen + optlen - hlen + IPPROTO_TCP));
1712 if (ADDED_BY_TOE(sc)) {
1713 struct toedev *tod = sc->sc_tod;
1715 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1720 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1727 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1728 * that exceed the capacity of the syncache by avoiding the storage of any
1729 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1730 * attacks where the attacker does not have access to our responses.
1732 * Syncookies encode and include all necessary information about the
1733 * connection setup within the SYN|ACK that we send back. That way we
1734 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1735 * (if ever). Normally the syncache and syncookies are running in parallel
1736 * with the latter taking over when the former is exhausted. When matching
1737 * syncache entry is found the syncookie is ignored.
1739 * The only reliable information persisting the 3WHS is our inital sequence
1740 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1741 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1742 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1743 * returns and signifies a legitimate connection if it matches the ACK.
1745 * The available space of 32 bits to store the hash and to encode the SYN
1746 * option information is very tight and we should have at least 24 bits for
1747 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1749 * SYN option information we have to encode to fully restore a connection:
1750 * MSS: is imporant to chose an optimal segment size to avoid IP level
1751 * fragmentation along the path. The common MSS values can be encoded
1752 * in a 3-bit table. Uncommon values are captured by the next lower value
1753 * in the table leading to a slight increase in packetization overhead.
1754 * WSCALE: is necessary to allow large windows to be used for high delay-
1755 * bandwidth product links. Not scaling the window when it was initially
1756 * negotiated is bad for performance as lack of scaling further decreases
1757 * the apparent available send window. We only need to encode the WSCALE
1758 * we received from the remote end. Our end can be recalculated at any
1759 * time. The common WSCALE values can be encoded in a 3-bit table.
1760 * Uncommon values are captured by the next lower value in the table
1761 * making us under-estimate the available window size halving our
1762 * theoretically possible maximum throughput for that connection.
1763 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1764 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1765 * that are included in all segments on a connection. We enable them when
1768 * Security of syncookies and attack vectors:
1770 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1771 * together with the gloabl secret to make it unique per connection attempt.
1772 * Thus any change of any of those parameters results in a different MAC output
1773 * in an unpredictable way unless a collision is encountered. 24 bits of the
1774 * MAC are embedded into the ISS.
1776 * To prevent replay attacks two rotating global secrets are updated with a
1777 * new random value every 15 seconds. The life-time of a syncookie is thus
1780 * Vector 1: Attacking the secret. This requires finding a weakness in the
1781 * MAC itself or the way it is used here. The attacker can do a chosen plain
1782 * text attack by varying and testing the all parameters under his control.
1783 * The strength depends on the size and randomness of the secret, and the
1784 * cryptographic security of the MAC function. Due to the constant updating
1785 * of the secret the attacker has at most 29.999 seconds to find the secret
1786 * and launch spoofed connections. After that he has to start all over again.
1788 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1789 * size an average of 4,823 attempts are required for a 50% chance of success
1790 * to spoof a single syncookie (birthday collision paradox). However the
1791 * attacker is blind and doesn't know if one of his attempts succeeded unless
1792 * he has a side channel to interfere success from. A single connection setup
1793 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1794 * This many attempts are required for each one blind spoofed connection. For
1795 * every additional spoofed connection he has to launch another N attempts.
1796 * Thus for a sustained rate 100 spoofed connections per second approximately
1797 * 1,800,000 packets per second would have to be sent.
1799 * NB: The MAC function should be fast so that it doesn't become a CPU
1800 * exhaustion attack vector itself.
1803 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1804 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1805 * http://cr.yp.to/syncookies.html (overview)
1806 * http://cr.yp.to/syncookies/archive (details)
1809 * Schematic construction of a syncookie enabled Initial Sequence Number:
1811 * 12345678901234567890123456789012
1812 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1814 * x 24 MAC (truncated)
1815 * W 3 Send Window Scale index
1817 * S 1 SACK permitted
1818 * P 1 Odd/even secret
1822 * Distribution and probability of certain MSS values. Those in between are
1823 * rounded down to the next lower one.
1824 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1825 * .2% .3% 5% 7% 7% 20% 15% 45%
1827 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1830 * Distribution and probability of certain WSCALE values. We have to map the
1831 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1832 * bits based on prevalence of certain values. Where we don't have an exact
1833 * match for are rounded down to the next lower one letting us under-estimate
1834 * the true available window. At the moment this would happen only for the
1835 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1836 * and window size). The absence of the WSCALE option (no scaling in either
1837 * direction) is encoded with index zero.
1838 * [WSCALE values histograms, Allman, 2012]
1839 * X 10 10 35 5 6 14 10% by host
1840 * X 11 4 5 5 18 49 3% by connections
1842 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1845 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1846 * and good cryptographic properties.
1849 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1850 uint8_t *secbits, uintptr_t secmod)
1853 uint32_t siphash[2];
1855 SipHash24_Init(&ctx);
1856 SipHash_SetKey(&ctx, secbits);
1857 switch (inc->inc_flags & INC_ISIPV6) {
1860 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1861 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1866 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1867 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1871 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1872 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1873 SipHash_Update(&ctx, &irs, sizeof(irs));
1874 SipHash_Update(&ctx, &flags, sizeof(flags));
1875 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1876 SipHash_Final((u_int8_t *)&siphash, &ctx);
1878 return (siphash[0] ^ siphash[1]);
1882 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1884 u_int i, mss, secbit, wscale;
1887 union syncookie cookie;
1889 SCH_LOCK_ASSERT(sch);
1893 /* Map our computed MSS into the 3-bit index. */
1894 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1895 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1896 tcp_sc_msstab[i] > mss && i > 0;
1899 cookie.flags.mss_idx = i;
1902 * Map the send window scale into the 3-bit index but only if
1903 * the wscale option was received.
1905 if (sc->sc_flags & SCF_WINSCALE) {
1906 wscale = sc->sc_requested_s_scale;
1907 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1908 tcp_sc_wstab[i] > wscale && i > 0;
1911 cookie.flags.wscale_idx = i;
1914 /* Can we do SACK? */
1915 if (sc->sc_flags & SCF_SACK)
1916 cookie.flags.sack_ok = 1;
1918 /* Which of the two secrets to use. */
1919 secbit = sch->sch_sc->secret.oddeven & 0x1;
1920 cookie.flags.odd_even = secbit;
1922 secbits = sch->sch_sc->secret.key[secbit];
1923 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1927 * Put the flags into the hash and XOR them to get better ISS number
1928 * variance. This doesn't enhance the cryptographic strength and is
1929 * done to prevent the 8 cookie bits from showing up directly on the
1933 iss |= cookie.cookie ^ (hash >> 24);
1935 /* Randomize the timestamp. */
1936 if (sc->sc_flags & SCF_TIMESTAMP) {
1937 sc->sc_ts = arc4random();
1938 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1941 TCPSTAT_INC(tcps_sc_sendcookie);
1945 static struct syncache *
1946 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1947 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1953 int wnd, wscale = 0;
1954 union syncookie cookie;
1956 SCH_LOCK_ASSERT(sch);
1959 * Pull information out of SYN-ACK/ACK and revert sequence number
1962 ack = th->th_ack - 1;
1963 seq = th->th_seq - 1;
1966 * Unpack the flags containing enough information to restore the
1969 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1971 /* Which of the two secrets to use. */
1972 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1974 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1976 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1977 if ((ack & ~0xff) != (hash & ~0xff))
1980 /* Fill in the syncache values. */
1982 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1983 sc->sc_ipopts = NULL;
1988 switch (inc->inc_flags & INC_ISIPV6) {
1991 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1992 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1997 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1998 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2003 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2005 /* We can simply recompute receive window scale we sent earlier. */
2006 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2009 /* Only use wscale if it was enabled in the orignal SYN. */
2010 if (cookie.flags.wscale_idx > 0) {
2011 sc->sc_requested_r_scale = wscale;
2012 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2013 sc->sc_flags |= SCF_WINSCALE;
2016 wnd = sbspace(&lso->so_rcv);
2018 wnd = imin(wnd, TCP_MAXWIN);
2021 if (cookie.flags.sack_ok)
2022 sc->sc_flags |= SCF_SACK;
2024 if (to->to_flags & TOF_TS) {
2025 sc->sc_flags |= SCF_TIMESTAMP;
2026 sc->sc_tsreflect = to->to_tsval;
2027 sc->sc_ts = to->to_tsecr;
2028 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2031 if (to->to_flags & TOF_SIGNATURE)
2032 sc->sc_flags |= SCF_SIGNATURE;
2036 TCPSTAT_INC(tcps_sc_recvcookie);
2042 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2043 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2046 struct syncache scs, *scx;
2049 bzero(&scs, sizeof(scs));
2050 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2052 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2056 if (sc->sc_peer_mss != scx->sc_peer_mss)
2057 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2058 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2060 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2061 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2062 s, __func__, sc->sc_requested_r_scale,
2063 scx->sc_requested_r_scale);
2065 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2066 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2067 s, __func__, sc->sc_requested_s_scale,
2068 scx->sc_requested_s_scale);
2070 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2071 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2078 #endif /* INVARIANTS */
2081 syncookie_reseed(void *arg)
2083 struct tcp_syncache *sc = arg;
2088 * Reseeding the secret doesn't have to be protected by a lock.
2089 * It only must be ensured that the new random values are visible
2090 * to all CPUs in a SMP environment. The atomic with release
2091 * semantics ensures that.
2093 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2094 secbits = sc->secret.key[secbit];
2095 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2096 atomic_add_rel_int(&sc->secret.oddeven, 1);
2098 /* Reschedule ourself. */
2099 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2103 * Exports the syncache entries to userland so that netstat can display
2104 * them alongside the other sockets. This function is intended to be
2105 * called only from tcp_pcblist.
2107 * Due to concurrency on an active system, the number of pcbs exported
2108 * may have no relation to max_pcbs. max_pcbs merely indicates the
2109 * amount of space the caller allocated for this function to use.
2112 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2115 struct syncache *sc;
2116 struct syncache_head *sch;
2117 int count, error, i;
2119 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2120 sch = &V_tcp_syncache.hashbase[i];
2122 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2123 if (count >= max_pcbs) {
2127 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2129 bzero(&xt, sizeof(xt));
2130 xt.xt_len = sizeof(xt);
2131 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2132 xt.xt_inp.inp_vflag = INP_IPV6;
2134 xt.xt_inp.inp_vflag = INP_IPV4;
2135 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2136 xt.xt_tp.t_inpcb = &xt.xt_inp;
2137 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2138 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2139 xt.xt_socket.xso_len = sizeof (struct xsocket);
2140 xt.xt_socket.so_type = SOCK_STREAM;
2141 xt.xt_socket.so_state = SS_ISCONNECTING;
2142 error = SYSCTL_OUT(req, &xt, sizeof xt);
2152 *pcbs_exported = count;