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 TCPSTAT_INC(tcps_sc_added);
358 * Remove and free entry from syncache bucket row.
359 * Expects locked syncache head.
362 syncache_drop(struct syncache *sc, struct syncache_head *sch)
365 SCH_LOCK_ASSERT(sch);
367 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
371 if (ADDED_BY_TOE(sc)) {
372 struct toedev *tod = sc->sc_tod;
374 tod->tod_syncache_removed(tod, sc->sc_todctx);
382 * Engage/reengage time on bucket row.
385 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
387 sc->sc_rxttime = ticks +
388 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
390 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
391 sch->sch_nextc = sc->sc_rxttime;
393 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
394 syncache_timer, (void *)sch);
399 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
400 * If we have retransmitted an entry the maximum number of times, expire it.
401 * One separate timer for each bucket row.
404 syncache_timer(void *xsch)
406 struct syncache_head *sch = (struct syncache_head *)xsch;
407 struct syncache *sc, *nsc;
411 CURVNET_SET(sch->sch_sc->vnet);
413 /* NB: syncache_head has already been locked by the callout. */
414 SCH_LOCK_ASSERT(sch);
417 * In the following cycle we may remove some entries and/or
418 * advance some timeouts, so re-initialize the bucket timer.
420 sch->sch_nextc = tick + INT_MAX;
422 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
424 * We do not check if the listen socket still exists
425 * and accept the case where the listen socket may be
426 * gone by the time we resend the SYN/ACK. We do
427 * not expect this to happens often. If it does,
428 * then the RST will be sent by the time the remote
429 * host does the SYN/ACK->ACK.
431 if (TSTMP_GT(sc->sc_rxttime, tick)) {
432 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
433 sch->sch_nextc = sc->sc_rxttime;
436 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
437 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
438 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
439 "giving up and removing syncache entry\n",
443 syncache_drop(sc, sch);
444 TCPSTAT_INC(tcps_sc_stale);
447 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
448 log(LOG_DEBUG, "%s; %s: Response timeout, "
449 "retransmitting (%u) SYN|ACK\n",
450 s, __func__, sc->sc_rxmits);
454 syncache_respond(sc, sch, 1);
455 TCPSTAT_INC(tcps_sc_retransmitted);
456 syncache_timeout(sc, sch, 0);
458 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
459 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
460 syncache_timer, (void *)(sch));
465 * Find an entry in the syncache.
466 * Returns always with locked syncache_head plus a matching entry or NULL.
468 static struct syncache *
469 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
472 struct syncache_head *sch;
476 * The hash is built on foreign port + local port + foreign address.
477 * We rely on the fact that struct in_conninfo starts with 16 bits
478 * of foreign port, then 16 bits of local port then followed by 128
479 * bits of foreign address. In case of IPv4 address, the first 3
480 * 32-bit words of the address always are zeroes.
482 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
483 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
485 sch = &V_tcp_syncache.hashbase[hash];
489 /* Circle through bucket row to find matching entry. */
490 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
491 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
492 sizeof(struct in_endpoints)) == 0)
495 return (sc); /* Always returns with locked sch. */
499 * This function is called when we get a RST for a
500 * non-existent connection, so that we can see if the
501 * connection is in the syn cache. If it is, zap it.
504 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
507 struct syncache_head *sch;
510 sc = syncache_lookup(inc, &sch); /* returns locked sch */
511 SCH_LOCK_ASSERT(sch);
514 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
515 * See RFC 793 page 65, section SEGMENT ARRIVES.
517 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
518 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
519 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
520 "FIN flag set, segment ignored\n", s, __func__);
521 TCPSTAT_INC(tcps_badrst);
526 * No corresponding connection was found in syncache.
527 * If syncookies are enabled and possibly exclusively
528 * used, or we are under memory pressure, a valid RST
529 * may not find a syncache entry. In that case we're
530 * done and no SYN|ACK retransmissions will happen.
531 * Otherwise the RST was misdirected or spoofed.
534 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
535 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
536 "syncache entry (possibly syncookie only), "
537 "segment ignored\n", s, __func__);
538 TCPSTAT_INC(tcps_badrst);
543 * If the RST bit is set, check the sequence number to see
544 * if this is a valid reset segment.
546 * In all states except SYN-SENT, all reset (RST) segments
547 * are validated by checking their SEQ-fields. A reset is
548 * valid if its sequence number is in the window.
550 * The sequence number in the reset segment is normally an
551 * echo of our outgoing acknowlegement numbers, but some hosts
552 * send a reset with the sequence number at the rightmost edge
553 * of our receive window, and we have to handle this case.
555 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
556 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
557 syncache_drop(sc, sch);
558 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
559 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
560 "connection attempt aborted by remote endpoint\n",
562 TCPSTAT_INC(tcps_sc_reset);
564 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
565 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
566 "IRS %u (+WND %u), segment ignored\n",
567 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
568 TCPSTAT_INC(tcps_badrst);
578 syncache_badack(struct in_conninfo *inc)
581 struct syncache_head *sch;
583 sc = syncache_lookup(inc, &sch); /* returns locked sch */
584 SCH_LOCK_ASSERT(sch);
586 syncache_drop(sc, sch);
587 TCPSTAT_INC(tcps_sc_badack);
593 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
596 struct syncache_head *sch;
598 sc = syncache_lookup(inc, &sch); /* returns locked sch */
599 SCH_LOCK_ASSERT(sch);
603 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
604 if (ntohl(th->th_seq) != sc->sc_iss)
608 * If we've rertransmitted 3 times and this is our second error,
609 * we remove the entry. Otherwise, we allow it to continue on.
610 * This prevents us from incorrectly nuking an entry during a
611 * spurious network outage.
615 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
616 sc->sc_flags |= SCF_UNREACH;
619 syncache_drop(sc, sch);
620 TCPSTAT_INC(tcps_sc_unreach);
626 * Build a new TCP socket structure from a syncache entry.
628 * On success return the newly created socket with its underlying inp locked.
630 static struct socket *
631 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
633 struct tcp_function_block *blk;
634 struct inpcb *inp = NULL;
640 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
643 * Ok, create the full blown connection, and set things up
644 * as they would have been set up if we had created the
645 * connection when the SYN arrived. If we can't create
646 * the connection, abort it.
648 so = sonewconn(lso, 0);
651 * Drop the connection; we will either send a RST or
652 * have the peer retransmit its SYN again after its
655 TCPSTAT_INC(tcps_listendrop);
656 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
657 log(LOG_DEBUG, "%s; %s: Socket create failed "
658 "due to limits or memory shortage\n",
665 mac_socketpeer_set_from_mbuf(m, so);
669 inp->inp_inc.inc_fibnum = so->so_fibnum;
672 * Exclusive pcbinfo lock is not required in syncache socket case even
673 * if two inpcb locks can be acquired simultaneously:
674 * - the inpcb in LISTEN state,
675 * - the newly created inp.
677 * In this case, an inp cannot be at same time in LISTEN state and
678 * just created by an accept() call.
680 INP_HASH_WLOCK(&V_tcbinfo);
682 /* Insert new socket into PCB hash list. */
683 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
685 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
686 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
688 inp->inp_vflag &= ~INP_IPV6;
689 inp->inp_vflag |= INP_IPV4;
691 inp->inp_laddr = sc->sc_inc.inc_laddr;
697 * If there's an mbuf and it has a flowid, then let's initialise the
698 * inp with that particular flowid.
700 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
701 inp->inp_flowid = m->m_pkthdr.flowid;
702 inp->inp_flowtype = M_HASHTYPE_GET(m);
706 * Install in the reservation hash table for now, but don't yet
707 * install a connection group since the full 4-tuple isn't yet
710 inp->inp_lport = sc->sc_inc.inc_lport;
711 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
713 * Undo the assignments above if we failed to
714 * put the PCB on the hash lists.
717 if (sc->sc_inc.inc_flags & INC_ISIPV6)
718 inp->in6p_laddr = in6addr_any;
721 inp->inp_laddr.s_addr = INADDR_ANY;
723 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
724 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
729 INP_HASH_WUNLOCK(&V_tcbinfo);
733 /* Copy old policy into new socket's. */
734 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
735 printf("syncache_socket: could not copy policy\n");
738 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
739 struct inpcb *oinp = sotoinpcb(lso);
740 struct in6_addr laddr6;
741 struct sockaddr_in6 sin6;
743 * Inherit socket options from the listening socket.
744 * Note that in6p_inputopts are not (and should not be)
745 * copied, since it stores previously received options and is
746 * used to detect if each new option is different than the
747 * previous one and hence should be passed to a user.
748 * If we copied in6p_inputopts, a user would not be able to
749 * receive options just after calling the accept system call.
751 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
752 if (oinp->in6p_outputopts)
753 inp->in6p_outputopts =
754 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
756 sin6.sin6_family = AF_INET6;
757 sin6.sin6_len = sizeof(sin6);
758 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
759 sin6.sin6_port = sc->sc_inc.inc_fport;
760 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
761 laddr6 = inp->in6p_laddr;
762 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
763 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
764 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
765 thread0.td_ucred, m)) != 0) {
766 inp->in6p_laddr = laddr6;
767 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
768 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
773 INP_HASH_WUNLOCK(&V_tcbinfo);
776 /* Override flowlabel from in6_pcbconnect. */
777 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
778 inp->inp_flow |= sc->sc_flowlabel;
781 #if defined(INET) && defined(INET6)
786 struct in_addr laddr;
787 struct sockaddr_in sin;
789 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
791 if (inp->inp_options == NULL) {
792 inp->inp_options = sc->sc_ipopts;
793 sc->sc_ipopts = NULL;
796 sin.sin_family = AF_INET;
797 sin.sin_len = sizeof(sin);
798 sin.sin_addr = sc->sc_inc.inc_faddr;
799 sin.sin_port = sc->sc_inc.inc_fport;
800 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
801 laddr = inp->inp_laddr;
802 if (inp->inp_laddr.s_addr == INADDR_ANY)
803 inp->inp_laddr = sc->sc_inc.inc_laddr;
804 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
805 thread0.td_ucred, m)) != 0) {
806 inp->inp_laddr = laddr;
807 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
808 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
813 INP_HASH_WUNLOCK(&V_tcbinfo);
818 INP_HASH_WUNLOCK(&V_tcbinfo);
820 tcp_state_change(tp, TCPS_SYN_RECEIVED);
821 tp->iss = sc->sc_iss;
822 tp->irs = sc->sc_irs;
825 blk = sototcpcb(lso)->t_fb;
826 if (blk != tp->t_fb) {
828 * Our parents t_fb was not the default,
829 * we need to release our ref on tp->t_fb and
830 * pickup one on the new entry.
832 struct tcp_function_block *rblk;
834 rblk = find_and_ref_tcp_fb(blk);
835 KASSERT(rblk != NULL,
836 ("cannot find blk %p out of syncache?", blk));
837 if (tp->t_fb->tfb_tcp_fb_fini)
838 (*tp->t_fb->tfb_tcp_fb_fini)(tp);
839 refcount_release(&tp->t_fb->tfb_refcnt);
841 if (tp->t_fb->tfb_tcp_fb_init) {
842 (*tp->t_fb->tfb_tcp_fb_init)(tp);
845 tp->snd_wl1 = sc->sc_irs;
846 tp->snd_max = tp->iss + 1;
847 tp->snd_nxt = tp->iss + 1;
848 tp->rcv_up = sc->sc_irs + 1;
849 tp->rcv_wnd = sc->sc_wnd;
850 tp->rcv_adv += tp->rcv_wnd;
851 tp->last_ack_sent = tp->rcv_nxt;
853 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
854 if (sc->sc_flags & SCF_NOOPT)
855 tp->t_flags |= TF_NOOPT;
857 if (sc->sc_flags & SCF_WINSCALE) {
858 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
859 tp->snd_scale = sc->sc_requested_s_scale;
860 tp->request_r_scale = sc->sc_requested_r_scale;
862 if (sc->sc_flags & SCF_TIMESTAMP) {
863 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
864 tp->ts_recent = sc->sc_tsreflect;
865 tp->ts_recent_age = tcp_ts_getticks();
866 tp->ts_offset = sc->sc_tsoff;
869 if (sc->sc_flags & SCF_SIGNATURE)
870 tp->t_flags |= TF_SIGNATURE;
872 if (sc->sc_flags & SCF_SACK)
873 tp->t_flags |= TF_SACK_PERMIT;
876 if (sc->sc_flags & SCF_ECN)
877 tp->t_flags |= TF_ECN_PERMIT;
880 * Set up MSS and get cached values from tcp_hostcache.
881 * This might overwrite some of the defaults we just set.
883 tcp_mss(tp, sc->sc_peer_mss);
886 * If the SYN,ACK was retransmitted, indicate that CWND to be
887 * limited to one segment in cc_conn_init().
888 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
890 if (sc->sc_rxmits > 1)
895 * Allow a TOE driver to install its hooks. Note that we hold the
896 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
897 * new connection before the TOE driver has done its thing.
899 if (ADDED_BY_TOE(sc)) {
900 struct toedev *tod = sc->sc_tod;
902 tod->tod_offload_socket(tod, sc->sc_todctx, so);
906 * Copy and activate timers.
908 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
909 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
910 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
911 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
912 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
916 TCPSTAT_INC(tcps_accepts);
928 * This function gets called when we receive an ACK for a
929 * socket in the LISTEN state. We look up the connection
930 * in the syncache, and if its there, we pull it out of
931 * the cache and turn it into a full-blown connection in
932 * the SYN-RECEIVED state.
934 * On syncache_socket() success the newly created socket
935 * has its underlying inp locked.
938 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
939 struct socket **lsop, struct mbuf *m)
942 struct syncache_head *sch;
947 * Global TCP locks are held because we manipulate the PCB lists
948 * and create a new socket.
950 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
951 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
952 ("%s: can handle only ACK", __func__));
954 sc = syncache_lookup(inc, &sch); /* returns locked sch */
955 SCH_LOCK_ASSERT(sch);
959 * Test code for syncookies comparing the syncache stored
960 * values with the reconstructed values from the cookie.
963 syncookie_cmp(inc, sch, sc, th, to, *lsop);
968 * There is no syncache entry, so see if this ACK is
969 * a returning syncookie. To do this, first:
970 * A. See if this socket has had a syncache entry dropped in
971 * the past. We don't want to accept a bogus syncookie
972 * if we've never received a SYN.
973 * B. check that the syncookie is valid. If it is, then
974 * cobble up a fake syncache entry, and return.
976 if (!V_tcp_syncookies) {
978 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
979 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
980 "segment rejected (syncookies disabled)\n",
984 bzero(&scs, sizeof(scs));
985 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
988 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
989 log(LOG_DEBUG, "%s; %s: Segment failed "
990 "SYNCOOKIE authentication, segment rejected "
991 "(probably spoofed)\n", s, __func__);
995 /* Pull out the entry to unlock the bucket row. */
996 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
999 if (ADDED_BY_TOE(sc)) {
1000 struct toedev *tod = sc->sc_tod;
1002 tod->tod_syncache_removed(tod, sc->sc_todctx);
1009 * Segment validation:
1010 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1012 if (th->th_ack != sc->sc_iss + 1) {
1013 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1014 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1015 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1020 * The SEQ must fall in the window starting at the received
1021 * initial receive sequence number + 1 (the SYN).
1023 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1024 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1025 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1026 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1027 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1032 * If timestamps were not negotiated during SYN/ACK they
1033 * must not appear on any segment during this session.
1035 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1036 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1037 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1038 "segment rejected\n", s, __func__);
1043 * If timestamps were negotiated during SYN/ACK they should
1044 * appear on every segment during this session.
1045 * XXXAO: This is only informal as there have been unverified
1046 * reports of non-compliants stacks.
1048 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1049 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1050 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1051 "no action\n", s, __func__);
1058 * If timestamps were negotiated the reflected timestamp
1059 * must be equal to what we actually sent in the SYN|ACK.
1061 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1062 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1063 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1064 "segment rejected\n",
1065 s, __func__, to->to_tsecr, sc->sc_ts);
1069 *lsop = syncache_socket(sc, *lsop, m);
1072 TCPSTAT_INC(tcps_sc_aborted);
1074 TCPSTAT_INC(tcps_sc_completed);
1076 /* how do we find the inp for the new socket? */
1081 if (sc != NULL && sc != &scs)
1091 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1092 uint64_t response_cookie)
1096 unsigned int *pending_counter;
1099 * Global TCP locks are held because we manipulate the PCB lists
1100 * and create a new socket.
1102 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1104 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1105 *lsop = syncache_socket(sc, *lsop, m);
1106 if (*lsop == NULL) {
1107 TCPSTAT_INC(tcps_sc_aborted);
1108 atomic_subtract_int(pending_counter, 1);
1110 inp = sotoinpcb(*lsop);
1111 tp = intotcpcb(inp);
1112 tp->t_flags |= TF_FASTOPEN;
1113 tp->t_tfo_cookie = response_cookie;
1114 tp->snd_max = tp->iss;
1115 tp->snd_nxt = tp->iss;
1116 tp->t_tfo_pending = pending_counter;
1117 TCPSTAT_INC(tcps_sc_completed);
1120 #endif /* TCP_RFC7413 */
1123 * Given a LISTEN socket and an inbound SYN request, add
1124 * this to the syn cache, and send back a segment:
1125 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1128 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1129 * Doing so would require that we hold onto the data and deliver it
1130 * to the application. However, if we are the target of a SYN-flood
1131 * DoS attack, an attacker could send data which would eventually
1132 * consume all available buffer space if it were ACKed. By not ACKing
1133 * the data, we avoid this DoS scenario.
1135 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1136 * cookie is processed, V_tcp_fastopen_enabled set to true, and the
1137 * TCP_FASTOPEN socket option is set. In this case, a new socket is created
1138 * and returned via lsop, the mbuf is not freed so that tcp_input() can
1139 * queue its data to the socket, and 1 is returned to indicate the
1140 * TFO-socket-creation path was taken.
1143 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1144 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1149 struct syncache *sc = NULL;
1150 struct syncache_head *sch;
1151 struct mbuf *ipopts = NULL;
1153 int win, sb_hiwat, ip_ttl, ip_tos;
1157 int autoflowlabel = 0;
1160 struct label *maclabel;
1162 struct syncache scs;
1165 uint64_t tfo_response_cookie;
1166 int tfo_cookie_valid = 0;
1167 int tfo_response_cookie_valid = 0;
1170 INP_WLOCK_ASSERT(inp); /* listen socket */
1171 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1172 ("%s: unexpected tcp flags", __func__));
1175 * Combine all so/tp operations very early to drop the INP lock as
1180 cred = crhold(so->so_cred);
1183 if ((inc->inc_flags & INC_ISIPV6) &&
1184 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1187 ip_ttl = inp->inp_ip_ttl;
1188 ip_tos = inp->inp_ip_tos;
1189 win = sbspace(&so->so_rcv);
1190 sb_hiwat = so->so_rcv.sb_hiwat;
1191 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1194 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
1195 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1197 * Limit the number of pending TFO connections to
1198 * approximately half of the queue limit. This prevents TFO
1199 * SYN floods from starving the service by filling the
1200 * listen queue with bogus TFO connections.
1202 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1203 (so->so_qlimit / 2)) {
1206 result = tcp_fastopen_check_cookie(inc,
1207 to->to_tfo_cookie, to->to_tfo_len,
1208 &tfo_response_cookie);
1209 tfo_cookie_valid = (result > 0);
1210 tfo_response_cookie_valid = (result >= 0);
1212 atomic_subtract_int(tp->t_tfo_pending, 1);
1216 /* By the time we drop the lock these should no longer be used. */
1221 if (mac_syncache_init(&maclabel) != 0) {
1225 mac_syncache_create(maclabel, inp);
1228 if (!tfo_cookie_valid)
1233 * Remember the IP options, if any.
1236 if (!(inc->inc_flags & INC_ISIPV6))
1239 ipopts = (m) ? ip_srcroute(m) : NULL;
1245 * See if we already have an entry for this connection.
1246 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1248 * XXX: should the syncache be re-initialized with the contents
1249 * of the new SYN here (which may have different options?)
1251 * XXX: We do not check the sequence number to see if this is a
1252 * real retransmit or a new connection attempt. The question is
1253 * how to handle such a case; either ignore it as spoofed, or
1254 * drop the current entry and create a new one?
1256 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1257 SCH_LOCK_ASSERT(sch);
1260 if (tfo_cookie_valid)
1263 TCPSTAT_INC(tcps_sc_dupsyn);
1266 * If we were remembering a previous source route,
1267 * forget it and use the new one we've been given.
1270 (void) m_free(sc->sc_ipopts);
1271 sc->sc_ipopts = ipopts;
1274 * Update timestamp if present.
1276 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1277 sc->sc_tsreflect = to->to_tsval;
1279 sc->sc_flags &= ~SCF_TIMESTAMP;
1282 * Since we have already unconditionally allocated label
1283 * storage, free it up. The syncache entry will already
1284 * have an initialized label we can use.
1286 mac_syncache_destroy(&maclabel);
1288 /* Retransmit SYN|ACK and reset retransmit count. */
1289 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1290 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1291 "resetting timer and retransmitting SYN|ACK\n",
1295 if (syncache_respond(sc, sch, 1) == 0) {
1297 syncache_timeout(sc, sch, 1);
1298 TCPSTAT_INC(tcps_sndacks);
1299 TCPSTAT_INC(tcps_sndtotal);
1306 if (tfo_cookie_valid) {
1307 bzero(&scs, sizeof(scs));
1313 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1316 * The zone allocator couldn't provide more entries.
1317 * Treat this as if the cache was full; drop the oldest
1318 * entry and insert the new one.
1320 TCPSTAT_INC(tcps_sc_zonefail);
1321 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1322 syncache_drop(sc, sch);
1323 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1325 if (V_tcp_syncookies) {
1326 bzero(&scs, sizeof(scs));
1331 (void) m_free(ipopts);
1339 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1340 sc->sc_tfo_cookie = &tfo_response_cookie;
1344 * Fill in the syncache values.
1347 sc->sc_label = maclabel;
1351 sc->sc_ipopts = ipopts;
1352 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1354 if (!(inc->inc_flags & INC_ISIPV6))
1357 sc->sc_ip_tos = ip_tos;
1358 sc->sc_ip_ttl = ip_ttl;
1362 sc->sc_todctx = todctx;
1364 sc->sc_irs = th->th_seq;
1365 sc->sc_iss = arc4random();
1367 sc->sc_flowlabel = 0;
1370 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1371 * win was derived from socket earlier in the function.
1374 win = imin(win, TCP_MAXWIN);
1377 if (V_tcp_do_rfc1323) {
1379 * A timestamp received in a SYN makes
1380 * it ok to send timestamp requests and replies.
1382 if (to->to_flags & TOF_TS) {
1383 sc->sc_tsreflect = to->to_tsval;
1384 sc->sc_ts = tcp_ts_getticks();
1385 sc->sc_flags |= SCF_TIMESTAMP;
1387 if (to->to_flags & TOF_SCALE) {
1391 * Pick the smallest possible scaling factor that
1392 * will still allow us to scale up to sb_max, aka
1393 * kern.ipc.maxsockbuf.
1395 * We do this because there are broken firewalls that
1396 * will corrupt the window scale option, leading to
1397 * the other endpoint believing that our advertised
1398 * window is unscaled. At scale factors larger than
1399 * 5 the unscaled window will drop below 1500 bytes,
1400 * leading to serious problems when traversing these
1403 * With the default maxsockbuf of 256K, a scale factor
1404 * of 3 will be chosen by this algorithm. Those who
1405 * choose a larger maxsockbuf should watch out
1406 * for the compatiblity problems mentioned above.
1408 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1409 * or <SYN,ACK>) segment itself is never scaled.
1411 while (wscale < TCP_MAX_WINSHIFT &&
1412 (TCP_MAXWIN << wscale) < sb_max)
1414 sc->sc_requested_r_scale = wscale;
1415 sc->sc_requested_s_scale = to->to_wscale;
1416 sc->sc_flags |= SCF_WINSCALE;
1419 #ifdef TCP_SIGNATURE
1421 * If listening socket requested TCP digests, OR received SYN
1422 * contains the option, flag this in the syncache so that
1423 * syncache_respond() will do the right thing with the SYN+ACK.
1425 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1426 sc->sc_flags |= SCF_SIGNATURE;
1428 if (to->to_flags & TOF_SACKPERM)
1429 sc->sc_flags |= SCF_SACK;
1430 if (to->to_flags & TOF_MSS)
1431 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1432 if (ltflags & TF_NOOPT)
1433 sc->sc_flags |= SCF_NOOPT;
1434 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1435 sc->sc_flags |= SCF_ECN;
1437 if (V_tcp_syncookies)
1438 sc->sc_iss = syncookie_generate(sch, sc);
1440 if (autoflowlabel) {
1441 if (V_tcp_syncookies)
1442 sc->sc_flowlabel = sc->sc_iss;
1444 sc->sc_flowlabel = ip6_randomflowlabel();
1445 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1451 if (tfo_cookie_valid) {
1452 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1453 /* INP_WUNLOCK(inp) will be performed by the called */
1460 * Do a standard 3-way handshake.
1462 if (syncache_respond(sc, sch, 0) == 0) {
1463 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1465 else if (sc != &scs)
1466 syncache_insert(sc, sch); /* locks and unlocks sch */
1467 TCPSTAT_INC(tcps_sndacks);
1468 TCPSTAT_INC(tcps_sndtotal);
1472 TCPSTAT_INC(tcps_sc_dropped);
1487 mac_syncache_destroy(&maclabel);
1493 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked)
1495 struct ip *ip = NULL;
1497 struct tcphdr *th = NULL;
1498 int optlen, error = 0; /* Make compiler happy */
1499 u_int16_t hlen, tlen, mssopt;
1502 struct ip6_hdr *ip6 = NULL;
1504 #ifdef TCP_SIGNATURE
1505 struct secasvar *sav;
1510 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1513 tlen = hlen + sizeof(struct tcphdr);
1515 /* Determine MSS we advertize to other end of connection. */
1516 mssopt = tcp_mssopt(&sc->sc_inc);
1517 if (sc->sc_peer_mss)
1518 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1520 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1521 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1522 ("syncache: mbuf too small"));
1524 /* Create the IP+TCP header from scratch. */
1525 m = m_gethdr(M_NOWAIT, MT_DATA);
1529 mac_syncache_create_mbuf(sc->sc_label, m);
1531 m->m_data += max_linkhdr;
1533 m->m_pkthdr.len = tlen;
1534 m->m_pkthdr.rcvif = NULL;
1537 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1538 ip6 = mtod(m, struct ip6_hdr *);
1539 ip6->ip6_vfc = IPV6_VERSION;
1540 ip6->ip6_nxt = IPPROTO_TCP;
1541 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1542 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1543 ip6->ip6_plen = htons(tlen - hlen);
1544 /* ip6_hlim is set after checksum */
1545 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1546 ip6->ip6_flow |= sc->sc_flowlabel;
1548 th = (struct tcphdr *)(ip6 + 1);
1551 #if defined(INET6) && defined(INET)
1556 ip = mtod(m, struct ip *);
1557 ip->ip_v = IPVERSION;
1558 ip->ip_hl = sizeof(struct ip) >> 2;
1559 ip->ip_len = htons(tlen);
1563 ip->ip_p = IPPROTO_TCP;
1564 ip->ip_src = sc->sc_inc.inc_laddr;
1565 ip->ip_dst = sc->sc_inc.inc_faddr;
1566 ip->ip_ttl = sc->sc_ip_ttl;
1567 ip->ip_tos = sc->sc_ip_tos;
1570 * See if we should do MTU discovery. Route lookups are
1571 * expensive, so we will only unset the DF bit if:
1573 * 1) path_mtu_discovery is disabled
1574 * 2) the SCF_UNREACH flag has been set
1576 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1577 ip->ip_off |= htons(IP_DF);
1579 th = (struct tcphdr *)(ip + 1);
1582 th->th_sport = sc->sc_inc.inc_lport;
1583 th->th_dport = sc->sc_inc.inc_fport;
1585 th->th_seq = htonl(sc->sc_iss);
1586 th->th_ack = htonl(sc->sc_irs + 1);
1587 th->th_off = sizeof(struct tcphdr) >> 2;
1589 th->th_flags = TH_SYN|TH_ACK;
1590 th->th_win = htons(sc->sc_wnd);
1593 if (sc->sc_flags & SCF_ECN) {
1594 th->th_flags |= TH_ECE;
1595 TCPSTAT_INC(tcps_ecn_shs);
1598 /* Tack on the TCP options. */
1599 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1603 to.to_flags = TOF_MSS;
1604 if (sc->sc_flags & SCF_WINSCALE) {
1605 to.to_wscale = sc->sc_requested_r_scale;
1606 to.to_flags |= TOF_SCALE;
1608 if (sc->sc_flags & SCF_TIMESTAMP) {
1609 /* Virgin timestamp or TCP cookie enhanced one. */
1610 to.to_tsval = sc->sc_ts;
1611 to.to_tsecr = sc->sc_tsreflect;
1612 to.to_flags |= TOF_TS;
1614 if (sc->sc_flags & SCF_SACK)
1615 to.to_flags |= TOF_SACKPERM;
1616 #ifdef TCP_SIGNATURE
1618 if (sc->sc_flags & SCF_SIGNATURE) {
1619 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1621 to.to_flags |= TOF_SIGNATURE;
1625 * We've got SCF_SIGNATURE flag
1626 * inherited from listening socket,
1627 * but no SADB key for given source
1628 * address. Assume signature is not
1629 * required and remove signature flag
1630 * instead of silently dropping
1635 sc->sc_flags &= ~SCF_SIGNATURE;
1643 if (sc->sc_tfo_cookie) {
1644 to.to_flags |= TOF_FASTOPEN;
1645 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1646 to.to_tfo_cookie = sc->sc_tfo_cookie;
1647 /* don't send cookie again when retransmitting response */
1648 sc->sc_tfo_cookie = NULL;
1651 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1653 /* Adjust headers by option size. */
1654 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1656 m->m_pkthdr.len += optlen;
1658 #ifdef TCP_SIGNATURE
1659 if (sc->sc_flags & SCF_SIGNATURE)
1660 tcp_signature_do_compute(m, 0, optlen,
1661 to.to_signature, sav);
1664 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1665 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1668 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1672 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1673 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1675 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1676 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1677 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1679 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1681 if (ADDED_BY_TOE(sc)) {
1682 struct toedev *tod = sc->sc_tod;
1684 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1689 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1692 #if defined(INET6) && defined(INET)
1697 m->m_pkthdr.csum_flags = CSUM_TCP;
1698 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1699 htons(tlen + optlen - hlen + IPPROTO_TCP));
1701 if (ADDED_BY_TOE(sc)) {
1702 struct toedev *tod = sc->sc_tod;
1704 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1709 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1716 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1717 * that exceed the capacity of the syncache by avoiding the storage of any
1718 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1719 * attacks where the attacker does not have access to our responses.
1721 * Syncookies encode and include all necessary information about the
1722 * connection setup within the SYN|ACK that we send back. That way we
1723 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1724 * (if ever). Normally the syncache and syncookies are running in parallel
1725 * with the latter taking over when the former is exhausted. When matching
1726 * syncache entry is found the syncookie is ignored.
1728 * The only reliable information persisting the 3WHS is our inital sequence
1729 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1730 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1731 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1732 * returns and signifies a legitimate connection if it matches the ACK.
1734 * The available space of 32 bits to store the hash and to encode the SYN
1735 * option information is very tight and we should have at least 24 bits for
1736 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1738 * SYN option information we have to encode to fully restore a connection:
1739 * MSS: is imporant to chose an optimal segment size to avoid IP level
1740 * fragmentation along the path. The common MSS values can be encoded
1741 * in a 3-bit table. Uncommon values are captured by the next lower value
1742 * in the table leading to a slight increase in packetization overhead.
1743 * WSCALE: is necessary to allow large windows to be used for high delay-
1744 * bandwidth product links. Not scaling the window when it was initially
1745 * negotiated is bad for performance as lack of scaling further decreases
1746 * the apparent available send window. We only need to encode the WSCALE
1747 * we received from the remote end. Our end can be recalculated at any
1748 * time. The common WSCALE values can be encoded in a 3-bit table.
1749 * Uncommon values are captured by the next lower value in the table
1750 * making us under-estimate the available window size halving our
1751 * theoretically possible maximum throughput for that connection.
1752 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1753 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1754 * that are included in all segments on a connection. We enable them when
1757 * Security of syncookies and attack vectors:
1759 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1760 * together with the gloabl secret to make it unique per connection attempt.
1761 * Thus any change of any of those parameters results in a different MAC output
1762 * in an unpredictable way unless a collision is encountered. 24 bits of the
1763 * MAC are embedded into the ISS.
1765 * To prevent replay attacks two rotating global secrets are updated with a
1766 * new random value every 15 seconds. The life-time of a syncookie is thus
1769 * Vector 1: Attacking the secret. This requires finding a weakness in the
1770 * MAC itself or the way it is used here. The attacker can do a chosen plain
1771 * text attack by varying and testing the all parameters under his control.
1772 * The strength depends on the size and randomness of the secret, and the
1773 * cryptographic security of the MAC function. Due to the constant updating
1774 * of the secret the attacker has at most 29.999 seconds to find the secret
1775 * and launch spoofed connections. After that he has to start all over again.
1777 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1778 * size an average of 4,823 attempts are required for a 50% chance of success
1779 * to spoof a single syncookie (birthday collision paradox). However the
1780 * attacker is blind and doesn't know if one of his attempts succeeded unless
1781 * he has a side channel to interfere success from. A single connection setup
1782 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1783 * This many attempts are required for each one blind spoofed connection. For
1784 * every additional spoofed connection he has to launch another N attempts.
1785 * Thus for a sustained rate 100 spoofed connections per second approximately
1786 * 1,800,000 packets per second would have to be sent.
1788 * NB: The MAC function should be fast so that it doesn't become a CPU
1789 * exhaustion attack vector itself.
1792 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1793 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1794 * http://cr.yp.to/syncookies.html (overview)
1795 * http://cr.yp.to/syncookies/archive (details)
1798 * Schematic construction of a syncookie enabled Initial Sequence Number:
1800 * 12345678901234567890123456789012
1801 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1803 * x 24 MAC (truncated)
1804 * W 3 Send Window Scale index
1806 * S 1 SACK permitted
1807 * P 1 Odd/even secret
1811 * Distribution and probability of certain MSS values. Those in between are
1812 * rounded down to the next lower one.
1813 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1814 * .2% .3% 5% 7% 7% 20% 15% 45%
1816 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1819 * Distribution and probability of certain WSCALE values. We have to map the
1820 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1821 * bits based on prevalence of certain values. Where we don't have an exact
1822 * match for are rounded down to the next lower one letting us under-estimate
1823 * the true available window. At the moment this would happen only for the
1824 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1825 * and window size). The absence of the WSCALE option (no scaling in either
1826 * direction) is encoded with index zero.
1827 * [WSCALE values histograms, Allman, 2012]
1828 * X 10 10 35 5 6 14 10% by host
1829 * X 11 4 5 5 18 49 3% by connections
1831 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1834 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1835 * and good cryptographic properties.
1838 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1839 uint8_t *secbits, uintptr_t secmod)
1842 uint32_t siphash[2];
1844 SipHash24_Init(&ctx);
1845 SipHash_SetKey(&ctx, secbits);
1846 switch (inc->inc_flags & INC_ISIPV6) {
1849 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1850 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1855 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1856 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1860 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1861 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1862 SipHash_Update(&ctx, &irs, sizeof(irs));
1863 SipHash_Update(&ctx, &flags, sizeof(flags));
1864 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1865 SipHash_Final((u_int8_t *)&siphash, &ctx);
1867 return (siphash[0] ^ siphash[1]);
1871 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1873 u_int i, mss, secbit, wscale;
1876 union syncookie cookie;
1878 SCH_LOCK_ASSERT(sch);
1882 /* Map our computed MSS into the 3-bit index. */
1883 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1884 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1885 tcp_sc_msstab[i] > mss && i > 0;
1888 cookie.flags.mss_idx = i;
1891 * Map the send window scale into the 3-bit index but only if
1892 * the wscale option was received.
1894 if (sc->sc_flags & SCF_WINSCALE) {
1895 wscale = sc->sc_requested_s_scale;
1896 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1897 tcp_sc_wstab[i] > wscale && i > 0;
1900 cookie.flags.wscale_idx = i;
1903 /* Can we do SACK? */
1904 if (sc->sc_flags & SCF_SACK)
1905 cookie.flags.sack_ok = 1;
1907 /* Which of the two secrets to use. */
1908 secbit = sch->sch_sc->secret.oddeven & 0x1;
1909 cookie.flags.odd_even = secbit;
1911 secbits = sch->sch_sc->secret.key[secbit];
1912 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1916 * Put the flags into the hash and XOR them to get better ISS number
1917 * variance. This doesn't enhance the cryptographic strength and is
1918 * done to prevent the 8 cookie bits from showing up directly on the
1922 iss |= cookie.cookie ^ (hash >> 24);
1924 /* Randomize the timestamp. */
1925 if (sc->sc_flags & SCF_TIMESTAMP) {
1926 sc->sc_ts = arc4random();
1927 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1930 TCPSTAT_INC(tcps_sc_sendcookie);
1934 static struct syncache *
1935 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1936 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1942 int wnd, wscale = 0;
1943 union syncookie cookie;
1945 SCH_LOCK_ASSERT(sch);
1948 * Pull information out of SYN-ACK/ACK and revert sequence number
1951 ack = th->th_ack - 1;
1952 seq = th->th_seq - 1;
1955 * Unpack the flags containing enough information to restore the
1958 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1960 /* Which of the two secrets to use. */
1961 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1963 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1965 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1966 if ((ack & ~0xff) != (hash & ~0xff))
1969 /* Fill in the syncache values. */
1971 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1972 sc->sc_ipopts = NULL;
1977 switch (inc->inc_flags & INC_ISIPV6) {
1980 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1981 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1986 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1987 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
1992 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
1994 /* We can simply recompute receive window scale we sent earlier. */
1995 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
1998 /* Only use wscale if it was enabled in the orignal SYN. */
1999 if (cookie.flags.wscale_idx > 0) {
2000 sc->sc_requested_r_scale = wscale;
2001 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2002 sc->sc_flags |= SCF_WINSCALE;
2005 wnd = sbspace(&lso->so_rcv);
2007 wnd = imin(wnd, TCP_MAXWIN);
2010 if (cookie.flags.sack_ok)
2011 sc->sc_flags |= SCF_SACK;
2013 if (to->to_flags & TOF_TS) {
2014 sc->sc_flags |= SCF_TIMESTAMP;
2015 sc->sc_tsreflect = to->to_tsval;
2016 sc->sc_ts = to->to_tsecr;
2017 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2020 if (to->to_flags & TOF_SIGNATURE)
2021 sc->sc_flags |= SCF_SIGNATURE;
2025 TCPSTAT_INC(tcps_sc_recvcookie);
2031 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2032 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2035 struct syncache scs, *scx;
2038 bzero(&scs, sizeof(scs));
2039 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2041 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2045 if (sc->sc_peer_mss != scx->sc_peer_mss)
2046 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2047 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2049 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2050 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2051 s, __func__, sc->sc_requested_r_scale,
2052 scx->sc_requested_r_scale);
2054 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2055 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2056 s, __func__, sc->sc_requested_s_scale,
2057 scx->sc_requested_s_scale);
2059 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2060 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2067 #endif /* INVARIANTS */
2070 syncookie_reseed(void *arg)
2072 struct tcp_syncache *sc = arg;
2077 * Reseeding the secret doesn't have to be protected by a lock.
2078 * It only must be ensured that the new random values are visible
2079 * to all CPUs in a SMP environment. The atomic with release
2080 * semantics ensures that.
2082 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2083 secbits = sc->secret.key[secbit];
2084 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2085 atomic_add_rel_int(&sc->secret.oddeven, 1);
2087 /* Reschedule ourself. */
2088 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2092 * Returns the current number of syncache entries. This number
2093 * will probably change before you get around to calling
2097 syncache_pcbcount(void)
2099 struct syncache_head *sch;
2102 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2103 /* No need to lock for a read. */
2104 sch = &V_tcp_syncache.hashbase[i];
2105 count += sch->sch_length;
2111 * Exports the syncache entries to userland so that netstat can display
2112 * them alongside the other sockets. This function is intended to be
2113 * called only from tcp_pcblist.
2115 * Due to concurrency on an active system, the number of pcbs exported
2116 * may have no relation to max_pcbs. max_pcbs merely indicates the
2117 * amount of space the caller allocated for this function to use.
2120 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2123 struct syncache *sc;
2124 struct syncache_head *sch;
2125 int count, error, i;
2127 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2128 sch = &V_tcp_syncache.hashbase[i];
2130 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2131 if (count >= max_pcbs) {
2135 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2137 bzero(&xt, sizeof(xt));
2138 xt.xt_len = sizeof(xt);
2139 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2140 xt.xt_inp.inp_vflag = INP_IPV6;
2142 xt.xt_inp.inp_vflag = INP_IPV4;
2143 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2144 xt.xt_tp.t_inpcb = &xt.xt_inp;
2145 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2146 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2147 xt.xt_socket.xso_len = sizeof (struct xsocket);
2148 xt.xt_socket.so_type = SOCK_STREAM;
2149 xt.xt_socket.so_state = SS_ISCONNECTING;
2150 error = SYSCTL_OUT(req, &xt, sizeof xt);
2160 *pcbs_exported = count;