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 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 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_flags |= TF_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 /* 1095 * Global TCP locks are held because we manipulate the PCB lists 1096 * and create a new socket. 1097 */ 1098 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1099 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1100 ("%s: can handle only ACK", __func__)); 1101 1102 if (syncache_cookiesonly()) { 1103 sc = NULL; 1104 sch = syncache_hashbucket(inc); 1105 locked = false; 1106 } else { 1107 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1108 locked = true; 1109 SCH_LOCK_ASSERT(sch); 1110 } 1111 1112 #ifdef INVARIANTS 1113 /* 1114 * Test code for syncookies comparing the syncache stored 1115 * values with the reconstructed values from the cookie. 1116 */ 1117 if (sc != NULL) 1118 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1119 #endif 1120 1121 if (sc == NULL) { 1122 /* 1123 * There is no syncache entry, so see if this ACK is 1124 * a returning syncookie. To do this, first: 1125 * A. Check if syncookies are used in case of syncache 1126 * overflows 1127 * B. See if this socket has had a syncache entry dropped in 1128 * the recent past. We don't want to accept a bogus 1129 * syncookie if we've never received a SYN or accept it 1130 * twice. 1131 * C. check that the syncookie is valid. If it is, then 1132 * cobble up a fake syncache entry, and return. 1133 */ 1134 if (locked && !V_tcp_syncookies) { 1135 SCH_UNLOCK(sch); 1136 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1137 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1138 "segment rejected (syncookies disabled)\n", 1139 s, __func__); 1140 goto failed; 1141 } 1142 if (locked && !V_tcp_syncookiesonly && 1143 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1144 SCH_UNLOCK(sch); 1145 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1146 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1147 "segment rejected (no syncache entry)\n", 1148 s, __func__); 1149 goto failed; 1150 } 1151 bzero(&scs, sizeof(scs)); 1152 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1153 if (locked) 1154 SCH_UNLOCK(sch); 1155 if (sc == NULL) { 1156 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1157 log(LOG_DEBUG, "%s; %s: Segment failed " 1158 "SYNCOOKIE authentication, segment rejected " 1159 "(probably spoofed)\n", s, __func__); 1160 goto failed; 1161 } 1162 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1163 /* If received ACK has MD5 signature, check it. */ 1164 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1165 (!TCPMD5_ENABLED() || 1166 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1167 /* Drop the ACK. */ 1168 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1169 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1170 "MD5 signature doesn't match.\n", 1171 s, __func__); 1172 free(s, M_TCPLOG); 1173 } 1174 TCPSTAT_INC(tcps_sig_err_sigopt); 1175 return (-1); /* Do not send RST */ 1176 } 1177 #endif /* TCP_SIGNATURE */ 1178 } else { 1179 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1180 /* 1181 * If listening socket requested TCP digests, check that 1182 * received ACK has signature and it is correct. 1183 * If not, drop the ACK and leave sc entry in th cache, 1184 * because SYN was received with correct signature. 1185 */ 1186 if (sc->sc_flags & SCF_SIGNATURE) { 1187 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1188 /* No signature */ 1189 TCPSTAT_INC(tcps_sig_err_nosigopt); 1190 SCH_UNLOCK(sch); 1191 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1192 log(LOG_DEBUG, "%s; %s: Segment " 1193 "rejected, MD5 signature wasn't " 1194 "provided.\n", s, __func__); 1195 free(s, M_TCPLOG); 1196 } 1197 return (-1); /* Do not send RST */ 1198 } 1199 if (!TCPMD5_ENABLED() || 1200 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1201 /* Doesn't match or no SA */ 1202 SCH_UNLOCK(sch); 1203 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1204 log(LOG_DEBUG, "%s; %s: Segment " 1205 "rejected, MD5 signature doesn't " 1206 "match.\n", s, __func__); 1207 free(s, M_TCPLOG); 1208 } 1209 return (-1); /* Do not send RST */ 1210 } 1211 } 1212 #endif /* TCP_SIGNATURE */ 1213 1214 /* 1215 * RFC 7323 PAWS: If we have a timestamp on this segment and 1216 * it's less than ts_recent, drop it. 1217 * XXXMT: RFC 7323 also requires to send an ACK. 1218 * In tcp_input.c this is only done for TCP segments 1219 * with user data, so be consistent here and just drop 1220 * the segment. 1221 */ 1222 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1223 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1224 SCH_UNLOCK(sch); 1225 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1226 log(LOG_DEBUG, 1227 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1228 "segment dropped\n", s, __func__, 1229 to->to_tsval, sc->sc_tsreflect); 1230 free(s, M_TCPLOG); 1231 } 1232 return (-1); /* Do not send RST */ 1233 } 1234 1235 /* 1236 * Pull out the entry to unlock the bucket row. 1237 * 1238 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1239 * tcp_state_change(). The tcpcb is not existent at this 1240 * moment. A new one will be allocated via syncache_socket-> 1241 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1242 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1243 */ 1244 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1245 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1246 sch->sch_length--; 1247 #ifdef TCP_OFFLOAD 1248 if (ADDED_BY_TOE(sc)) { 1249 struct toedev *tod = sc->sc_tod; 1250 1251 tod->tod_syncache_removed(tod, sc->sc_todctx); 1252 } 1253 #endif 1254 SCH_UNLOCK(sch); 1255 } 1256 1257 /* 1258 * Segment validation: 1259 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1260 */ 1261 if (th->th_ack != sc->sc_iss + 1) { 1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1263 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1264 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1265 goto failed; 1266 } 1267 1268 /* 1269 * The SEQ must fall in the window starting at the received 1270 * initial receive sequence number + 1 (the SYN). 1271 */ 1272 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1273 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1274 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1275 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1276 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1277 goto failed; 1278 } 1279 1280 /* 1281 * If timestamps were not negotiated during SYN/ACK they 1282 * must not appear on any segment during this session. 1283 */ 1284 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1285 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1286 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1287 "segment rejected\n", s, __func__); 1288 goto failed; 1289 } 1290 1291 /* 1292 * If timestamps were negotiated during SYN/ACK they should 1293 * appear on every segment during this session. 1294 * XXXAO: This is only informal as there have been unverified 1295 * reports of non-compliants stacks. 1296 */ 1297 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1298 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1299 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1300 "no action\n", s, __func__); 1301 free(s, M_TCPLOG); 1302 s = NULL; 1303 } 1304 } 1305 1306 *lsop = syncache_socket(sc, *lsop, m); 1307 1308 if (*lsop == NULL) 1309 TCPSTAT_INC(tcps_sc_aborted); 1310 else 1311 TCPSTAT_INC(tcps_sc_completed); 1312 1313 /* how do we find the inp for the new socket? */ 1314 if (sc != &scs) 1315 syncache_free(sc); 1316 return (1); 1317 failed: 1318 if (sc != NULL && sc != &scs) 1319 syncache_free(sc); 1320 if (s != NULL) 1321 free(s, M_TCPLOG); 1322 *lsop = NULL; 1323 return (0); 1324 } 1325 1326 static void 1327 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1328 uint64_t response_cookie) 1329 { 1330 struct inpcb *inp; 1331 struct tcpcb *tp; 1332 unsigned int *pending_counter; 1333 1334 /* 1335 * Global TCP locks are held because we manipulate the PCB lists 1336 * and create a new socket. 1337 */ 1338 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1339 1340 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1341 *lsop = syncache_socket(sc, *lsop, m); 1342 if (*lsop == NULL) { 1343 TCPSTAT_INC(tcps_sc_aborted); 1344 atomic_subtract_int(pending_counter, 1); 1345 } else { 1346 soisconnected(*lsop); 1347 inp = sotoinpcb(*lsop); 1348 tp = intotcpcb(inp); 1349 tp->t_flags |= TF_FASTOPEN; 1350 tp->t_tfo_cookie.server = response_cookie; 1351 tp->snd_max = tp->iss; 1352 tp->snd_nxt = tp->iss; 1353 tp->t_tfo_pending = pending_counter; 1354 TCPSTAT_INC(tcps_sc_completed); 1355 } 1356 } 1357 1358 /* 1359 * Given a LISTEN socket and an inbound SYN request, add 1360 * this to the syn cache, and send back a segment: 1361 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1362 * to the source. 1363 * 1364 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1365 * Doing so would require that we hold onto the data and deliver it 1366 * to the application. However, if we are the target of a SYN-flood 1367 * DoS attack, an attacker could send data which would eventually 1368 * consume all available buffer space if it were ACKed. By not ACKing 1369 * the data, we avoid this DoS scenario. 1370 * 1371 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1372 * cookie is processed and a new socket is created. In this case, any data 1373 * accompanying the SYN will be queued to the socket by tcp_input() and will 1374 * be ACKed either when the application sends response data or the delayed 1375 * ACK timer expires, whichever comes first. 1376 */ 1377 int 1378 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1379 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1380 void *todctx) 1381 { 1382 struct tcpcb *tp; 1383 struct socket *so; 1384 struct syncache *sc = NULL; 1385 struct syncache_head *sch; 1386 struct mbuf *ipopts = NULL; 1387 u_int ltflags; 1388 int win, ip_ttl, ip_tos; 1389 char *s; 1390 int rv = 0; 1391 #ifdef INET6 1392 int autoflowlabel = 0; 1393 #endif 1394 #ifdef MAC 1395 struct label *maclabel; 1396 #endif 1397 struct syncache scs; 1398 struct ucred *cred; 1399 uint64_t tfo_response_cookie; 1400 unsigned int *tfo_pending = NULL; 1401 int tfo_cookie_valid = 0; 1402 int tfo_response_cookie_valid = 0; 1403 bool locked; 1404 1405 INP_WLOCK_ASSERT(inp); /* listen socket */ 1406 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1407 ("%s: unexpected tcp flags", __func__)); 1408 1409 /* 1410 * Combine all so/tp operations very early to drop the INP lock as 1411 * soon as possible. 1412 */ 1413 so = *lsop; 1414 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1415 tp = sototcpcb(so); 1416 cred = crhold(so->so_cred); 1417 1418 #ifdef INET6 1419 if ((inc->inc_flags & INC_ISIPV6) && 1420 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1421 autoflowlabel = 1; 1422 #endif 1423 ip_ttl = inp->inp_ip_ttl; 1424 ip_tos = inp->inp_ip_tos; 1425 win = so->sol_sbrcv_hiwat; 1426 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1427 1428 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1429 (tp->t_tfo_pending != NULL) && 1430 (to->to_flags & TOF_FASTOPEN)) { 1431 /* 1432 * Limit the number of pending TFO connections to 1433 * approximately half of the queue limit. This prevents TFO 1434 * SYN floods from starving the service by filling the 1435 * listen queue with bogus TFO connections. 1436 */ 1437 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1438 (so->sol_qlimit / 2)) { 1439 int result; 1440 1441 result = tcp_fastopen_check_cookie(inc, 1442 to->to_tfo_cookie, to->to_tfo_len, 1443 &tfo_response_cookie); 1444 tfo_cookie_valid = (result > 0); 1445 tfo_response_cookie_valid = (result >= 0); 1446 } 1447 1448 /* 1449 * Remember the TFO pending counter as it will have to be 1450 * decremented below if we don't make it to syncache_tfo_expand(). 1451 */ 1452 tfo_pending = tp->t_tfo_pending; 1453 } 1454 1455 /* By the time we drop the lock these should no longer be used. */ 1456 so = NULL; 1457 tp = NULL; 1458 1459 #ifdef MAC 1460 if (mac_syncache_init(&maclabel) != 0) { 1461 INP_WUNLOCK(inp); 1462 goto done; 1463 } else 1464 mac_syncache_create(maclabel, inp); 1465 #endif 1466 if (!tfo_cookie_valid) 1467 INP_WUNLOCK(inp); 1468 1469 /* 1470 * Remember the IP options, if any. 1471 */ 1472 #ifdef INET6 1473 if (!(inc->inc_flags & INC_ISIPV6)) 1474 #endif 1475 #ifdef INET 1476 ipopts = (m) ? ip_srcroute(m) : NULL; 1477 #else 1478 ipopts = NULL; 1479 #endif 1480 1481 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1482 /* 1483 * If listening socket requested TCP digests, check that received 1484 * SYN has signature and it is correct. If signature doesn't match 1485 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1486 */ 1487 if (ltflags & TF_SIGNATURE) { 1488 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1489 TCPSTAT_INC(tcps_sig_err_nosigopt); 1490 goto done; 1491 } 1492 if (!TCPMD5_ENABLED() || 1493 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1494 goto done; 1495 } 1496 #endif /* TCP_SIGNATURE */ 1497 /* 1498 * See if we already have an entry for this connection. 1499 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1500 * 1501 * XXX: should the syncache be re-initialized with the contents 1502 * of the new SYN here (which may have different options?) 1503 * 1504 * XXX: We do not check the sequence number to see if this is a 1505 * real retransmit or a new connection attempt. The question is 1506 * how to handle such a case; either ignore it as spoofed, or 1507 * drop the current entry and create a new one? 1508 */ 1509 if (syncache_cookiesonly()) { 1510 sc = NULL; 1511 sch = syncache_hashbucket(inc); 1512 locked = false; 1513 } else { 1514 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1515 locked = true; 1516 SCH_LOCK_ASSERT(sch); 1517 } 1518 if (sc != NULL) { 1519 if (tfo_cookie_valid) 1520 INP_WUNLOCK(inp); 1521 TCPSTAT_INC(tcps_sc_dupsyn); 1522 if (ipopts) { 1523 /* 1524 * If we were remembering a previous source route, 1525 * forget it and use the new one we've been given. 1526 */ 1527 if (sc->sc_ipopts) 1528 (void) m_free(sc->sc_ipopts); 1529 sc->sc_ipopts = ipopts; 1530 } 1531 /* 1532 * Update timestamp if present. 1533 */ 1534 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1535 sc->sc_tsreflect = to->to_tsval; 1536 else 1537 sc->sc_flags &= ~SCF_TIMESTAMP; 1538 #ifdef MAC 1539 /* 1540 * Since we have already unconditionally allocated label 1541 * storage, free it up. The syncache entry will already 1542 * have an initialized label we can use. 1543 */ 1544 mac_syncache_destroy(&maclabel); 1545 #endif 1546 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1547 /* Retransmit SYN|ACK and reset retransmit count. */ 1548 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1549 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1550 "resetting timer and retransmitting SYN|ACK\n", 1551 s, __func__); 1552 free(s, M_TCPLOG); 1553 } 1554 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1555 sc->sc_rxmits = 0; 1556 syncache_timeout(sc, sch, 1); 1557 TCPSTAT_INC(tcps_sndacks); 1558 TCPSTAT_INC(tcps_sndtotal); 1559 } 1560 SCH_UNLOCK(sch); 1561 goto donenoprobe; 1562 } 1563 1564 if (tfo_cookie_valid) { 1565 bzero(&scs, sizeof(scs)); 1566 sc = &scs; 1567 goto skip_alloc; 1568 } 1569 1570 /* 1571 * Skip allocating a syncache entry if we are just going to discard 1572 * it later. 1573 */ 1574 if (!locked) { 1575 bzero(&scs, sizeof(scs)); 1576 sc = &scs; 1577 } else 1578 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1579 if (sc == NULL) { 1580 /* 1581 * The zone allocator couldn't provide more entries. 1582 * Treat this as if the cache was full; drop the oldest 1583 * entry and insert the new one. 1584 */ 1585 TCPSTAT_INC(tcps_sc_zonefail); 1586 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1587 sch->sch_last_overflow = time_uptime; 1588 syncache_drop(sc, sch); 1589 syncache_pause(inc); 1590 } 1591 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1592 if (sc == NULL) { 1593 if (V_tcp_syncookies) { 1594 bzero(&scs, sizeof(scs)); 1595 sc = &scs; 1596 } else { 1597 KASSERT(locked, 1598 ("%s: bucket unexpectedly unlocked", 1599 __func__)); 1600 SCH_UNLOCK(sch); 1601 if (ipopts) 1602 (void) m_free(ipopts); 1603 goto done; 1604 } 1605 } 1606 } 1607 1608 skip_alloc: 1609 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1610 sc->sc_tfo_cookie = &tfo_response_cookie; 1611 1612 /* 1613 * Fill in the syncache values. 1614 */ 1615 #ifdef MAC 1616 sc->sc_label = maclabel; 1617 #endif 1618 sc->sc_cred = cred; 1619 cred = NULL; 1620 sc->sc_ipopts = ipopts; 1621 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1622 #ifdef INET6 1623 if (!(inc->inc_flags & INC_ISIPV6)) 1624 #endif 1625 { 1626 sc->sc_ip_tos = ip_tos; 1627 sc->sc_ip_ttl = ip_ttl; 1628 } 1629 #ifdef TCP_OFFLOAD 1630 sc->sc_tod = tod; 1631 sc->sc_todctx = todctx; 1632 #endif 1633 sc->sc_irs = th->th_seq; 1634 sc->sc_flags = 0; 1635 sc->sc_flowlabel = 0; 1636 1637 /* 1638 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1639 * win was derived from socket earlier in the function. 1640 */ 1641 win = imax(win, 0); 1642 win = imin(win, TCP_MAXWIN); 1643 sc->sc_wnd = win; 1644 1645 if (V_tcp_do_rfc1323) { 1646 /* 1647 * A timestamp received in a SYN makes 1648 * it ok to send timestamp requests and replies. 1649 */ 1650 if (to->to_flags & TOF_TS) { 1651 sc->sc_tsreflect = to->to_tsval; 1652 sc->sc_flags |= SCF_TIMESTAMP; 1653 sc->sc_tsoff = tcp_new_ts_offset(inc); 1654 } 1655 if (to->to_flags & TOF_SCALE) { 1656 int wscale = 0; 1657 1658 /* 1659 * Pick the smallest possible scaling factor that 1660 * will still allow us to scale up to sb_max, aka 1661 * kern.ipc.maxsockbuf. 1662 * 1663 * We do this because there are broken firewalls that 1664 * will corrupt the window scale option, leading to 1665 * the other endpoint believing that our advertised 1666 * window is unscaled. At scale factors larger than 1667 * 5 the unscaled window will drop below 1500 bytes, 1668 * leading to serious problems when traversing these 1669 * broken firewalls. 1670 * 1671 * With the default maxsockbuf of 256K, a scale factor 1672 * of 3 will be chosen by this algorithm. Those who 1673 * choose a larger maxsockbuf should watch out 1674 * for the compatibility problems mentioned above. 1675 * 1676 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1677 * or <SYN,ACK>) segment itself is never scaled. 1678 */ 1679 while (wscale < TCP_MAX_WINSHIFT && 1680 (TCP_MAXWIN << wscale) < sb_max) 1681 wscale++; 1682 sc->sc_requested_r_scale = wscale; 1683 sc->sc_requested_s_scale = to->to_wscale; 1684 sc->sc_flags |= SCF_WINSCALE; 1685 } 1686 } 1687 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1688 /* 1689 * If listening socket requested TCP digests, flag this in the 1690 * syncache so that syncache_respond() will do the right thing 1691 * with the SYN+ACK. 1692 */ 1693 if (ltflags & TF_SIGNATURE) 1694 sc->sc_flags |= SCF_SIGNATURE; 1695 #endif /* TCP_SIGNATURE */ 1696 if (to->to_flags & TOF_SACKPERM) 1697 sc->sc_flags |= SCF_SACK; 1698 if (to->to_flags & TOF_MSS) 1699 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1700 if (ltflags & TF_NOOPT) 1701 sc->sc_flags |= SCF_NOOPT; 1702 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1703 sc->sc_flags |= SCF_ECN; 1704 1705 if (V_tcp_syncookies) 1706 sc->sc_iss = syncookie_generate(sch, sc); 1707 else 1708 sc->sc_iss = arc4random(); 1709 #ifdef INET6 1710 if (autoflowlabel) { 1711 if (V_tcp_syncookies) 1712 sc->sc_flowlabel = sc->sc_iss; 1713 else 1714 sc->sc_flowlabel = ip6_randomflowlabel(); 1715 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1716 } 1717 #endif 1718 if (locked) 1719 SCH_UNLOCK(sch); 1720 1721 if (tfo_cookie_valid) { 1722 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1723 /* INP_WUNLOCK(inp) will be performed by the caller */ 1724 rv = 1; 1725 goto tfo_expanded; 1726 } 1727 1728 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1729 /* 1730 * Do a standard 3-way handshake. 1731 */ 1732 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1733 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1734 syncache_free(sc); 1735 else if (sc != &scs) 1736 syncache_insert(sc, sch); /* locks and unlocks sch */ 1737 TCPSTAT_INC(tcps_sndacks); 1738 TCPSTAT_INC(tcps_sndtotal); 1739 } else { 1740 if (sc != &scs) 1741 syncache_free(sc); 1742 TCPSTAT_INC(tcps_sc_dropped); 1743 } 1744 goto donenoprobe; 1745 1746 done: 1747 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1748 donenoprobe: 1749 if (m) { 1750 *lsop = NULL; 1751 m_freem(m); 1752 } 1753 /* 1754 * If tfo_pending is not NULL here, then a TFO SYN that did not 1755 * result in a new socket was processed and the associated pending 1756 * counter has not yet been decremented. All such TFO processing paths 1757 * transit this point. 1758 */ 1759 if (tfo_pending != NULL) 1760 tcp_fastopen_decrement_counter(tfo_pending); 1761 1762 tfo_expanded: 1763 if (cred != NULL) 1764 crfree(cred); 1765 #ifdef MAC 1766 if (sc == &scs) 1767 mac_syncache_destroy(&maclabel); 1768 #endif 1769 return (rv); 1770 } 1771 1772 /* 1773 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1774 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1775 */ 1776 static int 1777 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1778 { 1779 struct ip *ip = NULL; 1780 struct mbuf *m; 1781 struct tcphdr *th = NULL; 1782 int optlen, error = 0; /* Make compiler happy */ 1783 u_int16_t hlen, tlen, mssopt; 1784 struct tcpopt to; 1785 #ifdef INET6 1786 struct ip6_hdr *ip6 = NULL; 1787 #endif 1788 hlen = 1789 #ifdef INET6 1790 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1791 #endif 1792 sizeof(struct ip); 1793 tlen = hlen + sizeof(struct tcphdr); 1794 1795 /* Determine MSS we advertize to other end of connection. */ 1796 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1797 1798 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1799 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1800 ("syncache: mbuf too small")); 1801 1802 /* Create the IP+TCP header from scratch. */ 1803 m = m_gethdr(M_NOWAIT, MT_DATA); 1804 if (m == NULL) 1805 return (ENOBUFS); 1806 #ifdef MAC 1807 mac_syncache_create_mbuf(sc->sc_label, m); 1808 #endif 1809 m->m_data += max_linkhdr; 1810 m->m_len = tlen; 1811 m->m_pkthdr.len = tlen; 1812 m->m_pkthdr.rcvif = NULL; 1813 1814 #ifdef INET6 1815 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1816 ip6 = mtod(m, struct ip6_hdr *); 1817 ip6->ip6_vfc = IPV6_VERSION; 1818 ip6->ip6_nxt = IPPROTO_TCP; 1819 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1820 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1821 ip6->ip6_plen = htons(tlen - hlen); 1822 /* ip6_hlim is set after checksum */ 1823 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1824 ip6->ip6_flow |= sc->sc_flowlabel; 1825 1826 th = (struct tcphdr *)(ip6 + 1); 1827 } 1828 #endif 1829 #if defined(INET6) && defined(INET) 1830 else 1831 #endif 1832 #ifdef INET 1833 { 1834 ip = mtod(m, struct ip *); 1835 ip->ip_v = IPVERSION; 1836 ip->ip_hl = sizeof(struct ip) >> 2; 1837 ip->ip_len = htons(tlen); 1838 ip->ip_id = 0; 1839 ip->ip_off = 0; 1840 ip->ip_sum = 0; 1841 ip->ip_p = IPPROTO_TCP; 1842 ip->ip_src = sc->sc_inc.inc_laddr; 1843 ip->ip_dst = sc->sc_inc.inc_faddr; 1844 ip->ip_ttl = sc->sc_ip_ttl; 1845 ip->ip_tos = sc->sc_ip_tos; 1846 1847 /* 1848 * See if we should do MTU discovery. Route lookups are 1849 * expensive, so we will only unset the DF bit if: 1850 * 1851 * 1) path_mtu_discovery is disabled 1852 * 2) the SCF_UNREACH flag has been set 1853 */ 1854 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1855 ip->ip_off |= htons(IP_DF); 1856 1857 th = (struct tcphdr *)(ip + 1); 1858 } 1859 #endif /* INET */ 1860 th->th_sport = sc->sc_inc.inc_lport; 1861 th->th_dport = sc->sc_inc.inc_fport; 1862 1863 if (flags & TH_SYN) 1864 th->th_seq = htonl(sc->sc_iss); 1865 else 1866 th->th_seq = htonl(sc->sc_iss + 1); 1867 th->th_ack = htonl(sc->sc_irs + 1); 1868 th->th_off = sizeof(struct tcphdr) >> 2; 1869 th->th_x2 = 0; 1870 th->th_flags = flags; 1871 th->th_win = htons(sc->sc_wnd); 1872 th->th_urp = 0; 1873 1874 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1875 th->th_flags |= TH_ECE; 1876 TCPSTAT_INC(tcps_ecn_shs); 1877 } 1878 1879 /* Tack on the TCP options. */ 1880 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1881 to.to_flags = 0; 1882 1883 if (flags & TH_SYN) { 1884 to.to_mss = mssopt; 1885 to.to_flags = TOF_MSS; 1886 if (sc->sc_flags & SCF_WINSCALE) { 1887 to.to_wscale = sc->sc_requested_r_scale; 1888 to.to_flags |= TOF_SCALE; 1889 } 1890 if (sc->sc_flags & SCF_SACK) 1891 to.to_flags |= TOF_SACKPERM; 1892 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1893 if (sc->sc_flags & SCF_SIGNATURE) 1894 to.to_flags |= TOF_SIGNATURE; 1895 #endif 1896 if (sc->sc_tfo_cookie) { 1897 to.to_flags |= TOF_FASTOPEN; 1898 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1899 to.to_tfo_cookie = sc->sc_tfo_cookie; 1900 /* don't send cookie again when retransmitting response */ 1901 sc->sc_tfo_cookie = NULL; 1902 } 1903 } 1904 if (sc->sc_flags & SCF_TIMESTAMP) { 1905 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1906 to.to_tsecr = sc->sc_tsreflect; 1907 to.to_flags |= TOF_TS; 1908 } 1909 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1910 1911 /* Adjust headers by option size. */ 1912 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1913 m->m_len += optlen; 1914 m->m_pkthdr.len += optlen; 1915 #ifdef INET6 1916 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1917 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1918 else 1919 #endif 1920 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1921 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1922 if (sc->sc_flags & SCF_SIGNATURE) { 1923 KASSERT(to.to_flags & TOF_SIGNATURE, 1924 ("tcp_addoptions() didn't set tcp_signature")); 1925 1926 /* NOTE: to.to_signature is inside of mbuf */ 1927 if (!TCPMD5_ENABLED() || 1928 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1929 m_freem(m); 1930 return (EACCES); 1931 } 1932 } 1933 #endif 1934 } else 1935 optlen = 0; 1936 1937 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1938 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1939 /* 1940 * If we have peer's SYN and it has a flowid, then let's assign it to 1941 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1942 * to SYN|ACK due to lack of inp here. 1943 */ 1944 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1945 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1946 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1947 } 1948 #ifdef INET6 1949 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1950 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1951 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1952 IPPROTO_TCP, 0); 1953 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1954 #ifdef TCP_OFFLOAD 1955 if (ADDED_BY_TOE(sc)) { 1956 struct toedev *tod = sc->sc_tod; 1957 1958 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1959 1960 return (error); 1961 } 1962 #endif 1963 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1964 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1965 } 1966 #endif 1967 #if defined(INET6) && defined(INET) 1968 else 1969 #endif 1970 #ifdef INET 1971 { 1972 m->m_pkthdr.csum_flags = CSUM_TCP; 1973 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1974 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1975 #ifdef TCP_OFFLOAD 1976 if (ADDED_BY_TOE(sc)) { 1977 struct toedev *tod = sc->sc_tod; 1978 1979 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1980 1981 return (error); 1982 } 1983 #endif 1984 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1985 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1986 } 1987 #endif 1988 return (error); 1989 } 1990 1991 /* 1992 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1993 * that exceed the capacity of the syncache by avoiding the storage of any 1994 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1995 * attacks where the attacker does not have access to our responses. 1996 * 1997 * Syncookies encode and include all necessary information about the 1998 * connection setup within the SYN|ACK that we send back. That way we 1999 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2000 * (if ever). Normally the syncache and syncookies are running in parallel 2001 * with the latter taking over when the former is exhausted. When matching 2002 * syncache entry is found the syncookie is ignored. 2003 * 2004 * The only reliable information persisting the 3WHS is our initial sequence 2005 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2006 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2007 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2008 * returns and signifies a legitimate connection if it matches the ACK. 2009 * 2010 * The available space of 32 bits to store the hash and to encode the SYN 2011 * option information is very tight and we should have at least 24 bits for 2012 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2013 * 2014 * SYN option information we have to encode to fully restore a connection: 2015 * MSS: is imporant to chose an optimal segment size to avoid IP level 2016 * fragmentation along the path. The common MSS values can be encoded 2017 * in a 3-bit table. Uncommon values are captured by the next lower value 2018 * in the table leading to a slight increase in packetization overhead. 2019 * WSCALE: is necessary to allow large windows to be used for high delay- 2020 * bandwidth product links. Not scaling the window when it was initially 2021 * negotiated is bad for performance as lack of scaling further decreases 2022 * the apparent available send window. We only need to encode the WSCALE 2023 * we received from the remote end. Our end can be recalculated at any 2024 * time. The common WSCALE values can be encoded in a 3-bit table. 2025 * Uncommon values are captured by the next lower value in the table 2026 * making us under-estimate the available window size halving our 2027 * theoretically possible maximum throughput for that connection. 2028 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2029 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2030 * that are included in all segments on a connection. We enable them when 2031 * the ACK has them. 2032 * 2033 * Security of syncookies and attack vectors: 2034 * 2035 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2036 * together with the gloabl secret to make it unique per connection attempt. 2037 * Thus any change of any of those parameters results in a different MAC output 2038 * in an unpredictable way unless a collision is encountered. 24 bits of the 2039 * MAC are embedded into the ISS. 2040 * 2041 * To prevent replay attacks two rotating global secrets are updated with a 2042 * new random value every 15 seconds. The life-time of a syncookie is thus 2043 * 15-30 seconds. 2044 * 2045 * Vector 1: Attacking the secret. This requires finding a weakness in the 2046 * MAC itself or the way it is used here. The attacker can do a chosen plain 2047 * text attack by varying and testing the all parameters under his control. 2048 * The strength depends on the size and randomness of the secret, and the 2049 * cryptographic security of the MAC function. Due to the constant updating 2050 * of the secret the attacker has at most 29.999 seconds to find the secret 2051 * and launch spoofed connections. After that he has to start all over again. 2052 * 2053 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2054 * size an average of 4,823 attempts are required for a 50% chance of success 2055 * to spoof a single syncookie (birthday collision paradox). However the 2056 * attacker is blind and doesn't know if one of his attempts succeeded unless 2057 * he has a side channel to interfere success from. A single connection setup 2058 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2059 * This many attempts are required for each one blind spoofed connection. For 2060 * every additional spoofed connection he has to launch another N attempts. 2061 * Thus for a sustained rate 100 spoofed connections per second approximately 2062 * 1,800,000 packets per second would have to be sent. 2063 * 2064 * NB: The MAC function should be fast so that it doesn't become a CPU 2065 * exhaustion attack vector itself. 2066 * 2067 * References: 2068 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2069 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2070 * http://cr.yp.to/syncookies.html (overview) 2071 * http://cr.yp.to/syncookies/archive (details) 2072 * 2073 * 2074 * Schematic construction of a syncookie enabled Initial Sequence Number: 2075 * 0 1 2 3 2076 * 12345678901234567890123456789012 2077 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2078 * 2079 * x 24 MAC (truncated) 2080 * W 3 Send Window Scale index 2081 * M 3 MSS index 2082 * S 1 SACK permitted 2083 * P 1 Odd/even secret 2084 */ 2085 2086 /* 2087 * Distribution and probability of certain MSS values. Those in between are 2088 * rounded down to the next lower one. 2089 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2090 * .2% .3% 5% 7% 7% 20% 15% 45% 2091 */ 2092 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2093 2094 /* 2095 * Distribution and probability of certain WSCALE values. We have to map the 2096 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2097 * bits based on prevalence of certain values. Where we don't have an exact 2098 * match for are rounded down to the next lower one letting us under-estimate 2099 * the true available window. At the moment this would happen only for the 2100 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2101 * and window size). The absence of the WSCALE option (no scaling in either 2102 * direction) is encoded with index zero. 2103 * [WSCALE values histograms, Allman, 2012] 2104 * X 10 10 35 5 6 14 10% by host 2105 * X 11 4 5 5 18 49 3% by connections 2106 */ 2107 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2108 2109 /* 2110 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2111 * and good cryptographic properties. 2112 */ 2113 static uint32_t 2114 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2115 uint8_t *secbits, uintptr_t secmod) 2116 { 2117 SIPHASH_CTX ctx; 2118 uint32_t siphash[2]; 2119 2120 SipHash24_Init(&ctx); 2121 SipHash_SetKey(&ctx, secbits); 2122 switch (inc->inc_flags & INC_ISIPV6) { 2123 #ifdef INET 2124 case 0: 2125 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2126 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2127 break; 2128 #endif 2129 #ifdef INET6 2130 case INC_ISIPV6: 2131 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2132 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2133 break; 2134 #endif 2135 } 2136 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2137 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2138 SipHash_Update(&ctx, &irs, sizeof(irs)); 2139 SipHash_Update(&ctx, &flags, sizeof(flags)); 2140 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2141 SipHash_Final((u_int8_t *)&siphash, &ctx); 2142 2143 return (siphash[0] ^ siphash[1]); 2144 } 2145 2146 static tcp_seq 2147 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2148 { 2149 u_int i, secbit, wscale; 2150 uint32_t iss, hash; 2151 uint8_t *secbits; 2152 union syncookie cookie; 2153 2154 cookie.cookie = 0; 2155 2156 /* Map our computed MSS into the 3-bit index. */ 2157 for (i = nitems(tcp_sc_msstab) - 1; 2158 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2159 i--) 2160 ; 2161 cookie.flags.mss_idx = i; 2162 2163 /* 2164 * Map the send window scale into the 3-bit index but only if 2165 * the wscale option was received. 2166 */ 2167 if (sc->sc_flags & SCF_WINSCALE) { 2168 wscale = sc->sc_requested_s_scale; 2169 for (i = nitems(tcp_sc_wstab) - 1; 2170 tcp_sc_wstab[i] > wscale && i > 0; 2171 i--) 2172 ; 2173 cookie.flags.wscale_idx = i; 2174 } 2175 2176 /* Can we do SACK? */ 2177 if (sc->sc_flags & SCF_SACK) 2178 cookie.flags.sack_ok = 1; 2179 2180 /* Which of the two secrets to use. */ 2181 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2182 cookie.flags.odd_even = secbit; 2183 2184 secbits = V_tcp_syncache.secret.key[secbit]; 2185 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2186 (uintptr_t)sch); 2187 2188 /* 2189 * Put the flags into the hash and XOR them to get better ISS number 2190 * variance. This doesn't enhance the cryptographic strength and is 2191 * done to prevent the 8 cookie bits from showing up directly on the 2192 * wire. 2193 */ 2194 iss = hash & ~0xff; 2195 iss |= cookie.cookie ^ (hash >> 24); 2196 2197 TCPSTAT_INC(tcps_sc_sendcookie); 2198 return (iss); 2199 } 2200 2201 static struct syncache * 2202 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2203 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2204 struct socket *lso) 2205 { 2206 uint32_t hash; 2207 uint8_t *secbits; 2208 tcp_seq ack, seq; 2209 int wnd, wscale = 0; 2210 union syncookie cookie; 2211 2212 /* 2213 * Pull information out of SYN-ACK/ACK and revert sequence number 2214 * advances. 2215 */ 2216 ack = th->th_ack - 1; 2217 seq = th->th_seq - 1; 2218 2219 /* 2220 * Unpack the flags containing enough information to restore the 2221 * connection. 2222 */ 2223 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2224 2225 /* Which of the two secrets to use. */ 2226 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2227 2228 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2229 2230 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2231 if ((ack & ~0xff) != (hash & ~0xff)) 2232 return (NULL); 2233 2234 /* Fill in the syncache values. */ 2235 sc->sc_flags = 0; 2236 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2237 sc->sc_ipopts = NULL; 2238 2239 sc->sc_irs = seq; 2240 sc->sc_iss = ack; 2241 2242 switch (inc->inc_flags & INC_ISIPV6) { 2243 #ifdef INET 2244 case 0: 2245 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2246 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2247 break; 2248 #endif 2249 #ifdef INET6 2250 case INC_ISIPV6: 2251 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2252 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2253 break; 2254 #endif 2255 } 2256 2257 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2258 2259 /* We can simply recompute receive window scale we sent earlier. */ 2260 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2261 wscale++; 2262 2263 /* Only use wscale if it was enabled in the orignal SYN. */ 2264 if (cookie.flags.wscale_idx > 0) { 2265 sc->sc_requested_r_scale = wscale; 2266 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2267 sc->sc_flags |= SCF_WINSCALE; 2268 } 2269 2270 wnd = lso->sol_sbrcv_hiwat; 2271 wnd = imax(wnd, 0); 2272 wnd = imin(wnd, TCP_MAXWIN); 2273 sc->sc_wnd = wnd; 2274 2275 if (cookie.flags.sack_ok) 2276 sc->sc_flags |= SCF_SACK; 2277 2278 if (to->to_flags & TOF_TS) { 2279 sc->sc_flags |= SCF_TIMESTAMP; 2280 sc->sc_tsreflect = to->to_tsval; 2281 sc->sc_tsoff = tcp_new_ts_offset(inc); 2282 } 2283 2284 if (to->to_flags & TOF_SIGNATURE) 2285 sc->sc_flags |= SCF_SIGNATURE; 2286 2287 sc->sc_rxmits = 0; 2288 2289 TCPSTAT_INC(tcps_sc_recvcookie); 2290 return (sc); 2291 } 2292 2293 #ifdef INVARIANTS 2294 static int 2295 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2296 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2297 struct socket *lso) 2298 { 2299 struct syncache scs, *scx; 2300 char *s; 2301 2302 bzero(&scs, sizeof(scs)); 2303 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2304 2305 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2306 return (0); 2307 2308 if (scx != NULL) { 2309 if (sc->sc_peer_mss != scx->sc_peer_mss) 2310 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2311 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2312 2313 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2314 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2315 s, __func__, sc->sc_requested_r_scale, 2316 scx->sc_requested_r_scale); 2317 2318 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2319 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2320 s, __func__, sc->sc_requested_s_scale, 2321 scx->sc_requested_s_scale); 2322 2323 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2324 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2325 } 2326 2327 if (s != NULL) 2328 free(s, M_TCPLOG); 2329 return (0); 2330 } 2331 #endif /* INVARIANTS */ 2332 2333 static void 2334 syncookie_reseed(void *arg) 2335 { 2336 struct tcp_syncache *sc = arg; 2337 uint8_t *secbits; 2338 int secbit; 2339 2340 /* 2341 * Reseeding the secret doesn't have to be protected by a lock. 2342 * It only must be ensured that the new random values are visible 2343 * to all CPUs in a SMP environment. The atomic with release 2344 * semantics ensures that. 2345 */ 2346 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2347 secbits = sc->secret.key[secbit]; 2348 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2349 atomic_add_rel_int(&sc->secret.oddeven, 1); 2350 2351 /* Reschedule ourself. */ 2352 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2353 } 2354 2355 /* 2356 * We have overflowed a bucket. Let's pause dealing with the syncache. 2357 * This function will increment the bucketoverflow statistics appropriately 2358 * (once per pause when pausing is enabled; otherwise, once per overflow). 2359 */ 2360 static void 2361 syncache_pause(struct in_conninfo *inc) 2362 { 2363 time_t delta; 2364 const char *s; 2365 2366 /* XXX: 2367 * 2. Add sysctl read here so we don't get the benefit of this 2368 * change without the new sysctl. 2369 */ 2370 2371 /* 2372 * Try an unlocked read. If we already know that another thread 2373 * has activated the feature, there is no need to proceed. 2374 */ 2375 if (V_tcp_syncache.paused) 2376 return; 2377 2378 /* Are cookied enabled? If not, we can't pause. */ 2379 if (!V_tcp_syncookies) { 2380 TCPSTAT_INC(tcps_sc_bucketoverflow); 2381 return; 2382 } 2383 2384 /* 2385 * We may be the first thread to find an overflow. Get the lock 2386 * and evaluate if we need to take action. 2387 */ 2388 mtx_lock(&V_tcp_syncache.pause_mtx); 2389 if (V_tcp_syncache.paused) { 2390 mtx_unlock(&V_tcp_syncache.pause_mtx); 2391 return; 2392 } 2393 2394 /* Activate protection. */ 2395 V_tcp_syncache.paused = true; 2396 TCPSTAT_INC(tcps_sc_bucketoverflow); 2397 2398 /* 2399 * Determine the last backoff time. If we are seeing a re-newed 2400 * attack within that same time after last reactivating the syncache, 2401 * consider it an extension of the same attack. 2402 */ 2403 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2404 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2405 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2406 delta <<= 1; 2407 V_tcp_syncache.pause_backoff++; 2408 } 2409 } else { 2410 delta = TCP_SYNCACHE_PAUSE_TIME; 2411 V_tcp_syncache.pause_backoff = 0; 2412 } 2413 2414 /* Log a warning, including IP addresses, if able. */ 2415 if (inc != NULL) 2416 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2417 else 2418 s = (const char *)NULL; 2419 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2420 "the next %lld seconds%s%s%s\n", (long long)delta, 2421 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2422 (s != NULL) ? ")" : ""); 2423 free(__DECONST(void *, s), M_TCPLOG); 2424 2425 /* Use the calculated delta to set a new pause time. */ 2426 V_tcp_syncache.pause_until = time_uptime + delta; 2427 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2428 &V_tcp_syncache); 2429 mtx_unlock(&V_tcp_syncache.pause_mtx); 2430 } 2431 2432 /* Evaluate whether we need to unpause. */ 2433 static void 2434 syncache_unpause(void *arg) 2435 { 2436 struct tcp_syncache *sc; 2437 time_t delta; 2438 2439 sc = arg; 2440 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2441 callout_deactivate(&sc->pause_co); 2442 2443 /* 2444 * Check to make sure we are not running early. If the pause 2445 * time has expired, then deactivate the protection. 2446 */ 2447 if ((delta = sc->pause_until - time_uptime) > 0) 2448 callout_schedule(&sc->pause_co, delta * hz); 2449 else 2450 sc->paused = false; 2451 } 2452 2453 /* 2454 * Exports the syncache entries to userland so that netstat can display 2455 * them alongside the other sockets. This function is intended to be 2456 * called only from tcp_pcblist. 2457 * 2458 * Due to concurrency on an active system, the number of pcbs exported 2459 * may have no relation to max_pcbs. max_pcbs merely indicates the 2460 * amount of space the caller allocated for this function to use. 2461 */ 2462 int 2463 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2464 { 2465 struct xtcpcb xt; 2466 struct syncache *sc; 2467 struct syncache_head *sch; 2468 int count, error, i; 2469 2470 for (count = 0, error = 0, 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 (count >= max_pcbs) { 2475 SCH_UNLOCK(sch); 2476 goto exit; 2477 } 2478 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2479 continue; 2480 bzero(&xt, sizeof(xt)); 2481 xt.xt_len = sizeof(xt); 2482 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2483 xt.xt_inp.inp_vflag = INP_IPV6; 2484 else 2485 xt.xt_inp.inp_vflag = INP_IPV4; 2486 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2487 sizeof (struct in_conninfo)); 2488 xt.t_state = TCPS_SYN_RECEIVED; 2489 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2490 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2491 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2492 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2493 error = SYSCTL_OUT(req, &xt, sizeof xt); 2494 if (error) { 2495 SCH_UNLOCK(sch); 2496 goto exit; 2497 } 2498 count++; 2499 } 2500 SCH_UNLOCK(sch); 2501 } 2502 exit: 2503 *pcbs_exported = count; 2504 return error; 2505 } 2506