xref: /freebsd/sys/netinet/tcp_syncache.c (revision a35f04fba2ebb8f86d4cbdc710c89a094572b08e)
1 /*-
2  * Copyright (c) 2001 McAfee, Inc.
3  * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
4  * All rights reserved.
5  *
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.]
10  *
11  * Redistribution and use in source and binary forms, with or without
12  * modification, are permitted provided that the following conditions
13  * are met:
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.
19  *
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
30  * SUCH DAMAGE.
31  */
32 
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
35 
36 #include "opt_inet.h"
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39 #include "opt_pcbgroup.h"
40 
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/hash.h>
44 #include <sys/refcount.h>
45 #include <sys/kernel.h>
46 #include <sys/sysctl.h>
47 #include <sys/limits.h>
48 #include <sys/lock.h>
49 #include <sys/mutex.h>
50 #include <sys/malloc.h>
51 #include <sys/mbuf.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>
58 
59 #include <sys/md5.h>
60 #include <crypto/siphash/siphash.h>
61 
62 #include <vm/uma.h>
63 
64 #include <net/if.h>
65 #include <net/if_var.h>
66 #include <net/route.h>
67 #include <net/vnet.h>
68 
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>
76 #ifdef INET6
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>
82 #endif
83 #include <netinet/tcp.h>
84 #ifdef TCP_RFC7413
85 #include <netinet/tcp_fastopen.h>
86 #endif
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>
92 #ifdef INET6
93 #include <netinet6/tcp6_var.h>
94 #endif
95 #ifdef TCP_OFFLOAD
96 #include <netinet/toecore.h>
97 #endif
98 
99 #include <netipsec/ipsec_support.h>
100 
101 #include <machine/in_cksum.h>
102 
103 #include <security/mac/mac_framework.h>
104 
105 static VNET_DEFINE(int, tcp_syncookies) = 1;
106 #define	V_tcp_syncookies		VNET(tcp_syncookies)
107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
108     &VNET_NAME(tcp_syncookies), 0,
109     "Use TCP SYN cookies if the syncache overflows");
110 
111 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
112 #define	V_tcp_syncookiesonly		VNET(tcp_syncookiesonly)
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
114     &VNET_NAME(tcp_syncookiesonly), 0,
115     "Use only TCP SYN cookies");
116 
117 static VNET_DEFINE(int, functions_inherit_listen_socket_stack) = 1;
118 #define V_functions_inherit_listen_socket_stack \
119     VNET(functions_inherit_listen_socket_stack)
120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack,
121     CTLFLAG_VNET | CTLFLAG_RW,
122     &VNET_NAME(functions_inherit_listen_socket_stack), 0,
123     "Inherit listen socket's stack");
124 
125 #ifdef TCP_OFFLOAD
126 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
127 #endif
128 
129 static void	 syncache_drop(struct syncache *, struct syncache_head *);
130 static void	 syncache_free(struct syncache *);
131 static void	 syncache_insert(struct syncache *, struct syncache_head *);
132 static int	 syncache_respond(struct syncache *, struct syncache_head *, int,
133 		    const struct mbuf *);
134 static struct	 socket *syncache_socket(struct syncache *, struct socket *,
135 		    struct mbuf *m);
136 static void	 syncache_timeout(struct syncache *sc, struct syncache_head *sch,
137 		    int docallout);
138 static void	 syncache_timer(void *);
139 
140 static uint32_t	 syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
141 		    uint8_t *, uintptr_t);
142 static tcp_seq	 syncookie_generate(struct syncache_head *, struct syncache *);
143 static struct syncache
144 		*syncookie_lookup(struct in_conninfo *, struct syncache_head *,
145 		    struct syncache *, struct tcphdr *, struct tcpopt *,
146 		    struct socket *);
147 static void	 syncookie_reseed(void *);
148 #ifdef INVARIANTS
149 static int	 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
150 		    struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
151 		    struct socket *lso);
152 #endif
153 
154 /*
155  * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
156  * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
157  * the odds are that the user has given up attempting to connect by then.
158  */
159 #define SYNCACHE_MAXREXMTS		3
160 
161 /* Arbitrary values */
162 #define TCP_SYNCACHE_HASHSIZE		512
163 #define TCP_SYNCACHE_BUCKETLIMIT	30
164 
165 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
166 #define	V_tcp_syncache			VNET(tcp_syncache)
167 
168 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
169     "TCP SYN cache");
170 
171 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
172     &VNET_NAME(tcp_syncache.bucket_limit), 0,
173     "Per-bucket hash limit for syncache");
174 
175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
176     &VNET_NAME(tcp_syncache.cache_limit), 0,
177     "Overall entry limit for syncache");
178 
179 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
180     &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
181 
182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
183     &VNET_NAME(tcp_syncache.hashsize), 0,
184     "Size of TCP syncache hashtable");
185 
186 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
187     &VNET_NAME(tcp_syncache.rexmt_limit), 0,
188     "Limit on SYN/ACK retransmissions");
189 
190 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
191 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
192     CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
193     "Send reset on socket allocation failure");
194 
195 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
196 
197 #define	SCH_LOCK(sch)		mtx_lock(&(sch)->sch_mtx)
198 #define	SCH_UNLOCK(sch)		mtx_unlock(&(sch)->sch_mtx)
199 #define	SCH_LOCK_ASSERT(sch)	mtx_assert(&(sch)->sch_mtx, MA_OWNED)
200 
201 /*
202  * Requires the syncache entry to be already removed from the bucket list.
203  */
204 static void
205 syncache_free(struct syncache *sc)
206 {
207 
208 	if (sc->sc_ipopts)
209 		(void) m_free(sc->sc_ipopts);
210 	if (sc->sc_cred)
211 		crfree(sc->sc_cred);
212 #ifdef MAC
213 	mac_syncache_destroy(&sc->sc_label);
214 #endif
215 
216 	uma_zfree(V_tcp_syncache.zone, sc);
217 }
218 
219 void
220 syncache_init(void)
221 {
222 	int i;
223 
224 	V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
225 	V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
226 	V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
227 	V_tcp_syncache.hash_secret = arc4random();
228 
229 	TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
230 	    &V_tcp_syncache.hashsize);
231 	TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
232 	    &V_tcp_syncache.bucket_limit);
233 	if (!powerof2(V_tcp_syncache.hashsize) ||
234 	    V_tcp_syncache.hashsize == 0) {
235 		printf("WARNING: syncache hash size is not a power of 2.\n");
236 		V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
237 	}
238 	V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
239 
240 	/* Set limits. */
241 	V_tcp_syncache.cache_limit =
242 	    V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
243 	TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
244 	    &V_tcp_syncache.cache_limit);
245 
246 	/* Allocate the hash table. */
247 	V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
248 	    sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
249 
250 #ifdef VIMAGE
251 	V_tcp_syncache.vnet = curvnet;
252 #endif
253 
254 	/* Initialize the hash buckets. */
255 	for (i = 0; i < V_tcp_syncache.hashsize; i++) {
256 		TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
257 		mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
258 			 NULL, MTX_DEF);
259 		callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
260 			 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
261 		V_tcp_syncache.hashbase[i].sch_length = 0;
262 		V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
263 	}
264 
265 	/* Create the syncache entry zone. */
266 	V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
267 	    NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
268 	V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
269 	    V_tcp_syncache.cache_limit);
270 
271 	/* Start the SYN cookie reseeder callout. */
272 	callout_init(&V_tcp_syncache.secret.reseed, 1);
273 	arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
274 	arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
275 	callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
276 	    syncookie_reseed, &V_tcp_syncache);
277 }
278 
279 #ifdef VIMAGE
280 void
281 syncache_destroy(void)
282 {
283 	struct syncache_head *sch;
284 	struct syncache *sc, *nsc;
285 	int i;
286 
287 	/*
288 	 * Stop the re-seed timer before freeing resources.  No need to
289 	 * possibly schedule it another time.
290 	 */
291 	callout_drain(&V_tcp_syncache.secret.reseed);
292 
293 	/* Cleanup hash buckets: stop timers, free entries, destroy locks. */
294 	for (i = 0; i < V_tcp_syncache.hashsize; i++) {
295 
296 		sch = &V_tcp_syncache.hashbase[i];
297 		callout_drain(&sch->sch_timer);
298 
299 		SCH_LOCK(sch);
300 		TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
301 			syncache_drop(sc, sch);
302 		SCH_UNLOCK(sch);
303 		KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
304 		    ("%s: sch->sch_bucket not empty", __func__));
305 		KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
306 		    __func__, sch->sch_length));
307 		mtx_destroy(&sch->sch_mtx);
308 	}
309 
310 	KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
311 	    ("%s: cache_count not 0", __func__));
312 
313 	/* Free the allocated global resources. */
314 	uma_zdestroy(V_tcp_syncache.zone);
315 	free(V_tcp_syncache.hashbase, M_SYNCACHE);
316 }
317 #endif
318 
319 /*
320  * Inserts a syncache entry into the specified bucket row.
321  * Locks and unlocks the syncache_head autonomously.
322  */
323 static void
324 syncache_insert(struct syncache *sc, struct syncache_head *sch)
325 {
326 	struct syncache *sc2;
327 
328 	SCH_LOCK(sch);
329 
330 	/*
331 	 * Make sure that we don't overflow the per-bucket limit.
332 	 * If the bucket is full, toss the oldest element.
333 	 */
334 	if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
335 		KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
336 			("sch->sch_length incorrect"));
337 		sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
338 		syncache_drop(sc2, sch);
339 		TCPSTAT_INC(tcps_sc_bucketoverflow);
340 	}
341 
342 	/* Put it into the bucket. */
343 	TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
344 	sch->sch_length++;
345 
346 #ifdef TCP_OFFLOAD
347 	if (ADDED_BY_TOE(sc)) {
348 		struct toedev *tod = sc->sc_tod;
349 
350 		tod->tod_syncache_added(tod, sc->sc_todctx);
351 	}
352 #endif
353 
354 	/* Reinitialize the bucket row's timer. */
355 	if (sch->sch_length == 1)
356 		sch->sch_nextc = ticks + INT_MAX;
357 	syncache_timeout(sc, sch, 1);
358 
359 	SCH_UNLOCK(sch);
360 
361 	TCPSTATES_INC(TCPS_SYN_RECEIVED);
362 	TCPSTAT_INC(tcps_sc_added);
363 }
364 
365 /*
366  * Remove and free entry from syncache bucket row.
367  * Expects locked syncache head.
368  */
369 static void
370 syncache_drop(struct syncache *sc, struct syncache_head *sch)
371 {
372 
373 	SCH_LOCK_ASSERT(sch);
374 
375 	TCPSTATES_DEC(TCPS_SYN_RECEIVED);
376 	TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
377 	sch->sch_length--;
378 
379 #ifdef TCP_OFFLOAD
380 	if (ADDED_BY_TOE(sc)) {
381 		struct toedev *tod = sc->sc_tod;
382 
383 		tod->tod_syncache_removed(tod, sc->sc_todctx);
384 	}
385 #endif
386 
387 	syncache_free(sc);
388 }
389 
390 /*
391  * Engage/reengage time on bucket row.
392  */
393 static void
394 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
395 {
396 	sc->sc_rxttime = ticks +
397 		TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
398 	sc->sc_rxmits++;
399 	if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
400 		sch->sch_nextc = sc->sc_rxttime;
401 		if (docallout)
402 			callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
403 			    syncache_timer, (void *)sch);
404 	}
405 }
406 
407 /*
408  * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
409  * If we have retransmitted an entry the maximum number of times, expire it.
410  * One separate timer for each bucket row.
411  */
412 static void
413 syncache_timer(void *xsch)
414 {
415 	struct syncache_head *sch = (struct syncache_head *)xsch;
416 	struct syncache *sc, *nsc;
417 	int tick = ticks;
418 	char *s;
419 
420 	CURVNET_SET(sch->sch_sc->vnet);
421 
422 	/* NB: syncache_head has already been locked by the callout. */
423 	SCH_LOCK_ASSERT(sch);
424 
425 	/*
426 	 * In the following cycle we may remove some entries and/or
427 	 * advance some timeouts, so re-initialize the bucket timer.
428 	 */
429 	sch->sch_nextc = tick + INT_MAX;
430 
431 	TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
432 		/*
433 		 * We do not check if the listen socket still exists
434 		 * and accept the case where the listen socket may be
435 		 * gone by the time we resend the SYN/ACK.  We do
436 		 * not expect this to happens often. If it does,
437 		 * then the RST will be sent by the time the remote
438 		 * host does the SYN/ACK->ACK.
439 		 */
440 		if (TSTMP_GT(sc->sc_rxttime, tick)) {
441 			if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
442 				sch->sch_nextc = sc->sc_rxttime;
443 			continue;
444 		}
445 		if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
446 			if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
447 				log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
448 				    "giving up and removing syncache entry\n",
449 				    s, __func__);
450 				free(s, M_TCPLOG);
451 			}
452 			syncache_drop(sc, sch);
453 			TCPSTAT_INC(tcps_sc_stale);
454 			continue;
455 		}
456 		if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
457 			log(LOG_DEBUG, "%s; %s: Response timeout, "
458 			    "retransmitting (%u) SYN|ACK\n",
459 			    s, __func__, sc->sc_rxmits);
460 			free(s, M_TCPLOG);
461 		}
462 
463 		syncache_respond(sc, sch, 1, NULL);
464 		TCPSTAT_INC(tcps_sc_retransmitted);
465 		syncache_timeout(sc, sch, 0);
466 	}
467 	if (!TAILQ_EMPTY(&(sch)->sch_bucket))
468 		callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
469 			syncache_timer, (void *)(sch));
470 	CURVNET_RESTORE();
471 }
472 
473 /*
474  * Find an entry in the syncache.
475  * Returns always with locked syncache_head plus a matching entry or NULL.
476  */
477 static struct syncache *
478 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
479 {
480 	struct syncache *sc;
481 	struct syncache_head *sch;
482 	uint32_t hash;
483 
484 	/*
485 	 * The hash is built on foreign port + local port + foreign address.
486 	 * We rely on the fact that struct in_conninfo starts with 16 bits
487 	 * of foreign port, then 16 bits of local port then followed by 128
488 	 * bits of foreign address.  In case of IPv4 address, the first 3
489 	 * 32-bit words of the address always are zeroes.
490 	 */
491 	hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
492 	    V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
493 
494 	sch = &V_tcp_syncache.hashbase[hash];
495 	*schp = sch;
496 	SCH_LOCK(sch);
497 
498 	/* Circle through bucket row to find matching entry. */
499 	TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
500 		if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
501 		    sizeof(struct in_endpoints)) == 0)
502 			break;
503 
504 	return (sc);	/* Always returns with locked sch. */
505 }
506 
507 /*
508  * This function is called when we get a RST for a
509  * non-existent connection, so that we can see if the
510  * connection is in the syn cache.  If it is, zap it.
511  */
512 void
513 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
514 {
515 	struct syncache *sc;
516 	struct syncache_head *sch;
517 	char *s = NULL;
518 
519 	sc = syncache_lookup(inc, &sch);	/* returns locked sch */
520 	SCH_LOCK_ASSERT(sch);
521 
522 	/*
523 	 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
524 	 * See RFC 793 page 65, section SEGMENT ARRIVES.
525 	 */
526 	if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
527 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
528 			log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
529 			    "FIN flag set, segment ignored\n", s, __func__);
530 		TCPSTAT_INC(tcps_badrst);
531 		goto done;
532 	}
533 
534 	/*
535 	 * No corresponding connection was found in syncache.
536 	 * If syncookies are enabled and possibly exclusively
537 	 * used, or we are under memory pressure, a valid RST
538 	 * may not find a syncache entry.  In that case we're
539 	 * done and no SYN|ACK retransmissions will happen.
540 	 * Otherwise the RST was misdirected or spoofed.
541 	 */
542 	if (sc == NULL) {
543 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
544 			log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
545 			    "syncache entry (possibly syncookie only), "
546 			    "segment ignored\n", s, __func__);
547 		TCPSTAT_INC(tcps_badrst);
548 		goto done;
549 	}
550 
551 	/*
552 	 * If the RST bit is set, check the sequence number to see
553 	 * if this is a valid reset segment.
554 	 * RFC 793 page 37:
555 	 *   In all states except SYN-SENT, all reset (RST) segments
556 	 *   are validated by checking their SEQ-fields.  A reset is
557 	 *   valid if its sequence number is in the window.
558 	 *
559 	 *   The sequence number in the reset segment is normally an
560 	 *   echo of our outgoing acknowlegement numbers, but some hosts
561 	 *   send a reset with the sequence number at the rightmost edge
562 	 *   of our receive window, and we have to handle this case.
563 	 */
564 	if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
565 	    SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
566 		syncache_drop(sc, sch);
567 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
568 			log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
569 			    "connection attempt aborted by remote endpoint\n",
570 			    s, __func__);
571 		TCPSTAT_INC(tcps_sc_reset);
572 	} else {
573 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
574 			log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
575 			    "IRS %u (+WND %u), segment ignored\n",
576 			    s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
577 		TCPSTAT_INC(tcps_badrst);
578 	}
579 
580 done:
581 	if (s != NULL)
582 		free(s, M_TCPLOG);
583 	SCH_UNLOCK(sch);
584 }
585 
586 void
587 syncache_badack(struct in_conninfo *inc)
588 {
589 	struct syncache *sc;
590 	struct syncache_head *sch;
591 
592 	sc = syncache_lookup(inc, &sch);	/* returns locked sch */
593 	SCH_LOCK_ASSERT(sch);
594 	if (sc != NULL) {
595 		syncache_drop(sc, sch);
596 		TCPSTAT_INC(tcps_sc_badack);
597 	}
598 	SCH_UNLOCK(sch);
599 }
600 
601 void
602 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
603 {
604 	struct syncache *sc;
605 	struct syncache_head *sch;
606 
607 	sc = syncache_lookup(inc, &sch);	/* returns locked sch */
608 	SCH_LOCK_ASSERT(sch);
609 	if (sc == NULL)
610 		goto done;
611 
612 	/* If the sequence number != sc_iss, then it's a bogus ICMP msg */
613 	if (ntohl(th->th_seq) != sc->sc_iss)
614 		goto done;
615 
616 	/*
617 	 * If we've rertransmitted 3 times and this is our second error,
618 	 * we remove the entry.  Otherwise, we allow it to continue on.
619 	 * This prevents us from incorrectly nuking an entry during a
620 	 * spurious network outage.
621 	 *
622 	 * See tcp_notify().
623 	 */
624 	if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
625 		sc->sc_flags |= SCF_UNREACH;
626 		goto done;
627 	}
628 	syncache_drop(sc, sch);
629 	TCPSTAT_INC(tcps_sc_unreach);
630 done:
631 	SCH_UNLOCK(sch);
632 }
633 
634 /*
635  * Build a new TCP socket structure from a syncache entry.
636  *
637  * On success return the newly created socket with its underlying inp locked.
638  */
639 static struct socket *
640 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
641 {
642 	struct tcp_function_block *blk;
643 	struct inpcb *inp = NULL;
644 	struct socket *so;
645 	struct tcpcb *tp;
646 	int error;
647 	char *s;
648 
649 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
650 
651 	/*
652 	 * Ok, create the full blown connection, and set things up
653 	 * as they would have been set up if we had created the
654 	 * connection when the SYN arrived.  If we can't create
655 	 * the connection, abort it.
656 	 */
657 	so = sonewconn(lso, 0);
658 	if (so == NULL) {
659 		/*
660 		 * Drop the connection; we will either send a RST or
661 		 * have the peer retransmit its SYN again after its
662 		 * RTO and try again.
663 		 */
664 		TCPSTAT_INC(tcps_listendrop);
665 		if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
666 			log(LOG_DEBUG, "%s; %s: Socket create failed "
667 			    "due to limits or memory shortage\n",
668 			    s, __func__);
669 			free(s, M_TCPLOG);
670 		}
671 		goto abort2;
672 	}
673 #ifdef MAC
674 	mac_socketpeer_set_from_mbuf(m, so);
675 #endif
676 
677 	inp = sotoinpcb(so);
678 	inp->inp_inc.inc_fibnum = so->so_fibnum;
679 	INP_WLOCK(inp);
680 	/*
681 	 * Exclusive pcbinfo lock is not required in syncache socket case even
682 	 * if two inpcb locks can be acquired simultaneously:
683 	 *  - the inpcb in LISTEN state,
684 	 *  - the newly created inp.
685 	 *
686 	 * In this case, an inp cannot be at same time in LISTEN state and
687 	 * just created by an accept() call.
688 	 */
689 	INP_HASH_WLOCK(&V_tcbinfo);
690 
691 	/* Insert new socket into PCB hash list. */
692 	inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
693 #ifdef INET6
694 	if (sc->sc_inc.inc_flags & INC_ISIPV6) {
695 		inp->in6p_laddr = sc->sc_inc.inc6_laddr;
696 	} else {
697 		inp->inp_vflag &= ~INP_IPV6;
698 		inp->inp_vflag |= INP_IPV4;
699 #endif
700 		inp->inp_laddr = sc->sc_inc.inc_laddr;
701 #ifdef INET6
702 	}
703 #endif
704 
705 	/*
706 	 * If there's an mbuf and it has a flowid, then let's initialise the
707 	 * inp with that particular flowid.
708 	 */
709 	if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
710 		inp->inp_flowid = m->m_pkthdr.flowid;
711 		inp->inp_flowtype = M_HASHTYPE_GET(m);
712 	}
713 
714 	/*
715 	 * Install in the reservation hash table for now, but don't yet
716 	 * install a connection group since the full 4-tuple isn't yet
717 	 * configured.
718 	 */
719 	inp->inp_lport = sc->sc_inc.inc_lport;
720 	if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
721 		/*
722 		 * Undo the assignments above if we failed to
723 		 * put the PCB on the hash lists.
724 		 */
725 #ifdef INET6
726 		if (sc->sc_inc.inc_flags & INC_ISIPV6)
727 			inp->in6p_laddr = in6addr_any;
728 		else
729 #endif
730 			inp->inp_laddr.s_addr = INADDR_ANY;
731 		inp->inp_lport = 0;
732 		if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
733 			log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
734 			    "with error %i\n",
735 			    s, __func__, error);
736 			free(s, M_TCPLOG);
737 		}
738 		INP_HASH_WUNLOCK(&V_tcbinfo);
739 		goto abort;
740 	}
741 #ifdef INET6
742 	if (sc->sc_inc.inc_flags & INC_ISIPV6) {
743 		struct inpcb *oinp = sotoinpcb(lso);
744 		struct in6_addr laddr6;
745 		struct sockaddr_in6 sin6;
746 		/*
747 		 * Inherit socket options from the listening socket.
748 		 * Note that in6p_inputopts are not (and should not be)
749 		 * copied, since it stores previously received options and is
750 		 * used to detect if each new option is different than the
751 		 * previous one and hence should be passed to a user.
752 		 * If we copied in6p_inputopts, a user would not be able to
753 		 * receive options just after calling the accept system call.
754 		 */
755 		inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
756 		if (oinp->in6p_outputopts)
757 			inp->in6p_outputopts =
758 			    ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
759 
760 		sin6.sin6_family = AF_INET6;
761 		sin6.sin6_len = sizeof(sin6);
762 		sin6.sin6_addr = sc->sc_inc.inc6_faddr;
763 		sin6.sin6_port = sc->sc_inc.inc_fport;
764 		sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
765 		laddr6 = inp->in6p_laddr;
766 		if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
767 			inp->in6p_laddr = sc->sc_inc.inc6_laddr;
768 		if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
769 		    thread0.td_ucred, m)) != 0) {
770 			inp->in6p_laddr = laddr6;
771 			if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
772 				log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
773 				    "with error %i\n",
774 				    s, __func__, error);
775 				free(s, M_TCPLOG);
776 			}
777 			INP_HASH_WUNLOCK(&V_tcbinfo);
778 			goto abort;
779 		}
780 		/* Override flowlabel from in6_pcbconnect. */
781 		inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
782 		inp->inp_flow |= sc->sc_flowlabel;
783 	}
784 #endif /* INET6 */
785 #if defined(INET) && defined(INET6)
786 	else
787 #endif
788 #ifdef INET
789 	{
790 		struct in_addr laddr;
791 		struct sockaddr_in sin;
792 
793 		inp->inp_options = (m) ? ip_srcroute(m) : NULL;
794 
795 		if (inp->inp_options == NULL) {
796 			inp->inp_options = sc->sc_ipopts;
797 			sc->sc_ipopts = NULL;
798 		}
799 
800 		sin.sin_family = AF_INET;
801 		sin.sin_len = sizeof(sin);
802 		sin.sin_addr = sc->sc_inc.inc_faddr;
803 		sin.sin_port = sc->sc_inc.inc_fport;
804 		bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
805 		laddr = inp->inp_laddr;
806 		if (inp->inp_laddr.s_addr == INADDR_ANY)
807 			inp->inp_laddr = sc->sc_inc.inc_laddr;
808 		if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
809 		    thread0.td_ucred, m)) != 0) {
810 			inp->inp_laddr = laddr;
811 			if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
812 				log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
813 				    "with error %i\n",
814 				    s, __func__, error);
815 				free(s, M_TCPLOG);
816 			}
817 			INP_HASH_WUNLOCK(&V_tcbinfo);
818 			goto abort;
819 		}
820 	}
821 #endif /* INET */
822 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
823 	/* Copy old policy into new socket's. */
824 	if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0)
825 		printf("syncache_socket: could not copy policy\n");
826 #endif
827 	INP_HASH_WUNLOCK(&V_tcbinfo);
828 	tp = intotcpcb(inp);
829 	tcp_state_change(tp, TCPS_SYN_RECEIVED);
830 	tp->iss = sc->sc_iss;
831 	tp->irs = sc->sc_irs;
832 	tcp_rcvseqinit(tp);
833 	tcp_sendseqinit(tp);
834 	blk = sototcpcb(lso)->t_fb;
835 	if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) {
836 		/*
837 		 * Our parents t_fb was not the default,
838 		 * we need to release our ref on tp->t_fb and
839 		 * pickup one on the new entry.
840 		 */
841 		struct tcp_function_block *rblk;
842 
843 		rblk = find_and_ref_tcp_fb(blk);
844 		KASSERT(rblk != NULL,
845 		    ("cannot find blk %p out of syncache?", blk));
846 		if (tp->t_fb->tfb_tcp_fb_fini)
847 			(*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
848 		refcount_release(&tp->t_fb->tfb_refcnt);
849 		tp->t_fb = rblk;
850 		if (tp->t_fb->tfb_tcp_fb_init) {
851 			(*tp->t_fb->tfb_tcp_fb_init)(tp);
852 		}
853 	}
854 	tp->snd_wl1 = sc->sc_irs;
855 	tp->snd_max = tp->iss + 1;
856 	tp->snd_nxt = tp->iss + 1;
857 	tp->rcv_up = sc->sc_irs + 1;
858 	tp->rcv_wnd = sc->sc_wnd;
859 	tp->rcv_adv += tp->rcv_wnd;
860 	tp->last_ack_sent = tp->rcv_nxt;
861 
862 	tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
863 	if (sc->sc_flags & SCF_NOOPT)
864 		tp->t_flags |= TF_NOOPT;
865 	else {
866 		if (sc->sc_flags & SCF_WINSCALE) {
867 			tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
868 			tp->snd_scale = sc->sc_requested_s_scale;
869 			tp->request_r_scale = sc->sc_requested_r_scale;
870 		}
871 		if (sc->sc_flags & SCF_TIMESTAMP) {
872 			tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
873 			tp->ts_recent = sc->sc_tsreflect;
874 			tp->ts_recent_age = tcp_ts_getticks();
875 			tp->ts_offset = sc->sc_tsoff;
876 		}
877 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
878 		if (sc->sc_flags & SCF_SIGNATURE)
879 			tp->t_flags |= TF_SIGNATURE;
880 #endif
881 		if (sc->sc_flags & SCF_SACK)
882 			tp->t_flags |= TF_SACK_PERMIT;
883 	}
884 
885 	if (sc->sc_flags & SCF_ECN)
886 		tp->t_flags |= TF_ECN_PERMIT;
887 
888 	/*
889 	 * Set up MSS and get cached values from tcp_hostcache.
890 	 * This might overwrite some of the defaults we just set.
891 	 */
892 	tcp_mss(tp, sc->sc_peer_mss);
893 
894 	/*
895 	 * If the SYN,ACK was retransmitted, indicate that CWND to be
896 	 * limited to one segment in cc_conn_init().
897 	 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
898 	 */
899 	if (sc->sc_rxmits > 1)
900 		tp->snd_cwnd = 1;
901 
902 #ifdef TCP_OFFLOAD
903 	/*
904 	 * Allow a TOE driver to install its hooks.  Note that we hold the
905 	 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
906 	 * new connection before the TOE driver has done its thing.
907 	 */
908 	if (ADDED_BY_TOE(sc)) {
909 		struct toedev *tod = sc->sc_tod;
910 
911 		tod->tod_offload_socket(tod, sc->sc_todctx, so);
912 	}
913 #endif
914 	/*
915 	 * Copy and activate timers.
916 	 */
917 	tp->t_keepinit = sototcpcb(lso)->t_keepinit;
918 	tp->t_keepidle = sototcpcb(lso)->t_keepidle;
919 	tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
920 	tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
921 	tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
922 
923 	TCPSTAT_INC(tcps_accepts);
924 	return (so);
925 
926 abort:
927 	INP_WUNLOCK(inp);
928 abort2:
929 	if (so != NULL)
930 		soabort(so);
931 	return (NULL);
932 }
933 
934 /*
935  * This function gets called when we receive an ACK for a
936  * socket in the LISTEN state.  We look up the connection
937  * in the syncache, and if its there, we pull it out of
938  * the cache and turn it into a full-blown connection in
939  * the SYN-RECEIVED state.
940  *
941  * On syncache_socket() success the newly created socket
942  * has its underlying inp locked.
943  */
944 int
945 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
946     struct socket **lsop, struct mbuf *m)
947 {
948 	struct syncache *sc;
949 	struct syncache_head *sch;
950 	struct syncache scs;
951 	char *s;
952 
953 	/*
954 	 * Global TCP locks are held because we manipulate the PCB lists
955 	 * and create a new socket.
956 	 */
957 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
958 	KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
959 	    ("%s: can handle only ACK", __func__));
960 
961 	sc = syncache_lookup(inc, &sch);	/* returns locked sch */
962 	SCH_LOCK_ASSERT(sch);
963 
964 #ifdef INVARIANTS
965 	/*
966 	 * Test code for syncookies comparing the syncache stored
967 	 * values with the reconstructed values from the cookie.
968 	 */
969 	if (sc != NULL)
970 		syncookie_cmp(inc, sch, sc, th, to, *lsop);
971 #endif
972 
973 	if (sc == NULL) {
974 		/*
975 		 * There is no syncache entry, so see if this ACK is
976 		 * a returning syncookie.  To do this, first:
977 		 *  A. See if this socket has had a syncache entry dropped in
978 		 *     the past.  We don't want to accept a bogus syncookie
979 		 *     if we've never received a SYN.
980 		 *  B. check that the syncookie is valid.  If it is, then
981 		 *     cobble up a fake syncache entry, and return.
982 		 */
983 		if (!V_tcp_syncookies) {
984 			SCH_UNLOCK(sch);
985 			if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
986 				log(LOG_DEBUG, "%s; %s: Spurious ACK, "
987 				    "segment rejected (syncookies disabled)\n",
988 				    s, __func__);
989 			goto failed;
990 		}
991 		bzero(&scs, sizeof(scs));
992 		sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
993 		SCH_UNLOCK(sch);
994 		if (sc == NULL) {
995 			if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
996 				log(LOG_DEBUG, "%s; %s: Segment failed "
997 				    "SYNCOOKIE authentication, segment rejected "
998 				    "(probably spoofed)\n", s, __func__);
999 			goto failed;
1000 		}
1001 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1002 		/* If received ACK has MD5 signature, check it. */
1003 		if ((to->to_flags & TOF_SIGNATURE) != 0 &&
1004 		    (!TCPMD5_ENABLED() ||
1005 		    TCPMD5_INPUT(m, th, to->to_signature) != 0)) {
1006 			/* Drop the ACK. */
1007 			if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1008 				log(LOG_DEBUG, "%s; %s: Segment rejected, "
1009 				    "MD5 signature doesn't match.\n",
1010 				    s, __func__);
1011 				free(s, M_TCPLOG);
1012 			}
1013 			TCPSTAT_INC(tcps_sig_err_sigopt);
1014 			return (-1); /* Do not send RST */
1015 		}
1016 #endif /* TCP_SIGNATURE */
1017 	} else {
1018 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1019 		/*
1020 		 * If listening socket requested TCP digests, check that
1021 		 * received ACK has signature and it is correct.
1022 		 * If not, drop the ACK and leave sc entry in th cache,
1023 		 * because SYN was received with correct signature.
1024 		 */
1025 		if (sc->sc_flags & SCF_SIGNATURE) {
1026 			if ((to->to_flags & TOF_SIGNATURE) == 0) {
1027 				/* No signature */
1028 				TCPSTAT_INC(tcps_sig_err_nosigopt);
1029 				SCH_UNLOCK(sch);
1030 				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1031 					log(LOG_DEBUG, "%s; %s: Segment "
1032 					    "rejected, MD5 signature wasn't "
1033 					    "provided.\n", s, __func__);
1034 					free(s, M_TCPLOG);
1035 				}
1036 				return (-1); /* Do not send RST */
1037 			}
1038 			if (!TCPMD5_ENABLED() ||
1039 			    TCPMD5_INPUT(m, th, to->to_signature) != 0) {
1040 				/* Doesn't match or no SA */
1041 				SCH_UNLOCK(sch);
1042 				if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1043 					log(LOG_DEBUG, "%s; %s: Segment "
1044 					    "rejected, MD5 signature doesn't "
1045 					    "match.\n", s, __func__);
1046 					free(s, M_TCPLOG);
1047 				}
1048 				return (-1); /* Do not send RST */
1049 			}
1050 		}
1051 #endif /* TCP_SIGNATURE */
1052 		/*
1053 		 * Pull out the entry to unlock the bucket row.
1054 		 *
1055 		 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1056 		 * tcp_state_change().  The tcpcb is not existent at this
1057 		 * moment.  A new one will be allocated via syncache_socket->
1058 		 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1059 		 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1060 		 */
1061 		TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1062 		TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1063 		sch->sch_length--;
1064 #ifdef TCP_OFFLOAD
1065 		if (ADDED_BY_TOE(sc)) {
1066 			struct toedev *tod = sc->sc_tod;
1067 
1068 			tod->tod_syncache_removed(tod, sc->sc_todctx);
1069 		}
1070 #endif
1071 		SCH_UNLOCK(sch);
1072 	}
1073 
1074 	/*
1075 	 * Segment validation:
1076 	 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1077 	 */
1078 	if (th->th_ack != sc->sc_iss + 1) {
1079 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1080 			log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1081 			    "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1082 		goto failed;
1083 	}
1084 
1085 	/*
1086 	 * The SEQ must fall in the window starting at the received
1087 	 * initial receive sequence number + 1 (the SYN).
1088 	 */
1089 	if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1090 	    SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1091 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1092 			log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1093 			    "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1094 		goto failed;
1095 	}
1096 
1097 	/*
1098 	 * If timestamps were not negotiated during SYN/ACK they
1099 	 * must not appear on any segment during this session.
1100 	 */
1101 	if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1102 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1103 			log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1104 			    "segment rejected\n", s, __func__);
1105 		goto failed;
1106 	}
1107 
1108 	/*
1109 	 * If timestamps were negotiated during SYN/ACK they should
1110 	 * appear on every segment during this session.
1111 	 * XXXAO: This is only informal as there have been unverified
1112 	 * reports of non-compliants stacks.
1113 	 */
1114 	if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1115 		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1116 			log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1117 			    "no action\n", s, __func__);
1118 			free(s, M_TCPLOG);
1119 			s = NULL;
1120 		}
1121 	}
1122 
1123 	/*
1124 	 * If timestamps were negotiated, the reflected timestamp
1125 	 * must be equal to what we actually sent in the SYN|ACK
1126 	 * except in the case of 0. Some boxes are known for sending
1127 	 * broken timestamp replies during the 3whs (and potentially
1128 	 * during the connection also).
1129 	 *
1130 	 * Accept the final ACK of 3whs with reflected timestamp of 0
1131 	 * instead of sending a RST and deleting the syncache entry.
1132 	 */
1133 	if ((to->to_flags & TOF_TS) && to->to_tsecr &&
1134 	    to->to_tsecr != sc->sc_ts) {
1135 		if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1136 			log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1137 			    "segment rejected\n",
1138 			    s, __func__, to->to_tsecr, sc->sc_ts);
1139 		goto failed;
1140 	}
1141 
1142 	*lsop = syncache_socket(sc, *lsop, m);
1143 
1144 	if (*lsop == NULL)
1145 		TCPSTAT_INC(tcps_sc_aborted);
1146 	else
1147 		TCPSTAT_INC(tcps_sc_completed);
1148 
1149 /* how do we find the inp for the new socket? */
1150 	if (sc != &scs)
1151 		syncache_free(sc);
1152 	return (1);
1153 failed:
1154 	if (sc != NULL && sc != &scs)
1155 		syncache_free(sc);
1156 	if (s != NULL)
1157 		free(s, M_TCPLOG);
1158 	*lsop = NULL;
1159 	return (0);
1160 }
1161 
1162 #ifdef TCP_RFC7413
1163 static void
1164 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1165     uint64_t response_cookie)
1166 {
1167 	struct inpcb *inp;
1168 	struct tcpcb *tp;
1169 	unsigned int *pending_counter;
1170 
1171 	/*
1172 	 * Global TCP locks are held because we manipulate the PCB lists
1173 	 * and create a new socket.
1174 	 */
1175 	INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1176 
1177 	pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1178 	*lsop = syncache_socket(sc, *lsop, m);
1179 	if (*lsop == NULL) {
1180 		TCPSTAT_INC(tcps_sc_aborted);
1181 		atomic_subtract_int(pending_counter, 1);
1182 	} else {
1183 		inp = sotoinpcb(*lsop);
1184 		tp = intotcpcb(inp);
1185 		tp->t_flags |= TF_FASTOPEN;
1186 		tp->t_tfo_cookie = response_cookie;
1187 		tp->snd_max = tp->iss;
1188 		tp->snd_nxt = tp->iss;
1189 		tp->t_tfo_pending = pending_counter;
1190 		TCPSTAT_INC(tcps_sc_completed);
1191 	}
1192 }
1193 #endif /* TCP_RFC7413 */
1194 
1195 /*
1196  * Given a LISTEN socket and an inbound SYN request, add
1197  * this to the syn cache, and send back a segment:
1198  *	<SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1199  * to the source.
1200  *
1201  * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1202  * Doing so would require that we hold onto the data and deliver it
1203  * to the application.  However, if we are the target of a SYN-flood
1204  * DoS attack, an attacker could send data which would eventually
1205  * consume all available buffer space if it were ACKed.  By not ACKing
1206  * the data, we avoid this DoS scenario.
1207  *
1208  * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1209  * cookie is processed and a new socket is created.  In this case, any data
1210  * accompanying the SYN will be queued to the socket by tcp_input() and will
1211  * be ACKed either when the application sends response data or the delayed
1212  * ACK timer expires, whichever comes first.
1213  */
1214 int
1215 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1216     struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1217     void *todctx)
1218 {
1219 	struct tcpcb *tp;
1220 	struct socket *so;
1221 	struct syncache *sc = NULL;
1222 	struct syncache_head *sch;
1223 	struct mbuf *ipopts = NULL;
1224 	u_int ltflags;
1225 	int win, ip_ttl, ip_tos;
1226 	char *s;
1227 	int rv = 0;
1228 #ifdef INET6
1229 	int autoflowlabel = 0;
1230 #endif
1231 #ifdef MAC
1232 	struct label *maclabel;
1233 #endif
1234 	struct syncache scs;
1235 	struct ucred *cred;
1236 #ifdef TCP_RFC7413
1237 	uint64_t tfo_response_cookie;
1238 	unsigned int *tfo_pending = NULL;
1239 	int tfo_cookie_valid = 0;
1240 	int tfo_response_cookie_valid = 0;
1241 #endif
1242 
1243 	INP_WLOCK_ASSERT(inp);			/* listen socket */
1244 	KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1245 	    ("%s: unexpected tcp flags", __func__));
1246 
1247 	/*
1248 	 * Combine all so/tp operations very early to drop the INP lock as
1249 	 * soon as possible.
1250 	 */
1251 	so = *lsop;
1252 	tp = sototcpcb(so);
1253 	cred = crhold(so->so_cred);
1254 
1255 #ifdef INET6
1256 	if ((inc->inc_flags & INC_ISIPV6) &&
1257 	    (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1258 		autoflowlabel = 1;
1259 #endif
1260 	ip_ttl = inp->inp_ip_ttl;
1261 	ip_tos = inp->inp_ip_tos;
1262 	win = sbspace(&so->so_rcv);
1263 	ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1264 
1265 #ifdef TCP_RFC7413
1266 	if (V_tcp_fastopen_enabled && IS_FASTOPEN(tp->t_flags) &&
1267 	    (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1268 		/*
1269 		 * Limit the number of pending TFO connections to
1270 		 * approximately half of the queue limit.  This prevents TFO
1271 		 * SYN floods from starving the service by filling the
1272 		 * listen queue with bogus TFO connections.
1273 		 */
1274 		if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1275 		    (so->so_qlimit / 2)) {
1276 			int result;
1277 
1278 			result = tcp_fastopen_check_cookie(inc,
1279 			    to->to_tfo_cookie, to->to_tfo_len,
1280 			    &tfo_response_cookie);
1281 			tfo_cookie_valid = (result > 0);
1282 			tfo_response_cookie_valid = (result >= 0);
1283 		}
1284 
1285 		/*
1286 		 * Remember the TFO pending counter as it will have to be
1287 		 * decremented below if we don't make it to syncache_tfo_expand().
1288 		 */
1289 		tfo_pending = tp->t_tfo_pending;
1290 	}
1291 #endif
1292 
1293 	/* By the time we drop the lock these should no longer be used. */
1294 	so = NULL;
1295 	tp = NULL;
1296 
1297 #ifdef MAC
1298 	if (mac_syncache_init(&maclabel) != 0) {
1299 		INP_WUNLOCK(inp);
1300 		goto done;
1301 	} else
1302 		mac_syncache_create(maclabel, inp);
1303 #endif
1304 #ifdef TCP_RFC7413
1305 	if (!tfo_cookie_valid)
1306 #endif
1307 		INP_WUNLOCK(inp);
1308 
1309 	/*
1310 	 * Remember the IP options, if any.
1311 	 */
1312 #ifdef INET6
1313 	if (!(inc->inc_flags & INC_ISIPV6))
1314 #endif
1315 #ifdef INET
1316 		ipopts = (m) ? ip_srcroute(m) : NULL;
1317 #else
1318 		ipopts = NULL;
1319 #endif
1320 
1321 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1322 	/*
1323 	 * If listening socket requested TCP digests, check that received
1324 	 * SYN has signature and it is correct. If signature doesn't match
1325 	 * or TCP_SIGNATURE support isn't enabled, drop the packet.
1326 	 */
1327 	if (ltflags & TF_SIGNATURE) {
1328 		if ((to->to_flags & TOF_SIGNATURE) == 0) {
1329 			TCPSTAT_INC(tcps_sig_err_nosigopt);
1330 			goto done;
1331 		}
1332 		if (!TCPMD5_ENABLED() ||
1333 		    TCPMD5_INPUT(m, th, to->to_signature) != 0)
1334 			goto done;
1335 	}
1336 #endif	/* TCP_SIGNATURE */
1337 	/*
1338 	 * See if we already have an entry for this connection.
1339 	 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1340 	 *
1341 	 * XXX: should the syncache be re-initialized with the contents
1342 	 * of the new SYN here (which may have different options?)
1343 	 *
1344 	 * XXX: We do not check the sequence number to see if this is a
1345 	 * real retransmit or a new connection attempt.  The question is
1346 	 * how to handle such a case; either ignore it as spoofed, or
1347 	 * drop the current entry and create a new one?
1348 	 */
1349 	sc = syncache_lookup(inc, &sch);	/* returns locked entry */
1350 	SCH_LOCK_ASSERT(sch);
1351 	if (sc != NULL) {
1352 #ifdef TCP_RFC7413
1353 		if (tfo_cookie_valid)
1354 			INP_WUNLOCK(inp);
1355 #endif
1356 		TCPSTAT_INC(tcps_sc_dupsyn);
1357 		if (ipopts) {
1358 			/*
1359 			 * If we were remembering a previous source route,
1360 			 * forget it and use the new one we've been given.
1361 			 */
1362 			if (sc->sc_ipopts)
1363 				(void) m_free(sc->sc_ipopts);
1364 			sc->sc_ipopts = ipopts;
1365 		}
1366 		/*
1367 		 * Update timestamp if present.
1368 		 */
1369 		if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1370 			sc->sc_tsreflect = to->to_tsval;
1371 		else
1372 			sc->sc_flags &= ~SCF_TIMESTAMP;
1373 #ifdef MAC
1374 		/*
1375 		 * Since we have already unconditionally allocated label
1376 		 * storage, free it up.  The syncache entry will already
1377 		 * have an initialized label we can use.
1378 		 */
1379 		mac_syncache_destroy(&maclabel);
1380 #endif
1381 		/* Retransmit SYN|ACK and reset retransmit count. */
1382 		if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1383 			log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1384 			    "resetting timer and retransmitting SYN|ACK\n",
1385 			    s, __func__);
1386 			free(s, M_TCPLOG);
1387 		}
1388 		if (syncache_respond(sc, sch, 1, m) == 0) {
1389 			sc->sc_rxmits = 0;
1390 			syncache_timeout(sc, sch, 1);
1391 			TCPSTAT_INC(tcps_sndacks);
1392 			TCPSTAT_INC(tcps_sndtotal);
1393 		}
1394 		SCH_UNLOCK(sch);
1395 		goto done;
1396 	}
1397 
1398 #ifdef TCP_RFC7413
1399 	if (tfo_cookie_valid) {
1400 		bzero(&scs, sizeof(scs));
1401 		sc = &scs;
1402 		goto skip_alloc;
1403 	}
1404 #endif
1405 
1406 	sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1407 	if (sc == NULL) {
1408 		/*
1409 		 * The zone allocator couldn't provide more entries.
1410 		 * Treat this as if the cache was full; drop the oldest
1411 		 * entry and insert the new one.
1412 		 */
1413 		TCPSTAT_INC(tcps_sc_zonefail);
1414 		if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1415 			syncache_drop(sc, sch);
1416 		sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1417 		if (sc == NULL) {
1418 			if (V_tcp_syncookies) {
1419 				bzero(&scs, sizeof(scs));
1420 				sc = &scs;
1421 			} else {
1422 				SCH_UNLOCK(sch);
1423 				if (ipopts)
1424 					(void) m_free(ipopts);
1425 				goto done;
1426 			}
1427 		}
1428 	}
1429 
1430 #ifdef TCP_RFC7413
1431 skip_alloc:
1432 	if (!tfo_cookie_valid && tfo_response_cookie_valid)
1433 		sc->sc_tfo_cookie = &tfo_response_cookie;
1434 #endif
1435 
1436 	/*
1437 	 * Fill in the syncache values.
1438 	 */
1439 #ifdef MAC
1440 	sc->sc_label = maclabel;
1441 #endif
1442 	sc->sc_cred = cred;
1443 	cred = NULL;
1444 	sc->sc_ipopts = ipopts;
1445 	bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1446 #ifdef INET6
1447 	if (!(inc->inc_flags & INC_ISIPV6))
1448 #endif
1449 	{
1450 		sc->sc_ip_tos = ip_tos;
1451 		sc->sc_ip_ttl = ip_ttl;
1452 	}
1453 #ifdef TCP_OFFLOAD
1454 	sc->sc_tod = tod;
1455 	sc->sc_todctx = todctx;
1456 #endif
1457 	sc->sc_irs = th->th_seq;
1458 	sc->sc_iss = arc4random();
1459 	sc->sc_flags = 0;
1460 	sc->sc_flowlabel = 0;
1461 
1462 	/*
1463 	 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1464 	 * win was derived from socket earlier in the function.
1465 	 */
1466 	win = imax(win, 0);
1467 	win = imin(win, TCP_MAXWIN);
1468 	sc->sc_wnd = win;
1469 
1470 	if (V_tcp_do_rfc1323) {
1471 		/*
1472 		 * A timestamp received in a SYN makes
1473 		 * it ok to send timestamp requests and replies.
1474 		 */
1475 		if (to->to_flags & TOF_TS) {
1476 			sc->sc_tsreflect = to->to_tsval;
1477 			sc->sc_ts = tcp_ts_getticks();
1478 			sc->sc_flags |= SCF_TIMESTAMP;
1479 		}
1480 		if (to->to_flags & TOF_SCALE) {
1481 			int wscale = 0;
1482 
1483 			/*
1484 			 * Pick the smallest possible scaling factor that
1485 			 * will still allow us to scale up to sb_max, aka
1486 			 * kern.ipc.maxsockbuf.
1487 			 *
1488 			 * We do this because there are broken firewalls that
1489 			 * will corrupt the window scale option, leading to
1490 			 * the other endpoint believing that our advertised
1491 			 * window is unscaled.  At scale factors larger than
1492 			 * 5 the unscaled window will drop below 1500 bytes,
1493 			 * leading to serious problems when traversing these
1494 			 * broken firewalls.
1495 			 *
1496 			 * With the default maxsockbuf of 256K, a scale factor
1497 			 * of 3 will be chosen by this algorithm.  Those who
1498 			 * choose a larger maxsockbuf should watch out
1499 			 * for the compatibility problems mentioned above.
1500 			 *
1501 			 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1502 			 * or <SYN,ACK>) segment itself is never scaled.
1503 			 */
1504 			while (wscale < TCP_MAX_WINSHIFT &&
1505 			    (TCP_MAXWIN << wscale) < sb_max)
1506 				wscale++;
1507 			sc->sc_requested_r_scale = wscale;
1508 			sc->sc_requested_s_scale = to->to_wscale;
1509 			sc->sc_flags |= SCF_WINSCALE;
1510 		}
1511 	}
1512 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1513 	/*
1514 	 * If listening socket requested TCP digests, flag this in the
1515 	 * syncache so that syncache_respond() will do the right thing
1516 	 * with the SYN+ACK.
1517 	 */
1518 	if (ltflags & TF_SIGNATURE)
1519 		sc->sc_flags |= SCF_SIGNATURE;
1520 #endif	/* TCP_SIGNATURE */
1521 	if (to->to_flags & TOF_SACKPERM)
1522 		sc->sc_flags |= SCF_SACK;
1523 	if (to->to_flags & TOF_MSS)
1524 		sc->sc_peer_mss = to->to_mss;	/* peer mss may be zero */
1525 	if (ltflags & TF_NOOPT)
1526 		sc->sc_flags |= SCF_NOOPT;
1527 	if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1528 		sc->sc_flags |= SCF_ECN;
1529 
1530 	if (V_tcp_syncookies)
1531 		sc->sc_iss = syncookie_generate(sch, sc);
1532 #ifdef INET6
1533 	if (autoflowlabel) {
1534 		if (V_tcp_syncookies)
1535 			sc->sc_flowlabel = sc->sc_iss;
1536 		else
1537 			sc->sc_flowlabel = ip6_randomflowlabel();
1538 		sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1539 	}
1540 #endif
1541 	SCH_UNLOCK(sch);
1542 
1543 #ifdef TCP_RFC7413
1544 	if (tfo_cookie_valid) {
1545 		syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1546 		/* INP_WUNLOCK(inp) will be performed by the caller */
1547 		rv = 1;
1548 		goto tfo_expanded;
1549 	}
1550 #endif
1551 
1552 	/*
1553 	 * Do a standard 3-way handshake.
1554 	 */
1555 	if (syncache_respond(sc, sch, 0, m) == 0) {
1556 		if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1557 			syncache_free(sc);
1558 		else if (sc != &scs)
1559 			syncache_insert(sc, sch);   /* locks and unlocks sch */
1560 		TCPSTAT_INC(tcps_sndacks);
1561 		TCPSTAT_INC(tcps_sndtotal);
1562 	} else {
1563 		if (sc != &scs)
1564 			syncache_free(sc);
1565 		TCPSTAT_INC(tcps_sc_dropped);
1566 	}
1567 
1568 done:
1569 	if (m) {
1570 		*lsop = NULL;
1571 		m_freem(m);
1572 	}
1573 #ifdef TCP_RFC7413
1574 	/*
1575 	 * If tfo_pending is not NULL here, then a TFO SYN that did not
1576 	 * result in a new socket was processed and the associated pending
1577 	 * counter has not yet been decremented.  All such TFO processing paths
1578 	 * transit this point.
1579 	 */
1580 	if (tfo_pending != NULL)
1581 		tcp_fastopen_decrement_counter(tfo_pending);
1582 
1583 tfo_expanded:
1584 #endif
1585 	if (cred != NULL)
1586 		crfree(cred);
1587 #ifdef MAC
1588 	if (sc == &scs)
1589 		mac_syncache_destroy(&maclabel);
1590 #endif
1591 	return (rv);
1592 }
1593 
1594 /*
1595  * Send SYN|ACK to the peer.  Either in response to the peer's SYN,
1596  * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1597  */
1598 static int
1599 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
1600     const struct mbuf *m0)
1601 {
1602 	struct ip *ip = NULL;
1603 	struct mbuf *m;
1604 	struct tcphdr *th = NULL;
1605 	int optlen, error = 0;	/* Make compiler happy */
1606 	u_int16_t hlen, tlen, mssopt;
1607 	struct tcpopt to;
1608 #ifdef INET6
1609 	struct ip6_hdr *ip6 = NULL;
1610 #endif
1611 	hlen =
1612 #ifdef INET6
1613 	       (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1614 #endif
1615 		sizeof(struct ip);
1616 	tlen = hlen + sizeof(struct tcphdr);
1617 
1618 	/* Determine MSS we advertize to other end of connection. */
1619 	mssopt = tcp_mssopt(&sc->sc_inc);
1620 	if (sc->sc_peer_mss)
1621 		mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1622 
1623 	/* XXX: Assume that the entire packet will fit in a header mbuf. */
1624 	KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1625 	    ("syncache: mbuf too small"));
1626 
1627 	/* Create the IP+TCP header from scratch. */
1628 	m = m_gethdr(M_NOWAIT, MT_DATA);
1629 	if (m == NULL)
1630 		return (ENOBUFS);
1631 #ifdef MAC
1632 	mac_syncache_create_mbuf(sc->sc_label, m);
1633 #endif
1634 	m->m_data += max_linkhdr;
1635 	m->m_len = tlen;
1636 	m->m_pkthdr.len = tlen;
1637 	m->m_pkthdr.rcvif = NULL;
1638 
1639 #ifdef INET6
1640 	if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1641 		ip6 = mtod(m, struct ip6_hdr *);
1642 		ip6->ip6_vfc = IPV6_VERSION;
1643 		ip6->ip6_nxt = IPPROTO_TCP;
1644 		ip6->ip6_src = sc->sc_inc.inc6_laddr;
1645 		ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1646 		ip6->ip6_plen = htons(tlen - hlen);
1647 		/* ip6_hlim is set after checksum */
1648 		ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1649 		ip6->ip6_flow |= sc->sc_flowlabel;
1650 
1651 		th = (struct tcphdr *)(ip6 + 1);
1652 	}
1653 #endif
1654 #if defined(INET6) && defined(INET)
1655 	else
1656 #endif
1657 #ifdef INET
1658 	{
1659 		ip = mtod(m, struct ip *);
1660 		ip->ip_v = IPVERSION;
1661 		ip->ip_hl = sizeof(struct ip) >> 2;
1662 		ip->ip_len = htons(tlen);
1663 		ip->ip_id = 0;
1664 		ip->ip_off = 0;
1665 		ip->ip_sum = 0;
1666 		ip->ip_p = IPPROTO_TCP;
1667 		ip->ip_src = sc->sc_inc.inc_laddr;
1668 		ip->ip_dst = sc->sc_inc.inc_faddr;
1669 		ip->ip_ttl = sc->sc_ip_ttl;
1670 		ip->ip_tos = sc->sc_ip_tos;
1671 
1672 		/*
1673 		 * See if we should do MTU discovery.  Route lookups are
1674 		 * expensive, so we will only unset the DF bit if:
1675 		 *
1676 		 *	1) path_mtu_discovery is disabled
1677 		 *	2) the SCF_UNREACH flag has been set
1678 		 */
1679 		if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1680 		       ip->ip_off |= htons(IP_DF);
1681 
1682 		th = (struct tcphdr *)(ip + 1);
1683 	}
1684 #endif /* INET */
1685 	th->th_sport = sc->sc_inc.inc_lport;
1686 	th->th_dport = sc->sc_inc.inc_fport;
1687 
1688 	th->th_seq = htonl(sc->sc_iss);
1689 	th->th_ack = htonl(sc->sc_irs + 1);
1690 	th->th_off = sizeof(struct tcphdr) >> 2;
1691 	th->th_x2 = 0;
1692 	th->th_flags = TH_SYN|TH_ACK;
1693 	th->th_win = htons(sc->sc_wnd);
1694 	th->th_urp = 0;
1695 
1696 	if (sc->sc_flags & SCF_ECN) {
1697 		th->th_flags |= TH_ECE;
1698 		TCPSTAT_INC(tcps_ecn_shs);
1699 	}
1700 
1701 	/* Tack on the TCP options. */
1702 	if ((sc->sc_flags & SCF_NOOPT) == 0) {
1703 		to.to_flags = 0;
1704 
1705 		to.to_mss = mssopt;
1706 		to.to_flags = TOF_MSS;
1707 		if (sc->sc_flags & SCF_WINSCALE) {
1708 			to.to_wscale = sc->sc_requested_r_scale;
1709 			to.to_flags |= TOF_SCALE;
1710 		}
1711 		if (sc->sc_flags & SCF_TIMESTAMP) {
1712 			/* Virgin timestamp or TCP cookie enhanced one. */
1713 			to.to_tsval = sc->sc_ts;
1714 			to.to_tsecr = sc->sc_tsreflect;
1715 			to.to_flags |= TOF_TS;
1716 		}
1717 		if (sc->sc_flags & SCF_SACK)
1718 			to.to_flags |= TOF_SACKPERM;
1719 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1720 		if (sc->sc_flags & SCF_SIGNATURE)
1721 			to.to_flags |= TOF_SIGNATURE;
1722 #endif
1723 #ifdef TCP_RFC7413
1724 		if (sc->sc_tfo_cookie) {
1725 			to.to_flags |= TOF_FASTOPEN;
1726 			to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1727 			to.to_tfo_cookie = sc->sc_tfo_cookie;
1728 			/* don't send cookie again when retransmitting response */
1729 			sc->sc_tfo_cookie = NULL;
1730 		}
1731 #endif
1732 		optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1733 
1734 		/* Adjust headers by option size. */
1735 		th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1736 		m->m_len += optlen;
1737 		m->m_pkthdr.len += optlen;
1738 #ifdef INET6
1739 		if (sc->sc_inc.inc_flags & INC_ISIPV6)
1740 			ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1741 		else
1742 #endif
1743 			ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1744 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1745 		if (sc->sc_flags & SCF_SIGNATURE) {
1746 			KASSERT(to.to_flags & TOF_SIGNATURE,
1747 			    ("tcp_addoptions() didn't set tcp_signature"));
1748 
1749 			/* NOTE: to.to_signature is inside of mbuf */
1750 			if (!TCPMD5_ENABLED() ||
1751 			    TCPMD5_OUTPUT(m, th, to.to_signature) != 0) {
1752 				m_freem(m);
1753 				return (EACCES);
1754 			}
1755 		}
1756 #endif
1757 	} else
1758 		optlen = 0;
1759 
1760 	M_SETFIB(m, sc->sc_inc.inc_fibnum);
1761 	m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1762 	/*
1763 	 * If we have peer's SYN and it has a flowid, then let's assign it to
1764 	 * our SYN|ACK.  ip6_output() and ip_output() will not assign flowid
1765 	 * to SYN|ACK due to lack of inp here.
1766 	 */
1767 	if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1768 		m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1769 		M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1770 	}
1771 #ifdef INET6
1772 	if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1773 		m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1774 		th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1775 		    IPPROTO_TCP, 0);
1776 		ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1777 #ifdef TCP_OFFLOAD
1778 		if (ADDED_BY_TOE(sc)) {
1779 			struct toedev *tod = sc->sc_tod;
1780 
1781 			error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1782 
1783 			return (error);
1784 		}
1785 #endif
1786 		error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1787 	}
1788 #endif
1789 #if defined(INET6) && defined(INET)
1790 	else
1791 #endif
1792 #ifdef INET
1793 	{
1794 		m->m_pkthdr.csum_flags = CSUM_TCP;
1795 		th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1796 		    htons(tlen + optlen - hlen + IPPROTO_TCP));
1797 #ifdef TCP_OFFLOAD
1798 		if (ADDED_BY_TOE(sc)) {
1799 			struct toedev *tod = sc->sc_tod;
1800 
1801 			error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1802 
1803 			return (error);
1804 		}
1805 #endif
1806 		error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1807 	}
1808 #endif
1809 	return (error);
1810 }
1811 
1812 /*
1813  * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1814  * that exceed the capacity of the syncache by avoiding the storage of any
1815  * of the SYNs we receive.  Syncookies defend against blind SYN flooding
1816  * attacks where the attacker does not have access to our responses.
1817  *
1818  * Syncookies encode and include all necessary information about the
1819  * connection setup within the SYN|ACK that we send back.  That way we
1820  * can avoid keeping any local state until the ACK to our SYN|ACK returns
1821  * (if ever).  Normally the syncache and syncookies are running in parallel
1822  * with the latter taking over when the former is exhausted.  When matching
1823  * syncache entry is found the syncookie is ignored.
1824  *
1825  * The only reliable information persisting the 3WHS is our initial sequence
1826  * number ISS of 32 bits.  Syncookies embed a cryptographically sufficient
1827  * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1828  * of our SYN|ACK.  The MAC can be recomputed when the ACK to our SYN|ACK
1829  * returns and signifies a legitimate connection if it matches the ACK.
1830  *
1831  * The available space of 32 bits to store the hash and to encode the SYN
1832  * option information is very tight and we should have at least 24 bits for
1833  * the MAC to keep the number of guesses by blind spoofing reasonably high.
1834  *
1835  * SYN option information we have to encode to fully restore a connection:
1836  * MSS: is imporant to chose an optimal segment size to avoid IP level
1837  *   fragmentation along the path.  The common MSS values can be encoded
1838  *   in a 3-bit table.  Uncommon values are captured by the next lower value
1839  *   in the table leading to a slight increase in packetization overhead.
1840  * WSCALE: is necessary to allow large windows to be used for high delay-
1841  *   bandwidth product links.  Not scaling the window when it was initially
1842  *   negotiated is bad for performance as lack of scaling further decreases
1843  *   the apparent available send window.  We only need to encode the WSCALE
1844  *   we received from the remote end.  Our end can be recalculated at any
1845  *   time.  The common WSCALE values can be encoded in a 3-bit table.
1846  *   Uncommon values are captured by the next lower value in the table
1847  *   making us under-estimate the available window size halving our
1848  *   theoretically possible maximum throughput for that connection.
1849  * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1850  * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1851  *   that are included in all segments on a connection.  We enable them when
1852  *   the ACK has them.
1853  *
1854  * Security of syncookies and attack vectors:
1855  *
1856  * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1857  * together with the gloabl secret to make it unique per connection attempt.
1858  * Thus any change of any of those parameters results in a different MAC output
1859  * in an unpredictable way unless a collision is encountered.  24 bits of the
1860  * MAC are embedded into the ISS.
1861  *
1862  * To prevent replay attacks two rotating global secrets are updated with a
1863  * new random value every 15 seconds.  The life-time of a syncookie is thus
1864  * 15-30 seconds.
1865  *
1866  * Vector 1: Attacking the secret.  This requires finding a weakness in the
1867  * MAC itself or the way it is used here.  The attacker can do a chosen plain
1868  * text attack by varying and testing the all parameters under his control.
1869  * The strength depends on the size and randomness of the secret, and the
1870  * cryptographic security of the MAC function.  Due to the constant updating
1871  * of the secret the attacker has at most 29.999 seconds to find the secret
1872  * and launch spoofed connections.  After that he has to start all over again.
1873  *
1874  * Vector 2: Collision attack on the MAC of a single ACK.  With a 24 bit MAC
1875  * size an average of 4,823 attempts are required for a 50% chance of success
1876  * to spoof a single syncookie (birthday collision paradox).  However the
1877  * attacker is blind and doesn't know if one of his attempts succeeded unless
1878  * he has a side channel to interfere success from.  A single connection setup
1879  * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1880  * This many attempts are required for each one blind spoofed connection.  For
1881  * every additional spoofed connection he has to launch another N attempts.
1882  * Thus for a sustained rate 100 spoofed connections per second approximately
1883  * 1,800,000 packets per second would have to be sent.
1884  *
1885  * NB: The MAC function should be fast so that it doesn't become a CPU
1886  * exhaustion attack vector itself.
1887  *
1888  * References:
1889  *  RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1890  *  SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1891  *   http://cr.yp.to/syncookies.html    (overview)
1892  *   http://cr.yp.to/syncookies/archive (details)
1893  *
1894  *
1895  * Schematic construction of a syncookie enabled Initial Sequence Number:
1896  *  0        1         2         3
1897  *  12345678901234567890123456789012
1898  * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1899  *
1900  *  x 24 MAC (truncated)
1901  *  W  3 Send Window Scale index
1902  *  M  3 MSS index
1903  *  S  1 SACK permitted
1904  *  P  1 Odd/even secret
1905  */
1906 
1907 /*
1908  * Distribution and probability of certain MSS values.  Those in between are
1909  * rounded down to the next lower one.
1910  * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1911  *                            .2%  .3%   5%    7%    7%    20%   15%   45%
1912  */
1913 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1914 
1915 /*
1916  * Distribution and probability of certain WSCALE values.  We have to map the
1917  * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1918  * bits based on prevalence of certain values.  Where we don't have an exact
1919  * match for are rounded down to the next lower one letting us under-estimate
1920  * the true available window.  At the moment this would happen only for the
1921  * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1922  * and window size).  The absence of the WSCALE option (no scaling in either
1923  * direction) is encoded with index zero.
1924  * [WSCALE values histograms, Allman, 2012]
1925  *                            X 10 10 35  5  6 14 10%   by host
1926  *                            X 11  4  5  5 18 49  3%   by connections
1927  */
1928 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1929 
1930 /*
1931  * Compute the MAC for the SYN cookie.  SIPHASH-2-4 is chosen for its speed
1932  * and good cryptographic properties.
1933  */
1934 static uint32_t
1935 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1936     uint8_t *secbits, uintptr_t secmod)
1937 {
1938 	SIPHASH_CTX ctx;
1939 	uint32_t siphash[2];
1940 
1941 	SipHash24_Init(&ctx);
1942 	SipHash_SetKey(&ctx, secbits);
1943 	switch (inc->inc_flags & INC_ISIPV6) {
1944 #ifdef INET
1945 	case 0:
1946 		SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1947 		SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1948 		break;
1949 #endif
1950 #ifdef INET6
1951 	case INC_ISIPV6:
1952 		SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1953 		SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1954 		break;
1955 #endif
1956 	}
1957 	SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1958 	SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1959 	SipHash_Update(&ctx, &irs, sizeof(irs));
1960 	SipHash_Update(&ctx, &flags, sizeof(flags));
1961 	SipHash_Update(&ctx, &secmod, sizeof(secmod));
1962 	SipHash_Final((u_int8_t *)&siphash, &ctx);
1963 
1964 	return (siphash[0] ^ siphash[1]);
1965 }
1966 
1967 static tcp_seq
1968 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1969 {
1970 	u_int i, mss, secbit, wscale;
1971 	uint32_t iss, hash;
1972 	uint8_t *secbits;
1973 	union syncookie cookie;
1974 
1975 	SCH_LOCK_ASSERT(sch);
1976 
1977 	cookie.cookie = 0;
1978 
1979 	/* Map our computed MSS into the 3-bit index. */
1980 	mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1981 	for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
1982 	     i--)
1983 		;
1984 	cookie.flags.mss_idx = i;
1985 
1986 	/*
1987 	 * Map the send window scale into the 3-bit index but only if
1988 	 * the wscale option was received.
1989 	 */
1990 	if (sc->sc_flags & SCF_WINSCALE) {
1991 		wscale = sc->sc_requested_s_scale;
1992 		for (i = nitems(tcp_sc_wstab) - 1;
1993 		    tcp_sc_wstab[i] > wscale && i > 0;
1994 		     i--)
1995 			;
1996 		cookie.flags.wscale_idx = i;
1997 	}
1998 
1999 	/* Can we do SACK? */
2000 	if (sc->sc_flags & SCF_SACK)
2001 		cookie.flags.sack_ok = 1;
2002 
2003 	/* Which of the two secrets to use. */
2004 	secbit = sch->sch_sc->secret.oddeven & 0x1;
2005 	cookie.flags.odd_even = secbit;
2006 
2007 	secbits = sch->sch_sc->secret.key[secbit];
2008 	hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
2009 	    (uintptr_t)sch);
2010 
2011 	/*
2012 	 * Put the flags into the hash and XOR them to get better ISS number
2013 	 * variance.  This doesn't enhance the cryptographic strength and is
2014 	 * done to prevent the 8 cookie bits from showing up directly on the
2015 	 * wire.
2016 	 */
2017 	iss = hash & ~0xff;
2018 	iss |= cookie.cookie ^ (hash >> 24);
2019 
2020 	/* Randomize the timestamp. */
2021 	if (sc->sc_flags & SCF_TIMESTAMP) {
2022 		sc->sc_ts = arc4random();
2023 		sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
2024 	}
2025 
2026 	TCPSTAT_INC(tcps_sc_sendcookie);
2027 	return (iss);
2028 }
2029 
2030 static struct syncache *
2031 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
2032     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2033     struct socket *lso)
2034 {
2035 	uint32_t hash;
2036 	uint8_t *secbits;
2037 	tcp_seq ack, seq;
2038 	int wnd, wscale = 0;
2039 	union syncookie cookie;
2040 
2041 	SCH_LOCK_ASSERT(sch);
2042 
2043 	/*
2044 	 * Pull information out of SYN-ACK/ACK and revert sequence number
2045 	 * advances.
2046 	 */
2047 	ack = th->th_ack - 1;
2048 	seq = th->th_seq - 1;
2049 
2050 	/*
2051 	 * Unpack the flags containing enough information to restore the
2052 	 * connection.
2053 	 */
2054 	cookie.cookie = (ack & 0xff) ^ (ack >> 24);
2055 
2056 	/* Which of the two secrets to use. */
2057 	secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
2058 
2059 	hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
2060 
2061 	/* The recomputed hash matches the ACK if this was a genuine cookie. */
2062 	if ((ack & ~0xff) != (hash & ~0xff))
2063 		return (NULL);
2064 
2065 	/* Fill in the syncache values. */
2066 	sc->sc_flags = 0;
2067 	bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2068 	sc->sc_ipopts = NULL;
2069 
2070 	sc->sc_irs = seq;
2071 	sc->sc_iss = ack;
2072 
2073 	switch (inc->inc_flags & INC_ISIPV6) {
2074 #ifdef INET
2075 	case 0:
2076 		sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2077 		sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2078 		break;
2079 #endif
2080 #ifdef INET6
2081 	case INC_ISIPV6:
2082 		if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2083 			sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2084 		break;
2085 #endif
2086 	}
2087 
2088 	sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2089 
2090 	/* We can simply recompute receive window scale we sent earlier. */
2091 	while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2092 		wscale++;
2093 
2094 	/* Only use wscale if it was enabled in the orignal SYN. */
2095 	if (cookie.flags.wscale_idx > 0) {
2096 		sc->sc_requested_r_scale = wscale;
2097 		sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2098 		sc->sc_flags |= SCF_WINSCALE;
2099 	}
2100 
2101 	wnd = sbspace(&lso->so_rcv);
2102 	wnd = imax(wnd, 0);
2103 	wnd = imin(wnd, TCP_MAXWIN);
2104 	sc->sc_wnd = wnd;
2105 
2106 	if (cookie.flags.sack_ok)
2107 		sc->sc_flags |= SCF_SACK;
2108 
2109 	if (to->to_flags & TOF_TS) {
2110 		sc->sc_flags |= SCF_TIMESTAMP;
2111 		sc->sc_tsreflect = to->to_tsval;
2112 		sc->sc_ts = to->to_tsecr;
2113 		sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2114 	}
2115 
2116 	if (to->to_flags & TOF_SIGNATURE)
2117 		sc->sc_flags |= SCF_SIGNATURE;
2118 
2119 	sc->sc_rxmits = 0;
2120 
2121 	TCPSTAT_INC(tcps_sc_recvcookie);
2122 	return (sc);
2123 }
2124 
2125 #ifdef INVARIANTS
2126 static int
2127 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2128     struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2129     struct socket *lso)
2130 {
2131 	struct syncache scs, *scx;
2132 	char *s;
2133 
2134 	bzero(&scs, sizeof(scs));
2135 	scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2136 
2137 	if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2138 		return (0);
2139 
2140 	if (scx != NULL) {
2141 		if (sc->sc_peer_mss != scx->sc_peer_mss)
2142 			log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2143 			    s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2144 
2145 		if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2146 			log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2147 			    s, __func__, sc->sc_requested_r_scale,
2148 			    scx->sc_requested_r_scale);
2149 
2150 		if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2151 			log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2152 			    s, __func__, sc->sc_requested_s_scale,
2153 			    scx->sc_requested_s_scale);
2154 
2155 		if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2156 			log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2157 	}
2158 
2159 	if (s != NULL)
2160 		free(s, M_TCPLOG);
2161 	return (0);
2162 }
2163 #endif /* INVARIANTS */
2164 
2165 static void
2166 syncookie_reseed(void *arg)
2167 {
2168 	struct tcp_syncache *sc = arg;
2169 	uint8_t *secbits;
2170 	int secbit;
2171 
2172 	/*
2173 	 * Reseeding the secret doesn't have to be protected by a lock.
2174 	 * It only must be ensured that the new random values are visible
2175 	 * to all CPUs in a SMP environment.  The atomic with release
2176 	 * semantics ensures that.
2177 	 */
2178 	secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2179 	secbits = sc->secret.key[secbit];
2180 	arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2181 	atomic_add_rel_int(&sc->secret.oddeven, 1);
2182 
2183 	/* Reschedule ourself. */
2184 	callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2185 }
2186 
2187 /*
2188  * Exports the syncache entries to userland so that netstat can display
2189  * them alongside the other sockets.  This function is intended to be
2190  * called only from tcp_pcblist.
2191  *
2192  * Due to concurrency on an active system, the number of pcbs exported
2193  * may have no relation to max_pcbs.  max_pcbs merely indicates the
2194  * amount of space the caller allocated for this function to use.
2195  */
2196 int
2197 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2198 {
2199 	struct xtcpcb xt;
2200 	struct syncache *sc;
2201 	struct syncache_head *sch;
2202 	int count, error, i;
2203 
2204 	for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2205 		sch = &V_tcp_syncache.hashbase[i];
2206 		SCH_LOCK(sch);
2207 		TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2208 			if (count >= max_pcbs) {
2209 				SCH_UNLOCK(sch);
2210 				goto exit;
2211 			}
2212 			if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2213 				continue;
2214 			bzero(&xt, sizeof(xt));
2215 			xt.xt_len = sizeof(xt);
2216 			if (sc->sc_inc.inc_flags & INC_ISIPV6)
2217 				xt.xt_inp.inp_vflag = INP_IPV6;
2218 			else
2219 				xt.xt_inp.inp_vflag = INP_IPV4;
2220 			bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2221 			xt.xt_tp.t_inpcb = &xt.xt_inp;
2222 			xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2223 			xt.xt_socket.xso_protocol = IPPROTO_TCP;
2224 			xt.xt_socket.xso_len = sizeof (struct xsocket);
2225 			xt.xt_socket.so_type = SOCK_STREAM;
2226 			xt.xt_socket.so_state = SS_ISCONNECTING;
2227 			error = SYSCTL_OUT(req, &xt, sizeof xt);
2228 			if (error) {
2229 				SCH_UNLOCK(sch);
2230 				goto exit;
2231 			}
2232 			count++;
2233 		}
2234 		SCH_UNLOCK(sch);
2235 	}
2236 exit:
2237 	*pcbs_exported = count;
2238 	return error;
2239 }
2240