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/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_systm.h> 70 #include <netinet/ip.h> 71 #include <netinet/in_var.h> 72 #include <netinet/in_pcb.h> 73 #include <netinet/ip_var.h> 74 #include <netinet/ip_options.h> 75 #ifdef INET6 76 #include <netinet/ip6.h> 77 #include <netinet/icmp6.h> 78 #include <netinet6/nd6.h> 79 #include <netinet6/ip6_var.h> 80 #include <netinet6/in6_pcb.h> 81 #endif 82 #include <netinet/tcp.h> 83 #include <netinet/tcp_fsm.h> 84 #include <netinet/tcp_seq.h> 85 #include <netinet/tcp_timer.h> 86 #include <netinet/tcp_var.h> 87 #include <netinet/tcp_syncache.h> 88 #ifdef INET6 89 #include <netinet6/tcp6_var.h> 90 #endif 91 #ifdef TCP_OFFLOAD 92 #include <netinet/toecore.h> 93 #endif 94 95 #ifdef IPSEC 96 #include <netipsec/ipsec.h> 97 #ifdef INET6 98 #include <netipsec/ipsec6.h> 99 #endif 100 #include <netipsec/key.h> 101 #endif /*IPSEC*/ 102 103 #include <machine/in_cksum.h> 104 105 #include <security/mac/mac_framework.h> 106 107 static VNET_DEFINE(int, tcp_syncookies) = 1; 108 #define V_tcp_syncookies VNET(tcp_syncookies) 109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 110 &VNET_NAME(tcp_syncookies), 0, 111 "Use TCP SYN cookies if the syncache overflows"); 112 113 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 114 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 116 &VNET_NAME(tcp_syncookiesonly), 0, 117 "Use only TCP SYN cookies"); 118 119 #ifdef TCP_OFFLOAD 120 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 121 #endif 122 123 static void syncache_drop(struct syncache *, struct syncache_head *); 124 static void syncache_free(struct syncache *); 125 static void syncache_insert(struct syncache *, struct syncache_head *); 126 static int syncache_respond(struct syncache *, struct syncache_head *, int); 127 static struct socket *syncache_socket(struct syncache *, struct socket *, 128 struct mbuf *m); 129 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 130 int docallout); 131 static void syncache_timer(void *); 132 133 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 134 uint8_t *, uintptr_t); 135 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 136 static struct syncache 137 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 138 struct syncache *, struct tcphdr *, struct tcpopt *, 139 struct socket *); 140 static void syncookie_reseed(void *); 141 #ifdef INVARIANTS 142 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 143 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 144 struct socket *lso); 145 #endif 146 147 /* 148 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 149 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 150 * the odds are that the user has given up attempting to connect by then. 151 */ 152 #define SYNCACHE_MAXREXMTS 3 153 154 /* Arbitrary values */ 155 #define TCP_SYNCACHE_HASHSIZE 512 156 #define TCP_SYNCACHE_BUCKETLIMIT 30 157 158 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 159 #define V_tcp_syncache VNET(tcp_syncache) 160 161 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 162 "TCP SYN cache"); 163 164 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 165 &VNET_NAME(tcp_syncache.bucket_limit), 0, 166 "Per-bucket hash limit for syncache"); 167 168 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 169 &VNET_NAME(tcp_syncache.cache_limit), 0, 170 "Overall entry limit for syncache"); 171 172 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 173 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 174 175 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 176 &VNET_NAME(tcp_syncache.hashsize), 0, 177 "Size of TCP syncache hashtable"); 178 179 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 180 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 181 "Limit on SYN/ACK retransmissions"); 182 183 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 184 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 185 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 186 "Send reset on socket allocation failure"); 187 188 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 189 190 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 191 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 192 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 193 194 /* 195 * Requires the syncache entry to be already removed from the bucket list. 196 */ 197 static void 198 syncache_free(struct syncache *sc) 199 { 200 201 if (sc->sc_ipopts) 202 (void) m_free(sc->sc_ipopts); 203 if (sc->sc_cred) 204 crfree(sc->sc_cred); 205 #ifdef MAC 206 mac_syncache_destroy(&sc->sc_label); 207 #endif 208 209 uma_zfree(V_tcp_syncache.zone, sc); 210 } 211 212 void 213 syncache_init(void) 214 { 215 int i; 216 217 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 218 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 219 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 220 V_tcp_syncache.hash_secret = arc4random(); 221 222 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 223 &V_tcp_syncache.hashsize); 224 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 225 &V_tcp_syncache.bucket_limit); 226 if (!powerof2(V_tcp_syncache.hashsize) || 227 V_tcp_syncache.hashsize == 0) { 228 printf("WARNING: syncache hash size is not a power of 2.\n"); 229 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 230 } 231 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 232 233 /* Set limits. */ 234 V_tcp_syncache.cache_limit = 235 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 236 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 237 &V_tcp_syncache.cache_limit); 238 239 /* Allocate the hash table. */ 240 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 241 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 242 243 #ifdef VIMAGE 244 V_tcp_syncache.vnet = curvnet; 245 #endif 246 247 /* Initialize the hash buckets. */ 248 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 249 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 250 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 251 NULL, MTX_DEF); 252 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 253 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 254 V_tcp_syncache.hashbase[i].sch_length = 0; 255 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 256 } 257 258 /* Create the syncache entry zone. */ 259 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 260 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 261 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 262 V_tcp_syncache.cache_limit); 263 264 /* Start the SYN cookie reseeder callout. */ 265 callout_init(&V_tcp_syncache.secret.reseed, 1); 266 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 267 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 268 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 269 syncookie_reseed, &V_tcp_syncache); 270 } 271 272 #ifdef VIMAGE 273 void 274 syncache_destroy(void) 275 { 276 struct syncache_head *sch; 277 struct syncache *sc, *nsc; 278 int i; 279 280 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 281 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 282 283 sch = &V_tcp_syncache.hashbase[i]; 284 callout_drain(&sch->sch_timer); 285 286 SCH_LOCK(sch); 287 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 288 syncache_drop(sc, sch); 289 SCH_UNLOCK(sch); 290 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 291 ("%s: sch->sch_bucket not empty", __func__)); 292 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 293 __func__, sch->sch_length)); 294 mtx_destroy(&sch->sch_mtx); 295 } 296 297 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 298 ("%s: cache_count not 0", __func__)); 299 300 /* Free the allocated global resources. */ 301 uma_zdestroy(V_tcp_syncache.zone); 302 free(V_tcp_syncache.hashbase, M_SYNCACHE); 303 304 callout_drain(&V_tcp_syncache.secret.reseed); 305 } 306 #endif 307 308 /* 309 * Inserts a syncache entry into the specified bucket row. 310 * Locks and unlocks the syncache_head autonomously. 311 */ 312 static void 313 syncache_insert(struct syncache *sc, struct syncache_head *sch) 314 { 315 struct syncache *sc2; 316 317 SCH_LOCK(sch); 318 319 /* 320 * Make sure that we don't overflow the per-bucket limit. 321 * If the bucket is full, toss the oldest element. 322 */ 323 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 324 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 325 ("sch->sch_length incorrect")); 326 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 327 syncache_drop(sc2, sch); 328 TCPSTAT_INC(tcps_sc_bucketoverflow); 329 } 330 331 /* Put it into the bucket. */ 332 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 333 sch->sch_length++; 334 335 #ifdef TCP_OFFLOAD 336 if (ADDED_BY_TOE(sc)) { 337 struct toedev *tod = sc->sc_tod; 338 339 tod->tod_syncache_added(tod, sc->sc_todctx); 340 } 341 #endif 342 343 /* Reinitialize the bucket row's timer. */ 344 if (sch->sch_length == 1) 345 sch->sch_nextc = ticks + INT_MAX; 346 syncache_timeout(sc, sch, 1); 347 348 SCH_UNLOCK(sch); 349 350 TCPSTAT_INC(tcps_sc_added); 351 } 352 353 /* 354 * Remove and free entry from syncache bucket row. 355 * Expects locked syncache head. 356 */ 357 static void 358 syncache_drop(struct syncache *sc, struct syncache_head *sch) 359 { 360 361 SCH_LOCK_ASSERT(sch); 362 363 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 364 sch->sch_length--; 365 366 #ifdef TCP_OFFLOAD 367 if (ADDED_BY_TOE(sc)) { 368 struct toedev *tod = sc->sc_tod; 369 370 tod->tod_syncache_removed(tod, sc->sc_todctx); 371 } 372 #endif 373 374 syncache_free(sc); 375 } 376 377 /* 378 * Engage/reengage time on bucket row. 379 */ 380 static void 381 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 382 { 383 sc->sc_rxttime = ticks + 384 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 385 sc->sc_rxmits++; 386 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 387 sch->sch_nextc = sc->sc_rxttime; 388 if (docallout) 389 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 390 syncache_timer, (void *)sch); 391 } 392 } 393 394 /* 395 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 396 * If we have retransmitted an entry the maximum number of times, expire it. 397 * One separate timer for each bucket row. 398 */ 399 static void 400 syncache_timer(void *xsch) 401 { 402 struct syncache_head *sch = (struct syncache_head *)xsch; 403 struct syncache *sc, *nsc; 404 int tick = ticks; 405 char *s; 406 407 CURVNET_SET(sch->sch_sc->vnet); 408 409 /* NB: syncache_head has already been locked by the callout. */ 410 SCH_LOCK_ASSERT(sch); 411 412 /* 413 * In the following cycle we may remove some entries and/or 414 * advance some timeouts, so re-initialize the bucket timer. 415 */ 416 sch->sch_nextc = tick + INT_MAX; 417 418 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 419 /* 420 * We do not check if the listen socket still exists 421 * and accept the case where the listen socket may be 422 * gone by the time we resend the SYN/ACK. We do 423 * not expect this to happens often. If it does, 424 * then the RST will be sent by the time the remote 425 * host does the SYN/ACK->ACK. 426 */ 427 if (TSTMP_GT(sc->sc_rxttime, tick)) { 428 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 429 sch->sch_nextc = sc->sc_rxttime; 430 continue; 431 } 432 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 433 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 434 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 435 "giving up and removing syncache entry\n", 436 s, __func__); 437 free(s, M_TCPLOG); 438 } 439 syncache_drop(sc, sch); 440 TCPSTAT_INC(tcps_sc_stale); 441 continue; 442 } 443 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 444 log(LOG_DEBUG, "%s; %s: Response timeout, " 445 "retransmitting (%u) SYN|ACK\n", 446 s, __func__, sc->sc_rxmits); 447 free(s, M_TCPLOG); 448 } 449 450 syncache_respond(sc, sch, 1); 451 TCPSTAT_INC(tcps_sc_retransmitted); 452 syncache_timeout(sc, sch, 0); 453 } 454 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 455 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 456 syncache_timer, (void *)(sch)); 457 CURVNET_RESTORE(); 458 } 459 460 /* 461 * Find an entry in the syncache. 462 * Returns always with locked syncache_head plus a matching entry or NULL. 463 */ 464 static struct syncache * 465 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 466 { 467 struct syncache *sc; 468 struct syncache_head *sch; 469 uint32_t hash; 470 471 /* 472 * The hash is built on foreign port + local port + foreign address. 473 * We rely on the fact that struct in_conninfo starts with 16 bits 474 * of foreign port, then 16 bits of local port then followed by 128 475 * bits of foreign address. In case of IPv4 address, the first 3 476 * 32-bit words of the address always are zeroes. 477 */ 478 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 479 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 480 481 sch = &V_tcp_syncache.hashbase[hash]; 482 *schp = sch; 483 SCH_LOCK(sch); 484 485 /* Circle through bucket row to find matching entry. */ 486 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 487 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 488 sizeof(struct in_endpoints)) == 0) 489 break; 490 491 return (sc); /* Always returns with locked sch. */ 492 } 493 494 /* 495 * This function is called when we get a RST for a 496 * non-existent connection, so that we can see if the 497 * connection is in the syn cache. If it is, zap it. 498 */ 499 void 500 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 501 { 502 struct syncache *sc; 503 struct syncache_head *sch; 504 char *s = NULL; 505 506 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 507 SCH_LOCK_ASSERT(sch); 508 509 /* 510 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 511 * See RFC 793 page 65, section SEGMENT ARRIVES. 512 */ 513 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 514 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 515 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 516 "FIN flag set, segment ignored\n", s, __func__); 517 TCPSTAT_INC(tcps_badrst); 518 goto done; 519 } 520 521 /* 522 * No corresponding connection was found in syncache. 523 * If syncookies are enabled and possibly exclusively 524 * used, or we are under memory pressure, a valid RST 525 * may not find a syncache entry. In that case we're 526 * done and no SYN|ACK retransmissions will happen. 527 * Otherwise the RST was misdirected or spoofed. 528 */ 529 if (sc == NULL) { 530 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 531 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 532 "syncache entry (possibly syncookie only), " 533 "segment ignored\n", s, __func__); 534 TCPSTAT_INC(tcps_badrst); 535 goto done; 536 } 537 538 /* 539 * If the RST bit is set, check the sequence number to see 540 * if this is a valid reset segment. 541 * RFC 793 page 37: 542 * In all states except SYN-SENT, all reset (RST) segments 543 * are validated by checking their SEQ-fields. A reset is 544 * valid if its sequence number is in the window. 545 * 546 * The sequence number in the reset segment is normally an 547 * echo of our outgoing acknowlegement numbers, but some hosts 548 * send a reset with the sequence number at the rightmost edge 549 * of our receive window, and we have to handle this case. 550 */ 551 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 552 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 553 syncache_drop(sc, sch); 554 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 555 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 556 "connection attempt aborted by remote endpoint\n", 557 s, __func__); 558 TCPSTAT_INC(tcps_sc_reset); 559 } else { 560 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 561 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 562 "IRS %u (+WND %u), segment ignored\n", 563 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 564 TCPSTAT_INC(tcps_badrst); 565 } 566 567 done: 568 if (s != NULL) 569 free(s, M_TCPLOG); 570 SCH_UNLOCK(sch); 571 } 572 573 void 574 syncache_badack(struct in_conninfo *inc) 575 { 576 struct syncache *sc; 577 struct syncache_head *sch; 578 579 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 580 SCH_LOCK_ASSERT(sch); 581 if (sc != NULL) { 582 syncache_drop(sc, sch); 583 TCPSTAT_INC(tcps_sc_badack); 584 } 585 SCH_UNLOCK(sch); 586 } 587 588 void 589 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 590 { 591 struct syncache *sc; 592 struct syncache_head *sch; 593 594 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 595 SCH_LOCK_ASSERT(sch); 596 if (sc == NULL) 597 goto done; 598 599 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 600 if (ntohl(th->th_seq) != sc->sc_iss) 601 goto done; 602 603 /* 604 * If we've rertransmitted 3 times and this is our second error, 605 * we remove the entry. Otherwise, we allow it to continue on. 606 * This prevents us from incorrectly nuking an entry during a 607 * spurious network outage. 608 * 609 * See tcp_notify(). 610 */ 611 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 612 sc->sc_flags |= SCF_UNREACH; 613 goto done; 614 } 615 syncache_drop(sc, sch); 616 TCPSTAT_INC(tcps_sc_unreach); 617 done: 618 SCH_UNLOCK(sch); 619 } 620 621 /* 622 * Build a new TCP socket structure from a syncache entry. 623 * 624 * On success return the newly created socket with its underlying inp locked. 625 */ 626 static struct socket * 627 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 628 { 629 struct inpcb *inp = NULL; 630 struct socket *so; 631 struct tcpcb *tp; 632 int error; 633 char *s; 634 635 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 636 637 /* 638 * Ok, create the full blown connection, and set things up 639 * as they would have been set up if we had created the 640 * connection when the SYN arrived. If we can't create 641 * the connection, abort it. 642 */ 643 so = sonewconn(lso, 0); 644 if (so == NULL) { 645 /* 646 * Drop the connection; we will either send a RST or 647 * have the peer retransmit its SYN again after its 648 * RTO and try again. 649 */ 650 TCPSTAT_INC(tcps_listendrop); 651 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 652 log(LOG_DEBUG, "%s; %s: Socket create failed " 653 "due to limits or memory shortage\n", 654 s, __func__); 655 free(s, M_TCPLOG); 656 } 657 goto abort2; 658 } 659 #ifdef MAC 660 mac_socketpeer_set_from_mbuf(m, so); 661 #endif 662 663 inp = sotoinpcb(so); 664 inp->inp_inc.inc_fibnum = so->so_fibnum; 665 INP_WLOCK(inp); 666 /* 667 * Exclusive pcbinfo lock is not required in syncache socket case even 668 * if two inpcb locks can be acquired simultaneously: 669 * - the inpcb in LISTEN state, 670 * - the newly created inp. 671 * 672 * In this case, an inp cannot be at same time in LISTEN state and 673 * just created by an accept() call. 674 */ 675 INP_HASH_WLOCK(&V_tcbinfo); 676 677 /* Insert new socket into PCB hash list. */ 678 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 679 #ifdef INET6 680 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 681 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 682 } else { 683 inp->inp_vflag &= ~INP_IPV6; 684 inp->inp_vflag |= INP_IPV4; 685 #endif 686 inp->inp_laddr = sc->sc_inc.inc_laddr; 687 #ifdef INET6 688 } 689 #endif 690 691 /* 692 * If there's an mbuf and it has a flowid, then let's initialise the 693 * inp with that particular flowid. 694 */ 695 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 696 inp->inp_flowid = m->m_pkthdr.flowid; 697 inp->inp_flowtype = M_HASHTYPE_GET(m); 698 } 699 700 /* 701 * Install in the reservation hash table for now, but don't yet 702 * install a connection group since the full 4-tuple isn't yet 703 * configured. 704 */ 705 inp->inp_lport = sc->sc_inc.inc_lport; 706 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 707 /* 708 * Undo the assignments above if we failed to 709 * put the PCB on the hash lists. 710 */ 711 #ifdef INET6 712 if (sc->sc_inc.inc_flags & INC_ISIPV6) 713 inp->in6p_laddr = in6addr_any; 714 else 715 #endif 716 inp->inp_laddr.s_addr = INADDR_ANY; 717 inp->inp_lport = 0; 718 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 719 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 720 "with error %i\n", 721 s, __func__, error); 722 free(s, M_TCPLOG); 723 } 724 INP_HASH_WUNLOCK(&V_tcbinfo); 725 goto abort; 726 } 727 #ifdef IPSEC 728 /* Copy old policy into new socket's. */ 729 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 730 printf("syncache_socket: could not copy policy\n"); 731 #endif 732 #ifdef INET6 733 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 734 struct inpcb *oinp = sotoinpcb(lso); 735 struct in6_addr laddr6; 736 struct sockaddr_in6 sin6; 737 /* 738 * Inherit socket options from the listening socket. 739 * Note that in6p_inputopts are not (and should not be) 740 * copied, since it stores previously received options and is 741 * used to detect if each new option is different than the 742 * previous one and hence should be passed to a user. 743 * If we copied in6p_inputopts, a user would not be able to 744 * receive options just after calling the accept system call. 745 */ 746 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 747 if (oinp->in6p_outputopts) 748 inp->in6p_outputopts = 749 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 750 751 sin6.sin6_family = AF_INET6; 752 sin6.sin6_len = sizeof(sin6); 753 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 754 sin6.sin6_port = sc->sc_inc.inc_fport; 755 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 756 laddr6 = inp->in6p_laddr; 757 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 758 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 759 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 760 thread0.td_ucred, m)) != 0) { 761 inp->in6p_laddr = laddr6; 762 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 763 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 764 "with error %i\n", 765 s, __func__, error); 766 free(s, M_TCPLOG); 767 } 768 INP_HASH_WUNLOCK(&V_tcbinfo); 769 goto abort; 770 } 771 /* Override flowlabel from in6_pcbconnect. */ 772 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 773 inp->inp_flow |= sc->sc_flowlabel; 774 } 775 #endif /* INET6 */ 776 #if defined(INET) && defined(INET6) 777 else 778 #endif 779 #ifdef INET 780 { 781 struct in_addr laddr; 782 struct sockaddr_in sin; 783 784 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 785 786 if (inp->inp_options == NULL) { 787 inp->inp_options = sc->sc_ipopts; 788 sc->sc_ipopts = NULL; 789 } 790 791 sin.sin_family = AF_INET; 792 sin.sin_len = sizeof(sin); 793 sin.sin_addr = sc->sc_inc.inc_faddr; 794 sin.sin_port = sc->sc_inc.inc_fport; 795 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 796 laddr = inp->inp_laddr; 797 if (inp->inp_laddr.s_addr == INADDR_ANY) 798 inp->inp_laddr = sc->sc_inc.inc_laddr; 799 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 800 thread0.td_ucred, m)) != 0) { 801 inp->inp_laddr = laddr; 802 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 803 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 804 "with error %i\n", 805 s, __func__, error); 806 free(s, M_TCPLOG); 807 } 808 INP_HASH_WUNLOCK(&V_tcbinfo); 809 goto abort; 810 } 811 } 812 #endif /* INET */ 813 INP_HASH_WUNLOCK(&V_tcbinfo); 814 tp = intotcpcb(inp); 815 tcp_state_change(tp, TCPS_SYN_RECEIVED); 816 tp->iss = sc->sc_iss; 817 tp->irs = sc->sc_irs; 818 tcp_rcvseqinit(tp); 819 tcp_sendseqinit(tp); 820 tp->snd_wl1 = sc->sc_irs; 821 tp->snd_max = tp->iss + 1; 822 tp->snd_nxt = tp->iss + 1; 823 tp->rcv_up = sc->sc_irs + 1; 824 tp->rcv_wnd = sc->sc_wnd; 825 tp->rcv_adv += tp->rcv_wnd; 826 tp->last_ack_sent = tp->rcv_nxt; 827 828 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 829 if (sc->sc_flags & SCF_NOOPT) 830 tp->t_flags |= TF_NOOPT; 831 else { 832 if (sc->sc_flags & SCF_WINSCALE) { 833 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 834 tp->snd_scale = sc->sc_requested_s_scale; 835 tp->request_r_scale = sc->sc_requested_r_scale; 836 } 837 if (sc->sc_flags & SCF_TIMESTAMP) { 838 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 839 tp->ts_recent = sc->sc_tsreflect; 840 tp->ts_recent_age = tcp_ts_getticks(); 841 tp->ts_offset = sc->sc_tsoff; 842 } 843 #ifdef TCP_SIGNATURE 844 if (sc->sc_flags & SCF_SIGNATURE) 845 tp->t_flags |= TF_SIGNATURE; 846 #endif 847 if (sc->sc_flags & SCF_SACK) 848 tp->t_flags |= TF_SACK_PERMIT; 849 } 850 851 if (sc->sc_flags & SCF_ECN) 852 tp->t_flags |= TF_ECN_PERMIT; 853 854 /* 855 * Set up MSS and get cached values from tcp_hostcache. 856 * This might overwrite some of the defaults we just set. 857 */ 858 tcp_mss(tp, sc->sc_peer_mss); 859 860 /* 861 * If the SYN,ACK was retransmitted, indicate that CWND to be 862 * limited to one segment in cc_conn_init(). 863 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 864 */ 865 if (sc->sc_rxmits > 1) 866 tp->snd_cwnd = 1; 867 868 #ifdef TCP_OFFLOAD 869 /* 870 * Allow a TOE driver to install its hooks. Note that we hold the 871 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 872 * new connection before the TOE driver has done its thing. 873 */ 874 if (ADDED_BY_TOE(sc)) { 875 struct toedev *tod = sc->sc_tod; 876 877 tod->tod_offload_socket(tod, sc->sc_todctx, so); 878 } 879 #endif 880 /* 881 * Copy and activate timers. 882 */ 883 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 884 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 885 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 886 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 887 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 888 889 soisconnected(so); 890 891 TCPSTAT_INC(tcps_accepts); 892 return (so); 893 894 abort: 895 INP_WUNLOCK(inp); 896 abort2: 897 if (so != NULL) 898 soabort(so); 899 return (NULL); 900 } 901 902 /* 903 * This function gets called when we receive an ACK for a 904 * socket in the LISTEN state. We look up the connection 905 * in the syncache, and if its there, we pull it out of 906 * the cache and turn it into a full-blown connection in 907 * the SYN-RECEIVED state. 908 * 909 * On syncache_socket() success the newly created socket 910 * has its underlying inp locked. 911 */ 912 int 913 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 914 struct socket **lsop, struct mbuf *m) 915 { 916 struct syncache *sc; 917 struct syncache_head *sch; 918 struct syncache scs; 919 char *s; 920 921 /* 922 * Global TCP locks are held because we manipulate the PCB lists 923 * and create a new socket. 924 */ 925 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 926 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 927 ("%s: can handle only ACK", __func__)); 928 929 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 930 SCH_LOCK_ASSERT(sch); 931 932 #ifdef INVARIANTS 933 /* 934 * Test code for syncookies comparing the syncache stored 935 * values with the reconstructed values from the cookie. 936 */ 937 if (sc != NULL) 938 syncookie_cmp(inc, sch, sc, th, to, *lsop); 939 #endif 940 941 if (sc == NULL) { 942 /* 943 * There is no syncache entry, so see if this ACK is 944 * a returning syncookie. To do this, first: 945 * A. See if this socket has had a syncache entry dropped in 946 * the past. We don't want to accept a bogus syncookie 947 * if we've never received a SYN. 948 * B. check that the syncookie is valid. If it is, then 949 * cobble up a fake syncache entry, and return. 950 */ 951 if (!V_tcp_syncookies) { 952 SCH_UNLOCK(sch); 953 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 954 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 955 "segment rejected (syncookies disabled)\n", 956 s, __func__); 957 goto failed; 958 } 959 bzero(&scs, sizeof(scs)); 960 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 961 SCH_UNLOCK(sch); 962 if (sc == NULL) { 963 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 964 log(LOG_DEBUG, "%s; %s: Segment failed " 965 "SYNCOOKIE authentication, segment rejected " 966 "(probably spoofed)\n", s, __func__); 967 goto failed; 968 } 969 } else { 970 /* Pull out the entry to unlock the bucket row. */ 971 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 972 sch->sch_length--; 973 #ifdef TCP_OFFLOAD 974 if (ADDED_BY_TOE(sc)) { 975 struct toedev *tod = sc->sc_tod; 976 977 tod->tod_syncache_removed(tod, sc->sc_todctx); 978 } 979 #endif 980 SCH_UNLOCK(sch); 981 } 982 983 /* 984 * Segment validation: 985 * ACK must match our initial sequence number + 1 (the SYN|ACK). 986 */ 987 if (th->th_ack != sc->sc_iss + 1) { 988 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 989 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 990 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 991 goto failed; 992 } 993 994 /* 995 * The SEQ must fall in the window starting at the received 996 * initial receive sequence number + 1 (the SYN). 997 */ 998 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 999 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1000 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1001 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1002 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1003 goto failed; 1004 } 1005 1006 /* 1007 * If timestamps were not negotiated during SYN/ACK they 1008 * must not appear on any segment during this session. 1009 */ 1010 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1011 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1012 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1013 "segment rejected\n", s, __func__); 1014 goto failed; 1015 } 1016 1017 /* 1018 * If timestamps were negotiated during SYN/ACK they should 1019 * appear on every segment during this session. 1020 * XXXAO: This is only informal as there have been unverified 1021 * reports of non-compliants stacks. 1022 */ 1023 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1024 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1025 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1026 "no action\n", s, __func__); 1027 free(s, M_TCPLOG); 1028 s = NULL; 1029 } 1030 } 1031 1032 /* 1033 * If timestamps were negotiated the reflected timestamp 1034 * must be equal to what we actually sent in the SYN|ACK. 1035 */ 1036 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1037 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1038 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1039 "segment rejected\n", 1040 s, __func__, to->to_tsecr, sc->sc_ts); 1041 goto failed; 1042 } 1043 1044 *lsop = syncache_socket(sc, *lsop, m); 1045 1046 if (*lsop == NULL) 1047 TCPSTAT_INC(tcps_sc_aborted); 1048 else 1049 TCPSTAT_INC(tcps_sc_completed); 1050 1051 /* how do we find the inp for the new socket? */ 1052 if (sc != &scs) 1053 syncache_free(sc); 1054 return (1); 1055 failed: 1056 if (sc != NULL && sc != &scs) 1057 syncache_free(sc); 1058 if (s != NULL) 1059 free(s, M_TCPLOG); 1060 *lsop = NULL; 1061 return (0); 1062 } 1063 1064 /* 1065 * Given a LISTEN socket and an inbound SYN request, add 1066 * this to the syn cache, and send back a segment: 1067 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1068 * to the source. 1069 * 1070 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1071 * Doing so would require that we hold onto the data and deliver it 1072 * to the application. However, if we are the target of a SYN-flood 1073 * DoS attack, an attacker could send data which would eventually 1074 * consume all available buffer space if it were ACKed. By not ACKing 1075 * the data, we avoid this DoS scenario. 1076 */ 1077 void 1078 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1079 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1080 void *todctx) 1081 { 1082 struct tcpcb *tp; 1083 struct socket *so; 1084 struct syncache *sc = NULL; 1085 struct syncache_head *sch; 1086 struct mbuf *ipopts = NULL; 1087 u_int ltflags; 1088 int win, sb_hiwat, ip_ttl, ip_tos; 1089 char *s; 1090 #ifdef INET6 1091 int autoflowlabel = 0; 1092 #endif 1093 #ifdef MAC 1094 struct label *maclabel; 1095 #endif 1096 struct syncache scs; 1097 struct ucred *cred; 1098 1099 INP_WLOCK_ASSERT(inp); /* listen socket */ 1100 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1101 ("%s: unexpected tcp flags", __func__)); 1102 1103 /* 1104 * Combine all so/tp operations very early to drop the INP lock as 1105 * soon as possible. 1106 */ 1107 so = *lsop; 1108 tp = sototcpcb(so); 1109 cred = crhold(so->so_cred); 1110 1111 #ifdef INET6 1112 if ((inc->inc_flags & INC_ISIPV6) && 1113 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1114 autoflowlabel = 1; 1115 #endif 1116 ip_ttl = inp->inp_ip_ttl; 1117 ip_tos = inp->inp_ip_tos; 1118 win = sbspace(&so->so_rcv); 1119 sb_hiwat = so->so_rcv.sb_hiwat; 1120 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1121 1122 /* By the time we drop the lock these should no longer be used. */ 1123 so = NULL; 1124 tp = NULL; 1125 1126 #ifdef MAC 1127 if (mac_syncache_init(&maclabel) != 0) { 1128 INP_WUNLOCK(inp); 1129 goto done; 1130 } else 1131 mac_syncache_create(maclabel, inp); 1132 #endif 1133 INP_WUNLOCK(inp); 1134 1135 /* 1136 * Remember the IP options, if any. 1137 */ 1138 #ifdef INET6 1139 if (!(inc->inc_flags & INC_ISIPV6)) 1140 #endif 1141 #ifdef INET 1142 ipopts = (m) ? ip_srcroute(m) : NULL; 1143 #else 1144 ipopts = NULL; 1145 #endif 1146 1147 /* 1148 * See if we already have an entry for this connection. 1149 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1150 * 1151 * XXX: should the syncache be re-initialized with the contents 1152 * of the new SYN here (which may have different options?) 1153 * 1154 * XXX: We do not check the sequence number to see if this is a 1155 * real retransmit or a new connection attempt. The question is 1156 * how to handle such a case; either ignore it as spoofed, or 1157 * drop the current entry and create a new one? 1158 */ 1159 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1160 SCH_LOCK_ASSERT(sch); 1161 if (sc != NULL) { 1162 TCPSTAT_INC(tcps_sc_dupsyn); 1163 if (ipopts) { 1164 /* 1165 * If we were remembering a previous source route, 1166 * forget it and use the new one we've been given. 1167 */ 1168 if (sc->sc_ipopts) 1169 (void) m_free(sc->sc_ipopts); 1170 sc->sc_ipopts = ipopts; 1171 } 1172 /* 1173 * Update timestamp if present. 1174 */ 1175 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1176 sc->sc_tsreflect = to->to_tsval; 1177 else 1178 sc->sc_flags &= ~SCF_TIMESTAMP; 1179 #ifdef MAC 1180 /* 1181 * Since we have already unconditionally allocated label 1182 * storage, free it up. The syncache entry will already 1183 * have an initialized label we can use. 1184 */ 1185 mac_syncache_destroy(&maclabel); 1186 #endif 1187 /* Retransmit SYN|ACK and reset retransmit count. */ 1188 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1189 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1190 "resetting timer and retransmitting SYN|ACK\n", 1191 s, __func__); 1192 free(s, M_TCPLOG); 1193 } 1194 if (syncache_respond(sc, sch, 1) == 0) { 1195 sc->sc_rxmits = 0; 1196 syncache_timeout(sc, sch, 1); 1197 TCPSTAT_INC(tcps_sndacks); 1198 TCPSTAT_INC(tcps_sndtotal); 1199 } 1200 SCH_UNLOCK(sch); 1201 goto done; 1202 } 1203 1204 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1205 if (sc == NULL) { 1206 /* 1207 * The zone allocator couldn't provide more entries. 1208 * Treat this as if the cache was full; drop the oldest 1209 * entry and insert the new one. 1210 */ 1211 TCPSTAT_INC(tcps_sc_zonefail); 1212 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1213 syncache_drop(sc, sch); 1214 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1215 if (sc == NULL) { 1216 if (V_tcp_syncookies) { 1217 bzero(&scs, sizeof(scs)); 1218 sc = &scs; 1219 } else { 1220 SCH_UNLOCK(sch); 1221 if (ipopts) 1222 (void) m_free(ipopts); 1223 goto done; 1224 } 1225 } 1226 } 1227 1228 /* 1229 * Fill in the syncache values. 1230 */ 1231 #ifdef MAC 1232 sc->sc_label = maclabel; 1233 #endif 1234 sc->sc_cred = cred; 1235 cred = NULL; 1236 sc->sc_ipopts = ipopts; 1237 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1238 #ifdef INET6 1239 if (!(inc->inc_flags & INC_ISIPV6)) 1240 #endif 1241 { 1242 sc->sc_ip_tos = ip_tos; 1243 sc->sc_ip_ttl = ip_ttl; 1244 } 1245 #ifdef TCP_OFFLOAD 1246 sc->sc_tod = tod; 1247 sc->sc_todctx = todctx; 1248 #endif 1249 sc->sc_irs = th->th_seq; 1250 sc->sc_iss = arc4random(); 1251 sc->sc_flags = 0; 1252 sc->sc_flowlabel = 0; 1253 1254 /* 1255 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1256 * win was derived from socket earlier in the function. 1257 */ 1258 win = imax(win, 0); 1259 win = imin(win, TCP_MAXWIN); 1260 sc->sc_wnd = win; 1261 1262 if (V_tcp_do_rfc1323) { 1263 /* 1264 * A timestamp received in a SYN makes 1265 * it ok to send timestamp requests and replies. 1266 */ 1267 if (to->to_flags & TOF_TS) { 1268 sc->sc_tsreflect = to->to_tsval; 1269 sc->sc_ts = tcp_ts_getticks(); 1270 sc->sc_flags |= SCF_TIMESTAMP; 1271 } 1272 if (to->to_flags & TOF_SCALE) { 1273 int wscale = 0; 1274 1275 /* 1276 * Pick the smallest possible scaling factor that 1277 * will still allow us to scale up to sb_max, aka 1278 * kern.ipc.maxsockbuf. 1279 * 1280 * We do this because there are broken firewalls that 1281 * will corrupt the window scale option, leading to 1282 * the other endpoint believing that our advertised 1283 * window is unscaled. At scale factors larger than 1284 * 5 the unscaled window will drop below 1500 bytes, 1285 * leading to serious problems when traversing these 1286 * broken firewalls. 1287 * 1288 * With the default maxsockbuf of 256K, a scale factor 1289 * of 3 will be chosen by this algorithm. Those who 1290 * choose a larger maxsockbuf should watch out 1291 * for the compatiblity problems mentioned above. 1292 * 1293 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1294 * or <SYN,ACK>) segment itself is never scaled. 1295 */ 1296 while (wscale < TCP_MAX_WINSHIFT && 1297 (TCP_MAXWIN << wscale) < sb_max) 1298 wscale++; 1299 sc->sc_requested_r_scale = wscale; 1300 sc->sc_requested_s_scale = to->to_wscale; 1301 sc->sc_flags |= SCF_WINSCALE; 1302 } 1303 } 1304 #ifdef TCP_SIGNATURE 1305 /* 1306 * If listening socket requested TCP digests, OR received SYN 1307 * contains the option, flag this in the syncache so that 1308 * syncache_respond() will do the right thing with the SYN+ACK. 1309 */ 1310 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1311 sc->sc_flags |= SCF_SIGNATURE; 1312 #endif 1313 if (to->to_flags & TOF_SACKPERM) 1314 sc->sc_flags |= SCF_SACK; 1315 if (to->to_flags & TOF_MSS) 1316 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1317 if (ltflags & TF_NOOPT) 1318 sc->sc_flags |= SCF_NOOPT; 1319 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1320 sc->sc_flags |= SCF_ECN; 1321 1322 if (V_tcp_syncookies) 1323 sc->sc_iss = syncookie_generate(sch, sc); 1324 #ifdef INET6 1325 if (autoflowlabel) { 1326 if (V_tcp_syncookies) 1327 sc->sc_flowlabel = sc->sc_iss; 1328 else 1329 sc->sc_flowlabel = ip6_randomflowlabel(); 1330 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1331 } 1332 #endif 1333 SCH_UNLOCK(sch); 1334 1335 /* 1336 * Do a standard 3-way handshake. 1337 */ 1338 if (syncache_respond(sc, sch, 0) == 0) { 1339 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1340 syncache_free(sc); 1341 else if (sc != &scs) 1342 syncache_insert(sc, sch); /* locks and unlocks sch */ 1343 TCPSTAT_INC(tcps_sndacks); 1344 TCPSTAT_INC(tcps_sndtotal); 1345 } else { 1346 if (sc != &scs) 1347 syncache_free(sc); 1348 TCPSTAT_INC(tcps_sc_dropped); 1349 } 1350 1351 done: 1352 if (cred != NULL) 1353 crfree(cred); 1354 #ifdef MAC 1355 if (sc == &scs) 1356 mac_syncache_destroy(&maclabel); 1357 #endif 1358 if (m) { 1359 1360 *lsop = NULL; 1361 m_freem(m); 1362 } 1363 } 1364 1365 static int 1366 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked) 1367 { 1368 struct ip *ip = NULL; 1369 struct mbuf *m; 1370 struct tcphdr *th = NULL; 1371 int optlen, error = 0; /* Make compiler happy */ 1372 u_int16_t hlen, tlen, mssopt; 1373 struct tcpopt to; 1374 #ifdef INET6 1375 struct ip6_hdr *ip6 = NULL; 1376 #endif 1377 #ifdef TCP_SIGNATURE 1378 struct secasvar *sav; 1379 #endif 1380 1381 hlen = 1382 #ifdef INET6 1383 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1384 #endif 1385 sizeof(struct ip); 1386 tlen = hlen + sizeof(struct tcphdr); 1387 1388 /* Determine MSS we advertize to other end of connection. */ 1389 mssopt = tcp_mssopt(&sc->sc_inc); 1390 if (sc->sc_peer_mss) 1391 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1392 1393 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1394 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1395 ("syncache: mbuf too small")); 1396 1397 /* Create the IP+TCP header from scratch. */ 1398 m = m_gethdr(M_NOWAIT, MT_DATA); 1399 if (m == NULL) 1400 return (ENOBUFS); 1401 #ifdef MAC 1402 mac_syncache_create_mbuf(sc->sc_label, m); 1403 #endif 1404 m->m_data += max_linkhdr; 1405 m->m_len = tlen; 1406 m->m_pkthdr.len = tlen; 1407 m->m_pkthdr.rcvif = NULL; 1408 1409 #ifdef INET6 1410 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1411 ip6 = mtod(m, struct ip6_hdr *); 1412 ip6->ip6_vfc = IPV6_VERSION; 1413 ip6->ip6_nxt = IPPROTO_TCP; 1414 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1415 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1416 ip6->ip6_plen = htons(tlen - hlen); 1417 /* ip6_hlim is set after checksum */ 1418 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1419 ip6->ip6_flow |= sc->sc_flowlabel; 1420 1421 th = (struct tcphdr *)(ip6 + 1); 1422 } 1423 #endif 1424 #if defined(INET6) && defined(INET) 1425 else 1426 #endif 1427 #ifdef INET 1428 { 1429 ip = mtod(m, struct ip *); 1430 ip->ip_v = IPVERSION; 1431 ip->ip_hl = sizeof(struct ip) >> 2; 1432 ip->ip_len = htons(tlen); 1433 ip->ip_id = 0; 1434 ip->ip_off = 0; 1435 ip->ip_sum = 0; 1436 ip->ip_p = IPPROTO_TCP; 1437 ip->ip_src = sc->sc_inc.inc_laddr; 1438 ip->ip_dst = sc->sc_inc.inc_faddr; 1439 ip->ip_ttl = sc->sc_ip_ttl; 1440 ip->ip_tos = sc->sc_ip_tos; 1441 1442 /* 1443 * See if we should do MTU discovery. Route lookups are 1444 * expensive, so we will only unset the DF bit if: 1445 * 1446 * 1) path_mtu_discovery is disabled 1447 * 2) the SCF_UNREACH flag has been set 1448 */ 1449 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1450 ip->ip_off |= htons(IP_DF); 1451 1452 th = (struct tcphdr *)(ip + 1); 1453 } 1454 #endif /* INET */ 1455 th->th_sport = sc->sc_inc.inc_lport; 1456 th->th_dport = sc->sc_inc.inc_fport; 1457 1458 th->th_seq = htonl(sc->sc_iss); 1459 th->th_ack = htonl(sc->sc_irs + 1); 1460 th->th_off = sizeof(struct tcphdr) >> 2; 1461 th->th_x2 = 0; 1462 th->th_flags = TH_SYN|TH_ACK; 1463 th->th_win = htons(sc->sc_wnd); 1464 th->th_urp = 0; 1465 1466 if (sc->sc_flags & SCF_ECN) { 1467 th->th_flags |= TH_ECE; 1468 TCPSTAT_INC(tcps_ecn_shs); 1469 } 1470 1471 /* Tack on the TCP options. */ 1472 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1473 to.to_flags = 0; 1474 1475 to.to_mss = mssopt; 1476 to.to_flags = TOF_MSS; 1477 if (sc->sc_flags & SCF_WINSCALE) { 1478 to.to_wscale = sc->sc_requested_r_scale; 1479 to.to_flags |= TOF_SCALE; 1480 } 1481 if (sc->sc_flags & SCF_TIMESTAMP) { 1482 /* Virgin timestamp or TCP cookie enhanced one. */ 1483 to.to_tsval = sc->sc_ts; 1484 to.to_tsecr = sc->sc_tsreflect; 1485 to.to_flags |= TOF_TS; 1486 } 1487 if (sc->sc_flags & SCF_SACK) 1488 to.to_flags |= TOF_SACKPERM; 1489 #ifdef TCP_SIGNATURE 1490 sav = NULL; 1491 if (sc->sc_flags & SCF_SIGNATURE) { 1492 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1493 if (sav != NULL) 1494 to.to_flags |= TOF_SIGNATURE; 1495 else { 1496 1497 /* 1498 * We've got SCF_SIGNATURE flag 1499 * inherited from listening socket, 1500 * but no SADB key for given source 1501 * address. Assume signature is not 1502 * required and remove signature flag 1503 * instead of silently dropping 1504 * connection. 1505 */ 1506 if (locked == 0) 1507 SCH_LOCK(sch); 1508 sc->sc_flags &= ~SCF_SIGNATURE; 1509 if (locked == 0) 1510 SCH_UNLOCK(sch); 1511 } 1512 } 1513 #endif 1514 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1515 1516 /* Adjust headers by option size. */ 1517 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1518 m->m_len += optlen; 1519 m->m_pkthdr.len += optlen; 1520 1521 #ifdef TCP_SIGNATURE 1522 if (sc->sc_flags & SCF_SIGNATURE) 1523 tcp_signature_do_compute(m, 0, optlen, 1524 to.to_signature, sav); 1525 #endif 1526 #ifdef INET6 1527 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1528 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1529 else 1530 #endif 1531 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1532 } else 1533 optlen = 0; 1534 1535 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1536 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1537 #ifdef INET6 1538 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1539 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1540 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1541 IPPROTO_TCP, 0); 1542 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1543 #ifdef TCP_OFFLOAD 1544 if (ADDED_BY_TOE(sc)) { 1545 struct toedev *tod = sc->sc_tod; 1546 1547 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1548 1549 return (error); 1550 } 1551 #endif 1552 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1553 } 1554 #endif 1555 #if defined(INET6) && defined(INET) 1556 else 1557 #endif 1558 #ifdef INET 1559 { 1560 m->m_pkthdr.csum_flags = CSUM_TCP; 1561 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1562 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1563 #ifdef TCP_OFFLOAD 1564 if (ADDED_BY_TOE(sc)) { 1565 struct toedev *tod = sc->sc_tod; 1566 1567 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1568 1569 return (error); 1570 } 1571 #endif 1572 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1573 } 1574 #endif 1575 return (error); 1576 } 1577 1578 /* 1579 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1580 * that exceed the capacity of the syncache by avoiding the storage of any 1581 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1582 * attacks where the attacker does not have access to our responses. 1583 * 1584 * Syncookies encode and include all necessary information about the 1585 * connection setup within the SYN|ACK that we send back. That way we 1586 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1587 * (if ever). Normally the syncache and syncookies are running in parallel 1588 * with the latter taking over when the former is exhausted. When matching 1589 * syncache entry is found the syncookie is ignored. 1590 * 1591 * The only reliable information persisting the 3WHS is our inital sequence 1592 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1593 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1594 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1595 * returns and signifies a legitimate connection if it matches the ACK. 1596 * 1597 * The available space of 32 bits to store the hash and to encode the SYN 1598 * option information is very tight and we should have at least 24 bits for 1599 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1600 * 1601 * SYN option information we have to encode to fully restore a connection: 1602 * MSS: is imporant to chose an optimal segment size to avoid IP level 1603 * fragmentation along the path. The common MSS values can be encoded 1604 * in a 3-bit table. Uncommon values are captured by the next lower value 1605 * in the table leading to a slight increase in packetization overhead. 1606 * WSCALE: is necessary to allow large windows to be used for high delay- 1607 * bandwidth product links. Not scaling the window when it was initially 1608 * negotiated is bad for performance as lack of scaling further decreases 1609 * the apparent available send window. We only need to encode the WSCALE 1610 * we received from the remote end. Our end can be recalculated at any 1611 * time. The common WSCALE values can be encoded in a 3-bit table. 1612 * Uncommon values are captured by the next lower value in the table 1613 * making us under-estimate the available window size halving our 1614 * theoretically possible maximum throughput for that connection. 1615 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1616 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1617 * that are included in all segments on a connection. We enable them when 1618 * the ACK has them. 1619 * 1620 * Security of syncookies and attack vectors: 1621 * 1622 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1623 * together with the gloabl secret to make it unique per connection attempt. 1624 * Thus any change of any of those parameters results in a different MAC output 1625 * in an unpredictable way unless a collision is encountered. 24 bits of the 1626 * MAC are embedded into the ISS. 1627 * 1628 * To prevent replay attacks two rotating global secrets are updated with a 1629 * new random value every 15 seconds. The life-time of a syncookie is thus 1630 * 15-30 seconds. 1631 * 1632 * Vector 1: Attacking the secret. This requires finding a weakness in the 1633 * MAC itself or the way it is used here. The attacker can do a chosen plain 1634 * text attack by varying and testing the all parameters under his control. 1635 * The strength depends on the size and randomness of the secret, and the 1636 * cryptographic security of the MAC function. Due to the constant updating 1637 * of the secret the attacker has at most 29.999 seconds to find the secret 1638 * and launch spoofed connections. After that he has to start all over again. 1639 * 1640 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1641 * size an average of 4,823 attempts are required for a 50% chance of success 1642 * to spoof a single syncookie (birthday collision paradox). However the 1643 * attacker is blind and doesn't know if one of his attempts succeeded unless 1644 * he has a side channel to interfere success from. A single connection setup 1645 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1646 * This many attempts are required for each one blind spoofed connection. For 1647 * every additional spoofed connection he has to launch another N attempts. 1648 * Thus for a sustained rate 100 spoofed connections per second approximately 1649 * 1,800,000 packets per second would have to be sent. 1650 * 1651 * NB: The MAC function should be fast so that it doesn't become a CPU 1652 * exhaustion attack vector itself. 1653 * 1654 * References: 1655 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1656 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1657 * http://cr.yp.to/syncookies.html (overview) 1658 * http://cr.yp.to/syncookies/archive (details) 1659 * 1660 * 1661 * Schematic construction of a syncookie enabled Initial Sequence Number: 1662 * 0 1 2 3 1663 * 12345678901234567890123456789012 1664 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1665 * 1666 * x 24 MAC (truncated) 1667 * W 3 Send Window Scale index 1668 * M 3 MSS index 1669 * S 1 SACK permitted 1670 * P 1 Odd/even secret 1671 */ 1672 1673 /* 1674 * Distribution and probability of certain MSS values. Those in between are 1675 * rounded down to the next lower one. 1676 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1677 * .2% .3% 5% 7% 7% 20% 15% 45% 1678 */ 1679 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1680 1681 /* 1682 * Distribution and probability of certain WSCALE values. We have to map the 1683 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1684 * bits based on prevalence of certain values. Where we don't have an exact 1685 * match for are rounded down to the next lower one letting us under-estimate 1686 * the true available window. At the moment this would happen only for the 1687 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1688 * and window size). The absence of the WSCALE option (no scaling in either 1689 * direction) is encoded with index zero. 1690 * [WSCALE values histograms, Allman, 2012] 1691 * X 10 10 35 5 6 14 10% by host 1692 * X 11 4 5 5 18 49 3% by connections 1693 */ 1694 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1695 1696 /* 1697 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1698 * and good cryptographic properties. 1699 */ 1700 static uint32_t 1701 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1702 uint8_t *secbits, uintptr_t secmod) 1703 { 1704 SIPHASH_CTX ctx; 1705 uint32_t siphash[2]; 1706 1707 SipHash24_Init(&ctx); 1708 SipHash_SetKey(&ctx, secbits); 1709 switch (inc->inc_flags & INC_ISIPV6) { 1710 #ifdef INET 1711 case 0: 1712 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1713 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1714 break; 1715 #endif 1716 #ifdef INET6 1717 case INC_ISIPV6: 1718 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1719 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1720 break; 1721 #endif 1722 } 1723 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1724 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1725 SipHash_Update(&ctx, &irs, sizeof(irs)); 1726 SipHash_Update(&ctx, &flags, sizeof(flags)); 1727 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1728 SipHash_Final((u_int8_t *)&siphash, &ctx); 1729 1730 return (siphash[0] ^ siphash[1]); 1731 } 1732 1733 static tcp_seq 1734 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1735 { 1736 u_int i, mss, secbit, wscale; 1737 uint32_t iss, hash; 1738 uint8_t *secbits; 1739 union syncookie cookie; 1740 1741 SCH_LOCK_ASSERT(sch); 1742 1743 cookie.cookie = 0; 1744 1745 /* Map our computed MSS into the 3-bit index. */ 1746 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1747 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1748 tcp_sc_msstab[i] > mss && i > 0; 1749 i--) 1750 ; 1751 cookie.flags.mss_idx = i; 1752 1753 /* 1754 * Map the send window scale into the 3-bit index but only if 1755 * the wscale option was received. 1756 */ 1757 if (sc->sc_flags & SCF_WINSCALE) { 1758 wscale = sc->sc_requested_s_scale; 1759 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1760 tcp_sc_wstab[i] > wscale && i > 0; 1761 i--) 1762 ; 1763 cookie.flags.wscale_idx = i; 1764 } 1765 1766 /* Can we do SACK? */ 1767 if (sc->sc_flags & SCF_SACK) 1768 cookie.flags.sack_ok = 1; 1769 1770 /* Which of the two secrets to use. */ 1771 secbit = sch->sch_sc->secret.oddeven & 0x1; 1772 cookie.flags.odd_even = secbit; 1773 1774 secbits = sch->sch_sc->secret.key[secbit]; 1775 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1776 (uintptr_t)sch); 1777 1778 /* 1779 * Put the flags into the hash and XOR them to get better ISS number 1780 * variance. This doesn't enhance the cryptographic strength and is 1781 * done to prevent the 8 cookie bits from showing up directly on the 1782 * wire. 1783 */ 1784 iss = hash & ~0xff; 1785 iss |= cookie.cookie ^ (hash >> 24); 1786 1787 /* Randomize the timestamp. */ 1788 if (sc->sc_flags & SCF_TIMESTAMP) { 1789 sc->sc_ts = arc4random(); 1790 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1791 } 1792 1793 TCPSTAT_INC(tcps_sc_sendcookie); 1794 return (iss); 1795 } 1796 1797 static struct syncache * 1798 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1799 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1800 struct socket *lso) 1801 { 1802 uint32_t hash; 1803 uint8_t *secbits; 1804 tcp_seq ack, seq; 1805 int wnd, wscale = 0; 1806 union syncookie cookie; 1807 1808 SCH_LOCK_ASSERT(sch); 1809 1810 /* 1811 * Pull information out of SYN-ACK/ACK and revert sequence number 1812 * advances. 1813 */ 1814 ack = th->th_ack - 1; 1815 seq = th->th_seq - 1; 1816 1817 /* 1818 * Unpack the flags containing enough information to restore the 1819 * connection. 1820 */ 1821 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1822 1823 /* Which of the two secrets to use. */ 1824 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1825 1826 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1827 1828 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1829 if ((ack & ~0xff) != (hash & ~0xff)) 1830 return (NULL); 1831 1832 /* Fill in the syncache values. */ 1833 sc->sc_flags = 0; 1834 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1835 sc->sc_ipopts = NULL; 1836 1837 sc->sc_irs = seq; 1838 sc->sc_iss = ack; 1839 1840 switch (inc->inc_flags & INC_ISIPV6) { 1841 #ifdef INET 1842 case 0: 1843 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1844 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1845 break; 1846 #endif 1847 #ifdef INET6 1848 case INC_ISIPV6: 1849 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1850 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1851 break; 1852 #endif 1853 } 1854 1855 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1856 1857 /* We can simply recompute receive window scale we sent earlier. */ 1858 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1859 wscale++; 1860 1861 /* Only use wscale if it was enabled in the orignal SYN. */ 1862 if (cookie.flags.wscale_idx > 0) { 1863 sc->sc_requested_r_scale = wscale; 1864 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1865 sc->sc_flags |= SCF_WINSCALE; 1866 } 1867 1868 wnd = sbspace(&lso->so_rcv); 1869 wnd = imax(wnd, 0); 1870 wnd = imin(wnd, TCP_MAXWIN); 1871 sc->sc_wnd = wnd; 1872 1873 if (cookie.flags.sack_ok) 1874 sc->sc_flags |= SCF_SACK; 1875 1876 if (to->to_flags & TOF_TS) { 1877 sc->sc_flags |= SCF_TIMESTAMP; 1878 sc->sc_tsreflect = to->to_tsval; 1879 sc->sc_ts = to->to_tsecr; 1880 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1881 } 1882 1883 if (to->to_flags & TOF_SIGNATURE) 1884 sc->sc_flags |= SCF_SIGNATURE; 1885 1886 sc->sc_rxmits = 0; 1887 1888 TCPSTAT_INC(tcps_sc_recvcookie); 1889 return (sc); 1890 } 1891 1892 #ifdef INVARIANTS 1893 static int 1894 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1895 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1896 struct socket *lso) 1897 { 1898 struct syncache scs, *scx; 1899 char *s; 1900 1901 bzero(&scs, sizeof(scs)); 1902 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1903 1904 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1905 return (0); 1906 1907 if (scx != NULL) { 1908 if (sc->sc_peer_mss != scx->sc_peer_mss) 1909 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1910 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1911 1912 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1913 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1914 s, __func__, sc->sc_requested_r_scale, 1915 scx->sc_requested_r_scale); 1916 1917 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1918 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1919 s, __func__, sc->sc_requested_s_scale, 1920 scx->sc_requested_s_scale); 1921 1922 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1923 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1924 } 1925 1926 if (s != NULL) 1927 free(s, M_TCPLOG); 1928 return (0); 1929 } 1930 #endif /* INVARIANTS */ 1931 1932 static void 1933 syncookie_reseed(void *arg) 1934 { 1935 struct tcp_syncache *sc = arg; 1936 uint8_t *secbits; 1937 int secbit; 1938 1939 /* 1940 * Reseeding the secret doesn't have to be protected by a lock. 1941 * It only must be ensured that the new random values are visible 1942 * to all CPUs in a SMP environment. The atomic with release 1943 * semantics ensures that. 1944 */ 1945 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1946 secbits = sc->secret.key[secbit]; 1947 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1948 atomic_add_rel_int(&sc->secret.oddeven, 1); 1949 1950 /* Reschedule ourself. */ 1951 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1952 } 1953 1954 /* 1955 * Returns the current number of syncache entries. This number 1956 * will probably change before you get around to calling 1957 * syncache_pcblist. 1958 */ 1959 int 1960 syncache_pcbcount(void) 1961 { 1962 struct syncache_head *sch; 1963 int count, i; 1964 1965 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1966 /* No need to lock for a read. */ 1967 sch = &V_tcp_syncache.hashbase[i]; 1968 count += sch->sch_length; 1969 } 1970 return count; 1971 } 1972 1973 /* 1974 * Exports the syncache entries to userland so that netstat can display 1975 * them alongside the other sockets. This function is intended to be 1976 * called only from tcp_pcblist. 1977 * 1978 * Due to concurrency on an active system, the number of pcbs exported 1979 * may have no relation to max_pcbs. max_pcbs merely indicates the 1980 * amount of space the caller allocated for this function to use. 1981 */ 1982 int 1983 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1984 { 1985 struct xtcpcb xt; 1986 struct syncache *sc; 1987 struct syncache_head *sch; 1988 int count, error, i; 1989 1990 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1991 sch = &V_tcp_syncache.hashbase[i]; 1992 SCH_LOCK(sch); 1993 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1994 if (count >= max_pcbs) { 1995 SCH_UNLOCK(sch); 1996 goto exit; 1997 } 1998 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 1999 continue; 2000 bzero(&xt, sizeof(xt)); 2001 xt.xt_len = sizeof(xt); 2002 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2003 xt.xt_inp.inp_vflag = INP_IPV6; 2004 else 2005 xt.xt_inp.inp_vflag = INP_IPV4; 2006 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2007 xt.xt_tp.t_inpcb = &xt.xt_inp; 2008 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2009 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2010 xt.xt_socket.xso_len = sizeof (struct xsocket); 2011 xt.xt_socket.so_type = SOCK_STREAM; 2012 xt.xt_socket.so_state = SS_ISCONNECTING; 2013 error = SYSCTL_OUT(req, &xt, sizeof xt); 2014 if (error) { 2015 SCH_UNLOCK(sch); 2016 goto exit; 2017 } 2018 count++; 2019 } 2020 SCH_UNLOCK(sch); 2021 } 2022 exit: 2023 *pcbs_exported = count; 2024 return error; 2025 } 2026