1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 #include "opt_pcbgroup.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/hash.h> 46 #include <sys/refcount.h> 47 #include <sys/kernel.h> 48 #include <sys/sysctl.h> 49 #include <sys/limits.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/malloc.h> 53 #include <sys/mbuf.h> 54 #include <sys/proc.h> /* for proc0 declaration */ 55 #include <sys/random.h> 56 #include <sys/socket.h> 57 #include <sys/socketvar.h> 58 #include <sys/syslog.h> 59 #include <sys/ucred.h> 60 61 #include <sys/md5.h> 62 #include <crypto/siphash/siphash.h> 63 64 #include <vm/uma.h> 65 66 #include <net/if.h> 67 #include <net/if_var.h> 68 #include <net/route.h> 69 #include <net/vnet.h> 70 71 #include <netinet/in.h> 72 #include <netinet/in_kdtrace.h> 73 #include <netinet/in_systm.h> 74 #include <netinet/ip.h> 75 #include <netinet/in_var.h> 76 #include <netinet/in_pcb.h> 77 #include <netinet/ip_var.h> 78 #include <netinet/ip_options.h> 79 #ifdef INET6 80 #include <netinet/ip6.h> 81 #include <netinet/icmp6.h> 82 #include <netinet6/nd6.h> 83 #include <netinet6/ip6_var.h> 84 #include <netinet6/in6_pcb.h> 85 #endif 86 #include <netinet/tcp.h> 87 #include <netinet/tcp_fastopen.h> 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(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 VNET_DEFINE_STATIC(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 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 119 #define V_functions_inherit_listen_socket_stack \ 120 VNET(functions_inherit_listen_socket_stack) 121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 122 CTLFLAG_VNET | CTLFLAG_RW, 123 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 124 "Inherit listen socket's stack"); 125 126 #ifdef TCP_OFFLOAD 127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 128 #endif 129 130 static void syncache_drop(struct syncache *, struct syncache_head *); 131 static void syncache_free(struct syncache *); 132 static void syncache_insert(struct syncache *, struct syncache_head *); 133 static int syncache_respond(struct syncache *, const struct mbuf *, int); 134 static struct socket *syncache_socket(struct syncache *, struct socket *, 135 struct mbuf *m); 136 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 137 int docallout); 138 static void syncache_timer(void *); 139 140 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 141 uint8_t *, uintptr_t); 142 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 143 static struct syncache 144 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 145 struct syncache *, struct tcphdr *, struct tcpopt *, 146 struct socket *); 147 static void syncache_pause(struct in_conninfo *); 148 static void syncache_unpause(void *); 149 static void syncookie_reseed(void *); 150 #ifdef INVARIANTS 151 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 152 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 153 struct socket *lso); 154 #endif 155 156 /* 157 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 158 * 3 retransmits corresponds to a timeout with default values of 159 * tcp_rexmit_initial * ( 1 + 160 * tcp_backoff[1] + 161 * tcp_backoff[2] + 162 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 163 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 164 * the odds are that the user has given up attempting to connect by then. 165 */ 166 #define SYNCACHE_MAXREXMTS 3 167 168 /* Arbitrary values */ 169 #define TCP_SYNCACHE_HASHSIZE 512 170 #define TCP_SYNCACHE_BUCKETLIMIT 30 171 172 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 173 #define V_tcp_syncache VNET(tcp_syncache) 174 175 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 176 "TCP SYN cache"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.bucket_limit), 0, 180 "Per-bucket hash limit for syncache"); 181 182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 183 &VNET_NAME(tcp_syncache.cache_limit), 0, 184 "Overall entry limit for syncache"); 185 186 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 187 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 188 189 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 190 &VNET_NAME(tcp_syncache.hashsize), 0, 191 "Size of TCP syncache hashtable"); 192 193 static int 194 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 195 { 196 int error; 197 u_int new; 198 199 new = V_tcp_syncache.rexmt_limit; 200 error = sysctl_handle_int(oidp, &new, 0, req); 201 if ((error == 0) && (req->newptr != NULL)) { 202 if (new > TCP_MAXRXTSHIFT) 203 error = EINVAL; 204 else 205 V_tcp_syncache.rexmt_limit = new; 206 } 207 return (error); 208 } 209 210 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 211 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW, 212 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 213 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 214 "Limit on SYN/ACK retransmissions"); 215 216 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 217 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 218 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 219 "Send reset on socket allocation failure"); 220 221 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 222 223 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 224 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 225 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 226 227 /* 228 * Requires the syncache entry to be already removed from the bucket list. 229 */ 230 static void 231 syncache_free(struct syncache *sc) 232 { 233 234 if (sc->sc_ipopts) 235 (void) m_free(sc->sc_ipopts); 236 if (sc->sc_cred) 237 crfree(sc->sc_cred); 238 #ifdef MAC 239 mac_syncache_destroy(&sc->sc_label); 240 #endif 241 242 uma_zfree(V_tcp_syncache.zone, sc); 243 } 244 245 void 246 syncache_init(void) 247 { 248 int i; 249 250 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 251 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 252 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 253 V_tcp_syncache.hash_secret = arc4random(); 254 255 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 256 &V_tcp_syncache.hashsize); 257 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 258 &V_tcp_syncache.bucket_limit); 259 if (!powerof2(V_tcp_syncache.hashsize) || 260 V_tcp_syncache.hashsize == 0) { 261 printf("WARNING: syncache hash size is not a power of 2.\n"); 262 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 263 } 264 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 265 266 /* Set limits. */ 267 V_tcp_syncache.cache_limit = 268 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 269 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 270 &V_tcp_syncache.cache_limit); 271 272 /* Allocate the hash table. */ 273 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 274 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 275 276 #ifdef VIMAGE 277 V_tcp_syncache.vnet = curvnet; 278 #endif 279 280 /* Initialize the hash buckets. */ 281 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 282 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 283 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 284 NULL, MTX_DEF); 285 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 286 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 287 V_tcp_syncache.hashbase[i].sch_length = 0; 288 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 289 V_tcp_syncache.hashbase[i].sch_last_overflow = 290 -(SYNCOOKIE_LIFETIME + 1); 291 } 292 293 /* Create the syncache entry zone. */ 294 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 295 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 296 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 297 V_tcp_syncache.cache_limit); 298 299 /* Start the SYN cookie reseeder callout. */ 300 callout_init(&V_tcp_syncache.secret.reseed, 1); 301 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 302 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 303 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 304 syncookie_reseed, &V_tcp_syncache); 305 306 /* Initialize the pause machinery. */ 307 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 308 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 309 0); 310 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 311 V_tcp_syncache.pause_backoff = 0; 312 V_tcp_syncache.paused = false; 313 } 314 315 #ifdef VIMAGE 316 void 317 syncache_destroy(void) 318 { 319 struct syncache_head *sch; 320 struct syncache *sc, *nsc; 321 int i; 322 323 /* 324 * Stop the re-seed timer before freeing resources. No need to 325 * possibly schedule it another time. 326 */ 327 callout_drain(&V_tcp_syncache.secret.reseed); 328 329 /* Stop the SYN cache pause callout. */ 330 mtx_lock(&V_tcp_syncache.pause_mtx); 331 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 332 mtx_unlock(&V_tcp_syncache.pause_mtx); 333 callout_drain(&V_tcp_syncache.pause_co); 334 } else 335 mtx_unlock(&V_tcp_syncache.pause_mtx); 336 337 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 338 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 339 340 sch = &V_tcp_syncache.hashbase[i]; 341 callout_drain(&sch->sch_timer); 342 343 SCH_LOCK(sch); 344 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 345 syncache_drop(sc, sch); 346 SCH_UNLOCK(sch); 347 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 348 ("%s: sch->sch_bucket not empty", __func__)); 349 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 350 __func__, sch->sch_length)); 351 mtx_destroy(&sch->sch_mtx); 352 } 353 354 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 355 ("%s: cache_count not 0", __func__)); 356 357 /* Free the allocated global resources. */ 358 uma_zdestroy(V_tcp_syncache.zone); 359 free(V_tcp_syncache.hashbase, M_SYNCACHE); 360 mtx_destroy(&V_tcp_syncache.pause_mtx); 361 } 362 #endif 363 364 /* 365 * Inserts a syncache entry into the specified bucket row. 366 * Locks and unlocks the syncache_head autonomously. 367 */ 368 static void 369 syncache_insert(struct syncache *sc, struct syncache_head *sch) 370 { 371 struct syncache *sc2; 372 373 SCH_LOCK(sch); 374 375 /* 376 * Make sure that we don't overflow the per-bucket limit. 377 * If the bucket is full, toss the oldest element. 378 */ 379 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 380 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 381 ("sch->sch_length incorrect")); 382 syncache_pause(&sc->sc_inc); 383 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 384 sch->sch_last_overflow = time_uptime; 385 syncache_drop(sc2, sch); 386 } 387 388 /* Put it into the bucket. */ 389 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 390 sch->sch_length++; 391 392 #ifdef TCP_OFFLOAD 393 if (ADDED_BY_TOE(sc)) { 394 struct toedev *tod = sc->sc_tod; 395 396 tod->tod_syncache_added(tod, sc->sc_todctx); 397 } 398 #endif 399 400 /* Reinitialize the bucket row's timer. */ 401 if (sch->sch_length == 1) 402 sch->sch_nextc = ticks + INT_MAX; 403 syncache_timeout(sc, sch, 1); 404 405 SCH_UNLOCK(sch); 406 407 TCPSTATES_INC(TCPS_SYN_RECEIVED); 408 TCPSTAT_INC(tcps_sc_added); 409 } 410 411 /* 412 * Remove and free entry from syncache bucket row. 413 * Expects locked syncache head. 414 */ 415 static void 416 syncache_drop(struct syncache *sc, struct syncache_head *sch) 417 { 418 419 SCH_LOCK_ASSERT(sch); 420 421 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 422 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 423 sch->sch_length--; 424 425 #ifdef TCP_OFFLOAD 426 if (ADDED_BY_TOE(sc)) { 427 struct toedev *tod = sc->sc_tod; 428 429 tod->tod_syncache_removed(tod, sc->sc_todctx); 430 } 431 #endif 432 433 syncache_free(sc); 434 } 435 436 /* 437 * Engage/reengage time on bucket row. 438 */ 439 static void 440 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 441 { 442 int rexmt; 443 444 if (sc->sc_rxmits == 0) 445 rexmt = tcp_rexmit_initial; 446 else 447 TCPT_RANGESET(rexmt, 448 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 449 tcp_rexmit_min, TCPTV_REXMTMAX); 450 sc->sc_rxttime = ticks + rexmt; 451 sc->sc_rxmits++; 452 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 453 sch->sch_nextc = sc->sc_rxttime; 454 if (docallout) 455 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 456 syncache_timer, (void *)sch); 457 } 458 } 459 460 /* 461 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 462 * If we have retransmitted an entry the maximum number of times, expire it. 463 * One separate timer for each bucket row. 464 */ 465 static void 466 syncache_timer(void *xsch) 467 { 468 struct syncache_head *sch = (struct syncache_head *)xsch; 469 struct syncache *sc, *nsc; 470 int tick = ticks; 471 char *s; 472 bool paused; 473 474 CURVNET_SET(sch->sch_sc->vnet); 475 476 /* NB: syncache_head has already been locked by the callout. */ 477 SCH_LOCK_ASSERT(sch); 478 479 /* 480 * In the following cycle we may remove some entries and/or 481 * advance some timeouts, so re-initialize the bucket timer. 482 */ 483 sch->sch_nextc = tick + INT_MAX; 484 485 /* 486 * If we have paused processing, unconditionally remove 487 * all syncache entries. 488 */ 489 mtx_lock(&V_tcp_syncache.pause_mtx); 490 paused = V_tcp_syncache.paused; 491 mtx_unlock(&V_tcp_syncache.pause_mtx); 492 493 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 494 if (paused) { 495 syncache_drop(sc, sch); 496 continue; 497 } 498 /* 499 * We do not check if the listen socket still exists 500 * and accept the case where the listen socket may be 501 * gone by the time we resend the SYN/ACK. We do 502 * not expect this to happens often. If it does, 503 * then the RST will be sent by the time the remote 504 * host does the SYN/ACK->ACK. 505 */ 506 if (TSTMP_GT(sc->sc_rxttime, tick)) { 507 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 508 sch->sch_nextc = sc->sc_rxttime; 509 continue; 510 } 511 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 512 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 513 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 514 "giving up and removing syncache entry\n", 515 s, __func__); 516 free(s, M_TCPLOG); 517 } 518 syncache_drop(sc, sch); 519 TCPSTAT_INC(tcps_sc_stale); 520 continue; 521 } 522 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 523 log(LOG_DEBUG, "%s; %s: Response timeout, " 524 "retransmitting (%u) SYN|ACK\n", 525 s, __func__, sc->sc_rxmits); 526 free(s, M_TCPLOG); 527 } 528 529 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 530 TCPSTAT_INC(tcps_sc_retransmitted); 531 syncache_timeout(sc, sch, 0); 532 } 533 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 534 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 535 syncache_timer, (void *)(sch)); 536 CURVNET_RESTORE(); 537 } 538 539 /* 540 * Returns true if the system is only using cookies at the moment. 541 * This could be due to a sysadmin decision to only use cookies, or it 542 * could be due to the system detecting an attack. 543 */ 544 static inline bool 545 syncache_cookiesonly(void) 546 { 547 548 return (V_tcp_syncookies && (V_tcp_syncache.paused || 549 V_tcp_syncookiesonly)); 550 } 551 552 /* 553 * Find the hash bucket for the given connection. 554 */ 555 static struct syncache_head * 556 syncache_hashbucket(struct in_conninfo *inc) 557 { 558 uint32_t hash; 559 560 /* 561 * The hash is built on foreign port + local port + foreign address. 562 * We rely on the fact that struct in_conninfo starts with 16 bits 563 * of foreign port, then 16 bits of local port then followed by 128 564 * bits of foreign address. In case of IPv4 address, the first 3 565 * 32-bit words of the address always are zeroes. 566 */ 567 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 568 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 569 570 return (&V_tcp_syncache.hashbase[hash]); 571 } 572 573 /* 574 * Find an entry in the syncache. 575 * Returns always with locked syncache_head plus a matching entry or NULL. 576 */ 577 static struct syncache * 578 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 579 { 580 struct syncache *sc; 581 struct syncache_head *sch; 582 583 *schp = sch = syncache_hashbucket(inc); 584 SCH_LOCK(sch); 585 586 /* Circle through bucket row to find matching entry. */ 587 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 588 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 589 sizeof(struct in_endpoints)) == 0) 590 break; 591 592 return (sc); /* Always returns with locked sch. */ 593 } 594 595 /* 596 * This function is called when we get a RST for a 597 * non-existent connection, so that we can see if the 598 * connection is in the syn cache. If it is, zap it. 599 * If required send a challenge ACK. 600 */ 601 void 602 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m) 603 { 604 struct syncache *sc; 605 struct syncache_head *sch; 606 char *s = NULL; 607 608 if (syncache_cookiesonly()) 609 return; 610 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 611 SCH_LOCK_ASSERT(sch); 612 613 /* 614 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 615 * See RFC 793 page 65, section SEGMENT ARRIVES. 616 */ 617 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 618 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 619 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 620 "FIN flag set, segment ignored\n", s, __func__); 621 TCPSTAT_INC(tcps_badrst); 622 goto done; 623 } 624 625 /* 626 * No corresponding connection was found in syncache. 627 * If syncookies are enabled and possibly exclusively 628 * used, or we are under memory pressure, a valid RST 629 * may not find a syncache entry. In that case we're 630 * done and no SYN|ACK retransmissions will happen. 631 * Otherwise the RST was misdirected or spoofed. 632 */ 633 if (sc == NULL) { 634 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 635 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 636 "syncache entry (possibly syncookie only), " 637 "segment ignored\n", s, __func__); 638 TCPSTAT_INC(tcps_badrst); 639 goto done; 640 } 641 642 /* 643 * If the RST bit is set, check the sequence number to see 644 * if this is a valid reset segment. 645 * 646 * RFC 793 page 37: 647 * In all states except SYN-SENT, all reset (RST) segments 648 * are validated by checking their SEQ-fields. A reset is 649 * valid if its sequence number is in the window. 650 * 651 * RFC 793 page 69: 652 * There are four cases for the acceptability test for an incoming 653 * segment: 654 * 655 * Segment Receive Test 656 * Length Window 657 * ------- ------- ------------------------------------------- 658 * 0 0 SEG.SEQ = RCV.NXT 659 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 660 * >0 0 not acceptable 661 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 662 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 663 * 664 * Note that when receiving a SYN segment in the LISTEN state, 665 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 666 * described in RFC 793, page 66. 667 */ 668 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 669 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 670 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 671 if (V_tcp_insecure_rst || 672 th->th_seq == sc->sc_irs + 1) { 673 syncache_drop(sc, sch); 674 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 675 log(LOG_DEBUG, 676 "%s; %s: Our SYN|ACK was rejected, " 677 "connection attempt aborted by remote " 678 "endpoint\n", 679 s, __func__); 680 TCPSTAT_INC(tcps_sc_reset); 681 } else { 682 TCPSTAT_INC(tcps_badrst); 683 /* Send challenge ACK. */ 684 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 685 log(LOG_DEBUG, "%s; %s: RST with invalid " 686 " SEQ %u != NXT %u (+WND %u), " 687 "sending challenge ACK\n", 688 s, __func__, 689 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 690 syncache_respond(sc, m, TH_ACK); 691 } 692 } else { 693 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 694 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 695 "NXT %u (+WND %u), segment ignored\n", 696 s, __func__, 697 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 698 TCPSTAT_INC(tcps_badrst); 699 } 700 701 done: 702 if (s != NULL) 703 free(s, M_TCPLOG); 704 SCH_UNLOCK(sch); 705 } 706 707 void 708 syncache_badack(struct in_conninfo *inc) 709 { 710 struct syncache *sc; 711 struct syncache_head *sch; 712 713 if (syncache_cookiesonly()) 714 return; 715 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 716 SCH_LOCK_ASSERT(sch); 717 if (sc != NULL) { 718 syncache_drop(sc, sch); 719 TCPSTAT_INC(tcps_sc_badack); 720 } 721 SCH_UNLOCK(sch); 722 } 723 724 void 725 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 726 { 727 struct syncache *sc; 728 struct syncache_head *sch; 729 730 if (syncache_cookiesonly()) 731 return; 732 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 733 SCH_LOCK_ASSERT(sch); 734 if (sc == NULL) 735 goto done; 736 737 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 738 if (ntohl(th_seq) != sc->sc_iss) 739 goto done; 740 741 /* 742 * If we've rertransmitted 3 times and this is our second error, 743 * we remove the entry. Otherwise, we allow it to continue on. 744 * This prevents us from incorrectly nuking an entry during a 745 * spurious network outage. 746 * 747 * See tcp_notify(). 748 */ 749 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 750 sc->sc_flags |= SCF_UNREACH; 751 goto done; 752 } 753 syncache_drop(sc, sch); 754 TCPSTAT_INC(tcps_sc_unreach); 755 done: 756 SCH_UNLOCK(sch); 757 } 758 759 /* 760 * Build a new TCP socket structure from a syncache entry. 761 * 762 * On success return the newly created socket with its underlying inp locked. 763 */ 764 static struct socket * 765 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 766 { 767 struct tcp_function_block *blk; 768 struct inpcb *inp = NULL; 769 struct socket *so; 770 struct tcpcb *tp; 771 int error; 772 char *s; 773 774 NET_EPOCH_ASSERT(); 775 776 /* 777 * Ok, create the full blown connection, and set things up 778 * as they would have been set up if we had created the 779 * connection when the SYN arrived. If we can't create 780 * the connection, abort it. 781 */ 782 so = sonewconn(lso, 0); 783 if (so == NULL) { 784 /* 785 * Drop the connection; we will either send a RST or 786 * have the peer retransmit its SYN again after its 787 * RTO and try again. 788 */ 789 TCPSTAT_INC(tcps_listendrop); 790 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 791 log(LOG_DEBUG, "%s; %s: Socket create failed " 792 "due to limits or memory shortage\n", 793 s, __func__); 794 free(s, M_TCPLOG); 795 } 796 goto abort2; 797 } 798 #ifdef MAC 799 mac_socketpeer_set_from_mbuf(m, so); 800 #endif 801 802 inp = sotoinpcb(so); 803 inp->inp_inc.inc_fibnum = so->so_fibnum; 804 INP_WLOCK(inp); 805 /* 806 * Exclusive pcbinfo lock is not required in syncache socket case even 807 * if two inpcb locks can be acquired simultaneously: 808 * - the inpcb in LISTEN state, 809 * - the newly created inp. 810 * 811 * In this case, an inp cannot be at same time in LISTEN state and 812 * just created by an accept() call. 813 */ 814 INP_HASH_WLOCK(&V_tcbinfo); 815 816 /* Insert new socket into PCB hash list. */ 817 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 818 #ifdef INET6 819 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 820 inp->inp_vflag &= ~INP_IPV4; 821 inp->inp_vflag |= INP_IPV6; 822 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 823 } else { 824 inp->inp_vflag &= ~INP_IPV6; 825 inp->inp_vflag |= INP_IPV4; 826 #endif 827 inp->inp_laddr = sc->sc_inc.inc_laddr; 828 #ifdef INET6 829 } 830 #endif 831 832 /* 833 * If there's an mbuf and it has a flowid, then let's initialise the 834 * inp with that particular flowid. 835 */ 836 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 837 inp->inp_flowid = m->m_pkthdr.flowid; 838 inp->inp_flowtype = M_HASHTYPE_GET(m); 839 #ifdef NUMA 840 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 841 #endif 842 } 843 844 /* 845 * Install in the reservation hash table for now, but don't yet 846 * install a connection group since the full 4-tuple isn't yet 847 * configured. 848 */ 849 inp->inp_lport = sc->sc_inc.inc_lport; 850 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 851 /* 852 * Undo the assignments above if we failed to 853 * put the PCB on the hash lists. 854 */ 855 #ifdef INET6 856 if (sc->sc_inc.inc_flags & INC_ISIPV6) 857 inp->in6p_laddr = in6addr_any; 858 else 859 #endif 860 inp->inp_laddr.s_addr = INADDR_ANY; 861 inp->inp_lport = 0; 862 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 863 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 864 "with error %i\n", 865 s, __func__, error); 866 free(s, M_TCPLOG); 867 } 868 INP_HASH_WUNLOCK(&V_tcbinfo); 869 goto abort; 870 } 871 #ifdef INET6 872 if (inp->inp_vflag & INP_IPV6PROTO) { 873 struct inpcb *oinp = sotoinpcb(lso); 874 875 /* 876 * Inherit socket options from the listening socket. 877 * Note that in6p_inputopts are not (and should not be) 878 * copied, since it stores previously received options and is 879 * used to detect if each new option is different than the 880 * previous one and hence should be passed to a user. 881 * If we copied in6p_inputopts, a user would not be able to 882 * receive options just after calling the accept system call. 883 */ 884 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 885 if (oinp->in6p_outputopts) 886 inp->in6p_outputopts = 887 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 888 } 889 890 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 891 struct in6_addr laddr6; 892 struct sockaddr_in6 sin6; 893 894 sin6.sin6_family = AF_INET6; 895 sin6.sin6_len = sizeof(sin6); 896 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 897 sin6.sin6_port = sc->sc_inc.inc_fport; 898 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 899 laddr6 = inp->in6p_laddr; 900 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 901 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 902 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 903 thread0.td_ucred, m)) != 0) { 904 inp->in6p_laddr = laddr6; 905 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 906 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 907 "with error %i\n", 908 s, __func__, error); 909 free(s, M_TCPLOG); 910 } 911 INP_HASH_WUNLOCK(&V_tcbinfo); 912 goto abort; 913 } 914 /* Override flowlabel from in6_pcbconnect. */ 915 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 916 inp->inp_flow |= sc->sc_flowlabel; 917 } 918 #endif /* INET6 */ 919 #if defined(INET) && defined(INET6) 920 else 921 #endif 922 #ifdef INET 923 { 924 struct in_addr laddr; 925 struct sockaddr_in sin; 926 927 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 928 929 if (inp->inp_options == NULL) { 930 inp->inp_options = sc->sc_ipopts; 931 sc->sc_ipopts = NULL; 932 } 933 934 sin.sin_family = AF_INET; 935 sin.sin_len = sizeof(sin); 936 sin.sin_addr = sc->sc_inc.inc_faddr; 937 sin.sin_port = sc->sc_inc.inc_fport; 938 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 939 laddr = inp->inp_laddr; 940 if (inp->inp_laddr.s_addr == INADDR_ANY) 941 inp->inp_laddr = sc->sc_inc.inc_laddr; 942 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 943 thread0.td_ucred, m)) != 0) { 944 inp->inp_laddr = laddr; 945 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 946 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 947 "with error %i\n", 948 s, __func__, error); 949 free(s, M_TCPLOG); 950 } 951 INP_HASH_WUNLOCK(&V_tcbinfo); 952 goto abort; 953 } 954 } 955 #endif /* INET */ 956 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 957 /* Copy old policy into new socket's. */ 958 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 959 printf("syncache_socket: could not copy policy\n"); 960 #endif 961 INP_HASH_WUNLOCK(&V_tcbinfo); 962 tp = intotcpcb(inp); 963 tcp_state_change(tp, TCPS_SYN_RECEIVED); 964 tp->iss = sc->sc_iss; 965 tp->irs = sc->sc_irs; 966 tcp_rcvseqinit(tp); 967 tcp_sendseqinit(tp); 968 blk = sototcpcb(lso)->t_fb; 969 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 970 /* 971 * Our parents t_fb was not the default, 972 * we need to release our ref on tp->t_fb and 973 * pickup one on the new entry. 974 */ 975 struct tcp_function_block *rblk; 976 977 rblk = find_and_ref_tcp_fb(blk); 978 KASSERT(rblk != NULL, 979 ("cannot find blk %p out of syncache?", blk)); 980 if (tp->t_fb->tfb_tcp_fb_fini) 981 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 982 refcount_release(&tp->t_fb->tfb_refcnt); 983 tp->t_fb = rblk; 984 /* 985 * XXXrrs this is quite dangerous, it is possible 986 * for the new function to fail to init. We also 987 * are not asking if the handoff_is_ok though at 988 * the very start thats probalbly ok. 989 */ 990 if (tp->t_fb->tfb_tcp_fb_init) { 991 (*tp->t_fb->tfb_tcp_fb_init)(tp); 992 } 993 } 994 tp->snd_wl1 = sc->sc_irs; 995 tp->snd_max = tp->iss + 1; 996 tp->snd_nxt = tp->iss + 1; 997 tp->rcv_up = sc->sc_irs + 1; 998 tp->rcv_wnd = sc->sc_wnd; 999 tp->rcv_adv += tp->rcv_wnd; 1000 tp->last_ack_sent = tp->rcv_nxt; 1001 1002 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 1003 if (sc->sc_flags & SCF_NOOPT) 1004 tp->t_flags |= TF_NOOPT; 1005 else { 1006 if (sc->sc_flags & SCF_WINSCALE) { 1007 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 1008 tp->snd_scale = sc->sc_requested_s_scale; 1009 tp->request_r_scale = sc->sc_requested_r_scale; 1010 } 1011 if (sc->sc_flags & SCF_TIMESTAMP) { 1012 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 1013 tp->ts_recent = sc->sc_tsreflect; 1014 tp->ts_recent_age = tcp_ts_getticks(); 1015 tp->ts_offset = sc->sc_tsoff; 1016 } 1017 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1018 if (sc->sc_flags & SCF_SIGNATURE) 1019 tp->t_flags |= TF_SIGNATURE; 1020 #endif 1021 if (sc->sc_flags & SCF_SACK) 1022 tp->t_flags |= TF_SACK_PERMIT; 1023 } 1024 1025 if (sc->sc_flags & SCF_ECN) 1026 tp->t_flags2 |= TF2_ECN_PERMIT; 1027 1028 /* 1029 * Set up MSS and get cached values from tcp_hostcache. 1030 * This might overwrite some of the defaults we just set. 1031 */ 1032 tcp_mss(tp, sc->sc_peer_mss); 1033 1034 /* 1035 * If the SYN,ACK was retransmitted, indicate that CWND to be 1036 * limited to one segment in cc_conn_init(). 1037 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1038 */ 1039 if (sc->sc_rxmits > 1) 1040 tp->snd_cwnd = 1; 1041 1042 #ifdef TCP_OFFLOAD 1043 /* 1044 * Allow a TOE driver to install its hooks. Note that we hold the 1045 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1046 * new connection before the TOE driver has done its thing. 1047 */ 1048 if (ADDED_BY_TOE(sc)) { 1049 struct toedev *tod = sc->sc_tod; 1050 1051 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1052 } 1053 #endif 1054 /* 1055 * Copy and activate timers. 1056 */ 1057 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1058 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1059 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1060 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1061 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1062 1063 TCPSTAT_INC(tcps_accepts); 1064 return (so); 1065 1066 abort: 1067 INP_WUNLOCK(inp); 1068 abort2: 1069 if (so != NULL) 1070 soabort(so); 1071 return (NULL); 1072 } 1073 1074 /* 1075 * This function gets called when we receive an ACK for a 1076 * socket in the LISTEN state. We look up the connection 1077 * in the syncache, and if its there, we pull it out of 1078 * the cache and turn it into a full-blown connection in 1079 * the SYN-RECEIVED state. 1080 * 1081 * On syncache_socket() success the newly created socket 1082 * has its underlying inp locked. 1083 */ 1084 int 1085 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1086 struct socket **lsop, struct mbuf *m) 1087 { 1088 struct syncache *sc; 1089 struct syncache_head *sch; 1090 struct syncache scs; 1091 char *s; 1092 bool locked; 1093 1094 NET_EPOCH_ASSERT(); 1095 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1096 ("%s: can handle only ACK", __func__)); 1097 1098 if (syncache_cookiesonly()) { 1099 sc = NULL; 1100 sch = syncache_hashbucket(inc); 1101 locked = false; 1102 } else { 1103 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1104 locked = true; 1105 SCH_LOCK_ASSERT(sch); 1106 } 1107 1108 #ifdef INVARIANTS 1109 /* 1110 * Test code for syncookies comparing the syncache stored 1111 * values with the reconstructed values from the cookie. 1112 */ 1113 if (sc != NULL) 1114 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1115 #endif 1116 1117 if (sc == NULL) { 1118 /* 1119 * There is no syncache entry, so see if this ACK is 1120 * a returning syncookie. To do this, first: 1121 * A. Check if syncookies are used in case of syncache 1122 * overflows 1123 * B. See if this socket has had a syncache entry dropped in 1124 * the recent past. We don't want to accept a bogus 1125 * syncookie if we've never received a SYN or accept it 1126 * twice. 1127 * C. check that the syncookie is valid. If it is, then 1128 * cobble up a fake syncache entry, and return. 1129 */ 1130 if (locked && !V_tcp_syncookies) { 1131 SCH_UNLOCK(sch); 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1133 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1134 "segment rejected (syncookies disabled)\n", 1135 s, __func__); 1136 goto failed; 1137 } 1138 if (locked && !V_tcp_syncookiesonly && 1139 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1140 SCH_UNLOCK(sch); 1141 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1142 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1143 "segment rejected (no syncache entry)\n", 1144 s, __func__); 1145 goto failed; 1146 } 1147 bzero(&scs, sizeof(scs)); 1148 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1149 if (locked) 1150 SCH_UNLOCK(sch); 1151 if (sc == NULL) { 1152 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1153 log(LOG_DEBUG, "%s; %s: Segment failed " 1154 "SYNCOOKIE authentication, segment rejected " 1155 "(probably spoofed)\n", s, __func__); 1156 goto failed; 1157 } 1158 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1159 /* If received ACK has MD5 signature, check it. */ 1160 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1161 (!TCPMD5_ENABLED() || 1162 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1163 /* Drop the ACK. */ 1164 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1165 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1166 "MD5 signature doesn't match.\n", 1167 s, __func__); 1168 free(s, M_TCPLOG); 1169 } 1170 TCPSTAT_INC(tcps_sig_err_sigopt); 1171 return (-1); /* Do not send RST */ 1172 } 1173 #endif /* TCP_SIGNATURE */ 1174 } else { 1175 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1176 /* 1177 * If listening socket requested TCP digests, check that 1178 * received ACK has signature and it is correct. 1179 * If not, drop the ACK and leave sc entry in th cache, 1180 * because SYN was received with correct signature. 1181 */ 1182 if (sc->sc_flags & SCF_SIGNATURE) { 1183 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1184 /* No signature */ 1185 TCPSTAT_INC(tcps_sig_err_nosigopt); 1186 SCH_UNLOCK(sch); 1187 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1188 log(LOG_DEBUG, "%s; %s: Segment " 1189 "rejected, MD5 signature wasn't " 1190 "provided.\n", s, __func__); 1191 free(s, M_TCPLOG); 1192 } 1193 return (-1); /* Do not send RST */ 1194 } 1195 if (!TCPMD5_ENABLED() || 1196 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1197 /* Doesn't match or no SA */ 1198 SCH_UNLOCK(sch); 1199 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1200 log(LOG_DEBUG, "%s; %s: Segment " 1201 "rejected, MD5 signature doesn't " 1202 "match.\n", s, __func__); 1203 free(s, M_TCPLOG); 1204 } 1205 return (-1); /* Do not send RST */ 1206 } 1207 } 1208 #endif /* TCP_SIGNATURE */ 1209 1210 /* 1211 * RFC 7323 PAWS: If we have a timestamp on this segment and 1212 * it's less than ts_recent, drop it. 1213 * XXXMT: RFC 7323 also requires to send an ACK. 1214 * In tcp_input.c this is only done for TCP segments 1215 * with user data, so be consistent here and just drop 1216 * the segment. 1217 */ 1218 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1219 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1220 SCH_UNLOCK(sch); 1221 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1222 log(LOG_DEBUG, 1223 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1224 "segment dropped\n", s, __func__, 1225 to->to_tsval, sc->sc_tsreflect); 1226 free(s, M_TCPLOG); 1227 } 1228 return (-1); /* Do not send RST */ 1229 } 1230 1231 /* 1232 * Pull out the entry to unlock the bucket row. 1233 * 1234 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1235 * tcp_state_change(). The tcpcb is not existent at this 1236 * moment. A new one will be allocated via syncache_socket-> 1237 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1238 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1239 */ 1240 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1241 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1242 sch->sch_length--; 1243 #ifdef TCP_OFFLOAD 1244 if (ADDED_BY_TOE(sc)) { 1245 struct toedev *tod = sc->sc_tod; 1246 1247 tod->tod_syncache_removed(tod, sc->sc_todctx); 1248 } 1249 #endif 1250 SCH_UNLOCK(sch); 1251 } 1252 1253 /* 1254 * Segment validation: 1255 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1256 */ 1257 if (th->th_ack != sc->sc_iss + 1) { 1258 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1259 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1260 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1261 goto failed; 1262 } 1263 1264 /* 1265 * The SEQ must fall in the window starting at the received 1266 * initial receive sequence number + 1 (the SYN). 1267 */ 1268 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1269 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1270 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1271 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1272 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1273 goto failed; 1274 } 1275 1276 /* 1277 * If timestamps were not negotiated during SYN/ACK they 1278 * must not appear on any segment during this session. 1279 */ 1280 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1281 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1282 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1283 "segment rejected\n", s, __func__); 1284 goto failed; 1285 } 1286 1287 /* 1288 * If timestamps were negotiated during SYN/ACK they should 1289 * appear on every segment during this session. 1290 * XXXAO: This is only informal as there have been unverified 1291 * reports of non-compliants stacks. 1292 */ 1293 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1294 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1295 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1296 "no action\n", s, __func__); 1297 free(s, M_TCPLOG); 1298 s = NULL; 1299 } 1300 } 1301 1302 *lsop = syncache_socket(sc, *lsop, m); 1303 1304 if (*lsop == NULL) 1305 TCPSTAT_INC(tcps_sc_aborted); 1306 else 1307 TCPSTAT_INC(tcps_sc_completed); 1308 1309 /* how do we find the inp for the new socket? */ 1310 if (sc != &scs) 1311 syncache_free(sc); 1312 return (1); 1313 failed: 1314 if (sc != NULL && sc != &scs) 1315 syncache_free(sc); 1316 if (s != NULL) 1317 free(s, M_TCPLOG); 1318 *lsop = NULL; 1319 return (0); 1320 } 1321 1322 static void 1323 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1324 uint64_t response_cookie) 1325 { 1326 struct inpcb *inp; 1327 struct tcpcb *tp; 1328 unsigned int *pending_counter; 1329 1330 NET_EPOCH_ASSERT(); 1331 1332 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1333 *lsop = syncache_socket(sc, *lsop, m); 1334 if (*lsop == NULL) { 1335 TCPSTAT_INC(tcps_sc_aborted); 1336 atomic_subtract_int(pending_counter, 1); 1337 } else { 1338 soisconnected(*lsop); 1339 inp = sotoinpcb(*lsop); 1340 tp = intotcpcb(inp); 1341 tp->t_flags |= TF_FASTOPEN; 1342 tp->t_tfo_cookie.server = response_cookie; 1343 tp->snd_max = tp->iss; 1344 tp->snd_nxt = tp->iss; 1345 tp->t_tfo_pending = pending_counter; 1346 TCPSTAT_INC(tcps_sc_completed); 1347 } 1348 } 1349 1350 /* 1351 * Given a LISTEN socket and an inbound SYN request, add 1352 * this to the syn cache, and send back a segment: 1353 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1354 * to the source. 1355 * 1356 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1357 * Doing so would require that we hold onto the data and deliver it 1358 * to the application. However, if we are the target of a SYN-flood 1359 * DoS attack, an attacker could send data which would eventually 1360 * consume all available buffer space if it were ACKed. By not ACKing 1361 * the data, we avoid this DoS scenario. 1362 * 1363 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1364 * cookie is processed and a new socket is created. In this case, any data 1365 * accompanying the SYN will be queued to the socket by tcp_input() and will 1366 * be ACKed either when the application sends response data or the delayed 1367 * ACK timer expires, whichever comes first. 1368 */ 1369 int 1370 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1371 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1372 void *todctx, uint8_t iptos) 1373 { 1374 struct tcpcb *tp; 1375 struct socket *so; 1376 struct syncache *sc = NULL; 1377 struct syncache_head *sch; 1378 struct mbuf *ipopts = NULL; 1379 u_int ltflags; 1380 int win, ip_ttl, ip_tos; 1381 char *s; 1382 int rv = 0; 1383 #ifdef INET6 1384 int autoflowlabel = 0; 1385 #endif 1386 #ifdef MAC 1387 struct label *maclabel; 1388 #endif 1389 struct syncache scs; 1390 struct ucred *cred; 1391 uint64_t tfo_response_cookie; 1392 unsigned int *tfo_pending = NULL; 1393 int tfo_cookie_valid = 0; 1394 int tfo_response_cookie_valid = 0; 1395 bool locked; 1396 1397 INP_WLOCK_ASSERT(inp); /* listen socket */ 1398 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1399 ("%s: unexpected tcp flags", __func__)); 1400 1401 /* 1402 * Combine all so/tp operations very early to drop the INP lock as 1403 * soon as possible. 1404 */ 1405 so = *lsop; 1406 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1407 tp = sototcpcb(so); 1408 cred = crhold(so->so_cred); 1409 1410 #ifdef INET6 1411 if ((inc->inc_flags & INC_ISIPV6) && 1412 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1413 autoflowlabel = 1; 1414 #endif 1415 ip_ttl = inp->inp_ip_ttl; 1416 ip_tos = inp->inp_ip_tos; 1417 win = so->sol_sbrcv_hiwat; 1418 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1419 1420 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1421 (tp->t_tfo_pending != NULL) && 1422 (to->to_flags & TOF_FASTOPEN)) { 1423 /* 1424 * Limit the number of pending TFO connections to 1425 * approximately half of the queue limit. This prevents TFO 1426 * SYN floods from starving the service by filling the 1427 * listen queue with bogus TFO connections. 1428 */ 1429 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1430 (so->sol_qlimit / 2)) { 1431 int result; 1432 1433 result = tcp_fastopen_check_cookie(inc, 1434 to->to_tfo_cookie, to->to_tfo_len, 1435 &tfo_response_cookie); 1436 tfo_cookie_valid = (result > 0); 1437 tfo_response_cookie_valid = (result >= 0); 1438 } 1439 1440 /* 1441 * Remember the TFO pending counter as it will have to be 1442 * decremented below if we don't make it to syncache_tfo_expand(). 1443 */ 1444 tfo_pending = tp->t_tfo_pending; 1445 } 1446 1447 /* By the time we drop the lock these should no longer be used. */ 1448 so = NULL; 1449 tp = NULL; 1450 1451 #ifdef MAC 1452 if (mac_syncache_init(&maclabel) != 0) { 1453 INP_WUNLOCK(inp); 1454 goto done; 1455 } else 1456 mac_syncache_create(maclabel, inp); 1457 #endif 1458 if (!tfo_cookie_valid) 1459 INP_WUNLOCK(inp); 1460 1461 /* 1462 * Remember the IP options, if any. 1463 */ 1464 #ifdef INET6 1465 if (!(inc->inc_flags & INC_ISIPV6)) 1466 #endif 1467 #ifdef INET 1468 ipopts = (m) ? ip_srcroute(m) : NULL; 1469 #else 1470 ipopts = NULL; 1471 #endif 1472 1473 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1474 /* 1475 * If listening socket requested TCP digests, check that received 1476 * SYN has signature and it is correct. If signature doesn't match 1477 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1478 */ 1479 if (ltflags & TF_SIGNATURE) { 1480 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1481 TCPSTAT_INC(tcps_sig_err_nosigopt); 1482 goto done; 1483 } 1484 if (!TCPMD5_ENABLED() || 1485 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1486 goto done; 1487 } 1488 #endif /* TCP_SIGNATURE */ 1489 /* 1490 * See if we already have an entry for this connection. 1491 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1492 * 1493 * XXX: should the syncache be re-initialized with the contents 1494 * of the new SYN here (which may have different options?) 1495 * 1496 * XXX: We do not check the sequence number to see if this is a 1497 * real retransmit or a new connection attempt. The question is 1498 * how to handle such a case; either ignore it as spoofed, or 1499 * drop the current entry and create a new one? 1500 */ 1501 if (syncache_cookiesonly()) { 1502 sc = NULL; 1503 sch = syncache_hashbucket(inc); 1504 locked = false; 1505 } else { 1506 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1507 locked = true; 1508 SCH_LOCK_ASSERT(sch); 1509 } 1510 if (sc != NULL) { 1511 if (tfo_cookie_valid) 1512 INP_WUNLOCK(inp); 1513 TCPSTAT_INC(tcps_sc_dupsyn); 1514 if (ipopts) { 1515 /* 1516 * If we were remembering a previous source route, 1517 * forget it and use the new one we've been given. 1518 */ 1519 if (sc->sc_ipopts) 1520 (void) m_free(sc->sc_ipopts); 1521 sc->sc_ipopts = ipopts; 1522 } 1523 /* 1524 * Update timestamp if present. 1525 */ 1526 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1527 sc->sc_tsreflect = to->to_tsval; 1528 else 1529 sc->sc_flags &= ~SCF_TIMESTAMP; 1530 #ifdef MAC 1531 /* 1532 * Since we have already unconditionally allocated label 1533 * storage, free it up. The syncache entry will already 1534 * have an initialized label we can use. 1535 */ 1536 mac_syncache_destroy(&maclabel); 1537 #endif 1538 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1539 /* Retransmit SYN|ACK and reset retransmit count. */ 1540 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1541 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1542 "resetting timer and retransmitting SYN|ACK\n", 1543 s, __func__); 1544 free(s, M_TCPLOG); 1545 } 1546 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1547 sc->sc_rxmits = 0; 1548 syncache_timeout(sc, sch, 1); 1549 TCPSTAT_INC(tcps_sndacks); 1550 TCPSTAT_INC(tcps_sndtotal); 1551 } 1552 SCH_UNLOCK(sch); 1553 goto donenoprobe; 1554 } 1555 1556 if (tfo_cookie_valid) { 1557 bzero(&scs, sizeof(scs)); 1558 sc = &scs; 1559 goto skip_alloc; 1560 } 1561 1562 /* 1563 * Skip allocating a syncache entry if we are just going to discard 1564 * it later. 1565 */ 1566 if (!locked) { 1567 bzero(&scs, sizeof(scs)); 1568 sc = &scs; 1569 } else 1570 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1571 if (sc == NULL) { 1572 /* 1573 * The zone allocator couldn't provide more entries. 1574 * Treat this as if the cache was full; drop the oldest 1575 * entry and insert the new one. 1576 */ 1577 TCPSTAT_INC(tcps_sc_zonefail); 1578 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1579 sch->sch_last_overflow = time_uptime; 1580 syncache_drop(sc, sch); 1581 syncache_pause(inc); 1582 } 1583 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1584 if (sc == NULL) { 1585 if (V_tcp_syncookies) { 1586 bzero(&scs, sizeof(scs)); 1587 sc = &scs; 1588 } else { 1589 KASSERT(locked, 1590 ("%s: bucket unexpectedly unlocked", 1591 __func__)); 1592 SCH_UNLOCK(sch); 1593 if (ipopts) 1594 (void) m_free(ipopts); 1595 goto done; 1596 } 1597 } 1598 } 1599 1600 skip_alloc: 1601 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1602 sc->sc_tfo_cookie = &tfo_response_cookie; 1603 1604 /* 1605 * Fill in the syncache values. 1606 */ 1607 #ifdef MAC 1608 sc->sc_label = maclabel; 1609 #endif 1610 sc->sc_cred = cred; 1611 cred = NULL; 1612 sc->sc_ipopts = ipopts; 1613 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1614 #ifdef INET6 1615 if (!(inc->inc_flags & INC_ISIPV6)) 1616 #endif 1617 { 1618 sc->sc_ip_tos = ip_tos; 1619 sc->sc_ip_ttl = ip_ttl; 1620 } 1621 #ifdef TCP_OFFLOAD 1622 sc->sc_tod = tod; 1623 sc->sc_todctx = todctx; 1624 #endif 1625 sc->sc_irs = th->th_seq; 1626 sc->sc_flags = 0; 1627 sc->sc_flowlabel = 0; 1628 1629 /* 1630 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1631 * win was derived from socket earlier in the function. 1632 */ 1633 win = imax(win, 0); 1634 win = imin(win, TCP_MAXWIN); 1635 sc->sc_wnd = win; 1636 1637 if (V_tcp_do_rfc1323) { 1638 /* 1639 * A timestamp received in a SYN makes 1640 * it ok to send timestamp requests and replies. 1641 */ 1642 if (to->to_flags & TOF_TS) { 1643 sc->sc_tsreflect = to->to_tsval; 1644 sc->sc_flags |= SCF_TIMESTAMP; 1645 sc->sc_tsoff = tcp_new_ts_offset(inc); 1646 } 1647 if (to->to_flags & TOF_SCALE) { 1648 int wscale = 0; 1649 1650 /* 1651 * Pick the smallest possible scaling factor that 1652 * will still allow us to scale up to sb_max, aka 1653 * kern.ipc.maxsockbuf. 1654 * 1655 * We do this because there are broken firewalls that 1656 * will corrupt the window scale option, leading to 1657 * the other endpoint believing that our advertised 1658 * window is unscaled. At scale factors larger than 1659 * 5 the unscaled window will drop below 1500 bytes, 1660 * leading to serious problems when traversing these 1661 * broken firewalls. 1662 * 1663 * With the default maxsockbuf of 256K, a scale factor 1664 * of 3 will be chosen by this algorithm. Those who 1665 * choose a larger maxsockbuf should watch out 1666 * for the compatibility problems mentioned above. 1667 * 1668 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1669 * or <SYN,ACK>) segment itself is never scaled. 1670 */ 1671 while (wscale < TCP_MAX_WINSHIFT && 1672 (TCP_MAXWIN << wscale) < sb_max) 1673 wscale++; 1674 sc->sc_requested_r_scale = wscale; 1675 sc->sc_requested_s_scale = to->to_wscale; 1676 sc->sc_flags |= SCF_WINSCALE; 1677 } 1678 } 1679 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1680 /* 1681 * If listening socket requested TCP digests, flag this in the 1682 * syncache so that syncache_respond() will do the right thing 1683 * with the SYN+ACK. 1684 */ 1685 if (ltflags & TF_SIGNATURE) 1686 sc->sc_flags |= SCF_SIGNATURE; 1687 #endif /* TCP_SIGNATURE */ 1688 if (to->to_flags & TOF_SACKPERM) 1689 sc->sc_flags |= SCF_SACK; 1690 if (to->to_flags & TOF_MSS) 1691 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1692 if (ltflags & TF_NOOPT) 1693 sc->sc_flags |= SCF_NOOPT; 1694 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1695 sc->sc_flags |= SCF_ECN; 1696 1697 if (V_tcp_syncookies) 1698 sc->sc_iss = syncookie_generate(sch, sc); 1699 else 1700 sc->sc_iss = arc4random(); 1701 #ifdef INET6 1702 if (autoflowlabel) { 1703 if (V_tcp_syncookies) 1704 sc->sc_flowlabel = sc->sc_iss; 1705 else 1706 sc->sc_flowlabel = ip6_randomflowlabel(); 1707 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1708 } 1709 #endif 1710 if (locked) 1711 SCH_UNLOCK(sch); 1712 1713 if (tfo_cookie_valid) { 1714 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1715 /* INP_WUNLOCK(inp) will be performed by the caller */ 1716 rv = 1; 1717 goto tfo_expanded; 1718 } 1719 1720 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1721 /* 1722 * Do a standard 3-way handshake. 1723 */ 1724 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1725 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1726 syncache_free(sc); 1727 else if (sc != &scs) 1728 syncache_insert(sc, sch); /* locks and unlocks sch */ 1729 TCPSTAT_INC(tcps_sndacks); 1730 TCPSTAT_INC(tcps_sndtotal); 1731 } else { 1732 if (sc != &scs) 1733 syncache_free(sc); 1734 TCPSTAT_INC(tcps_sc_dropped); 1735 } 1736 goto donenoprobe; 1737 1738 done: 1739 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1740 donenoprobe: 1741 if (m) { 1742 *lsop = NULL; 1743 m_freem(m); 1744 } 1745 /* 1746 * If tfo_pending is not NULL here, then a TFO SYN that did not 1747 * result in a new socket was processed and the associated pending 1748 * counter has not yet been decremented. All such TFO processing paths 1749 * transit this point. 1750 */ 1751 if (tfo_pending != NULL) 1752 tcp_fastopen_decrement_counter(tfo_pending); 1753 1754 tfo_expanded: 1755 if (cred != NULL) 1756 crfree(cred); 1757 #ifdef MAC 1758 if (sc == &scs) 1759 mac_syncache_destroy(&maclabel); 1760 #endif 1761 return (rv); 1762 } 1763 1764 /* 1765 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1766 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1767 */ 1768 static int 1769 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1770 { 1771 struct ip *ip = NULL; 1772 struct mbuf *m; 1773 struct tcphdr *th = NULL; 1774 int optlen, error = 0; /* Make compiler happy */ 1775 u_int16_t hlen, tlen, mssopt; 1776 struct tcpopt to; 1777 #ifdef INET6 1778 struct ip6_hdr *ip6 = NULL; 1779 #endif 1780 hlen = 1781 #ifdef INET6 1782 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1783 #endif 1784 sizeof(struct ip); 1785 tlen = hlen + sizeof(struct tcphdr); 1786 1787 /* Determine MSS we advertize to other end of connection. */ 1788 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1789 1790 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1791 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1792 ("syncache: mbuf too small")); 1793 1794 /* Create the IP+TCP header from scratch. */ 1795 m = m_gethdr(M_NOWAIT, MT_DATA); 1796 if (m == NULL) 1797 return (ENOBUFS); 1798 #ifdef MAC 1799 mac_syncache_create_mbuf(sc->sc_label, m); 1800 #endif 1801 m->m_data += max_linkhdr; 1802 m->m_len = tlen; 1803 m->m_pkthdr.len = tlen; 1804 m->m_pkthdr.rcvif = NULL; 1805 1806 #ifdef INET6 1807 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1808 ip6 = mtod(m, struct ip6_hdr *); 1809 ip6->ip6_vfc = IPV6_VERSION; 1810 ip6->ip6_nxt = IPPROTO_TCP; 1811 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1812 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1813 ip6->ip6_plen = htons(tlen - hlen); 1814 /* ip6_hlim is set after checksum */ 1815 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1816 ip6->ip6_flow |= sc->sc_flowlabel; 1817 1818 th = (struct tcphdr *)(ip6 + 1); 1819 } 1820 #endif 1821 #if defined(INET6) && defined(INET) 1822 else 1823 #endif 1824 #ifdef INET 1825 { 1826 ip = mtod(m, struct ip *); 1827 ip->ip_v = IPVERSION; 1828 ip->ip_hl = sizeof(struct ip) >> 2; 1829 ip->ip_len = htons(tlen); 1830 ip->ip_id = 0; 1831 ip->ip_off = 0; 1832 ip->ip_sum = 0; 1833 ip->ip_p = IPPROTO_TCP; 1834 ip->ip_src = sc->sc_inc.inc_laddr; 1835 ip->ip_dst = sc->sc_inc.inc_faddr; 1836 ip->ip_ttl = sc->sc_ip_ttl; 1837 ip->ip_tos = sc->sc_ip_tos; 1838 1839 /* 1840 * See if we should do MTU discovery. Route lookups are 1841 * expensive, so we will only unset the DF bit if: 1842 * 1843 * 1) path_mtu_discovery is disabled 1844 * 2) the SCF_UNREACH flag has been set 1845 */ 1846 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1847 ip->ip_off |= htons(IP_DF); 1848 1849 th = (struct tcphdr *)(ip + 1); 1850 } 1851 #endif /* INET */ 1852 th->th_sport = sc->sc_inc.inc_lport; 1853 th->th_dport = sc->sc_inc.inc_fport; 1854 1855 if (flags & TH_SYN) 1856 th->th_seq = htonl(sc->sc_iss); 1857 else 1858 th->th_seq = htonl(sc->sc_iss + 1); 1859 th->th_ack = htonl(sc->sc_irs + 1); 1860 th->th_off = sizeof(struct tcphdr) >> 2; 1861 th->th_x2 = 0; 1862 th->th_flags = flags; 1863 th->th_win = htons(sc->sc_wnd); 1864 th->th_urp = 0; 1865 1866 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1867 th->th_flags |= TH_ECE; 1868 TCPSTAT_INC(tcps_ecn_shs); 1869 } 1870 1871 /* Tack on the TCP options. */ 1872 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1873 to.to_flags = 0; 1874 1875 if (flags & TH_SYN) { 1876 to.to_mss = mssopt; 1877 to.to_flags = TOF_MSS; 1878 if (sc->sc_flags & SCF_WINSCALE) { 1879 to.to_wscale = sc->sc_requested_r_scale; 1880 to.to_flags |= TOF_SCALE; 1881 } 1882 if (sc->sc_flags & SCF_SACK) 1883 to.to_flags |= TOF_SACKPERM; 1884 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1885 if (sc->sc_flags & SCF_SIGNATURE) 1886 to.to_flags |= TOF_SIGNATURE; 1887 #endif 1888 if (sc->sc_tfo_cookie) { 1889 to.to_flags |= TOF_FASTOPEN; 1890 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1891 to.to_tfo_cookie = sc->sc_tfo_cookie; 1892 /* don't send cookie again when retransmitting response */ 1893 sc->sc_tfo_cookie = NULL; 1894 } 1895 } 1896 if (sc->sc_flags & SCF_TIMESTAMP) { 1897 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1898 to.to_tsecr = sc->sc_tsreflect; 1899 to.to_flags |= TOF_TS; 1900 } 1901 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1902 1903 /* Adjust headers by option size. */ 1904 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1905 m->m_len += optlen; 1906 m->m_pkthdr.len += optlen; 1907 #ifdef INET6 1908 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1909 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1910 else 1911 #endif 1912 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1913 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1914 if (sc->sc_flags & SCF_SIGNATURE) { 1915 KASSERT(to.to_flags & TOF_SIGNATURE, 1916 ("tcp_addoptions() didn't set tcp_signature")); 1917 1918 /* NOTE: to.to_signature is inside of mbuf */ 1919 if (!TCPMD5_ENABLED() || 1920 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1921 m_freem(m); 1922 return (EACCES); 1923 } 1924 } 1925 #endif 1926 } else 1927 optlen = 0; 1928 1929 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1930 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1931 /* 1932 * If we have peer's SYN and it has a flowid, then let's assign it to 1933 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1934 * to SYN|ACK due to lack of inp here. 1935 */ 1936 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1937 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1938 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1939 } 1940 #ifdef INET6 1941 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1942 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1943 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1944 IPPROTO_TCP, 0); 1945 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1946 #ifdef TCP_OFFLOAD 1947 if (ADDED_BY_TOE(sc)) { 1948 struct toedev *tod = sc->sc_tod; 1949 1950 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1951 1952 return (error); 1953 } 1954 #endif 1955 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1956 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1957 } 1958 #endif 1959 #if defined(INET6) && defined(INET) 1960 else 1961 #endif 1962 #ifdef INET 1963 { 1964 m->m_pkthdr.csum_flags = CSUM_TCP; 1965 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1966 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1967 #ifdef TCP_OFFLOAD 1968 if (ADDED_BY_TOE(sc)) { 1969 struct toedev *tod = sc->sc_tod; 1970 1971 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1972 1973 return (error); 1974 } 1975 #endif 1976 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1977 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1978 } 1979 #endif 1980 return (error); 1981 } 1982 1983 /* 1984 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1985 * that exceed the capacity of the syncache by avoiding the storage of any 1986 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1987 * attacks where the attacker does not have access to our responses. 1988 * 1989 * Syncookies encode and include all necessary information about the 1990 * connection setup within the SYN|ACK that we send back. That way we 1991 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1992 * (if ever). Normally the syncache and syncookies are running in parallel 1993 * with the latter taking over when the former is exhausted. When matching 1994 * syncache entry is found the syncookie is ignored. 1995 * 1996 * The only reliable information persisting the 3WHS is our initial sequence 1997 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1998 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1999 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2000 * returns and signifies a legitimate connection if it matches the ACK. 2001 * 2002 * The available space of 32 bits to store the hash and to encode the SYN 2003 * option information is very tight and we should have at least 24 bits for 2004 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2005 * 2006 * SYN option information we have to encode to fully restore a connection: 2007 * MSS: is imporant to chose an optimal segment size to avoid IP level 2008 * fragmentation along the path. The common MSS values can be encoded 2009 * in a 3-bit table. Uncommon values are captured by the next lower value 2010 * in the table leading to a slight increase in packetization overhead. 2011 * WSCALE: is necessary to allow large windows to be used for high delay- 2012 * bandwidth product links. Not scaling the window when it was initially 2013 * negotiated is bad for performance as lack of scaling further decreases 2014 * the apparent available send window. We only need to encode the WSCALE 2015 * we received from the remote end. Our end can be recalculated at any 2016 * time. The common WSCALE values can be encoded in a 3-bit table. 2017 * Uncommon values are captured by the next lower value in the table 2018 * making us under-estimate the available window size halving our 2019 * theoretically possible maximum throughput for that connection. 2020 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2021 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2022 * that are included in all segments on a connection. We enable them when 2023 * the ACK has them. 2024 * 2025 * Security of syncookies and attack vectors: 2026 * 2027 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2028 * together with the gloabl secret to make it unique per connection attempt. 2029 * Thus any change of any of those parameters results in a different MAC output 2030 * in an unpredictable way unless a collision is encountered. 24 bits of the 2031 * MAC are embedded into the ISS. 2032 * 2033 * To prevent replay attacks two rotating global secrets are updated with a 2034 * new random value every 15 seconds. The life-time of a syncookie is thus 2035 * 15-30 seconds. 2036 * 2037 * Vector 1: Attacking the secret. This requires finding a weakness in the 2038 * MAC itself or the way it is used here. The attacker can do a chosen plain 2039 * text attack by varying and testing the all parameters under his control. 2040 * The strength depends on the size and randomness of the secret, and the 2041 * cryptographic security of the MAC function. Due to the constant updating 2042 * of the secret the attacker has at most 29.999 seconds to find the secret 2043 * and launch spoofed connections. After that he has to start all over again. 2044 * 2045 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2046 * size an average of 4,823 attempts are required for a 50% chance of success 2047 * to spoof a single syncookie (birthday collision paradox). However the 2048 * attacker is blind and doesn't know if one of his attempts succeeded unless 2049 * he has a side channel to interfere success from. A single connection setup 2050 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2051 * This many attempts are required for each one blind spoofed connection. For 2052 * every additional spoofed connection he has to launch another N attempts. 2053 * Thus for a sustained rate 100 spoofed connections per second approximately 2054 * 1,800,000 packets per second would have to be sent. 2055 * 2056 * NB: The MAC function should be fast so that it doesn't become a CPU 2057 * exhaustion attack vector itself. 2058 * 2059 * References: 2060 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2061 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2062 * http://cr.yp.to/syncookies.html (overview) 2063 * http://cr.yp.to/syncookies/archive (details) 2064 * 2065 * 2066 * Schematic construction of a syncookie enabled Initial Sequence Number: 2067 * 0 1 2 3 2068 * 12345678901234567890123456789012 2069 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2070 * 2071 * x 24 MAC (truncated) 2072 * W 3 Send Window Scale index 2073 * M 3 MSS index 2074 * S 1 SACK permitted 2075 * P 1 Odd/even secret 2076 */ 2077 2078 /* 2079 * Distribution and probability of certain MSS values. Those in between are 2080 * rounded down to the next lower one. 2081 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2082 * .2% .3% 5% 7% 7% 20% 15% 45% 2083 */ 2084 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2085 2086 /* 2087 * Distribution and probability of certain WSCALE values. We have to map the 2088 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2089 * bits based on prevalence of certain values. Where we don't have an exact 2090 * match for are rounded down to the next lower one letting us under-estimate 2091 * the true available window. At the moment this would happen only for the 2092 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2093 * and window size). The absence of the WSCALE option (no scaling in either 2094 * direction) is encoded with index zero. 2095 * [WSCALE values histograms, Allman, 2012] 2096 * X 10 10 35 5 6 14 10% by host 2097 * X 11 4 5 5 18 49 3% by connections 2098 */ 2099 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2100 2101 /* 2102 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2103 * and good cryptographic properties. 2104 */ 2105 static uint32_t 2106 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2107 uint8_t *secbits, uintptr_t secmod) 2108 { 2109 SIPHASH_CTX ctx; 2110 uint32_t siphash[2]; 2111 2112 SipHash24_Init(&ctx); 2113 SipHash_SetKey(&ctx, secbits); 2114 switch (inc->inc_flags & INC_ISIPV6) { 2115 #ifdef INET 2116 case 0: 2117 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2118 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2119 break; 2120 #endif 2121 #ifdef INET6 2122 case INC_ISIPV6: 2123 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2124 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2125 break; 2126 #endif 2127 } 2128 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2129 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2130 SipHash_Update(&ctx, &irs, sizeof(irs)); 2131 SipHash_Update(&ctx, &flags, sizeof(flags)); 2132 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2133 SipHash_Final((u_int8_t *)&siphash, &ctx); 2134 2135 return (siphash[0] ^ siphash[1]); 2136 } 2137 2138 static tcp_seq 2139 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2140 { 2141 u_int i, secbit, wscale; 2142 uint32_t iss, hash; 2143 uint8_t *secbits; 2144 union syncookie cookie; 2145 2146 cookie.cookie = 0; 2147 2148 /* Map our computed MSS into the 3-bit index. */ 2149 for (i = nitems(tcp_sc_msstab) - 1; 2150 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2151 i--) 2152 ; 2153 cookie.flags.mss_idx = i; 2154 2155 /* 2156 * Map the send window scale into the 3-bit index but only if 2157 * the wscale option was received. 2158 */ 2159 if (sc->sc_flags & SCF_WINSCALE) { 2160 wscale = sc->sc_requested_s_scale; 2161 for (i = nitems(tcp_sc_wstab) - 1; 2162 tcp_sc_wstab[i] > wscale && i > 0; 2163 i--) 2164 ; 2165 cookie.flags.wscale_idx = i; 2166 } 2167 2168 /* Can we do SACK? */ 2169 if (sc->sc_flags & SCF_SACK) 2170 cookie.flags.sack_ok = 1; 2171 2172 /* Which of the two secrets to use. */ 2173 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2174 cookie.flags.odd_even = secbit; 2175 2176 secbits = V_tcp_syncache.secret.key[secbit]; 2177 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2178 (uintptr_t)sch); 2179 2180 /* 2181 * Put the flags into the hash and XOR them to get better ISS number 2182 * variance. This doesn't enhance the cryptographic strength and is 2183 * done to prevent the 8 cookie bits from showing up directly on the 2184 * wire. 2185 */ 2186 iss = hash & ~0xff; 2187 iss |= cookie.cookie ^ (hash >> 24); 2188 2189 TCPSTAT_INC(tcps_sc_sendcookie); 2190 return (iss); 2191 } 2192 2193 static struct syncache * 2194 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2195 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2196 struct socket *lso) 2197 { 2198 uint32_t hash; 2199 uint8_t *secbits; 2200 tcp_seq ack, seq; 2201 int wnd, wscale = 0; 2202 union syncookie cookie; 2203 2204 /* 2205 * Pull information out of SYN-ACK/ACK and revert sequence number 2206 * advances. 2207 */ 2208 ack = th->th_ack - 1; 2209 seq = th->th_seq - 1; 2210 2211 /* 2212 * Unpack the flags containing enough information to restore the 2213 * connection. 2214 */ 2215 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2216 2217 /* Which of the two secrets to use. */ 2218 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2219 2220 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2221 2222 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2223 if ((ack & ~0xff) != (hash & ~0xff)) 2224 return (NULL); 2225 2226 /* Fill in the syncache values. */ 2227 sc->sc_flags = 0; 2228 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2229 sc->sc_ipopts = NULL; 2230 2231 sc->sc_irs = seq; 2232 sc->sc_iss = ack; 2233 2234 switch (inc->inc_flags & INC_ISIPV6) { 2235 #ifdef INET 2236 case 0: 2237 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2238 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2239 break; 2240 #endif 2241 #ifdef INET6 2242 case INC_ISIPV6: 2243 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2244 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2245 break; 2246 #endif 2247 } 2248 2249 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2250 2251 /* We can simply recompute receive window scale we sent earlier. */ 2252 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2253 wscale++; 2254 2255 /* Only use wscale if it was enabled in the orignal SYN. */ 2256 if (cookie.flags.wscale_idx > 0) { 2257 sc->sc_requested_r_scale = wscale; 2258 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2259 sc->sc_flags |= SCF_WINSCALE; 2260 } 2261 2262 wnd = lso->sol_sbrcv_hiwat; 2263 wnd = imax(wnd, 0); 2264 wnd = imin(wnd, TCP_MAXWIN); 2265 sc->sc_wnd = wnd; 2266 2267 if (cookie.flags.sack_ok) 2268 sc->sc_flags |= SCF_SACK; 2269 2270 if (to->to_flags & TOF_TS) { 2271 sc->sc_flags |= SCF_TIMESTAMP; 2272 sc->sc_tsreflect = to->to_tsval; 2273 sc->sc_tsoff = tcp_new_ts_offset(inc); 2274 } 2275 2276 if (to->to_flags & TOF_SIGNATURE) 2277 sc->sc_flags |= SCF_SIGNATURE; 2278 2279 sc->sc_rxmits = 0; 2280 2281 TCPSTAT_INC(tcps_sc_recvcookie); 2282 return (sc); 2283 } 2284 2285 #ifdef INVARIANTS 2286 static int 2287 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2289 struct socket *lso) 2290 { 2291 struct syncache scs, *scx; 2292 char *s; 2293 2294 bzero(&scs, sizeof(scs)); 2295 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2296 2297 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2298 return (0); 2299 2300 if (scx != NULL) { 2301 if (sc->sc_peer_mss != scx->sc_peer_mss) 2302 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2303 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2304 2305 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2306 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2307 s, __func__, sc->sc_requested_r_scale, 2308 scx->sc_requested_r_scale); 2309 2310 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2311 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2312 s, __func__, sc->sc_requested_s_scale, 2313 scx->sc_requested_s_scale); 2314 2315 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2316 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2317 } 2318 2319 if (s != NULL) 2320 free(s, M_TCPLOG); 2321 return (0); 2322 } 2323 #endif /* INVARIANTS */ 2324 2325 static void 2326 syncookie_reseed(void *arg) 2327 { 2328 struct tcp_syncache *sc = arg; 2329 uint8_t *secbits; 2330 int secbit; 2331 2332 /* 2333 * Reseeding the secret doesn't have to be protected by a lock. 2334 * It only must be ensured that the new random values are visible 2335 * to all CPUs in a SMP environment. The atomic with release 2336 * semantics ensures that. 2337 */ 2338 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2339 secbits = sc->secret.key[secbit]; 2340 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2341 atomic_add_rel_int(&sc->secret.oddeven, 1); 2342 2343 /* Reschedule ourself. */ 2344 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2345 } 2346 2347 /* 2348 * We have overflowed a bucket. Let's pause dealing with the syncache. 2349 * This function will increment the bucketoverflow statistics appropriately 2350 * (once per pause when pausing is enabled; otherwise, once per overflow). 2351 */ 2352 static void 2353 syncache_pause(struct in_conninfo *inc) 2354 { 2355 time_t delta; 2356 const char *s; 2357 2358 /* XXX: 2359 * 2. Add sysctl read here so we don't get the benefit of this 2360 * change without the new sysctl. 2361 */ 2362 2363 /* 2364 * Try an unlocked read. If we already know that another thread 2365 * has activated the feature, there is no need to proceed. 2366 */ 2367 if (V_tcp_syncache.paused) 2368 return; 2369 2370 /* Are cookied enabled? If not, we can't pause. */ 2371 if (!V_tcp_syncookies) { 2372 TCPSTAT_INC(tcps_sc_bucketoverflow); 2373 return; 2374 } 2375 2376 /* 2377 * We may be the first thread to find an overflow. Get the lock 2378 * and evaluate if we need to take action. 2379 */ 2380 mtx_lock(&V_tcp_syncache.pause_mtx); 2381 if (V_tcp_syncache.paused) { 2382 mtx_unlock(&V_tcp_syncache.pause_mtx); 2383 return; 2384 } 2385 2386 /* Activate protection. */ 2387 V_tcp_syncache.paused = true; 2388 TCPSTAT_INC(tcps_sc_bucketoverflow); 2389 2390 /* 2391 * Determine the last backoff time. If we are seeing a re-newed 2392 * attack within that same time after last reactivating the syncache, 2393 * consider it an extension of the same attack. 2394 */ 2395 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2396 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2397 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2398 delta <<= 1; 2399 V_tcp_syncache.pause_backoff++; 2400 } 2401 } else { 2402 delta = TCP_SYNCACHE_PAUSE_TIME; 2403 V_tcp_syncache.pause_backoff = 0; 2404 } 2405 2406 /* Log a warning, including IP addresses, if able. */ 2407 if (inc != NULL) 2408 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2409 else 2410 s = (const char *)NULL; 2411 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2412 "the next %lld seconds%s%s%s\n", (long long)delta, 2413 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2414 (s != NULL) ? ")" : ""); 2415 free(__DECONST(void *, s), M_TCPLOG); 2416 2417 /* Use the calculated delta to set a new pause time. */ 2418 V_tcp_syncache.pause_until = time_uptime + delta; 2419 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2420 &V_tcp_syncache); 2421 mtx_unlock(&V_tcp_syncache.pause_mtx); 2422 } 2423 2424 /* Evaluate whether we need to unpause. */ 2425 static void 2426 syncache_unpause(void *arg) 2427 { 2428 struct tcp_syncache *sc; 2429 time_t delta; 2430 2431 sc = arg; 2432 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2433 callout_deactivate(&sc->pause_co); 2434 2435 /* 2436 * Check to make sure we are not running early. If the pause 2437 * time has expired, then deactivate the protection. 2438 */ 2439 if ((delta = sc->pause_until - time_uptime) > 0) 2440 callout_schedule(&sc->pause_co, delta * hz); 2441 else 2442 sc->paused = false; 2443 } 2444 2445 /* 2446 * Exports the syncache entries to userland so that netstat can display 2447 * them alongside the other sockets. This function is intended to be 2448 * called only from tcp_pcblist. 2449 * 2450 * Due to concurrency on an active system, the number of pcbs exported 2451 * may have no relation to max_pcbs. max_pcbs merely indicates the 2452 * amount of space the caller allocated for this function to use. 2453 */ 2454 int 2455 syncache_pcblist(struct sysctl_req *req) 2456 { 2457 struct xtcpcb xt; 2458 struct syncache *sc; 2459 struct syncache_head *sch; 2460 int error, i; 2461 2462 bzero(&xt, sizeof(xt)); 2463 xt.xt_len = sizeof(xt); 2464 xt.t_state = TCPS_SYN_RECEIVED; 2465 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2466 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2467 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2468 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2469 2470 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2471 sch = &V_tcp_syncache.hashbase[i]; 2472 SCH_LOCK(sch); 2473 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2474 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2475 continue; 2476 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2477 xt.xt_inp.inp_vflag = INP_IPV6; 2478 else 2479 xt.xt_inp.inp_vflag = INP_IPV4; 2480 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2481 sizeof (struct in_conninfo)); 2482 error = SYSCTL_OUT(req, &xt, sizeof xt); 2483 if (error) { 2484 SCH_UNLOCK(sch); 2485 return (0); 2486 } 2487 } 2488 SCH_UNLOCK(sch); 2489 } 2490 2491 return (0); 2492 } 2493