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/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/limits.h> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 #include <sys/ucred.h> 56 57 #include <sys/md5.h> 58 #include <crypto/siphash/siphash.h> 59 60 #include <vm/uma.h> 61 62 #include <net/if.h> 63 #include <net/if_var.h> 64 #include <net/route.h> 65 #include <net/vnet.h> 66 67 #include <netinet/in.h> 68 #include <netinet/in_systm.h> 69 #include <netinet/ip.h> 70 #include <netinet/in_var.h> 71 #include <netinet/in_pcb.h> 72 #include <netinet/ip_var.h> 73 #include <netinet/ip_options.h> 74 #ifdef INET6 75 #include <netinet/ip6.h> 76 #include <netinet/icmp6.h> 77 #include <netinet6/nd6.h> 78 #include <netinet6/ip6_var.h> 79 #include <netinet6/in6_pcb.h> 80 #endif 81 #include <netinet/tcp.h> 82 #include <netinet/tcp_fsm.h> 83 #include <netinet/tcp_seq.h> 84 #include <netinet/tcp_timer.h> 85 #include <netinet/tcp_var.h> 86 #include <netinet/tcp_syncache.h> 87 #ifdef INET6 88 #include <netinet6/tcp6_var.h> 89 #endif 90 #ifdef TCP_OFFLOAD 91 #include <netinet/toecore.h> 92 #endif 93 94 #ifdef IPSEC 95 #include <netipsec/ipsec.h> 96 #ifdef INET6 97 #include <netipsec/ipsec6.h> 98 #endif 99 #include <netipsec/key.h> 100 #endif /*IPSEC*/ 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 static VNET_DEFINE(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 #ifdef TCP_OFFLOAD 119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 120 #endif 121 122 static void syncache_drop(struct syncache *, struct syncache_head *); 123 static void syncache_free(struct syncache *); 124 static void syncache_insert(struct syncache *, struct syncache_head *); 125 static int syncache_respond(struct syncache *, struct syncache_head *, int); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 129 int docallout); 130 static void syncache_timer(void *); 131 132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 133 uint8_t *, uintptr_t); 134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 135 static struct syncache 136 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 137 struct syncache *, struct tcphdr *, struct tcpopt *, 138 struct socket *); 139 static void syncookie_reseed(void *); 140 #ifdef INVARIANTS 141 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 142 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 143 struct socket *lso); 144 #endif 145 146 /* 147 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 148 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 149 * the odds are that the user has given up attempting to connect by then. 150 */ 151 #define SYNCACHE_MAXREXMTS 3 152 153 /* Arbitrary values */ 154 #define TCP_SYNCACHE_HASHSIZE 512 155 #define TCP_SYNCACHE_BUCKETLIMIT 30 156 157 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 158 #define V_tcp_syncache VNET(tcp_syncache) 159 160 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 161 "TCP SYN cache"); 162 163 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 164 &VNET_NAME(tcp_syncache.bucket_limit), 0, 165 "Per-bucket hash limit for syncache"); 166 167 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 168 &VNET_NAME(tcp_syncache.cache_limit), 0, 169 "Overall entry limit for syncache"); 170 171 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 172 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 173 174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 175 &VNET_NAME(tcp_syncache.hashsize), 0, 176 "Size of TCP syncache hashtable"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 179 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 180 "Limit on SYN/ACK retransmissions"); 181 182 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 183 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 184 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 185 "Send reset on socket allocation failure"); 186 187 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 188 189 #define SYNCACHE_HASH(inc, mask) \ 190 ((V_tcp_syncache.hash_secret ^ \ 191 (inc)->inc_faddr.s_addr ^ \ 192 ((inc)->inc_faddr.s_addr >> 16) ^ \ 193 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 194 195 #define SYNCACHE_HASH6(inc, mask) \ 196 ((V_tcp_syncache.hash_secret ^ \ 197 (inc)->inc6_faddr.s6_addr32[0] ^ \ 198 (inc)->inc6_faddr.s6_addr32[3] ^ \ 199 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 200 201 #define ENDPTS_EQ(a, b) ( \ 202 (a)->ie_fport == (b)->ie_fport && \ 203 (a)->ie_lport == (b)->ie_lport && \ 204 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 205 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 206 ) 207 208 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 209 210 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 211 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 212 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 213 214 /* 215 * Requires the syncache entry to be already removed from the bucket list. 216 */ 217 static void 218 syncache_free(struct syncache *sc) 219 { 220 221 if (sc->sc_ipopts) 222 (void) m_free(sc->sc_ipopts); 223 if (sc->sc_cred) 224 crfree(sc->sc_cred); 225 #ifdef MAC 226 mac_syncache_destroy(&sc->sc_label); 227 #endif 228 229 uma_zfree(V_tcp_syncache.zone, sc); 230 } 231 232 void 233 syncache_init(void) 234 { 235 int i; 236 237 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 238 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 239 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 240 V_tcp_syncache.hash_secret = arc4random(); 241 242 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 243 &V_tcp_syncache.hashsize); 244 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 245 &V_tcp_syncache.bucket_limit); 246 if (!powerof2(V_tcp_syncache.hashsize) || 247 V_tcp_syncache.hashsize == 0) { 248 printf("WARNING: syncache hash size is not a power of 2.\n"); 249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 250 } 251 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 252 253 /* Set limits. */ 254 V_tcp_syncache.cache_limit = 255 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 257 &V_tcp_syncache.cache_limit); 258 259 /* Allocate the hash table. */ 260 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 261 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 262 263 #ifdef VIMAGE 264 V_tcp_syncache.vnet = curvnet; 265 #endif 266 267 /* Initialize the hash buckets. */ 268 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 269 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 270 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 271 NULL, MTX_DEF); 272 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 273 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 274 V_tcp_syncache.hashbase[i].sch_length = 0; 275 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 276 } 277 278 /* Create the syncache entry zone. */ 279 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 280 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 281 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 282 V_tcp_syncache.cache_limit); 283 284 /* Start the SYN cookie reseeder callout. */ 285 callout_init(&V_tcp_syncache.secret.reseed, 1); 286 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 287 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 288 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 289 syncookie_reseed, &V_tcp_syncache); 290 } 291 292 #ifdef VIMAGE 293 void 294 syncache_destroy(void) 295 { 296 struct syncache_head *sch; 297 struct syncache *sc, *nsc; 298 int i; 299 300 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 301 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 302 303 sch = &V_tcp_syncache.hashbase[i]; 304 callout_drain(&sch->sch_timer); 305 306 SCH_LOCK(sch); 307 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 308 syncache_drop(sc, sch); 309 SCH_UNLOCK(sch); 310 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 311 ("%s: sch->sch_bucket not empty", __func__)); 312 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 313 __func__, sch->sch_length)); 314 mtx_destroy(&sch->sch_mtx); 315 } 316 317 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 318 ("%s: cache_count not 0", __func__)); 319 320 /* Free the allocated global resources. */ 321 uma_zdestroy(V_tcp_syncache.zone); 322 free(V_tcp_syncache.hashbase, M_SYNCACHE); 323 324 callout_drain(&V_tcp_syncache.secret.reseed); 325 } 326 #endif 327 328 /* 329 * Inserts a syncache entry into the specified bucket row. 330 * Locks and unlocks the syncache_head autonomously. 331 */ 332 static void 333 syncache_insert(struct syncache *sc, struct syncache_head *sch) 334 { 335 struct syncache *sc2; 336 337 SCH_LOCK(sch); 338 339 /* 340 * Make sure that we don't overflow the per-bucket limit. 341 * If the bucket is full, toss the oldest element. 342 */ 343 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 344 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 345 ("sch->sch_length incorrect")); 346 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 347 syncache_drop(sc2, sch); 348 TCPSTAT_INC(tcps_sc_bucketoverflow); 349 } 350 351 /* Put it into the bucket. */ 352 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 353 sch->sch_length++; 354 355 #ifdef TCP_OFFLOAD 356 if (ADDED_BY_TOE(sc)) { 357 struct toedev *tod = sc->sc_tod; 358 359 tod->tod_syncache_added(tod, sc->sc_todctx); 360 } 361 #endif 362 363 /* Reinitialize the bucket row's timer. */ 364 if (sch->sch_length == 1) 365 sch->sch_nextc = ticks + INT_MAX; 366 syncache_timeout(sc, sch, 1); 367 368 SCH_UNLOCK(sch); 369 370 TCPSTAT_INC(tcps_sc_added); 371 } 372 373 /* 374 * Remove and free entry from syncache bucket row. 375 * Expects locked syncache head. 376 */ 377 static void 378 syncache_drop(struct syncache *sc, struct syncache_head *sch) 379 { 380 381 SCH_LOCK_ASSERT(sch); 382 383 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 384 sch->sch_length--; 385 386 #ifdef TCP_OFFLOAD 387 if (ADDED_BY_TOE(sc)) { 388 struct toedev *tod = sc->sc_tod; 389 390 tod->tod_syncache_removed(tod, sc->sc_todctx); 391 } 392 #endif 393 394 syncache_free(sc); 395 } 396 397 /* 398 * Engage/reengage time on bucket row. 399 */ 400 static void 401 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 402 { 403 sc->sc_rxttime = ticks + 404 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 405 sc->sc_rxmits++; 406 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 407 sch->sch_nextc = sc->sc_rxttime; 408 if (docallout) 409 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 410 syncache_timer, (void *)sch); 411 } 412 } 413 414 /* 415 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 416 * If we have retransmitted an entry the maximum number of times, expire it. 417 * One separate timer for each bucket row. 418 */ 419 static void 420 syncache_timer(void *xsch) 421 { 422 struct syncache_head *sch = (struct syncache_head *)xsch; 423 struct syncache *sc, *nsc; 424 int tick = ticks; 425 char *s; 426 427 CURVNET_SET(sch->sch_sc->vnet); 428 429 /* NB: syncache_head has already been locked by the callout. */ 430 SCH_LOCK_ASSERT(sch); 431 432 /* 433 * In the following cycle we may remove some entries and/or 434 * advance some timeouts, so re-initialize the bucket timer. 435 */ 436 sch->sch_nextc = tick + INT_MAX; 437 438 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 439 /* 440 * We do not check if the listen socket still exists 441 * and accept the case where the listen socket may be 442 * gone by the time we resend the SYN/ACK. We do 443 * not expect this to happens often. If it does, 444 * then the RST will be sent by the time the remote 445 * host does the SYN/ACK->ACK. 446 */ 447 if (TSTMP_GT(sc->sc_rxttime, tick)) { 448 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 449 sch->sch_nextc = sc->sc_rxttime; 450 continue; 451 } 452 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 453 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 454 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 455 "giving up and removing syncache entry\n", 456 s, __func__); 457 free(s, M_TCPLOG); 458 } 459 syncache_drop(sc, sch); 460 TCPSTAT_INC(tcps_sc_stale); 461 continue; 462 } 463 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 464 log(LOG_DEBUG, "%s; %s: Response timeout, " 465 "retransmitting (%u) SYN|ACK\n", 466 s, __func__, sc->sc_rxmits); 467 free(s, M_TCPLOG); 468 } 469 470 syncache_respond(sc, sch, 1); 471 TCPSTAT_INC(tcps_sc_retransmitted); 472 syncache_timeout(sc, sch, 0); 473 } 474 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 475 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 476 syncache_timer, (void *)(sch)); 477 CURVNET_RESTORE(); 478 } 479 480 /* 481 * Find an entry in the syncache. 482 * Returns always with locked syncache_head plus a matching entry or NULL. 483 */ 484 static struct syncache * 485 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 486 { 487 struct syncache *sc; 488 struct syncache_head *sch; 489 490 #ifdef INET6 491 if (inc->inc_flags & INC_ISIPV6) { 492 sch = &V_tcp_syncache.hashbase[ 493 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 494 *schp = sch; 495 496 SCH_LOCK(sch); 497 498 /* Circle through bucket row to find matching entry. */ 499 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 500 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 501 return (sc); 502 } 503 } else 504 #endif 505 { 506 sch = &V_tcp_syncache.hashbase[ 507 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 508 *schp = sch; 509 510 SCH_LOCK(sch); 511 512 /* Circle through bucket row to find matching entry. */ 513 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 514 #ifdef INET6 515 if (sc->sc_inc.inc_flags & INC_ISIPV6) 516 continue; 517 #endif 518 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 519 return (sc); 520 } 521 } 522 SCH_LOCK_ASSERT(*schp); 523 return (NULL); /* always returns with locked sch */ 524 } 525 526 /* 527 * This function is called when we get a RST for a 528 * non-existent connection, so that we can see if the 529 * connection is in the syn cache. If it is, zap it. 530 */ 531 void 532 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 533 { 534 struct syncache *sc; 535 struct syncache_head *sch; 536 char *s = NULL; 537 538 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 539 SCH_LOCK_ASSERT(sch); 540 541 /* 542 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 543 * See RFC 793 page 65, section SEGMENT ARRIVES. 544 */ 545 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 546 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 547 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 548 "FIN flag set, segment ignored\n", s, __func__); 549 TCPSTAT_INC(tcps_badrst); 550 goto done; 551 } 552 553 /* 554 * No corresponding connection was found in syncache. 555 * If syncookies are enabled and possibly exclusively 556 * used, or we are under memory pressure, a valid RST 557 * may not find a syncache entry. In that case we're 558 * done and no SYN|ACK retransmissions will happen. 559 * Otherwise the RST was misdirected or spoofed. 560 */ 561 if (sc == NULL) { 562 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 563 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 564 "syncache entry (possibly syncookie only), " 565 "segment ignored\n", s, __func__); 566 TCPSTAT_INC(tcps_badrst); 567 goto done; 568 } 569 570 /* 571 * If the RST bit is set, check the sequence number to see 572 * if this is a valid reset segment. 573 * RFC 793 page 37: 574 * In all states except SYN-SENT, all reset (RST) segments 575 * are validated by checking their SEQ-fields. A reset is 576 * valid if its sequence number is in the window. 577 * 578 * The sequence number in the reset segment is normally an 579 * echo of our outgoing acknowlegement numbers, but some hosts 580 * send a reset with the sequence number at the rightmost edge 581 * of our receive window, and we have to handle this case. 582 */ 583 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 584 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 585 syncache_drop(sc, sch); 586 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 587 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 588 "connection attempt aborted by remote endpoint\n", 589 s, __func__); 590 TCPSTAT_INC(tcps_sc_reset); 591 } else { 592 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 593 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 594 "IRS %u (+WND %u), segment ignored\n", 595 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 596 TCPSTAT_INC(tcps_badrst); 597 } 598 599 done: 600 if (s != NULL) 601 free(s, M_TCPLOG); 602 SCH_UNLOCK(sch); 603 } 604 605 void 606 syncache_badack(struct in_conninfo *inc) 607 { 608 struct syncache *sc; 609 struct syncache_head *sch; 610 611 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 612 SCH_LOCK_ASSERT(sch); 613 if (sc != NULL) { 614 syncache_drop(sc, sch); 615 TCPSTAT_INC(tcps_sc_badack); 616 } 617 SCH_UNLOCK(sch); 618 } 619 620 void 621 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 622 { 623 struct syncache *sc; 624 struct syncache_head *sch; 625 626 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 627 SCH_LOCK_ASSERT(sch); 628 if (sc == NULL) 629 goto done; 630 631 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 632 if (ntohl(th->th_seq) != sc->sc_iss) 633 goto done; 634 635 /* 636 * If we've rertransmitted 3 times and this is our second error, 637 * we remove the entry. Otherwise, we allow it to continue on. 638 * This prevents us from incorrectly nuking an entry during a 639 * spurious network outage. 640 * 641 * See tcp_notify(). 642 */ 643 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 644 sc->sc_flags |= SCF_UNREACH; 645 goto done; 646 } 647 syncache_drop(sc, sch); 648 TCPSTAT_INC(tcps_sc_unreach); 649 done: 650 SCH_UNLOCK(sch); 651 } 652 653 /* 654 * Build a new TCP socket structure from a syncache entry. 655 */ 656 static struct socket * 657 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 658 { 659 struct inpcb *inp = NULL; 660 struct socket *so; 661 struct tcpcb *tp; 662 int error; 663 char *s; 664 665 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 666 667 /* 668 * Ok, create the full blown connection, and set things up 669 * as they would have been set up if we had created the 670 * connection when the SYN arrived. If we can't create 671 * the connection, abort it. 672 */ 673 so = sonewconn(lso, 0); 674 if (so == NULL) { 675 /* 676 * Drop the connection; we will either send a RST or 677 * have the peer retransmit its SYN again after its 678 * RTO and try again. 679 */ 680 TCPSTAT_INC(tcps_listendrop); 681 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 682 log(LOG_DEBUG, "%s; %s: Socket create failed " 683 "due to limits or memory shortage\n", 684 s, __func__); 685 free(s, M_TCPLOG); 686 } 687 goto abort2; 688 } 689 #ifdef MAC 690 mac_socketpeer_set_from_mbuf(m, so); 691 #endif 692 693 inp = sotoinpcb(so); 694 inp->inp_inc.inc_fibnum = so->so_fibnum; 695 INP_WLOCK(inp); 696 INP_HASH_WLOCK(&V_tcbinfo); 697 698 /* Insert new socket into PCB hash list. */ 699 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 700 #ifdef INET6 701 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 702 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 703 } else { 704 inp->inp_vflag &= ~INP_IPV6; 705 inp->inp_vflag |= INP_IPV4; 706 #endif 707 inp->inp_laddr = sc->sc_inc.inc_laddr; 708 #ifdef INET6 709 } 710 #endif 711 712 /* 713 * If there's an mbuf and it has a flowid, then let's initialise the 714 * inp with that particular flowid. 715 */ 716 if (m != NULL && m->m_flags & M_FLOWID) { 717 inp->inp_flags |= INP_HW_FLOWID; 718 inp->inp_flags &= ~INP_SW_FLOWID; 719 inp->inp_flowid = m->m_pkthdr.flowid; 720 inp->inp_flowtype = M_HASHTYPE_GET(m); 721 } 722 723 /* 724 * Install in the reservation hash table for now, but don't yet 725 * install a connection group since the full 4-tuple isn't yet 726 * configured. 727 */ 728 inp->inp_lport = sc->sc_inc.inc_lport; 729 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 730 /* 731 * Undo the assignments above if we failed to 732 * put the PCB on the hash lists. 733 */ 734 #ifdef INET6 735 if (sc->sc_inc.inc_flags & INC_ISIPV6) 736 inp->in6p_laddr = in6addr_any; 737 else 738 #endif 739 inp->inp_laddr.s_addr = INADDR_ANY; 740 inp->inp_lport = 0; 741 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 742 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 743 "with error %i\n", 744 s, __func__, error); 745 free(s, M_TCPLOG); 746 } 747 INP_HASH_WUNLOCK(&V_tcbinfo); 748 goto abort; 749 } 750 #ifdef IPSEC 751 /* Copy old policy into new socket's. */ 752 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 753 printf("syncache_socket: could not copy policy\n"); 754 #endif 755 #ifdef INET6 756 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 757 struct inpcb *oinp = sotoinpcb(lso); 758 struct in6_addr laddr6; 759 struct sockaddr_in6 sin6; 760 /* 761 * Inherit socket options from the listening socket. 762 * Note that in6p_inputopts are not (and should not be) 763 * copied, since it stores previously received options and is 764 * used to detect if each new option is different than the 765 * previous one and hence should be passed to a user. 766 * If we copied in6p_inputopts, a user would not be able to 767 * receive options just after calling the accept system call. 768 */ 769 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 770 if (oinp->in6p_outputopts) 771 inp->in6p_outputopts = 772 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 773 774 sin6.sin6_family = AF_INET6; 775 sin6.sin6_len = sizeof(sin6); 776 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 777 sin6.sin6_port = sc->sc_inc.inc_fport; 778 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 779 laddr6 = inp->in6p_laddr; 780 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 781 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 782 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 783 thread0.td_ucred, m)) != 0) { 784 inp->in6p_laddr = laddr6; 785 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 786 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 787 "with error %i\n", 788 s, __func__, error); 789 free(s, M_TCPLOG); 790 } 791 INP_HASH_WUNLOCK(&V_tcbinfo); 792 goto abort; 793 } 794 /* Override flowlabel from in6_pcbconnect. */ 795 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 796 inp->inp_flow |= sc->sc_flowlabel; 797 } 798 #endif /* INET6 */ 799 #if defined(INET) && defined(INET6) 800 else 801 #endif 802 #ifdef INET 803 { 804 struct in_addr laddr; 805 struct sockaddr_in sin; 806 807 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 808 809 if (inp->inp_options == NULL) { 810 inp->inp_options = sc->sc_ipopts; 811 sc->sc_ipopts = NULL; 812 } 813 814 sin.sin_family = AF_INET; 815 sin.sin_len = sizeof(sin); 816 sin.sin_addr = sc->sc_inc.inc_faddr; 817 sin.sin_port = sc->sc_inc.inc_fport; 818 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 819 laddr = inp->inp_laddr; 820 if (inp->inp_laddr.s_addr == INADDR_ANY) 821 inp->inp_laddr = sc->sc_inc.inc_laddr; 822 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 823 thread0.td_ucred, m)) != 0) { 824 inp->inp_laddr = laddr; 825 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 826 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 827 "with error %i\n", 828 s, __func__, error); 829 free(s, M_TCPLOG); 830 } 831 INP_HASH_WUNLOCK(&V_tcbinfo); 832 goto abort; 833 } 834 } 835 #endif /* INET */ 836 INP_HASH_WUNLOCK(&V_tcbinfo); 837 tp = intotcpcb(inp); 838 tcp_state_change(tp, TCPS_SYN_RECEIVED); 839 tp->iss = sc->sc_iss; 840 tp->irs = sc->sc_irs; 841 tcp_rcvseqinit(tp); 842 tcp_sendseqinit(tp); 843 tp->snd_wl1 = sc->sc_irs; 844 tp->snd_max = tp->iss + 1; 845 tp->snd_nxt = tp->iss + 1; 846 tp->rcv_up = sc->sc_irs + 1; 847 tp->rcv_wnd = sc->sc_wnd; 848 tp->rcv_adv += tp->rcv_wnd; 849 tp->last_ack_sent = tp->rcv_nxt; 850 851 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 852 if (sc->sc_flags & SCF_NOOPT) 853 tp->t_flags |= TF_NOOPT; 854 else { 855 if (sc->sc_flags & SCF_WINSCALE) { 856 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 857 tp->snd_scale = sc->sc_requested_s_scale; 858 tp->request_r_scale = sc->sc_requested_r_scale; 859 } 860 if (sc->sc_flags & SCF_TIMESTAMP) { 861 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 862 tp->ts_recent = sc->sc_tsreflect; 863 tp->ts_recent_age = tcp_ts_getticks(); 864 tp->ts_offset = sc->sc_tsoff; 865 } 866 #ifdef TCP_SIGNATURE 867 if (sc->sc_flags & SCF_SIGNATURE) 868 tp->t_flags |= TF_SIGNATURE; 869 #endif 870 if (sc->sc_flags & SCF_SACK) 871 tp->t_flags |= TF_SACK_PERMIT; 872 } 873 874 if (sc->sc_flags & SCF_ECN) 875 tp->t_flags |= TF_ECN_PERMIT; 876 877 /* 878 * Set up MSS and get cached values from tcp_hostcache. 879 * This might overwrite some of the defaults we just set. 880 */ 881 tcp_mss(tp, sc->sc_peer_mss); 882 883 /* 884 * If the SYN,ACK was retransmitted, indicate that CWND to be 885 * limited to one segment in cc_conn_init(). 886 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 887 */ 888 if (sc->sc_rxmits > 1) 889 tp->snd_cwnd = 1; 890 891 #ifdef TCP_OFFLOAD 892 /* 893 * Allow a TOE driver to install its hooks. Note that we hold the 894 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 895 * new connection before the TOE driver has done its thing. 896 */ 897 if (ADDED_BY_TOE(sc)) { 898 struct toedev *tod = sc->sc_tod; 899 900 tod->tod_offload_socket(tod, sc->sc_todctx, so); 901 } 902 #endif 903 /* 904 * Copy and activate timers. 905 */ 906 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 907 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 908 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 909 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 910 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 911 912 INP_WUNLOCK(inp); 913 914 soisconnected(so); 915 916 TCPSTAT_INC(tcps_accepts); 917 return (so); 918 919 abort: 920 INP_WUNLOCK(inp); 921 abort2: 922 if (so != NULL) 923 soabort(so); 924 return (NULL); 925 } 926 927 /* 928 * This function gets called when we receive an ACK for a 929 * socket in the LISTEN state. We look up the connection 930 * in the syncache, and if its there, we pull it out of 931 * the cache and turn it into a full-blown connection in 932 * the SYN-RECEIVED state. 933 */ 934 int 935 syncache_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_WLOCK_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); 1077 failed: 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 */ 1099 void 1100 syncache_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 1373 done: 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 1387 static int 1388 syncache_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 */ 1701 static 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 */ 1716 static 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 */ 1722 static uint32_t 1723 syncookie_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, &flags, sizeof(flags)); 1748 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1749 SipHash_Final((u_int8_t *)&siphash, &ctx); 1750 1751 return (siphash[0] ^ siphash[1]); 1752 } 1753 1754 static tcp_seq 1755 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1756 { 1757 u_int i, mss, secbit, wscale; 1758 uint32_t iss, hash; 1759 uint8_t *secbits; 1760 union syncookie cookie; 1761 1762 SCH_LOCK_ASSERT(sch); 1763 1764 cookie.cookie = 0; 1765 1766 /* Map our computed MSS into the 3-bit index. */ 1767 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1768 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1769 tcp_sc_msstab[i] > mss && i > 0; 1770 i--) 1771 ; 1772 cookie.flags.mss_idx = i; 1773 1774 /* 1775 * Map the send window scale into the 3-bit index but only if 1776 * the wscale option was received. 1777 */ 1778 if (sc->sc_flags & SCF_WINSCALE) { 1779 wscale = sc->sc_requested_s_scale; 1780 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1781 tcp_sc_wstab[i] > wscale && i > 0; 1782 i--) 1783 ; 1784 cookie.flags.wscale_idx = i; 1785 } 1786 1787 /* Can we do SACK? */ 1788 if (sc->sc_flags & SCF_SACK) 1789 cookie.flags.sack_ok = 1; 1790 1791 /* Which of the two secrets to use. */ 1792 secbit = sch->sch_sc->secret.oddeven & 0x1; 1793 cookie.flags.odd_even = secbit; 1794 1795 secbits = sch->sch_sc->secret.key[secbit]; 1796 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1797 (uintptr_t)sch); 1798 1799 /* 1800 * Put the flags into the hash and XOR them to get better ISS number 1801 * variance. This doesn't enhance the cryptographic strength and is 1802 * done to prevent the 8 cookie bits from showing up directly on the 1803 * wire. 1804 */ 1805 iss = hash & ~0xff; 1806 iss |= cookie.cookie ^ (hash >> 24); 1807 1808 /* Randomize the timestamp. */ 1809 if (sc->sc_flags & SCF_TIMESTAMP) { 1810 sc->sc_ts = arc4random(); 1811 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1812 } 1813 1814 TCPSTAT_INC(tcps_sc_sendcookie); 1815 return (iss); 1816 } 1817 1818 static struct syncache * 1819 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1820 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1821 struct socket *lso) 1822 { 1823 uint32_t hash; 1824 uint8_t *secbits; 1825 tcp_seq ack, seq; 1826 int wnd, wscale = 0; 1827 union syncookie cookie; 1828 1829 SCH_LOCK_ASSERT(sch); 1830 1831 /* 1832 * Pull information out of SYN-ACK/ACK and revert sequence number 1833 * advances. 1834 */ 1835 ack = th->th_ack - 1; 1836 seq = th->th_seq - 1; 1837 1838 /* 1839 * Unpack the flags containing enough information to restore the 1840 * connection. 1841 */ 1842 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1843 1844 /* Which of the two secrets to use. */ 1845 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1846 1847 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1848 1849 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1850 if ((ack & ~0xff) != (hash & ~0xff)) 1851 return (NULL); 1852 1853 /* Fill in the syncache values. */ 1854 sc->sc_flags = 0; 1855 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1856 sc->sc_ipopts = NULL; 1857 1858 sc->sc_irs = seq; 1859 sc->sc_iss = ack; 1860 1861 switch (inc->inc_flags & INC_ISIPV6) { 1862 #ifdef INET 1863 case 0: 1864 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1865 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1866 break; 1867 #endif 1868 #ifdef INET6 1869 case INC_ISIPV6: 1870 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1871 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1872 break; 1873 #endif 1874 } 1875 1876 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1877 1878 /* We can simply recompute receive window scale we sent earlier. */ 1879 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1880 wscale++; 1881 1882 /* Only use wscale if it was enabled in the orignal SYN. */ 1883 if (cookie.flags.wscale_idx > 0) { 1884 sc->sc_requested_r_scale = wscale; 1885 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1886 sc->sc_flags |= SCF_WINSCALE; 1887 } 1888 1889 wnd = sbspace(&lso->so_rcv); 1890 wnd = imax(wnd, 0); 1891 wnd = imin(wnd, TCP_MAXWIN); 1892 sc->sc_wnd = wnd; 1893 1894 if (cookie.flags.sack_ok) 1895 sc->sc_flags |= SCF_SACK; 1896 1897 if (to->to_flags & TOF_TS) { 1898 sc->sc_flags |= SCF_TIMESTAMP; 1899 sc->sc_tsreflect = to->to_tsval; 1900 sc->sc_ts = to->to_tsecr; 1901 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1902 } 1903 1904 if (to->to_flags & TOF_SIGNATURE) 1905 sc->sc_flags |= SCF_SIGNATURE; 1906 1907 sc->sc_rxmits = 0; 1908 1909 TCPSTAT_INC(tcps_sc_recvcookie); 1910 return (sc); 1911 } 1912 1913 #ifdef INVARIANTS 1914 static int 1915 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1916 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1917 struct socket *lso) 1918 { 1919 struct syncache scs, *scx; 1920 char *s; 1921 1922 bzero(&scs, sizeof(scs)); 1923 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1924 1925 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1926 return (0); 1927 1928 if (scx != NULL) { 1929 if (sc->sc_peer_mss != scx->sc_peer_mss) 1930 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1931 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1932 1933 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1934 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1935 s, __func__, sc->sc_requested_r_scale, 1936 scx->sc_requested_r_scale); 1937 1938 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1939 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1940 s, __func__, sc->sc_requested_s_scale, 1941 scx->sc_requested_s_scale); 1942 1943 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1944 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1945 } 1946 1947 if (s != NULL) 1948 free(s, M_TCPLOG); 1949 return (0); 1950 } 1951 #endif /* INVARIANTS */ 1952 1953 static void 1954 syncookie_reseed(void *arg) 1955 { 1956 struct tcp_syncache *sc = arg; 1957 uint8_t *secbits; 1958 int secbit; 1959 1960 /* 1961 * Reseeding the secret doesn't have to be protected by a lock. 1962 * It only must be ensured that the new random values are visible 1963 * to all CPUs in a SMP environment. The atomic with release 1964 * semantics ensures that. 1965 */ 1966 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1967 secbits = sc->secret.key[secbit]; 1968 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1969 atomic_add_rel_int(&sc->secret.oddeven, 1); 1970 1971 /* Reschedule ourself. */ 1972 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1973 } 1974 1975 /* 1976 * Returns the current number of syncache entries. This number 1977 * will probably change before you get around to calling 1978 * syncache_pcblist. 1979 */ 1980 int 1981 syncache_pcbcount(void) 1982 { 1983 struct syncache_head *sch; 1984 int count, i; 1985 1986 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1987 /* No need to lock for a read. */ 1988 sch = &V_tcp_syncache.hashbase[i]; 1989 count += sch->sch_length; 1990 } 1991 return count; 1992 } 1993 1994 /* 1995 * Exports the syncache entries to userland so that netstat can display 1996 * them alongside the other sockets. This function is intended to be 1997 * called only from tcp_pcblist. 1998 * 1999 * Due to concurrency on an active system, the number of pcbs exported 2000 * may have no relation to max_pcbs. max_pcbs merely indicates the 2001 * amount of space the caller allocated for this function to use. 2002 */ 2003 int 2004 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2005 { 2006 struct xtcpcb xt; 2007 struct syncache *sc; 2008 struct syncache_head *sch; 2009 int count, error, i; 2010 2011 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2012 sch = &V_tcp_syncache.hashbase[i]; 2013 SCH_LOCK(sch); 2014 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2015 if (count >= max_pcbs) { 2016 SCH_UNLOCK(sch); 2017 goto exit; 2018 } 2019 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2020 continue; 2021 bzero(&xt, sizeof(xt)); 2022 xt.xt_len = sizeof(xt); 2023 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2024 xt.xt_inp.inp_vflag = INP_IPV6; 2025 else 2026 xt.xt_inp.inp_vflag = INP_IPV4; 2027 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2028 xt.xt_tp.t_inpcb = &xt.xt_inp; 2029 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2030 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2031 xt.xt_socket.xso_len = sizeof (struct xsocket); 2032 xt.xt_socket.so_type = SOCK_STREAM; 2033 xt.xt_socket.so_state = SS_ISCONNECTING; 2034 error = SYSCTL_OUT(req, &xt, sizeof xt); 2035 if (error) { 2036 SCH_UNLOCK(sch); 2037 goto exit; 2038 } 2039 count++; 2040 } 2041 SCH_UNLOCK(sch); 2042 } 2043 exit: 2044 *pcbs_exported = count; 2045 return error; 2046 } 2047