tcp_syncache.c revision 292309
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: head/sys/netinet/tcp_syncache.c 292309 2015-12-16 00:56:45Z rrs $"); 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#include <netinet/tcp_fsm.h> 85#include <netinet/tcp_seq.h> 86#include <netinet/tcp_timer.h> 87#include <netinet/tcp_var.h> 88#include <netinet/tcp_syncache.h> 89#ifdef INET6 90#include <netinet6/tcp6_var.h> 91#endif 92#ifdef TCP_OFFLOAD 93#include <netinet/toecore.h> 94#endif 95 96#ifdef IPSEC 97#include <netipsec/ipsec.h> 98#ifdef INET6 99#include <netipsec/ipsec6.h> 100#endif 101#include <netipsec/key.h> 102#endif /*IPSEC*/ 103 104#include <machine/in_cksum.h> 105 106#include <security/mac/mac_framework.h> 107 108static VNET_DEFINE(int, tcp_syncookies) = 1; 109#define V_tcp_syncookies VNET(tcp_syncookies) 110SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 115#define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120#ifdef TCP_OFFLOAD 121#define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 122#endif 123 124static void syncache_drop(struct syncache *, struct syncache_head *); 125static void syncache_free(struct syncache *); 126static void syncache_insert(struct syncache *, struct syncache_head *); 127static int syncache_respond(struct syncache *, struct syncache_head *, int); 128static struct socket *syncache_socket(struct syncache *, struct socket *, 129 struct mbuf *m); 130static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 131 int docallout); 132static void syncache_timer(void *); 133 134static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 135 uint8_t *, uintptr_t); 136static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 137static struct syncache 138 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 139 struct syncache *, struct tcphdr *, struct tcpopt *, 140 struct socket *); 141static void syncookie_reseed(void *); 142#ifdef INVARIANTS 143static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 144 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 145 struct socket *lso); 146#endif 147 148/* 149 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 150 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 151 * the odds are that the user has given up attempting to connect by then. 152 */ 153#define SYNCACHE_MAXREXMTS 3 154 155/* Arbitrary values */ 156#define TCP_SYNCACHE_HASHSIZE 512 157#define TCP_SYNCACHE_BUCKETLIMIT 30 158 159static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 160#define V_tcp_syncache VNET(tcp_syncache) 161 162static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 163 "TCP SYN cache"); 164 165SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 166 &VNET_NAME(tcp_syncache.bucket_limit), 0, 167 "Per-bucket hash limit for syncache"); 168 169SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 170 &VNET_NAME(tcp_syncache.cache_limit), 0, 171 "Overall entry limit for syncache"); 172 173SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 174 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 175 176SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.hashsize), 0, 178 "Size of TCP syncache hashtable"); 179 180SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 181 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 182 "Limit on SYN/ACK retransmissions"); 183 184VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 185SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 186 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 187 "Send reset on socket allocation failure"); 188 189static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 190 191#define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 192#define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 193#define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 194 195/* 196 * Requires the syncache entry to be already removed from the bucket list. 197 */ 198static void 199syncache_free(struct syncache *sc) 200{ 201 202 if (sc->sc_ipopts) 203 (void) m_free(sc->sc_ipopts); 204 if (sc->sc_cred) 205 crfree(sc->sc_cred); 206#ifdef MAC 207 mac_syncache_destroy(&sc->sc_label); 208#endif 209 210 uma_zfree(V_tcp_syncache.zone, sc); 211} 212 213void 214syncache_init(void) 215{ 216 int i; 217 218 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 219 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 220 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 221 V_tcp_syncache.hash_secret = arc4random(); 222 223 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 224 &V_tcp_syncache.hashsize); 225 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 226 &V_tcp_syncache.bucket_limit); 227 if (!powerof2(V_tcp_syncache.hashsize) || 228 V_tcp_syncache.hashsize == 0) { 229 printf("WARNING: syncache hash size is not a power of 2.\n"); 230 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 231 } 232 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 233 234 /* Set limits. */ 235 V_tcp_syncache.cache_limit = 236 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 237 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 238 &V_tcp_syncache.cache_limit); 239 240 /* Allocate the hash table. */ 241 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 242 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 243 244#ifdef VIMAGE 245 V_tcp_syncache.vnet = curvnet; 246#endif 247 248 /* Initialize the hash buckets. */ 249 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 250 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 251 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 252 NULL, MTX_DEF); 253 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 254 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 255 V_tcp_syncache.hashbase[i].sch_length = 0; 256 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 257 } 258 259 /* Create the syncache entry zone. */ 260 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 261 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 262 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 263 V_tcp_syncache.cache_limit); 264 265 /* Start the SYN cookie reseeder callout. */ 266 callout_init(&V_tcp_syncache.secret.reseed, 1); 267 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 268 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 269 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 270 syncookie_reseed, &V_tcp_syncache); 271} 272 273#ifdef VIMAGE 274void 275syncache_destroy(void) 276{ 277 struct syncache_head *sch; 278 struct syncache *sc, *nsc; 279 int i; 280 281 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 282 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 283 284 sch = &V_tcp_syncache.hashbase[i]; 285 callout_drain(&sch->sch_timer); 286 287 SCH_LOCK(sch); 288 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 289 syncache_drop(sc, sch); 290 SCH_UNLOCK(sch); 291 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 292 ("%s: sch->sch_bucket not empty", __func__)); 293 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 294 __func__, sch->sch_length)); 295 mtx_destroy(&sch->sch_mtx); 296 } 297 298 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 299 ("%s: cache_count not 0", __func__)); 300 301 /* Free the allocated global resources. */ 302 uma_zdestroy(V_tcp_syncache.zone); 303 free(V_tcp_syncache.hashbase, M_SYNCACHE); 304 305 callout_drain(&V_tcp_syncache.secret.reseed); 306} 307#endif 308 309/* 310 * Inserts a syncache entry into the specified bucket row. 311 * Locks and unlocks the syncache_head autonomously. 312 */ 313static void 314syncache_insert(struct syncache *sc, struct syncache_head *sch) 315{ 316 struct syncache *sc2; 317 318 SCH_LOCK(sch); 319 320 /* 321 * Make sure that we don't overflow the per-bucket limit. 322 * If the bucket is full, toss the oldest element. 323 */ 324 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 325 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 326 ("sch->sch_length incorrect")); 327 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 328 syncache_drop(sc2, sch); 329 TCPSTAT_INC(tcps_sc_bucketoverflow); 330 } 331 332 /* Put it into the bucket. */ 333 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 334 sch->sch_length++; 335 336#ifdef TCP_OFFLOAD 337 if (ADDED_BY_TOE(sc)) { 338 struct toedev *tod = sc->sc_tod; 339 340 tod->tod_syncache_added(tod, sc->sc_todctx); 341 } 342#endif 343 344 /* Reinitialize the bucket row's timer. */ 345 if (sch->sch_length == 1) 346 sch->sch_nextc = ticks + INT_MAX; 347 syncache_timeout(sc, sch, 1); 348 349 SCH_UNLOCK(sch); 350 351 TCPSTAT_INC(tcps_sc_added); 352} 353 354/* 355 * Remove and free entry from syncache bucket row. 356 * Expects locked syncache head. 357 */ 358static void 359syncache_drop(struct syncache *sc, struct syncache_head *sch) 360{ 361 362 SCH_LOCK_ASSERT(sch); 363 364 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 365 sch->sch_length--; 366 367#ifdef TCP_OFFLOAD 368 if (ADDED_BY_TOE(sc)) { 369 struct toedev *tod = sc->sc_tod; 370 371 tod->tod_syncache_removed(tod, sc->sc_todctx); 372 } 373#endif 374 375 syncache_free(sc); 376} 377 378/* 379 * Engage/reengage time on bucket row. 380 */ 381static void 382syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 383{ 384 sc->sc_rxttime = ticks + 385 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 386 sc->sc_rxmits++; 387 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 388 sch->sch_nextc = sc->sc_rxttime; 389 if (docallout) 390 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 391 syncache_timer, (void *)sch); 392 } 393} 394 395/* 396 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 397 * If we have retransmitted an entry the maximum number of times, expire it. 398 * One separate timer for each bucket row. 399 */ 400static void 401syncache_timer(void *xsch) 402{ 403 struct syncache_head *sch = (struct syncache_head *)xsch; 404 struct syncache *sc, *nsc; 405 int tick = ticks; 406 char *s; 407 408 CURVNET_SET(sch->sch_sc->vnet); 409 410 /* NB: syncache_head has already been locked by the callout. */ 411 SCH_LOCK_ASSERT(sch); 412 413 /* 414 * In the following cycle we may remove some entries and/or 415 * advance some timeouts, so re-initialize the bucket timer. 416 */ 417 sch->sch_nextc = tick + INT_MAX; 418 419 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 420 /* 421 * We do not check if the listen socket still exists 422 * and accept the case where the listen socket may be 423 * gone by the time we resend the SYN/ACK. We do 424 * not expect this to happens often. If it does, 425 * then the RST will be sent by the time the remote 426 * host does the SYN/ACK->ACK. 427 */ 428 if (TSTMP_GT(sc->sc_rxttime, tick)) { 429 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 430 sch->sch_nextc = sc->sc_rxttime; 431 continue; 432 } 433 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 434 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 435 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 436 "giving up and removing syncache entry\n", 437 s, __func__); 438 free(s, M_TCPLOG); 439 } 440 syncache_drop(sc, sch); 441 TCPSTAT_INC(tcps_sc_stale); 442 continue; 443 } 444 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 445 log(LOG_DEBUG, "%s; %s: Response timeout, " 446 "retransmitting (%u) SYN|ACK\n", 447 s, __func__, sc->sc_rxmits); 448 free(s, M_TCPLOG); 449 } 450 451 syncache_respond(sc, sch, 1); 452 TCPSTAT_INC(tcps_sc_retransmitted); 453 syncache_timeout(sc, sch, 0); 454 } 455 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 456 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 457 syncache_timer, (void *)(sch)); 458 CURVNET_RESTORE(); 459} 460 461/* 462 * Find an entry in the syncache. 463 * Returns always with locked syncache_head plus a matching entry or NULL. 464 */ 465static struct syncache * 466syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 467{ 468 struct syncache *sc; 469 struct syncache_head *sch; 470 uint32_t hash; 471 472 /* 473 * The hash is built on foreign port + local port + foreign address. 474 * We rely on the fact that struct in_conninfo starts with 16 bits 475 * of foreign port, then 16 bits of local port then followed by 128 476 * bits of foreign address. In case of IPv4 address, the first 3 477 * 32-bit words of the address always are zeroes. 478 */ 479 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 480 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 481 482 sch = &V_tcp_syncache.hashbase[hash]; 483 *schp = sch; 484 SCH_LOCK(sch); 485 486 /* Circle through bucket row to find matching entry. */ 487 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 488 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 489 sizeof(struct in_endpoints)) == 0) 490 break; 491 492 return (sc); /* Always returns with locked sch. */ 493} 494 495/* 496 * This function is called when we get a RST for a 497 * non-existent connection, so that we can see if the 498 * connection is in the syn cache. If it is, zap it. 499 */ 500void 501syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 502{ 503 struct syncache *sc; 504 struct syncache_head *sch; 505 char *s = NULL; 506 507 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 508 SCH_LOCK_ASSERT(sch); 509 510 /* 511 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 512 * See RFC 793 page 65, section SEGMENT ARRIVES. 513 */ 514 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 515 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 516 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 517 "FIN flag set, segment ignored\n", s, __func__); 518 TCPSTAT_INC(tcps_badrst); 519 goto done; 520 } 521 522 /* 523 * No corresponding connection was found in syncache. 524 * If syncookies are enabled and possibly exclusively 525 * used, or we are under memory pressure, a valid RST 526 * may not find a syncache entry. In that case we're 527 * done and no SYN|ACK retransmissions will happen. 528 * Otherwise the RST was misdirected or spoofed. 529 */ 530 if (sc == NULL) { 531 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 532 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 533 "syncache entry (possibly syncookie only), " 534 "segment ignored\n", s, __func__); 535 TCPSTAT_INC(tcps_badrst); 536 goto done; 537 } 538 539 /* 540 * If the RST bit is set, check the sequence number to see 541 * if this is a valid reset segment. 542 * RFC 793 page 37: 543 * In all states except SYN-SENT, all reset (RST) segments 544 * are validated by checking their SEQ-fields. A reset is 545 * valid if its sequence number is in the window. 546 * 547 * The sequence number in the reset segment is normally an 548 * echo of our outgoing acknowlegement numbers, but some hosts 549 * send a reset with the sequence number at the rightmost edge 550 * of our receive window, and we have to handle this case. 551 */ 552 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 553 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 554 syncache_drop(sc, sch); 555 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 556 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 557 "connection attempt aborted by remote endpoint\n", 558 s, __func__); 559 TCPSTAT_INC(tcps_sc_reset); 560 } else { 561 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 562 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 563 "IRS %u (+WND %u), segment ignored\n", 564 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 565 TCPSTAT_INC(tcps_badrst); 566 } 567 568done: 569 if (s != NULL) 570 free(s, M_TCPLOG); 571 SCH_UNLOCK(sch); 572} 573 574void 575syncache_badack(struct in_conninfo *inc) 576{ 577 struct syncache *sc; 578 struct syncache_head *sch; 579 580 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 581 SCH_LOCK_ASSERT(sch); 582 if (sc != NULL) { 583 syncache_drop(sc, sch); 584 TCPSTAT_INC(tcps_sc_badack); 585 } 586 SCH_UNLOCK(sch); 587} 588 589void 590syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 591{ 592 struct syncache *sc; 593 struct syncache_head *sch; 594 595 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 596 SCH_LOCK_ASSERT(sch); 597 if (sc == NULL) 598 goto done; 599 600 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 601 if (ntohl(th->th_seq) != sc->sc_iss) 602 goto done; 603 604 /* 605 * If we've rertransmitted 3 times and this is our second error, 606 * we remove the entry. Otherwise, we allow it to continue on. 607 * This prevents us from incorrectly nuking an entry during a 608 * spurious network outage. 609 * 610 * See tcp_notify(). 611 */ 612 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 613 sc->sc_flags |= SCF_UNREACH; 614 goto done; 615 } 616 syncache_drop(sc, sch); 617 TCPSTAT_INC(tcps_sc_unreach); 618done: 619 SCH_UNLOCK(sch); 620} 621 622/* 623 * Build a new TCP socket structure from a syncache entry. 624 * 625 * On success return the newly created socket with its underlying inp locked. 626 */ 627static struct socket * 628syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 629{ 630 struct tcp_function_block *blk; 631 struct inpcb *inp = NULL; 632 struct socket *so; 633 struct tcpcb *tp; 634 int error; 635 char *s; 636 637 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 638 639 /* 640 * Ok, create the full blown connection, and set things up 641 * as they would have been set up if we had created the 642 * connection when the SYN arrived. If we can't create 643 * the connection, abort it. 644 */ 645 so = sonewconn(lso, 0); 646 if (so == NULL) { 647 /* 648 * Drop the connection; we will either send a RST or 649 * have the peer retransmit its SYN again after its 650 * RTO and try again. 651 */ 652 TCPSTAT_INC(tcps_listendrop); 653 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 654 log(LOG_DEBUG, "%s; %s: Socket create failed " 655 "due to limits or memory shortage\n", 656 s, __func__); 657 free(s, M_TCPLOG); 658 } 659 goto abort2; 660 } 661#ifdef MAC 662 mac_socketpeer_set_from_mbuf(m, so); 663#endif 664 665 inp = sotoinpcb(so); 666 inp->inp_inc.inc_fibnum = so->so_fibnum; 667 INP_WLOCK(inp); 668 /* 669 * Exclusive pcbinfo lock is not required in syncache socket case even 670 * if two inpcb locks can be acquired simultaneously: 671 * - the inpcb in LISTEN state, 672 * - the newly created inp. 673 * 674 * In this case, an inp cannot be at same time in LISTEN state and 675 * just created by an accept() call. 676 */ 677 INP_HASH_WLOCK(&V_tcbinfo); 678 679 /* Insert new socket into PCB hash list. */ 680 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 681#ifdef INET6 682 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 683 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 684 } else { 685 inp->inp_vflag &= ~INP_IPV6; 686 inp->inp_vflag |= INP_IPV4; 687#endif 688 inp->inp_laddr = sc->sc_inc.inc_laddr; 689#ifdef INET6 690 } 691#endif 692 693 /* 694 * If there's an mbuf and it has a flowid, then let's initialise the 695 * inp with that particular flowid. 696 */ 697 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 698 inp->inp_flowid = m->m_pkthdr.flowid; 699 inp->inp_flowtype = M_HASHTYPE_GET(m); 700 } 701 702 /* 703 * Install in the reservation hash table for now, but don't yet 704 * install a connection group since the full 4-tuple isn't yet 705 * configured. 706 */ 707 inp->inp_lport = sc->sc_inc.inc_lport; 708 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 709 /* 710 * Undo the assignments above if we failed to 711 * put the PCB on the hash lists. 712 */ 713#ifdef INET6 714 if (sc->sc_inc.inc_flags & INC_ISIPV6) 715 inp->in6p_laddr = in6addr_any; 716 else 717#endif 718 inp->inp_laddr.s_addr = INADDR_ANY; 719 inp->inp_lport = 0; 720 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 721 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 722 "with error %i\n", 723 s, __func__, error); 724 free(s, M_TCPLOG); 725 } 726 INP_HASH_WUNLOCK(&V_tcbinfo); 727 goto abort; 728 } 729#ifdef IPSEC 730 /* Copy old policy into new socket's. */ 731 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 732 printf("syncache_socket: could not copy policy\n"); 733#endif 734#ifdef INET6 735 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 736 struct inpcb *oinp = sotoinpcb(lso); 737 struct in6_addr laddr6; 738 struct sockaddr_in6 sin6; 739 /* 740 * Inherit socket options from the listening socket. 741 * Note that in6p_inputopts are not (and should not be) 742 * copied, since it stores previously received options and is 743 * used to detect if each new option is different than the 744 * previous one and hence should be passed to a user. 745 * If we copied in6p_inputopts, a user would not be able to 746 * receive options just after calling the accept system call. 747 */ 748 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 749 if (oinp->in6p_outputopts) 750 inp->in6p_outputopts = 751 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 752 753 sin6.sin6_family = AF_INET6; 754 sin6.sin6_len = sizeof(sin6); 755 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 756 sin6.sin6_port = sc->sc_inc.inc_fport; 757 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 758 laddr6 = inp->in6p_laddr; 759 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 760 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 761 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 762 thread0.td_ucred, m)) != 0) { 763 inp->in6p_laddr = laddr6; 764 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 765 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 766 "with error %i\n", 767 s, __func__, error); 768 free(s, M_TCPLOG); 769 } 770 INP_HASH_WUNLOCK(&V_tcbinfo); 771 goto abort; 772 } 773 /* Override flowlabel from in6_pcbconnect. */ 774 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 775 inp->inp_flow |= sc->sc_flowlabel; 776 } 777#endif /* INET6 */ 778#if defined(INET) && defined(INET6) 779 else 780#endif 781#ifdef INET 782 { 783 struct in_addr laddr; 784 struct sockaddr_in sin; 785 786 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 787 788 if (inp->inp_options == NULL) { 789 inp->inp_options = sc->sc_ipopts; 790 sc->sc_ipopts = NULL; 791 } 792 793 sin.sin_family = AF_INET; 794 sin.sin_len = sizeof(sin); 795 sin.sin_addr = sc->sc_inc.inc_faddr; 796 sin.sin_port = sc->sc_inc.inc_fport; 797 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 798 laddr = inp->inp_laddr; 799 if (inp->inp_laddr.s_addr == INADDR_ANY) 800 inp->inp_laddr = sc->sc_inc.inc_laddr; 801 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 802 thread0.td_ucred, m)) != 0) { 803 inp->inp_laddr = laddr; 804 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 805 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 806 "with error %i\n", 807 s, __func__, error); 808 free(s, M_TCPLOG); 809 } 810 INP_HASH_WUNLOCK(&V_tcbinfo); 811 goto abort; 812 } 813 } 814#endif /* INET */ 815 INP_HASH_WUNLOCK(&V_tcbinfo); 816 tp = intotcpcb(inp); 817 tcp_state_change(tp, TCPS_SYN_RECEIVED); 818 tp->iss = sc->sc_iss; 819 tp->irs = sc->sc_irs; 820 tcp_rcvseqinit(tp); 821 tcp_sendseqinit(tp); 822 blk = sototcpcb(lso)->t_fb; 823 if (blk != tp->t_fb) { 824 /* 825 * Our parents t_fb was not the default, 826 * we need to release our ref on tp->t_fb and 827 * pickup one on the new entry. 828 */ 829 struct tcp_function_block *rblk; 830 831 rblk = find_and_ref_tcp_fb(blk); 832 KASSERT(rblk != NULL, 833 ("cannot find blk %p out of syncache?", blk)); 834 if (tp->t_fb->tfb_tcp_fb_fini) 835 (*tp->t_fb->tfb_tcp_fb_fini)(tp); 836 refcount_release(&tp->t_fb->tfb_refcnt); 837 tp->t_fb = rblk; 838 if (tp->t_fb->tfb_tcp_fb_init) { 839 (*tp->t_fb->tfb_tcp_fb_init)(tp); 840 } 841 } 842 tp->snd_wl1 = sc->sc_irs; 843 tp->snd_max = tp->iss + 1; 844 tp->snd_nxt = tp->iss + 1; 845 tp->rcv_up = sc->sc_irs + 1; 846 tp->rcv_wnd = sc->sc_wnd; 847 tp->rcv_adv += tp->rcv_wnd; 848 tp->last_ack_sent = tp->rcv_nxt; 849 850 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 851 if (sc->sc_flags & SCF_NOOPT) 852 tp->t_flags |= TF_NOOPT; 853 else { 854 if (sc->sc_flags & SCF_WINSCALE) { 855 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 856 tp->snd_scale = sc->sc_requested_s_scale; 857 tp->request_r_scale = sc->sc_requested_r_scale; 858 } 859 if (sc->sc_flags & SCF_TIMESTAMP) { 860 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 861 tp->ts_recent = sc->sc_tsreflect; 862 tp->ts_recent_age = tcp_ts_getticks(); 863 tp->ts_offset = sc->sc_tsoff; 864 } 865#ifdef TCP_SIGNATURE 866 if (sc->sc_flags & SCF_SIGNATURE) 867 tp->t_flags |= TF_SIGNATURE; 868#endif 869 if (sc->sc_flags & SCF_SACK) 870 tp->t_flags |= TF_SACK_PERMIT; 871 } 872 873 if (sc->sc_flags & SCF_ECN) 874 tp->t_flags |= TF_ECN_PERMIT; 875 876 /* 877 * Set up MSS and get cached values from tcp_hostcache. 878 * This might overwrite some of the defaults we just set. 879 */ 880 tcp_mss(tp, sc->sc_peer_mss); 881 882 /* 883 * If the SYN,ACK was retransmitted, indicate that CWND to be 884 * limited to one segment in cc_conn_init(). 885 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 886 */ 887 if (sc->sc_rxmits > 1) 888 tp->snd_cwnd = 1; 889 890#ifdef TCP_OFFLOAD 891 /* 892 * Allow a TOE driver to install its hooks. Note that we hold the 893 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 894 * new connection before the TOE driver has done its thing. 895 */ 896 if (ADDED_BY_TOE(sc)) { 897 struct toedev *tod = sc->sc_tod; 898 899 tod->tod_offload_socket(tod, sc->sc_todctx, so); 900 } 901#endif 902 /* 903 * Copy and activate timers. 904 */ 905 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 906 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 907 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 908 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 909 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 910 911 soisconnected(so); 912 913 TCPSTAT_INC(tcps_accepts); 914 return (so); 915 916abort: 917 INP_WUNLOCK(inp); 918abort2: 919 if (so != NULL) 920 soabort(so); 921 return (NULL); 922} 923 924/* 925 * This function gets called when we receive an ACK for a 926 * socket in the LISTEN state. We look up the connection 927 * in the syncache, and if its there, we pull it out of 928 * the cache and turn it into a full-blown connection in 929 * the SYN-RECEIVED state. 930 * 931 * On syncache_socket() success the newly created socket 932 * has its underlying inp locked. 933 */ 934int 935syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 936 struct socket **lsop, struct mbuf *m) 937{ 938 struct syncache *sc; 939 struct syncache_head *sch; 940 struct syncache scs; 941 char *s; 942 943 /* 944 * Global TCP locks are held because we manipulate the PCB lists 945 * and create a new socket. 946 */ 947 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 948 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 949 ("%s: can handle only ACK", __func__)); 950 951 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 952 SCH_LOCK_ASSERT(sch); 953 954#ifdef INVARIANTS 955 /* 956 * Test code for syncookies comparing the syncache stored 957 * values with the reconstructed values from the cookie. 958 */ 959 if (sc != NULL) 960 syncookie_cmp(inc, sch, sc, th, to, *lsop); 961#endif 962 963 if (sc == NULL) { 964 /* 965 * There is no syncache entry, so see if this ACK is 966 * a returning syncookie. To do this, first: 967 * A. See if this socket has had a syncache entry dropped in 968 * the past. We don't want to accept a bogus syncookie 969 * if we've never received a SYN. 970 * B. check that the syncookie is valid. If it is, then 971 * cobble up a fake syncache entry, and return. 972 */ 973 if (!V_tcp_syncookies) { 974 SCH_UNLOCK(sch); 975 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 976 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 977 "segment rejected (syncookies disabled)\n", 978 s, __func__); 979 goto failed; 980 } 981 bzero(&scs, sizeof(scs)); 982 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 983 SCH_UNLOCK(sch); 984 if (sc == NULL) { 985 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 986 log(LOG_DEBUG, "%s; %s: Segment failed " 987 "SYNCOOKIE authentication, segment rejected " 988 "(probably spoofed)\n", s, __func__); 989 goto failed; 990 } 991 } else { 992 /* Pull out the entry to unlock the bucket row. */ 993 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 994 sch->sch_length--; 995#ifdef TCP_OFFLOAD 996 if (ADDED_BY_TOE(sc)) { 997 struct toedev *tod = sc->sc_tod; 998 999 tod->tod_syncache_removed(tod, sc->sc_todctx); 1000 } 1001#endif 1002 SCH_UNLOCK(sch); 1003 } 1004 1005 /* 1006 * Segment validation: 1007 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1008 */ 1009 if (th->th_ack != sc->sc_iss + 1) { 1010 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1011 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1012 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1013 goto failed; 1014 } 1015 1016 /* 1017 * The SEQ must fall in the window starting at the received 1018 * initial receive sequence number + 1 (the SYN). 1019 */ 1020 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1021 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1022 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1023 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1024 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1025 goto failed; 1026 } 1027 1028 /* 1029 * If timestamps were not negotiated during SYN/ACK they 1030 * must not appear on any segment during this session. 1031 */ 1032 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1033 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1034 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1035 "segment rejected\n", s, __func__); 1036 goto failed; 1037 } 1038 1039 /* 1040 * If timestamps were negotiated during SYN/ACK they should 1041 * appear on every segment during this session. 1042 * XXXAO: This is only informal as there have been unverified 1043 * reports of non-compliants stacks. 1044 */ 1045 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1046 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1047 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1048 "no action\n", s, __func__); 1049 free(s, M_TCPLOG); 1050 s = NULL; 1051 } 1052 } 1053 1054 /* 1055 * If timestamps were negotiated the reflected timestamp 1056 * must be equal to what we actually sent in the SYN|ACK. 1057 */ 1058 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1059 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1060 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1061 "segment rejected\n", 1062 s, __func__, to->to_tsecr, sc->sc_ts); 1063 goto failed; 1064 } 1065 1066 *lsop = syncache_socket(sc, *lsop, m); 1067 1068 if (*lsop == NULL) 1069 TCPSTAT_INC(tcps_sc_aborted); 1070 else 1071 TCPSTAT_INC(tcps_sc_completed); 1072 1073/* how do we find the inp for the new socket? */ 1074 if (sc != &scs) 1075 syncache_free(sc); 1076 return (1); 1077failed: 1078 if (sc != NULL && sc != &scs) 1079 syncache_free(sc); 1080 if (s != NULL) 1081 free(s, M_TCPLOG); 1082 *lsop = NULL; 1083 return (0); 1084} 1085 1086/* 1087 * Given a LISTEN socket and an inbound SYN request, add 1088 * this to the syn cache, and send back a segment: 1089 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1090 * to the source. 1091 * 1092 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1093 * Doing so would require that we hold onto the data and deliver it 1094 * to the application. However, if we are the target of a SYN-flood 1095 * DoS attack, an attacker could send data which would eventually 1096 * consume all available buffer space if it were ACKed. By not ACKing 1097 * the data, we avoid this DoS scenario. 1098 */ 1099void 1100syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1101 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1102 void *todctx) 1103{ 1104 struct tcpcb *tp; 1105 struct socket *so; 1106 struct syncache *sc = NULL; 1107 struct syncache_head *sch; 1108 struct mbuf *ipopts = NULL; 1109 u_int ltflags; 1110 int win, sb_hiwat, ip_ttl, ip_tos; 1111 char *s; 1112#ifdef INET6 1113 int autoflowlabel = 0; 1114#endif 1115#ifdef MAC 1116 struct label *maclabel; 1117#endif 1118 struct syncache scs; 1119 struct ucred *cred; 1120 1121 INP_WLOCK_ASSERT(inp); /* listen socket */ 1122 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1123 ("%s: unexpected tcp flags", __func__)); 1124 1125 /* 1126 * Combine all so/tp operations very early to drop the INP lock as 1127 * soon as possible. 1128 */ 1129 so = *lsop; 1130 tp = sototcpcb(so); 1131 cred = crhold(so->so_cred); 1132 1133#ifdef INET6 1134 if ((inc->inc_flags & INC_ISIPV6) && 1135 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1136 autoflowlabel = 1; 1137#endif 1138 ip_ttl = inp->inp_ip_ttl; 1139 ip_tos = inp->inp_ip_tos; 1140 win = sbspace(&so->so_rcv); 1141 sb_hiwat = so->so_rcv.sb_hiwat; 1142 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1143 1144 /* By the time we drop the lock these should no longer be used. */ 1145 so = NULL; 1146 tp = NULL; 1147 1148#ifdef MAC 1149 if (mac_syncache_init(&maclabel) != 0) { 1150 INP_WUNLOCK(inp); 1151 goto done; 1152 } else 1153 mac_syncache_create(maclabel, inp); 1154#endif 1155 INP_WUNLOCK(inp); 1156 1157 /* 1158 * Remember the IP options, if any. 1159 */ 1160#ifdef INET6 1161 if (!(inc->inc_flags & INC_ISIPV6)) 1162#endif 1163#ifdef INET 1164 ipopts = (m) ? ip_srcroute(m) : NULL; 1165#else 1166 ipopts = NULL; 1167#endif 1168 1169 /* 1170 * See if we already have an entry for this connection. 1171 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1172 * 1173 * XXX: should the syncache be re-initialized with the contents 1174 * of the new SYN here (which may have different options?) 1175 * 1176 * XXX: We do not check the sequence number to see if this is a 1177 * real retransmit or a new connection attempt. The question is 1178 * how to handle such a case; either ignore it as spoofed, or 1179 * drop the current entry and create a new one? 1180 */ 1181 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1182 SCH_LOCK_ASSERT(sch); 1183 if (sc != NULL) { 1184 TCPSTAT_INC(tcps_sc_dupsyn); 1185 if (ipopts) { 1186 /* 1187 * If we were remembering a previous source route, 1188 * forget it and use the new one we've been given. 1189 */ 1190 if (sc->sc_ipopts) 1191 (void) m_free(sc->sc_ipopts); 1192 sc->sc_ipopts = ipopts; 1193 } 1194 /* 1195 * Update timestamp if present. 1196 */ 1197 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1198 sc->sc_tsreflect = to->to_tsval; 1199 else 1200 sc->sc_flags &= ~SCF_TIMESTAMP; 1201#ifdef MAC 1202 /* 1203 * Since we have already unconditionally allocated label 1204 * storage, free it up. The syncache entry will already 1205 * have an initialized label we can use. 1206 */ 1207 mac_syncache_destroy(&maclabel); 1208#endif 1209 /* Retransmit SYN|ACK and reset retransmit count. */ 1210 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1211 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1212 "resetting timer and retransmitting SYN|ACK\n", 1213 s, __func__); 1214 free(s, M_TCPLOG); 1215 } 1216 if (syncache_respond(sc, sch, 1) == 0) { 1217 sc->sc_rxmits = 0; 1218 syncache_timeout(sc, sch, 1); 1219 TCPSTAT_INC(tcps_sndacks); 1220 TCPSTAT_INC(tcps_sndtotal); 1221 } 1222 SCH_UNLOCK(sch); 1223 goto done; 1224 } 1225 1226 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1227 if (sc == NULL) { 1228 /* 1229 * The zone allocator couldn't provide more entries. 1230 * Treat this as if the cache was full; drop the oldest 1231 * entry and insert the new one. 1232 */ 1233 TCPSTAT_INC(tcps_sc_zonefail); 1234 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1235 syncache_drop(sc, sch); 1236 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1237 if (sc == NULL) { 1238 if (V_tcp_syncookies) { 1239 bzero(&scs, sizeof(scs)); 1240 sc = &scs; 1241 } else { 1242 SCH_UNLOCK(sch); 1243 if (ipopts) 1244 (void) m_free(ipopts); 1245 goto done; 1246 } 1247 } 1248 } 1249 1250 /* 1251 * Fill in the syncache values. 1252 */ 1253#ifdef MAC 1254 sc->sc_label = maclabel; 1255#endif 1256 sc->sc_cred = cred; 1257 cred = NULL; 1258 sc->sc_ipopts = ipopts; 1259 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1260#ifdef INET6 1261 if (!(inc->inc_flags & INC_ISIPV6)) 1262#endif 1263 { 1264 sc->sc_ip_tos = ip_tos; 1265 sc->sc_ip_ttl = ip_ttl; 1266 } 1267#ifdef TCP_OFFLOAD 1268 sc->sc_tod = tod; 1269 sc->sc_todctx = todctx; 1270#endif 1271 sc->sc_irs = th->th_seq; 1272 sc->sc_iss = arc4random(); 1273 sc->sc_flags = 0; 1274 sc->sc_flowlabel = 0; 1275 1276 /* 1277 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1278 * win was derived from socket earlier in the function. 1279 */ 1280 win = imax(win, 0); 1281 win = imin(win, TCP_MAXWIN); 1282 sc->sc_wnd = win; 1283 1284 if (V_tcp_do_rfc1323) { 1285 /* 1286 * A timestamp received in a SYN makes 1287 * it ok to send timestamp requests and replies. 1288 */ 1289 if (to->to_flags & TOF_TS) { 1290 sc->sc_tsreflect = to->to_tsval; 1291 sc->sc_ts = tcp_ts_getticks(); 1292 sc->sc_flags |= SCF_TIMESTAMP; 1293 } 1294 if (to->to_flags & TOF_SCALE) { 1295 int wscale = 0; 1296 1297 /* 1298 * Pick the smallest possible scaling factor that 1299 * will still allow us to scale up to sb_max, aka 1300 * kern.ipc.maxsockbuf. 1301 * 1302 * We do this because there are broken firewalls that 1303 * will corrupt the window scale option, leading to 1304 * the other endpoint believing that our advertised 1305 * window is unscaled. At scale factors larger than 1306 * 5 the unscaled window will drop below 1500 bytes, 1307 * leading to serious problems when traversing these 1308 * broken firewalls. 1309 * 1310 * With the default maxsockbuf of 256K, a scale factor 1311 * of 3 will be chosen by this algorithm. Those who 1312 * choose a larger maxsockbuf should watch out 1313 * for the compatiblity problems mentioned above. 1314 * 1315 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1316 * or <SYN,ACK>) segment itself is never scaled. 1317 */ 1318 while (wscale < TCP_MAX_WINSHIFT && 1319 (TCP_MAXWIN << wscale) < sb_max) 1320 wscale++; 1321 sc->sc_requested_r_scale = wscale; 1322 sc->sc_requested_s_scale = to->to_wscale; 1323 sc->sc_flags |= SCF_WINSCALE; 1324 } 1325 } 1326#ifdef TCP_SIGNATURE 1327 /* 1328 * If listening socket requested TCP digests, OR received SYN 1329 * contains the option, flag this in the syncache so that 1330 * syncache_respond() will do the right thing with the SYN+ACK. 1331 */ 1332 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1333 sc->sc_flags |= SCF_SIGNATURE; 1334#endif 1335 if (to->to_flags & TOF_SACKPERM) 1336 sc->sc_flags |= SCF_SACK; 1337 if (to->to_flags & TOF_MSS) 1338 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1339 if (ltflags & TF_NOOPT) 1340 sc->sc_flags |= SCF_NOOPT; 1341 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1342 sc->sc_flags |= SCF_ECN; 1343 1344 if (V_tcp_syncookies) 1345 sc->sc_iss = syncookie_generate(sch, sc); 1346#ifdef INET6 1347 if (autoflowlabel) { 1348 if (V_tcp_syncookies) 1349 sc->sc_flowlabel = sc->sc_iss; 1350 else 1351 sc->sc_flowlabel = ip6_randomflowlabel(); 1352 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1353 } 1354#endif 1355 SCH_UNLOCK(sch); 1356 1357 /* 1358 * Do a standard 3-way handshake. 1359 */ 1360 if (syncache_respond(sc, sch, 0) == 0) { 1361 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1362 syncache_free(sc); 1363 else if (sc != &scs) 1364 syncache_insert(sc, sch); /* locks and unlocks sch */ 1365 TCPSTAT_INC(tcps_sndacks); 1366 TCPSTAT_INC(tcps_sndtotal); 1367 } else { 1368 if (sc != &scs) 1369 syncache_free(sc); 1370 TCPSTAT_INC(tcps_sc_dropped); 1371 } 1372 1373done: 1374 if (cred != NULL) 1375 crfree(cred); 1376#ifdef MAC 1377 if (sc == &scs) 1378 mac_syncache_destroy(&maclabel); 1379#endif 1380 if (m) { 1381 1382 *lsop = NULL; 1383 m_freem(m); 1384 } 1385} 1386 1387static int 1388syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked) 1389{ 1390 struct ip *ip = NULL; 1391 struct mbuf *m; 1392 struct tcphdr *th = NULL; 1393 int optlen, error = 0; /* Make compiler happy */ 1394 u_int16_t hlen, tlen, mssopt; 1395 struct tcpopt to; 1396#ifdef INET6 1397 struct ip6_hdr *ip6 = NULL; 1398#endif 1399#ifdef TCP_SIGNATURE 1400 struct secasvar *sav; 1401#endif 1402 1403 hlen = 1404#ifdef INET6 1405 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1406#endif 1407 sizeof(struct ip); 1408 tlen = hlen + sizeof(struct tcphdr); 1409 1410 /* Determine MSS we advertize to other end of connection. */ 1411 mssopt = tcp_mssopt(&sc->sc_inc); 1412 if (sc->sc_peer_mss) 1413 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1414 1415 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1416 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1417 ("syncache: mbuf too small")); 1418 1419 /* Create the IP+TCP header from scratch. */ 1420 m = m_gethdr(M_NOWAIT, MT_DATA); 1421 if (m == NULL) 1422 return (ENOBUFS); 1423#ifdef MAC 1424 mac_syncache_create_mbuf(sc->sc_label, m); 1425#endif 1426 m->m_data += max_linkhdr; 1427 m->m_len = tlen; 1428 m->m_pkthdr.len = tlen; 1429 m->m_pkthdr.rcvif = NULL; 1430 1431#ifdef INET6 1432 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1433 ip6 = mtod(m, struct ip6_hdr *); 1434 ip6->ip6_vfc = IPV6_VERSION; 1435 ip6->ip6_nxt = IPPROTO_TCP; 1436 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1437 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1438 ip6->ip6_plen = htons(tlen - hlen); 1439 /* ip6_hlim is set after checksum */ 1440 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1441 ip6->ip6_flow |= sc->sc_flowlabel; 1442 1443 th = (struct tcphdr *)(ip6 + 1); 1444 } 1445#endif 1446#if defined(INET6) && defined(INET) 1447 else 1448#endif 1449#ifdef INET 1450 { 1451 ip = mtod(m, struct ip *); 1452 ip->ip_v = IPVERSION; 1453 ip->ip_hl = sizeof(struct ip) >> 2; 1454 ip->ip_len = htons(tlen); 1455 ip->ip_id = 0; 1456 ip->ip_off = 0; 1457 ip->ip_sum = 0; 1458 ip->ip_p = IPPROTO_TCP; 1459 ip->ip_src = sc->sc_inc.inc_laddr; 1460 ip->ip_dst = sc->sc_inc.inc_faddr; 1461 ip->ip_ttl = sc->sc_ip_ttl; 1462 ip->ip_tos = sc->sc_ip_tos; 1463 1464 /* 1465 * See if we should do MTU discovery. Route lookups are 1466 * expensive, so we will only unset the DF bit if: 1467 * 1468 * 1) path_mtu_discovery is disabled 1469 * 2) the SCF_UNREACH flag has been set 1470 */ 1471 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1472 ip->ip_off |= htons(IP_DF); 1473 1474 th = (struct tcphdr *)(ip + 1); 1475 } 1476#endif /* INET */ 1477 th->th_sport = sc->sc_inc.inc_lport; 1478 th->th_dport = sc->sc_inc.inc_fport; 1479 1480 th->th_seq = htonl(sc->sc_iss); 1481 th->th_ack = htonl(sc->sc_irs + 1); 1482 th->th_off = sizeof(struct tcphdr) >> 2; 1483 th->th_x2 = 0; 1484 th->th_flags = TH_SYN|TH_ACK; 1485 th->th_win = htons(sc->sc_wnd); 1486 th->th_urp = 0; 1487 1488 if (sc->sc_flags & SCF_ECN) { 1489 th->th_flags |= TH_ECE; 1490 TCPSTAT_INC(tcps_ecn_shs); 1491 } 1492 1493 /* Tack on the TCP options. */ 1494 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1495 to.to_flags = 0; 1496 1497 to.to_mss = mssopt; 1498 to.to_flags = TOF_MSS; 1499 if (sc->sc_flags & SCF_WINSCALE) { 1500 to.to_wscale = sc->sc_requested_r_scale; 1501 to.to_flags |= TOF_SCALE; 1502 } 1503 if (sc->sc_flags & SCF_TIMESTAMP) { 1504 /* Virgin timestamp or TCP cookie enhanced one. */ 1505 to.to_tsval = sc->sc_ts; 1506 to.to_tsecr = sc->sc_tsreflect; 1507 to.to_flags |= TOF_TS; 1508 } 1509 if (sc->sc_flags & SCF_SACK) 1510 to.to_flags |= TOF_SACKPERM; 1511#ifdef TCP_SIGNATURE 1512 sav = NULL; 1513 if (sc->sc_flags & SCF_SIGNATURE) { 1514 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1515 if (sav != NULL) 1516 to.to_flags |= TOF_SIGNATURE; 1517 else { 1518 1519 /* 1520 * We've got SCF_SIGNATURE flag 1521 * inherited from listening socket, 1522 * but no SADB key for given source 1523 * address. Assume signature is not 1524 * required and remove signature flag 1525 * instead of silently dropping 1526 * connection. 1527 */ 1528 if (locked == 0) 1529 SCH_LOCK(sch); 1530 sc->sc_flags &= ~SCF_SIGNATURE; 1531 if (locked == 0) 1532 SCH_UNLOCK(sch); 1533 } 1534 } 1535#endif 1536 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1537 1538 /* Adjust headers by option size. */ 1539 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1540 m->m_len += optlen; 1541 m->m_pkthdr.len += optlen; 1542 1543#ifdef TCP_SIGNATURE 1544 if (sc->sc_flags & SCF_SIGNATURE) 1545 tcp_signature_do_compute(m, 0, optlen, 1546 to.to_signature, sav); 1547#endif 1548#ifdef INET6 1549 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1550 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1551 else 1552#endif 1553 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1554 } else 1555 optlen = 0; 1556 1557 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1558 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1559#ifdef INET6 1560 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1561 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1562 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1563 IPPROTO_TCP, 0); 1564 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1565#ifdef TCP_OFFLOAD 1566 if (ADDED_BY_TOE(sc)) { 1567 struct toedev *tod = sc->sc_tod; 1568 1569 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1570 1571 return (error); 1572 } 1573#endif 1574 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1575 } 1576#endif 1577#if defined(INET6) && defined(INET) 1578 else 1579#endif 1580#ifdef INET 1581 { 1582 m->m_pkthdr.csum_flags = CSUM_TCP; 1583 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1584 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1585#ifdef TCP_OFFLOAD 1586 if (ADDED_BY_TOE(sc)) { 1587 struct toedev *tod = sc->sc_tod; 1588 1589 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1590 1591 return (error); 1592 } 1593#endif 1594 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1595 } 1596#endif 1597 return (error); 1598} 1599 1600/* 1601 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1602 * that exceed the capacity of the syncache by avoiding the storage of any 1603 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1604 * attacks where the attacker does not have access to our responses. 1605 * 1606 * Syncookies encode and include all necessary information about the 1607 * connection setup within the SYN|ACK that we send back. That way we 1608 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1609 * (if ever). Normally the syncache and syncookies are running in parallel 1610 * with the latter taking over when the former is exhausted. When matching 1611 * syncache entry is found the syncookie is ignored. 1612 * 1613 * The only reliable information persisting the 3WHS is our inital sequence 1614 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1615 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1616 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1617 * returns and signifies a legitimate connection if it matches the ACK. 1618 * 1619 * The available space of 32 bits to store the hash and to encode the SYN 1620 * option information is very tight and we should have at least 24 bits for 1621 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1622 * 1623 * SYN option information we have to encode to fully restore a connection: 1624 * MSS: is imporant to chose an optimal segment size to avoid IP level 1625 * fragmentation along the path. The common MSS values can be encoded 1626 * in a 3-bit table. Uncommon values are captured by the next lower value 1627 * in the table leading to a slight increase in packetization overhead. 1628 * WSCALE: is necessary to allow large windows to be used for high delay- 1629 * bandwidth product links. Not scaling the window when it was initially 1630 * negotiated is bad for performance as lack of scaling further decreases 1631 * the apparent available send window. We only need to encode the WSCALE 1632 * we received from the remote end. Our end can be recalculated at any 1633 * time. The common WSCALE values can be encoded in a 3-bit table. 1634 * Uncommon values are captured by the next lower value in the table 1635 * making us under-estimate the available window size halving our 1636 * theoretically possible maximum throughput for that connection. 1637 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1638 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1639 * that are included in all segments on a connection. We enable them when 1640 * the ACK has them. 1641 * 1642 * Security of syncookies and attack vectors: 1643 * 1644 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1645 * together with the gloabl secret to make it unique per connection attempt. 1646 * Thus any change of any of those parameters results in a different MAC output 1647 * in an unpredictable way unless a collision is encountered. 24 bits of the 1648 * MAC are embedded into the ISS. 1649 * 1650 * To prevent replay attacks two rotating global secrets are updated with a 1651 * new random value every 15 seconds. The life-time of a syncookie is thus 1652 * 15-30 seconds. 1653 * 1654 * Vector 1: Attacking the secret. This requires finding a weakness in the 1655 * MAC itself or the way it is used here. The attacker can do a chosen plain 1656 * text attack by varying and testing the all parameters under his control. 1657 * The strength depends on the size and randomness of the secret, and the 1658 * cryptographic security of the MAC function. Due to the constant updating 1659 * of the secret the attacker has at most 29.999 seconds to find the secret 1660 * and launch spoofed connections. After that he has to start all over again. 1661 * 1662 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1663 * size an average of 4,823 attempts are required for a 50% chance of success 1664 * to spoof a single syncookie (birthday collision paradox). However the 1665 * attacker is blind and doesn't know if one of his attempts succeeded unless 1666 * he has a side channel to interfere success from. A single connection setup 1667 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1668 * This many attempts are required for each one blind spoofed connection. For 1669 * every additional spoofed connection he has to launch another N attempts. 1670 * Thus for a sustained rate 100 spoofed connections per second approximately 1671 * 1,800,000 packets per second would have to be sent. 1672 * 1673 * NB: The MAC function should be fast so that it doesn't become a CPU 1674 * exhaustion attack vector itself. 1675 * 1676 * References: 1677 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1678 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1679 * http://cr.yp.to/syncookies.html (overview) 1680 * http://cr.yp.to/syncookies/archive (details) 1681 * 1682 * 1683 * Schematic construction of a syncookie enabled Initial Sequence Number: 1684 * 0 1 2 3 1685 * 12345678901234567890123456789012 1686 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1687 * 1688 * x 24 MAC (truncated) 1689 * W 3 Send Window Scale index 1690 * M 3 MSS index 1691 * S 1 SACK permitted 1692 * P 1 Odd/even secret 1693 */ 1694 1695/* 1696 * Distribution and probability of certain MSS values. Those in between are 1697 * rounded down to the next lower one. 1698 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1699 * .2% .3% 5% 7% 7% 20% 15% 45% 1700 */ 1701static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1702 1703/* 1704 * Distribution and probability of certain WSCALE values. We have to map the 1705 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1706 * bits based on prevalence of certain values. Where we don't have an exact 1707 * match for are rounded down to the next lower one letting us under-estimate 1708 * the true available window. At the moment this would happen only for the 1709 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1710 * and window size). The absence of the WSCALE option (no scaling in either 1711 * direction) is encoded with index zero. 1712 * [WSCALE values histograms, Allman, 2012] 1713 * X 10 10 35 5 6 14 10% by host 1714 * X 11 4 5 5 18 49 3% by connections 1715 */ 1716static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1717 1718/* 1719 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1720 * and good cryptographic properties. 1721 */ 1722static uint32_t 1723syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1724 uint8_t *secbits, uintptr_t secmod) 1725{ 1726 SIPHASH_CTX ctx; 1727 uint32_t siphash[2]; 1728 1729 SipHash24_Init(&ctx); 1730 SipHash_SetKey(&ctx, secbits); 1731 switch (inc->inc_flags & INC_ISIPV6) { 1732#ifdef INET 1733 case 0: 1734 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1735 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1736 break; 1737#endif 1738#ifdef INET6 1739 case INC_ISIPV6: 1740 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1741 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1742 break; 1743#endif 1744 } 1745 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1746 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1747 SipHash_Update(&ctx, &irs, sizeof(irs)); 1748 SipHash_Update(&ctx, &flags, sizeof(flags)); 1749 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1750 SipHash_Final((u_int8_t *)&siphash, &ctx); 1751 1752 return (siphash[0] ^ siphash[1]); 1753} 1754 1755static tcp_seq 1756syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1757{ 1758 u_int i, mss, secbit, wscale; 1759 uint32_t iss, hash; 1760 uint8_t *secbits; 1761 union syncookie cookie; 1762 1763 SCH_LOCK_ASSERT(sch); 1764 1765 cookie.cookie = 0; 1766 1767 /* Map our computed MSS into the 3-bit index. */ 1768 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1769 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1770 tcp_sc_msstab[i] > mss && i > 0; 1771 i--) 1772 ; 1773 cookie.flags.mss_idx = i; 1774 1775 /* 1776 * Map the send window scale into the 3-bit index but only if 1777 * the wscale option was received. 1778 */ 1779 if (sc->sc_flags & SCF_WINSCALE) { 1780 wscale = sc->sc_requested_s_scale; 1781 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1782 tcp_sc_wstab[i] > wscale && i > 0; 1783 i--) 1784 ; 1785 cookie.flags.wscale_idx = i; 1786 } 1787 1788 /* Can we do SACK? */ 1789 if (sc->sc_flags & SCF_SACK) 1790 cookie.flags.sack_ok = 1; 1791 1792 /* Which of the two secrets to use. */ 1793 secbit = sch->sch_sc->secret.oddeven & 0x1; 1794 cookie.flags.odd_even = secbit; 1795 1796 secbits = sch->sch_sc->secret.key[secbit]; 1797 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1798 (uintptr_t)sch); 1799 1800 /* 1801 * Put the flags into the hash and XOR them to get better ISS number 1802 * variance. This doesn't enhance the cryptographic strength and is 1803 * done to prevent the 8 cookie bits from showing up directly on the 1804 * wire. 1805 */ 1806 iss = hash & ~0xff; 1807 iss |= cookie.cookie ^ (hash >> 24); 1808 1809 /* Randomize the timestamp. */ 1810 if (sc->sc_flags & SCF_TIMESTAMP) { 1811 sc->sc_ts = arc4random(); 1812 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1813 } 1814 1815 TCPSTAT_INC(tcps_sc_sendcookie); 1816 return (iss); 1817} 1818 1819static struct syncache * 1820syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1821 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1822 struct socket *lso) 1823{ 1824 uint32_t hash; 1825 uint8_t *secbits; 1826 tcp_seq ack, seq; 1827 int wnd, wscale = 0; 1828 union syncookie cookie; 1829 1830 SCH_LOCK_ASSERT(sch); 1831 1832 /* 1833 * Pull information out of SYN-ACK/ACK and revert sequence number 1834 * advances. 1835 */ 1836 ack = th->th_ack - 1; 1837 seq = th->th_seq - 1; 1838 1839 /* 1840 * Unpack the flags containing enough information to restore the 1841 * connection. 1842 */ 1843 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1844 1845 /* Which of the two secrets to use. */ 1846 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1847 1848 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1849 1850 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1851 if ((ack & ~0xff) != (hash & ~0xff)) 1852 return (NULL); 1853 1854 /* Fill in the syncache values. */ 1855 sc->sc_flags = 0; 1856 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1857 sc->sc_ipopts = NULL; 1858 1859 sc->sc_irs = seq; 1860 sc->sc_iss = ack; 1861 1862 switch (inc->inc_flags & INC_ISIPV6) { 1863#ifdef INET 1864 case 0: 1865 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1866 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1867 break; 1868#endif 1869#ifdef INET6 1870 case INC_ISIPV6: 1871 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1872 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1873 break; 1874#endif 1875 } 1876 1877 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1878 1879 /* We can simply recompute receive window scale we sent earlier. */ 1880 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1881 wscale++; 1882 1883 /* Only use wscale if it was enabled in the orignal SYN. */ 1884 if (cookie.flags.wscale_idx > 0) { 1885 sc->sc_requested_r_scale = wscale; 1886 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1887 sc->sc_flags |= SCF_WINSCALE; 1888 } 1889 1890 wnd = sbspace(&lso->so_rcv); 1891 wnd = imax(wnd, 0); 1892 wnd = imin(wnd, TCP_MAXWIN); 1893 sc->sc_wnd = wnd; 1894 1895 if (cookie.flags.sack_ok) 1896 sc->sc_flags |= SCF_SACK; 1897 1898 if (to->to_flags & TOF_TS) { 1899 sc->sc_flags |= SCF_TIMESTAMP; 1900 sc->sc_tsreflect = to->to_tsval; 1901 sc->sc_ts = to->to_tsecr; 1902 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1903 } 1904 1905 if (to->to_flags & TOF_SIGNATURE) 1906 sc->sc_flags |= SCF_SIGNATURE; 1907 1908 sc->sc_rxmits = 0; 1909 1910 TCPSTAT_INC(tcps_sc_recvcookie); 1911 return (sc); 1912} 1913 1914#ifdef INVARIANTS 1915static int 1916syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1917 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1918 struct socket *lso) 1919{ 1920 struct syncache scs, *scx; 1921 char *s; 1922 1923 bzero(&scs, sizeof(scs)); 1924 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1925 1926 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1927 return (0); 1928 1929 if (scx != NULL) { 1930 if (sc->sc_peer_mss != scx->sc_peer_mss) 1931 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1932 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1933 1934 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1935 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1936 s, __func__, sc->sc_requested_r_scale, 1937 scx->sc_requested_r_scale); 1938 1939 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1940 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1941 s, __func__, sc->sc_requested_s_scale, 1942 scx->sc_requested_s_scale); 1943 1944 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1945 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1946 } 1947 1948 if (s != NULL) 1949 free(s, M_TCPLOG); 1950 return (0); 1951} 1952#endif /* INVARIANTS */ 1953 1954static void 1955syncookie_reseed(void *arg) 1956{ 1957 struct tcp_syncache *sc = arg; 1958 uint8_t *secbits; 1959 int secbit; 1960 1961 /* 1962 * Reseeding the secret doesn't have to be protected by a lock. 1963 * It only must be ensured that the new random values are visible 1964 * to all CPUs in a SMP environment. The atomic with release 1965 * semantics ensures that. 1966 */ 1967 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1968 secbits = sc->secret.key[secbit]; 1969 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1970 atomic_add_rel_int(&sc->secret.oddeven, 1); 1971 1972 /* Reschedule ourself. */ 1973 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1974} 1975 1976/* 1977 * Returns the current number of syncache entries. This number 1978 * will probably change before you get around to calling 1979 * syncache_pcblist. 1980 */ 1981int 1982syncache_pcbcount(void) 1983{ 1984 struct syncache_head *sch; 1985 int count, i; 1986 1987 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1988 /* No need to lock for a read. */ 1989 sch = &V_tcp_syncache.hashbase[i]; 1990 count += sch->sch_length; 1991 } 1992 return count; 1993} 1994 1995/* 1996 * Exports the syncache entries to userland so that netstat can display 1997 * them alongside the other sockets. This function is intended to be 1998 * called only from tcp_pcblist. 1999 * 2000 * Due to concurrency on an active system, the number of pcbs exported 2001 * may have no relation to max_pcbs. max_pcbs merely indicates the 2002 * amount of space the caller allocated for this function to use. 2003 */ 2004int 2005syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2006{ 2007 struct xtcpcb xt; 2008 struct syncache *sc; 2009 struct syncache_head *sch; 2010 int count, error, i; 2011 2012 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2013 sch = &V_tcp_syncache.hashbase[i]; 2014 SCH_LOCK(sch); 2015 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2016 if (count >= max_pcbs) { 2017 SCH_UNLOCK(sch); 2018 goto exit; 2019 } 2020 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2021 continue; 2022 bzero(&xt, sizeof(xt)); 2023 xt.xt_len = sizeof(xt); 2024 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2025 xt.xt_inp.inp_vflag = INP_IPV6; 2026 else 2027 xt.xt_inp.inp_vflag = INP_IPV4; 2028 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2029 xt.xt_tp.t_inpcb = &xt.xt_inp; 2030 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2031 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2032 xt.xt_socket.xso_len = sizeof (struct xsocket); 2033 xt.xt_socket.so_type = SOCK_STREAM; 2034 xt.xt_socket.so_state = SS_ISCONNECTING; 2035 error = SYSCTL_OUT(req, &xt, sizeof xt); 2036 if (error) { 2037 SCH_UNLOCK(sch); 2038 goto exit; 2039 } 2040 count++; 2041 } 2042 SCH_UNLOCK(sch); 2043 } 2044exit: 2045 *pcbs_exported = count; 2046 return error; 2047} 2048