1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD$"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_pcbgroup.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/limits.h> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/malloc.h> 49 #include <sys/mbuf.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 #include <sys/ucred.h> 56 57 #include <sys/md5.h> 58 #include <crypto/siphash/siphash.h> 59 60 #include <vm/uma.h> 61 62 #include <net/if.h> 63 #include <net/if_var.h> 64 #include <net/route.h> 65 #include <net/vnet.h> 66 67 #include <netinet/in.h> 68 #include <netinet/in_systm.h> 69 #include <netinet/ip.h> 70 #include <netinet/in_var.h> 71 #include <netinet/in_pcb.h> 72 #include <netinet/ip_var.h> 73 #include <netinet/ip_options.h> 74 #ifdef INET6 75 #include <netinet/ip6.h> 76 #include <netinet/icmp6.h> 77 #include <netinet6/nd6.h> 78 #include <netinet6/ip6_var.h> 79 #include <netinet6/in6_pcb.h> 80 #endif 81 #include <netinet/tcp.h> 82 #include <netinet/tcp_fsm.h> 83 #include <netinet/tcp_seq.h> 84 #include <netinet/tcp_timer.h> 85 #include <netinet/tcp_var.h> 86 #include <netinet/tcp_syncache.h> 87 #ifdef INET6 88 #include <netinet6/tcp6_var.h> 89 #endif 90 #ifdef TCP_OFFLOAD 91 #include <netinet/toecore.h> 92 #endif 93 94 #ifdef IPSEC 95 #include <netipsec/ipsec.h> 96 #ifdef INET6 97 #include <netipsec/ipsec6.h> 98 #endif 99 #include <netipsec/key.h> 100 #endif /*IPSEC*/ 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 static VNET_DEFINE(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 #ifdef TCP_OFFLOAD 119 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 120 #endif 121 122 static void syncache_drop(struct syncache *, struct syncache_head *); 123 static void syncache_free(struct syncache *); 124 static void syncache_insert(struct syncache *, struct syncache_head *); 125 static int syncache_respond(struct syncache *, struct syncache_head *, int); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 129 int docallout); 130 static void syncache_timer(void *); 131 132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 133 uint8_t *, uintptr_t); 134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 135 static struct syncache 136 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 137 struct syncache *, struct tcphdr *, struct tcpopt *, 138 struct socket *); 139 static void syncookie_reseed(void *); 140 #ifdef INVARIANTS 141 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 142 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 143 struct socket *lso); 144 #endif 145 146 /* 147 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 148 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 149 * the odds are that the user has given up attempting to connect by then. 150 */ 151 #define SYNCACHE_MAXREXMTS 3 152 153 /* Arbitrary values */ 154 #define TCP_SYNCACHE_HASHSIZE 512 155 #define TCP_SYNCACHE_BUCKETLIMIT 30 156 157 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 158 #define V_tcp_syncache VNET(tcp_syncache) 159 160 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 161 "TCP SYN cache"); 162 163 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 164 &VNET_NAME(tcp_syncache.bucket_limit), 0, 165 "Per-bucket hash limit for syncache"); 166 167 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 168 &VNET_NAME(tcp_syncache.cache_limit), 0, 169 "Overall entry limit for syncache"); 170 171 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 172 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 173 174 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 175 &VNET_NAME(tcp_syncache.hashsize), 0, 176 "Size of TCP syncache hashtable"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 179 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 180 "Limit on SYN/ACK retransmissions"); 181 182 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 183 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 184 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 185 "Send reset on socket allocation failure"); 186 187 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 188 189 #define SYNCACHE_HASH(inc, mask) \ 190 ((V_tcp_syncache.hash_secret ^ \ 191 (inc)->inc_faddr.s_addr ^ \ 192 ((inc)->inc_faddr.s_addr >> 16) ^ \ 193 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 194 195 #define SYNCACHE_HASH6(inc, mask) \ 196 ((V_tcp_syncache.hash_secret ^ \ 197 (inc)->inc6_faddr.s6_addr32[0] ^ \ 198 (inc)->inc6_faddr.s6_addr32[3] ^ \ 199 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 200 201 #define ENDPTS_EQ(a, b) ( \ 202 (a)->ie_fport == (b)->ie_fport && \ 203 (a)->ie_lport == (b)->ie_lport && \ 204 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 205 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 206 ) 207 208 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 209 210 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 211 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 212 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 213 214 /* 215 * Requires the syncache entry to be already removed from the bucket list. 216 */ 217 static void 218 syncache_free(struct syncache *sc) 219 { 220 221 if (sc->sc_ipopts) 222 (void) m_free(sc->sc_ipopts); 223 if (sc->sc_cred) 224 crfree(sc->sc_cred); 225 #ifdef MAC 226 mac_syncache_destroy(&sc->sc_label); 227 #endif 228 229 uma_zfree(V_tcp_syncache.zone, sc); 230 } 231 232 void 233 syncache_init(void) 234 { 235 int i; 236 237 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 238 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 239 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 240 V_tcp_syncache.hash_secret = arc4random(); 241 242 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 243 &V_tcp_syncache.hashsize); 244 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 245 &V_tcp_syncache.bucket_limit); 246 if (!powerof2(V_tcp_syncache.hashsize) || 247 V_tcp_syncache.hashsize == 0) { 248 printf("WARNING: syncache hash size is not a power of 2.\n"); 249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 250 } 251 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 252 253 /* Set limits. */ 254 V_tcp_syncache.cache_limit = 255 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 257 &V_tcp_syncache.cache_limit); 258 259 /* Allocate the hash table. */ 260 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 261 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 262 263 #ifdef VIMAGE 264 V_tcp_syncache.vnet = curvnet; 265 #endif 266 267 /* Initialize the hash buckets. */ 268 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 269 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 270 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 271 NULL, MTX_DEF); 272 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 273 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 274 V_tcp_syncache.hashbase[i].sch_length = 0; 275 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 276 } 277 278 /* Create the syncache entry zone. */ 279 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 280 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 281 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 282 V_tcp_syncache.cache_limit); 283 284 /* Start the SYN cookie reseeder callout. */ 285 callout_init(&V_tcp_syncache.secret.reseed, 1); 286 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 287 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 288 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 289 syncookie_reseed, &V_tcp_syncache); 290 } 291 292 #ifdef VIMAGE 293 void 294 syncache_destroy(void) 295 { 296 struct syncache_head *sch; 297 struct syncache *sc, *nsc; 298 int i; 299 300 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 301 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 302 303 sch = &V_tcp_syncache.hashbase[i]; 304 callout_drain(&sch->sch_timer); 305 306 SCH_LOCK(sch); 307 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 308 syncache_drop(sc, sch); 309 SCH_UNLOCK(sch); 310 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 311 ("%s: sch->sch_bucket not empty", __func__)); 312 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 313 __func__, sch->sch_length)); 314 mtx_destroy(&sch->sch_mtx); 315 } 316 317 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 318 ("%s: cache_count not 0", __func__)); 319 320 /* Free the allocated global resources. */ 321 uma_zdestroy(V_tcp_syncache.zone); 322 free(V_tcp_syncache.hashbase, M_SYNCACHE); 323 324 callout_drain(&V_tcp_syncache.secret.reseed); 325 } 326 #endif 327 328 /* 329 * Inserts a syncache entry into the specified bucket row. 330 * Locks and unlocks the syncache_head autonomously. 331 */ 332 static void 333 syncache_insert(struct syncache *sc, struct syncache_head *sch) 334 { 335 struct syncache *sc2; 336 337 SCH_LOCK(sch); 338 339 /* 340 * Make sure that we don't overflow the per-bucket limit. 341 * If the bucket is full, toss the oldest element. 342 */ 343 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 344 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 345 ("sch->sch_length incorrect")); 346 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 347 syncache_drop(sc2, sch); 348 TCPSTAT_INC(tcps_sc_bucketoverflow); 349 } 350 351 /* Put it into the bucket. */ 352 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 353 sch->sch_length++; 354 355 #ifdef TCP_OFFLOAD 356 if (ADDED_BY_TOE(sc)) { 357 struct toedev *tod = sc->sc_tod; 358 359 tod->tod_syncache_added(tod, sc->sc_todctx); 360 } 361 #endif 362 363 /* Reinitialize the bucket row's timer. */ 364 if (sch->sch_length == 1) 365 sch->sch_nextc = ticks + INT_MAX; 366 syncache_timeout(sc, sch, 1); 367 368 SCH_UNLOCK(sch); 369 370 TCPSTAT_INC(tcps_sc_added); 371 } 372 373 /* 374 * Remove and free entry from syncache bucket row. 375 * Expects locked syncache head. 376 */ 377 static void 378 syncache_drop(struct syncache *sc, struct syncache_head *sch) 379 { 380 381 SCH_LOCK_ASSERT(sch); 382 383 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 384 sch->sch_length--; 385 386 #ifdef TCP_OFFLOAD 387 if (ADDED_BY_TOE(sc)) { 388 struct toedev *tod = sc->sc_tod; 389 390 tod->tod_syncache_removed(tod, sc->sc_todctx); 391 } 392 #endif 393 394 syncache_free(sc); 395 } 396 397 /* 398 * Engage/reengage time on bucket row. 399 */ 400 static void 401 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 402 { 403 sc->sc_rxttime = ticks + 404 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 405 sc->sc_rxmits++; 406 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 407 sch->sch_nextc = sc->sc_rxttime; 408 if (docallout) 409 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 410 syncache_timer, (void *)sch); 411 } 412 } 413 414 /* 415 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 416 * If we have retransmitted an entry the maximum number of times, expire it. 417 * One separate timer for each bucket row. 418 */ 419 static void 420 syncache_timer(void *xsch) 421 { 422 struct syncache_head *sch = (struct syncache_head *)xsch; 423 struct syncache *sc, *nsc; 424 int tick = ticks; 425 char *s; 426 427 CURVNET_SET(sch->sch_sc->vnet); 428 429 /* NB: syncache_head has already been locked by the callout. */ 430 SCH_LOCK_ASSERT(sch); 431 432 /* 433 * In the following cycle we may remove some entries and/or 434 * advance some timeouts, so re-initialize the bucket timer. 435 */ 436 sch->sch_nextc = tick + INT_MAX; 437 438 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 439 /* 440 * We do not check if the listen socket still exists 441 * and accept the case where the listen socket may be 442 * gone by the time we resend the SYN/ACK. We do 443 * not expect this to happens often. If it does, 444 * then the RST will be sent by the time the remote 445 * host does the SYN/ACK->ACK. 446 */ 447 if (TSTMP_GT(sc->sc_rxttime, tick)) { 448 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 449 sch->sch_nextc = sc->sc_rxttime; 450 continue; 451 } 452 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 453 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 454 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 455 "giving up and removing syncache entry\n", 456 s, __func__); 457 free(s, M_TCPLOG); 458 } 459 syncache_drop(sc, sch); 460 TCPSTAT_INC(tcps_sc_stale); 461 continue; 462 } 463 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 464 log(LOG_DEBUG, "%s; %s: Response timeout, " 465 "retransmitting (%u) SYN|ACK\n", 466 s, __func__, sc->sc_rxmits); 467 free(s, M_TCPLOG); 468 } 469 470 syncache_respond(sc, sch, 1); 471 TCPSTAT_INC(tcps_sc_retransmitted); 472 syncache_timeout(sc, sch, 0); 473 } 474 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 475 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 476 syncache_timer, (void *)(sch)); 477 CURVNET_RESTORE(); 478 } 479 480 /* 481 * Find an entry in the syncache. 482 * Returns always with locked syncache_head plus a matching entry or NULL. 483 */ 484 static struct syncache * 485 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 486 { 487 struct syncache *sc; 488 struct syncache_head *sch; 489 490 #ifdef INET6 491 if (inc->inc_flags & INC_ISIPV6) { 492 sch = &V_tcp_syncache.hashbase[ 493 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)]; 494 *schp = sch; 495 496 SCH_LOCK(sch); 497 498 /* Circle through bucket row to find matching entry. */ 499 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 500 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 501 return (sc); 502 } 503 } else 504 #endif 505 { 506 sch = &V_tcp_syncache.hashbase[ 507 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)]; 508 *schp = sch; 509 510 SCH_LOCK(sch); 511 512 /* Circle through bucket row to find matching entry. */ 513 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 514 #ifdef INET6 515 if (sc->sc_inc.inc_flags & INC_ISIPV6) 516 continue; 517 #endif 518 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 519 return (sc); 520 } 521 } 522 SCH_LOCK_ASSERT(*schp); 523 return (NULL); /* always returns with locked sch */ 524 } 525 526 /* 527 * This function is called when we get a RST for a 528 * non-existent connection, so that we can see if the 529 * connection is in the syn cache. If it is, zap it. 530 */ 531 void 532 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 533 { 534 struct syncache *sc; 535 struct syncache_head *sch; 536 char *s = NULL; 537 538 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 539 SCH_LOCK_ASSERT(sch); 540 541 /* 542 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 543 * See RFC 793 page 65, section SEGMENT ARRIVES. 544 */ 545 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 546 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 547 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 548 "FIN flag set, segment ignored\n", s, __func__); 549 TCPSTAT_INC(tcps_badrst); 550 goto done; 551 } 552 553 /* 554 * No corresponding connection was found in syncache. 555 * If syncookies are enabled and possibly exclusively 556 * used, or we are under memory pressure, a valid RST 557 * may not find a syncache entry. In that case we're 558 * done and no SYN|ACK retransmissions will happen. 559 * Otherwise the RST was misdirected or spoofed. 560 */ 561 if (sc == NULL) { 562 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 563 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 564 "syncache entry (possibly syncookie only), " 565 "segment ignored\n", s, __func__); 566 TCPSTAT_INC(tcps_badrst); 567 goto done; 568 } 569 570 /* 571 * If the RST bit is set, check the sequence number to see 572 * if this is a valid reset segment. 573 * RFC 793 page 37: 574 * In all states except SYN-SENT, all reset (RST) segments 575 * are validated by checking their SEQ-fields. A reset is 576 * valid if its sequence number is in the window. 577 * 578 * The sequence number in the reset segment is normally an 579 * echo of our outgoing acknowlegement numbers, but some hosts 580 * send a reset with the sequence number at the rightmost edge 581 * of our receive window, and we have to handle this case. 582 */ 583 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 584 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 585 syncache_drop(sc, sch); 586 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 587 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 588 "connection attempt aborted by remote endpoint\n", 589 s, __func__); 590 TCPSTAT_INC(tcps_sc_reset); 591 } else { 592 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 593 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 594 "IRS %u (+WND %u), segment ignored\n", 595 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 596 TCPSTAT_INC(tcps_badrst); 597 } 598 599 done: 600 if (s != NULL) 601 free(s, M_TCPLOG); 602 SCH_UNLOCK(sch); 603 } 604 605 void 606 syncache_badack(struct in_conninfo *inc) 607 { 608 struct syncache *sc; 609 struct syncache_head *sch; 610 611 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 612 SCH_LOCK_ASSERT(sch); 613 if (sc != NULL) { 614 syncache_drop(sc, sch); 615 TCPSTAT_INC(tcps_sc_badack); 616 } 617 SCH_UNLOCK(sch); 618 } 619 620 void 621 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 622 { 623 struct syncache *sc; 624 struct syncache_head *sch; 625 626 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 627 SCH_LOCK_ASSERT(sch); 628 if (sc == NULL) 629 goto done; 630 631 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 632 if (ntohl(th->th_seq) != sc->sc_iss) 633 goto done; 634 635 /* 636 * If we've rertransmitted 3 times and this is our second error, 637 * we remove the entry. Otherwise, we allow it to continue on. 638 * This prevents us from incorrectly nuking an entry during a 639 * spurious network outage. 640 * 641 * See tcp_notify(). 642 */ 643 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 644 sc->sc_flags |= SCF_UNREACH; 645 goto done; 646 } 647 syncache_drop(sc, sch); 648 TCPSTAT_INC(tcps_sc_unreach); 649 done: 650 SCH_UNLOCK(sch); 651 } 652 653 /* 654 * Build a new TCP socket structure from a syncache entry. 655 * 656 * On success return the newly created socket with its underlying inp locked. 657 */ 658 static struct socket * 659 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 660 { 661 struct inpcb *inp = NULL; 662 struct socket *so; 663 struct tcpcb *tp; 664 int error; 665 char *s; 666 667 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 668 669 /* 670 * Ok, create the full blown connection, and set things up 671 * as they would have been set up if we had created the 672 * connection when the SYN arrived. If we can't create 673 * the connection, abort it. 674 */ 675 so = sonewconn(lso, 0); 676 if (so == NULL) { 677 /* 678 * Drop the connection; we will either send a RST or 679 * have the peer retransmit its SYN again after its 680 * RTO and try again. 681 */ 682 TCPSTAT_INC(tcps_listendrop); 683 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 684 log(LOG_DEBUG, "%s; %s: Socket create failed " 685 "due to limits or memory shortage\n", 686 s, __func__); 687 free(s, M_TCPLOG); 688 } 689 goto abort2; 690 } 691 #ifdef MAC 692 mac_socketpeer_set_from_mbuf(m, so); 693 #endif 694 695 inp = sotoinpcb(so); 696 inp->inp_inc.inc_fibnum = so->so_fibnum; 697 INP_WLOCK(inp); 698 /* 699 * Exclusive pcbinfo lock is not required in syncache socket case even 700 * if two inpcb locks can be acquired simultaneously: 701 * - the inpcb in LISTEN state, 702 * - the newly created inp. 703 * 704 * In this case, an inp cannot be at same time in LISTEN state and 705 * just created by an accept() call. 706 */ 707 INP_HASH_WLOCK(&V_tcbinfo); 708 709 /* Insert new socket into PCB hash list. */ 710 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 711 #ifdef INET6 712 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 713 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 714 } else { 715 inp->inp_vflag &= ~INP_IPV6; 716 inp->inp_vflag |= INP_IPV4; 717 #endif 718 inp->inp_laddr = sc->sc_inc.inc_laddr; 719 #ifdef INET6 720 } 721 #endif 722 723 /* 724 * If there's an mbuf and it has a flowid, then let's initialise the 725 * inp with that particular flowid. 726 */ 727 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 728 inp->inp_flowid = m->m_pkthdr.flowid; 729 inp->inp_flowtype = M_HASHTYPE_GET(m); 730 } 731 732 /* 733 * Install in the reservation hash table for now, but don't yet 734 * install a connection group since the full 4-tuple isn't yet 735 * configured. 736 */ 737 inp->inp_lport = sc->sc_inc.inc_lport; 738 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 739 /* 740 * Undo the assignments above if we failed to 741 * put the PCB on the hash lists. 742 */ 743 #ifdef INET6 744 if (sc->sc_inc.inc_flags & INC_ISIPV6) 745 inp->in6p_laddr = in6addr_any; 746 else 747 #endif 748 inp->inp_laddr.s_addr = INADDR_ANY; 749 inp->inp_lport = 0; 750 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 751 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 752 "with error %i\n", 753 s, __func__, error); 754 free(s, M_TCPLOG); 755 } 756 INP_HASH_WUNLOCK(&V_tcbinfo); 757 goto abort; 758 } 759 #ifdef IPSEC 760 /* Copy old policy into new socket's. */ 761 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 762 printf("syncache_socket: could not copy policy\n"); 763 #endif 764 #ifdef INET6 765 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 766 struct inpcb *oinp = sotoinpcb(lso); 767 struct in6_addr laddr6; 768 struct sockaddr_in6 sin6; 769 /* 770 * Inherit socket options from the listening socket. 771 * Note that in6p_inputopts are not (and should not be) 772 * copied, since it stores previously received options and is 773 * used to detect if each new option is different than the 774 * previous one and hence should be passed to a user. 775 * If we copied in6p_inputopts, a user would not be able to 776 * receive options just after calling the accept system call. 777 */ 778 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 779 if (oinp->in6p_outputopts) 780 inp->in6p_outputopts = 781 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 782 783 sin6.sin6_family = AF_INET6; 784 sin6.sin6_len = sizeof(sin6); 785 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 786 sin6.sin6_port = sc->sc_inc.inc_fport; 787 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 788 laddr6 = inp->in6p_laddr; 789 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 790 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 791 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 792 thread0.td_ucred, m)) != 0) { 793 inp->in6p_laddr = laddr6; 794 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 795 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 796 "with error %i\n", 797 s, __func__, error); 798 free(s, M_TCPLOG); 799 } 800 INP_HASH_WUNLOCK(&V_tcbinfo); 801 goto abort; 802 } 803 /* Override flowlabel from in6_pcbconnect. */ 804 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 805 inp->inp_flow |= sc->sc_flowlabel; 806 } 807 #endif /* INET6 */ 808 #if defined(INET) && defined(INET6) 809 else 810 #endif 811 #ifdef INET 812 { 813 struct in_addr laddr; 814 struct sockaddr_in sin; 815 816 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 817 818 if (inp->inp_options == NULL) { 819 inp->inp_options = sc->sc_ipopts; 820 sc->sc_ipopts = NULL; 821 } 822 823 sin.sin_family = AF_INET; 824 sin.sin_len = sizeof(sin); 825 sin.sin_addr = sc->sc_inc.inc_faddr; 826 sin.sin_port = sc->sc_inc.inc_fport; 827 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 828 laddr = inp->inp_laddr; 829 if (inp->inp_laddr.s_addr == INADDR_ANY) 830 inp->inp_laddr = sc->sc_inc.inc_laddr; 831 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 832 thread0.td_ucred, m)) != 0) { 833 inp->inp_laddr = laddr; 834 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 835 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 836 "with error %i\n", 837 s, __func__, error); 838 free(s, M_TCPLOG); 839 } 840 INP_HASH_WUNLOCK(&V_tcbinfo); 841 goto abort; 842 } 843 } 844 #endif /* INET */ 845 INP_HASH_WUNLOCK(&V_tcbinfo); 846 tp = intotcpcb(inp); 847 tcp_state_change(tp, TCPS_SYN_RECEIVED); 848 tp->iss = sc->sc_iss; 849 tp->irs = sc->sc_irs; 850 tcp_rcvseqinit(tp); 851 tcp_sendseqinit(tp); 852 tp->snd_wl1 = sc->sc_irs; 853 tp->snd_max = tp->iss + 1; 854 tp->snd_nxt = tp->iss + 1; 855 tp->rcv_up = sc->sc_irs + 1; 856 tp->rcv_wnd = sc->sc_wnd; 857 tp->rcv_adv += tp->rcv_wnd; 858 tp->last_ack_sent = tp->rcv_nxt; 859 860 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 861 if (sc->sc_flags & SCF_NOOPT) 862 tp->t_flags |= TF_NOOPT; 863 else { 864 if (sc->sc_flags & SCF_WINSCALE) { 865 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 866 tp->snd_scale = sc->sc_requested_s_scale; 867 tp->request_r_scale = sc->sc_requested_r_scale; 868 } 869 if (sc->sc_flags & SCF_TIMESTAMP) { 870 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 871 tp->ts_recent = sc->sc_tsreflect; 872 tp->ts_recent_age = tcp_ts_getticks(); 873 tp->ts_offset = sc->sc_tsoff; 874 } 875 #ifdef TCP_SIGNATURE 876 if (sc->sc_flags & SCF_SIGNATURE) 877 tp->t_flags |= TF_SIGNATURE; 878 #endif 879 if (sc->sc_flags & SCF_SACK) 880 tp->t_flags |= TF_SACK_PERMIT; 881 } 882 883 if (sc->sc_flags & SCF_ECN) 884 tp->t_flags |= TF_ECN_PERMIT; 885 886 /* 887 * Set up MSS and get cached values from tcp_hostcache. 888 * This might overwrite some of the defaults we just set. 889 */ 890 tcp_mss(tp, sc->sc_peer_mss); 891 892 /* 893 * If the SYN,ACK was retransmitted, indicate that CWND to be 894 * limited to one segment in cc_conn_init(). 895 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 896 */ 897 if (sc->sc_rxmits > 1) 898 tp->snd_cwnd = 1; 899 900 #ifdef TCP_OFFLOAD 901 /* 902 * Allow a TOE driver to install its hooks. Note that we hold the 903 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 904 * new connection before the TOE driver has done its thing. 905 */ 906 if (ADDED_BY_TOE(sc)) { 907 struct toedev *tod = sc->sc_tod; 908 909 tod->tod_offload_socket(tod, sc->sc_todctx, so); 910 } 911 #endif 912 /* 913 * Copy and activate timers. 914 */ 915 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 916 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 917 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 918 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 919 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 920 921 soisconnected(so); 922 923 TCPSTAT_INC(tcps_accepts); 924 return (so); 925 926 abort: 927 INP_WUNLOCK(inp); 928 abort2: 929 if (so != NULL) 930 soabort(so); 931 return (NULL); 932 } 933 934 /* 935 * This function gets called when we receive an ACK for a 936 * socket in the LISTEN state. We look up the connection 937 * in the syncache, and if its there, we pull it out of 938 * the cache and turn it into a full-blown connection in 939 * the SYN-RECEIVED state. 940 * 941 * On syncache_socket() success the newly created socket 942 * has its underlying inp locked. 943 */ 944 int 945 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 946 struct socket **lsop, struct mbuf *m) 947 { 948 struct syncache *sc; 949 struct syncache_head *sch; 950 struct syncache scs; 951 char *s; 952 953 /* 954 * Global TCP locks are held because we manipulate the PCB lists 955 * and create a new socket. 956 */ 957 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 958 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 959 ("%s: can handle only ACK", __func__)); 960 961 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 962 SCH_LOCK_ASSERT(sch); 963 964 #ifdef INVARIANTS 965 /* 966 * Test code for syncookies comparing the syncache stored 967 * values with the reconstructed values from the cookie. 968 */ 969 if (sc != NULL) 970 syncookie_cmp(inc, sch, sc, th, to, *lsop); 971 #endif 972 973 if (sc == NULL) { 974 /* 975 * There is no syncache entry, so see if this ACK is 976 * a returning syncookie. To do this, first: 977 * A. See if this socket has had a syncache entry dropped in 978 * the past. We don't want to accept a bogus syncookie 979 * if we've never received a SYN. 980 * B. check that the syncookie is valid. If it is, then 981 * cobble up a fake syncache entry, and return. 982 */ 983 if (!V_tcp_syncookies) { 984 SCH_UNLOCK(sch); 985 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 986 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 987 "segment rejected (syncookies disabled)\n", 988 s, __func__); 989 goto failed; 990 } 991 bzero(&scs, sizeof(scs)); 992 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 993 SCH_UNLOCK(sch); 994 if (sc == NULL) { 995 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 996 log(LOG_DEBUG, "%s; %s: Segment failed " 997 "SYNCOOKIE authentication, segment rejected " 998 "(probably spoofed)\n", s, __func__); 999 goto failed; 1000 } 1001 } else { 1002 /* Pull out the entry to unlock the bucket row. */ 1003 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1004 sch->sch_length--; 1005 #ifdef TCP_OFFLOAD 1006 if (ADDED_BY_TOE(sc)) { 1007 struct toedev *tod = sc->sc_tod; 1008 1009 tod->tod_syncache_removed(tod, sc->sc_todctx); 1010 } 1011 #endif 1012 SCH_UNLOCK(sch); 1013 } 1014 1015 /* 1016 * Segment validation: 1017 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1018 */ 1019 if (th->th_ack != sc->sc_iss + 1) { 1020 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1021 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1022 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1023 goto failed; 1024 } 1025 1026 /* 1027 * The SEQ must fall in the window starting at the received 1028 * initial receive sequence number + 1 (the SYN). 1029 */ 1030 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1031 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1032 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1033 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1034 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1035 goto failed; 1036 } 1037 1038 /* 1039 * If timestamps were not negotiated during SYN/ACK they 1040 * must not appear on any segment during this session. 1041 */ 1042 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1043 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1044 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1045 "segment rejected\n", s, __func__); 1046 goto failed; 1047 } 1048 1049 /* 1050 * If timestamps were negotiated during SYN/ACK they should 1051 * appear on every segment during this session. 1052 * XXXAO: This is only informal as there have been unverified 1053 * reports of non-compliants stacks. 1054 */ 1055 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1056 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1057 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1058 "no action\n", s, __func__); 1059 free(s, M_TCPLOG); 1060 s = NULL; 1061 } 1062 } 1063 1064 /* 1065 * If timestamps were negotiated the reflected timestamp 1066 * must be equal to what we actually sent in the SYN|ACK. 1067 */ 1068 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 1069 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1070 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1071 "segment rejected\n", 1072 s, __func__, to->to_tsecr, sc->sc_ts); 1073 goto failed; 1074 } 1075 1076 *lsop = syncache_socket(sc, *lsop, m); 1077 1078 if (*lsop == NULL) 1079 TCPSTAT_INC(tcps_sc_aborted); 1080 else 1081 TCPSTAT_INC(tcps_sc_completed); 1082 1083 /* how do we find the inp for the new socket? */ 1084 if (sc != &scs) 1085 syncache_free(sc); 1086 return (1); 1087 failed: 1088 if (sc != NULL && sc != &scs) 1089 syncache_free(sc); 1090 if (s != NULL) 1091 free(s, M_TCPLOG); 1092 *lsop = NULL; 1093 return (0); 1094 } 1095 1096 /* 1097 * Given a LISTEN socket and an inbound SYN request, add 1098 * this to the syn cache, and send back a segment: 1099 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1100 * to the source. 1101 * 1102 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1103 * Doing so would require that we hold onto the data and deliver it 1104 * to the application. However, if we are the target of a SYN-flood 1105 * DoS attack, an attacker could send data which would eventually 1106 * consume all available buffer space if it were ACKed. By not ACKing 1107 * the data, we avoid this DoS scenario. 1108 */ 1109 void 1110 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1111 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1112 void *todctx) 1113 { 1114 struct tcpcb *tp; 1115 struct socket *so; 1116 struct syncache *sc = NULL; 1117 struct syncache_head *sch; 1118 struct mbuf *ipopts = NULL; 1119 u_int ltflags; 1120 int win, sb_hiwat, ip_ttl, ip_tos; 1121 char *s; 1122 #ifdef INET6 1123 int autoflowlabel = 0; 1124 #endif 1125 #ifdef MAC 1126 struct label *maclabel; 1127 #endif 1128 struct syncache scs; 1129 struct ucred *cred; 1130 1131 INP_WLOCK_ASSERT(inp); /* listen socket */ 1132 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1133 ("%s: unexpected tcp flags", __func__)); 1134 1135 /* 1136 * Combine all so/tp operations very early to drop the INP lock as 1137 * soon as possible. 1138 */ 1139 so = *lsop; 1140 tp = sototcpcb(so); 1141 cred = crhold(so->so_cred); 1142 1143 #ifdef INET6 1144 if ((inc->inc_flags & INC_ISIPV6) && 1145 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1146 autoflowlabel = 1; 1147 #endif 1148 ip_ttl = inp->inp_ip_ttl; 1149 ip_tos = inp->inp_ip_tos; 1150 win = sbspace(&so->so_rcv); 1151 sb_hiwat = so->so_rcv.sb_hiwat; 1152 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1153 1154 /* By the time we drop the lock these should no longer be used. */ 1155 so = NULL; 1156 tp = NULL; 1157 1158 #ifdef MAC 1159 if (mac_syncache_init(&maclabel) != 0) { 1160 INP_WUNLOCK(inp); 1161 goto done; 1162 } else 1163 mac_syncache_create(maclabel, inp); 1164 #endif 1165 INP_WUNLOCK(inp); 1166 1167 /* 1168 * Remember the IP options, if any. 1169 */ 1170 #ifdef INET6 1171 if (!(inc->inc_flags & INC_ISIPV6)) 1172 #endif 1173 #ifdef INET 1174 ipopts = (m) ? ip_srcroute(m) : NULL; 1175 #else 1176 ipopts = NULL; 1177 #endif 1178 1179 /* 1180 * See if we already have an entry for this connection. 1181 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1182 * 1183 * XXX: should the syncache be re-initialized with the contents 1184 * of the new SYN here (which may have different options?) 1185 * 1186 * XXX: We do not check the sequence number to see if this is a 1187 * real retransmit or a new connection attempt. The question is 1188 * how to handle such a case; either ignore it as spoofed, or 1189 * drop the current entry and create a new one? 1190 */ 1191 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1192 SCH_LOCK_ASSERT(sch); 1193 if (sc != NULL) { 1194 TCPSTAT_INC(tcps_sc_dupsyn); 1195 if (ipopts) { 1196 /* 1197 * If we were remembering a previous source route, 1198 * forget it and use the new one we've been given. 1199 */ 1200 if (sc->sc_ipopts) 1201 (void) m_free(sc->sc_ipopts); 1202 sc->sc_ipopts = ipopts; 1203 } 1204 /* 1205 * Update timestamp if present. 1206 */ 1207 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1208 sc->sc_tsreflect = to->to_tsval; 1209 else 1210 sc->sc_flags &= ~SCF_TIMESTAMP; 1211 #ifdef MAC 1212 /* 1213 * Since we have already unconditionally allocated label 1214 * storage, free it up. The syncache entry will already 1215 * have an initialized label we can use. 1216 */ 1217 mac_syncache_destroy(&maclabel); 1218 #endif 1219 /* Retransmit SYN|ACK and reset retransmit count. */ 1220 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1221 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1222 "resetting timer and retransmitting SYN|ACK\n", 1223 s, __func__); 1224 free(s, M_TCPLOG); 1225 } 1226 if (syncache_respond(sc, sch, 1) == 0) { 1227 sc->sc_rxmits = 0; 1228 syncache_timeout(sc, sch, 1); 1229 TCPSTAT_INC(tcps_sndacks); 1230 TCPSTAT_INC(tcps_sndtotal); 1231 } 1232 SCH_UNLOCK(sch); 1233 goto done; 1234 } 1235 1236 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1237 if (sc == NULL) { 1238 /* 1239 * The zone allocator couldn't provide more entries. 1240 * Treat this as if the cache was full; drop the oldest 1241 * entry and insert the new one. 1242 */ 1243 TCPSTAT_INC(tcps_sc_zonefail); 1244 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1245 syncache_drop(sc, sch); 1246 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1247 if (sc == NULL) { 1248 if (V_tcp_syncookies) { 1249 bzero(&scs, sizeof(scs)); 1250 sc = &scs; 1251 } else { 1252 SCH_UNLOCK(sch); 1253 if (ipopts) 1254 (void) m_free(ipopts); 1255 goto done; 1256 } 1257 } 1258 } 1259 1260 /* 1261 * Fill in the syncache values. 1262 */ 1263 #ifdef MAC 1264 sc->sc_label = maclabel; 1265 #endif 1266 sc->sc_cred = cred; 1267 cred = NULL; 1268 sc->sc_ipopts = ipopts; 1269 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1270 #ifdef INET6 1271 if (!(inc->inc_flags & INC_ISIPV6)) 1272 #endif 1273 { 1274 sc->sc_ip_tos = ip_tos; 1275 sc->sc_ip_ttl = ip_ttl; 1276 } 1277 #ifdef TCP_OFFLOAD 1278 sc->sc_tod = tod; 1279 sc->sc_todctx = todctx; 1280 #endif 1281 sc->sc_irs = th->th_seq; 1282 sc->sc_iss = arc4random(); 1283 sc->sc_flags = 0; 1284 sc->sc_flowlabel = 0; 1285 1286 /* 1287 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1288 * win was derived from socket earlier in the function. 1289 */ 1290 win = imax(win, 0); 1291 win = imin(win, TCP_MAXWIN); 1292 sc->sc_wnd = win; 1293 1294 if (V_tcp_do_rfc1323) { 1295 /* 1296 * A timestamp received in a SYN makes 1297 * it ok to send timestamp requests and replies. 1298 */ 1299 if (to->to_flags & TOF_TS) { 1300 sc->sc_tsreflect = to->to_tsval; 1301 sc->sc_ts = tcp_ts_getticks(); 1302 sc->sc_flags |= SCF_TIMESTAMP; 1303 } 1304 if (to->to_flags & TOF_SCALE) { 1305 int wscale = 0; 1306 1307 /* 1308 * Pick the smallest possible scaling factor that 1309 * will still allow us to scale up to sb_max, aka 1310 * kern.ipc.maxsockbuf. 1311 * 1312 * We do this because there are broken firewalls that 1313 * will corrupt the window scale option, leading to 1314 * the other endpoint believing that our advertised 1315 * window is unscaled. At scale factors larger than 1316 * 5 the unscaled window will drop below 1500 bytes, 1317 * leading to serious problems when traversing these 1318 * broken firewalls. 1319 * 1320 * With the default maxsockbuf of 256K, a scale factor 1321 * of 3 will be chosen by this algorithm. Those who 1322 * choose a larger maxsockbuf should watch out 1323 * for the compatiblity problems mentioned above. 1324 * 1325 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1326 * or <SYN,ACK>) segment itself is never scaled. 1327 */ 1328 while (wscale < TCP_MAX_WINSHIFT && 1329 (TCP_MAXWIN << wscale) < sb_max) 1330 wscale++; 1331 sc->sc_requested_r_scale = wscale; 1332 sc->sc_requested_s_scale = to->to_wscale; 1333 sc->sc_flags |= SCF_WINSCALE; 1334 } 1335 } 1336 #ifdef TCP_SIGNATURE 1337 /* 1338 * If listening socket requested TCP digests, OR received SYN 1339 * contains the option, flag this in the syncache so that 1340 * syncache_respond() will do the right thing with the SYN+ACK. 1341 */ 1342 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1343 sc->sc_flags |= SCF_SIGNATURE; 1344 #endif 1345 if (to->to_flags & TOF_SACKPERM) 1346 sc->sc_flags |= SCF_SACK; 1347 if (to->to_flags & TOF_MSS) 1348 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1349 if (ltflags & TF_NOOPT) 1350 sc->sc_flags |= SCF_NOOPT; 1351 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1352 sc->sc_flags |= SCF_ECN; 1353 1354 if (V_tcp_syncookies) 1355 sc->sc_iss = syncookie_generate(sch, sc); 1356 #ifdef INET6 1357 if (autoflowlabel) { 1358 if (V_tcp_syncookies) 1359 sc->sc_flowlabel = sc->sc_iss; 1360 else 1361 sc->sc_flowlabel = ip6_randomflowlabel(); 1362 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1363 } 1364 #endif 1365 SCH_UNLOCK(sch); 1366 1367 /* 1368 * Do a standard 3-way handshake. 1369 */ 1370 if (syncache_respond(sc, sch, 0) == 0) { 1371 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1372 syncache_free(sc); 1373 else if (sc != &scs) 1374 syncache_insert(sc, sch); /* locks and unlocks sch */ 1375 TCPSTAT_INC(tcps_sndacks); 1376 TCPSTAT_INC(tcps_sndtotal); 1377 } else { 1378 if (sc != &scs) 1379 syncache_free(sc); 1380 TCPSTAT_INC(tcps_sc_dropped); 1381 } 1382 1383 done: 1384 if (cred != NULL) 1385 crfree(cred); 1386 #ifdef MAC 1387 if (sc == &scs) 1388 mac_syncache_destroy(&maclabel); 1389 #endif 1390 if (m) { 1391 1392 *lsop = NULL; 1393 m_freem(m); 1394 } 1395 } 1396 1397 static int 1398 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked) 1399 { 1400 struct ip *ip = NULL; 1401 struct mbuf *m; 1402 struct tcphdr *th = NULL; 1403 int optlen, error = 0; /* Make compiler happy */ 1404 u_int16_t hlen, tlen, mssopt; 1405 struct tcpopt to; 1406 #ifdef INET6 1407 struct ip6_hdr *ip6 = NULL; 1408 #endif 1409 #ifdef TCP_SIGNATURE 1410 struct secasvar *sav; 1411 #endif 1412 1413 hlen = 1414 #ifdef INET6 1415 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1416 #endif 1417 sizeof(struct ip); 1418 tlen = hlen + sizeof(struct tcphdr); 1419 1420 /* Determine MSS we advertize to other end of connection. */ 1421 mssopt = tcp_mssopt(&sc->sc_inc); 1422 if (sc->sc_peer_mss) 1423 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1424 1425 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1426 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1427 ("syncache: mbuf too small")); 1428 1429 /* Create the IP+TCP header from scratch. */ 1430 m = m_gethdr(M_NOWAIT, MT_DATA); 1431 if (m == NULL) 1432 return (ENOBUFS); 1433 #ifdef MAC 1434 mac_syncache_create_mbuf(sc->sc_label, m); 1435 #endif 1436 m->m_data += max_linkhdr; 1437 m->m_len = tlen; 1438 m->m_pkthdr.len = tlen; 1439 m->m_pkthdr.rcvif = NULL; 1440 1441 #ifdef INET6 1442 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1443 ip6 = mtod(m, struct ip6_hdr *); 1444 ip6->ip6_vfc = IPV6_VERSION; 1445 ip6->ip6_nxt = IPPROTO_TCP; 1446 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1447 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1448 ip6->ip6_plen = htons(tlen - hlen); 1449 /* ip6_hlim is set after checksum */ 1450 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1451 ip6->ip6_flow |= sc->sc_flowlabel; 1452 1453 th = (struct tcphdr *)(ip6 + 1); 1454 } 1455 #endif 1456 #if defined(INET6) && defined(INET) 1457 else 1458 #endif 1459 #ifdef INET 1460 { 1461 ip = mtod(m, struct ip *); 1462 ip->ip_v = IPVERSION; 1463 ip->ip_hl = sizeof(struct ip) >> 2; 1464 ip->ip_len = htons(tlen); 1465 ip->ip_id = 0; 1466 ip->ip_off = 0; 1467 ip->ip_sum = 0; 1468 ip->ip_p = IPPROTO_TCP; 1469 ip->ip_src = sc->sc_inc.inc_laddr; 1470 ip->ip_dst = sc->sc_inc.inc_faddr; 1471 ip->ip_ttl = sc->sc_ip_ttl; 1472 ip->ip_tos = sc->sc_ip_tos; 1473 1474 /* 1475 * See if we should do MTU discovery. Route lookups are 1476 * expensive, so we will only unset the DF bit if: 1477 * 1478 * 1) path_mtu_discovery is disabled 1479 * 2) the SCF_UNREACH flag has been set 1480 */ 1481 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1482 ip->ip_off |= htons(IP_DF); 1483 1484 th = (struct tcphdr *)(ip + 1); 1485 } 1486 #endif /* INET */ 1487 th->th_sport = sc->sc_inc.inc_lport; 1488 th->th_dport = sc->sc_inc.inc_fport; 1489 1490 th->th_seq = htonl(sc->sc_iss); 1491 th->th_ack = htonl(sc->sc_irs + 1); 1492 th->th_off = sizeof(struct tcphdr) >> 2; 1493 th->th_x2 = 0; 1494 th->th_flags = TH_SYN|TH_ACK; 1495 th->th_win = htons(sc->sc_wnd); 1496 th->th_urp = 0; 1497 1498 if (sc->sc_flags & SCF_ECN) { 1499 th->th_flags |= TH_ECE; 1500 TCPSTAT_INC(tcps_ecn_shs); 1501 } 1502 1503 /* Tack on the TCP options. */ 1504 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1505 to.to_flags = 0; 1506 1507 to.to_mss = mssopt; 1508 to.to_flags = TOF_MSS; 1509 if (sc->sc_flags & SCF_WINSCALE) { 1510 to.to_wscale = sc->sc_requested_r_scale; 1511 to.to_flags |= TOF_SCALE; 1512 } 1513 if (sc->sc_flags & SCF_TIMESTAMP) { 1514 /* Virgin timestamp or TCP cookie enhanced one. */ 1515 to.to_tsval = sc->sc_ts; 1516 to.to_tsecr = sc->sc_tsreflect; 1517 to.to_flags |= TOF_TS; 1518 } 1519 if (sc->sc_flags & SCF_SACK) 1520 to.to_flags |= TOF_SACKPERM; 1521 #ifdef TCP_SIGNATURE 1522 sav = NULL; 1523 if (sc->sc_flags & SCF_SIGNATURE) { 1524 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1525 if (sav != NULL) 1526 to.to_flags |= TOF_SIGNATURE; 1527 else { 1528 1529 /* 1530 * We've got SCF_SIGNATURE flag 1531 * inherited from listening socket, 1532 * but no SADB key for given source 1533 * address. Assume signature is not 1534 * required and remove signature flag 1535 * instead of silently dropping 1536 * connection. 1537 */ 1538 if (locked == 0) 1539 SCH_LOCK(sch); 1540 sc->sc_flags &= ~SCF_SIGNATURE; 1541 if (locked == 0) 1542 SCH_UNLOCK(sch); 1543 } 1544 } 1545 #endif 1546 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1547 1548 /* Adjust headers by option size. */ 1549 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1550 m->m_len += optlen; 1551 m->m_pkthdr.len += optlen; 1552 1553 #ifdef TCP_SIGNATURE 1554 if (sc->sc_flags & SCF_SIGNATURE) 1555 tcp_signature_do_compute(m, 0, optlen, 1556 to.to_signature, sav); 1557 #endif 1558 #ifdef INET6 1559 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1560 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1561 else 1562 #endif 1563 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1564 } else 1565 optlen = 0; 1566 1567 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1568 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1569 #ifdef INET6 1570 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1571 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1572 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1573 IPPROTO_TCP, 0); 1574 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1575 #ifdef TCP_OFFLOAD 1576 if (ADDED_BY_TOE(sc)) { 1577 struct toedev *tod = sc->sc_tod; 1578 1579 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1580 1581 return (error); 1582 } 1583 #endif 1584 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1585 } 1586 #endif 1587 #if defined(INET6) && defined(INET) 1588 else 1589 #endif 1590 #ifdef INET 1591 { 1592 m->m_pkthdr.csum_flags = CSUM_TCP; 1593 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1594 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1595 #ifdef TCP_OFFLOAD 1596 if (ADDED_BY_TOE(sc)) { 1597 struct toedev *tod = sc->sc_tod; 1598 1599 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1600 1601 return (error); 1602 } 1603 #endif 1604 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1605 } 1606 #endif 1607 return (error); 1608 } 1609 1610 /* 1611 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1612 * that exceed the capacity of the syncache by avoiding the storage of any 1613 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1614 * attacks where the attacker does not have access to our responses. 1615 * 1616 * Syncookies encode and include all necessary information about the 1617 * connection setup within the SYN|ACK that we send back. That way we 1618 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1619 * (if ever). Normally the syncache and syncookies are running in parallel 1620 * with the latter taking over when the former is exhausted. When matching 1621 * syncache entry is found the syncookie is ignored. 1622 * 1623 * The only reliable information persisting the 3WHS is our inital sequence 1624 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1625 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1626 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1627 * returns and signifies a legitimate connection if it matches the ACK. 1628 * 1629 * The available space of 32 bits to store the hash and to encode the SYN 1630 * option information is very tight and we should have at least 24 bits for 1631 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1632 * 1633 * SYN option information we have to encode to fully restore a connection: 1634 * MSS: is imporant to chose an optimal segment size to avoid IP level 1635 * fragmentation along the path. The common MSS values can be encoded 1636 * in a 3-bit table. Uncommon values are captured by the next lower value 1637 * in the table leading to a slight increase in packetization overhead. 1638 * WSCALE: is necessary to allow large windows to be used for high delay- 1639 * bandwidth product links. Not scaling the window when it was initially 1640 * negotiated is bad for performance as lack of scaling further decreases 1641 * the apparent available send window. We only need to encode the WSCALE 1642 * we received from the remote end. Our end can be recalculated at any 1643 * time. The common WSCALE values can be encoded in a 3-bit table. 1644 * Uncommon values are captured by the next lower value in the table 1645 * making us under-estimate the available window size halving our 1646 * theoretically possible maximum throughput for that connection. 1647 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1648 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1649 * that are included in all segments on a connection. We enable them when 1650 * the ACK has them. 1651 * 1652 * Security of syncookies and attack vectors: 1653 * 1654 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1655 * together with the gloabl secret to make it unique per connection attempt. 1656 * Thus any change of any of those parameters results in a different MAC output 1657 * in an unpredictable way unless a collision is encountered. 24 bits of the 1658 * MAC are embedded into the ISS. 1659 * 1660 * To prevent replay attacks two rotating global secrets are updated with a 1661 * new random value every 15 seconds. The life-time of a syncookie is thus 1662 * 15-30 seconds. 1663 * 1664 * Vector 1: Attacking the secret. This requires finding a weakness in the 1665 * MAC itself or the way it is used here. The attacker can do a chosen plain 1666 * text attack by varying and testing the all parameters under his control. 1667 * The strength depends on the size and randomness of the secret, and the 1668 * cryptographic security of the MAC function. Due to the constant updating 1669 * of the secret the attacker has at most 29.999 seconds to find the secret 1670 * and launch spoofed connections. After that he has to start all over again. 1671 * 1672 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1673 * size an average of 4,823 attempts are required for a 50% chance of success 1674 * to spoof a single syncookie (birthday collision paradox). However the 1675 * attacker is blind and doesn't know if one of his attempts succeeded unless 1676 * he has a side channel to interfere success from. A single connection setup 1677 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1678 * This many attempts are required for each one blind spoofed connection. For 1679 * every additional spoofed connection he has to launch another N attempts. 1680 * Thus for a sustained rate 100 spoofed connections per second approximately 1681 * 1,800,000 packets per second would have to be sent. 1682 * 1683 * NB: The MAC function should be fast so that it doesn't become a CPU 1684 * exhaustion attack vector itself. 1685 * 1686 * References: 1687 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1688 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1689 * http://cr.yp.to/syncookies.html (overview) 1690 * http://cr.yp.to/syncookies/archive (details) 1691 * 1692 * 1693 * Schematic construction of a syncookie enabled Initial Sequence Number: 1694 * 0 1 2 3 1695 * 12345678901234567890123456789012 1696 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1697 * 1698 * x 24 MAC (truncated) 1699 * W 3 Send Window Scale index 1700 * M 3 MSS index 1701 * S 1 SACK permitted 1702 * P 1 Odd/even secret 1703 */ 1704 1705 /* 1706 * Distribution and probability of certain MSS values. Those in between are 1707 * rounded down to the next lower one. 1708 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1709 * .2% .3% 5% 7% 7% 20% 15% 45% 1710 */ 1711 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1712 1713 /* 1714 * Distribution and probability of certain WSCALE values. We have to map the 1715 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1716 * bits based on prevalence of certain values. Where we don't have an exact 1717 * match for are rounded down to the next lower one letting us under-estimate 1718 * the true available window. At the moment this would happen only for the 1719 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1720 * and window size). The absence of the WSCALE option (no scaling in either 1721 * direction) is encoded with index zero. 1722 * [WSCALE values histograms, Allman, 2012] 1723 * X 10 10 35 5 6 14 10% by host 1724 * X 11 4 5 5 18 49 3% by connections 1725 */ 1726 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1727 1728 /* 1729 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1730 * and good cryptographic properties. 1731 */ 1732 static uint32_t 1733 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1734 uint8_t *secbits, uintptr_t secmod) 1735 { 1736 SIPHASH_CTX ctx; 1737 uint32_t siphash[2]; 1738 1739 SipHash24_Init(&ctx); 1740 SipHash_SetKey(&ctx, secbits); 1741 switch (inc->inc_flags & INC_ISIPV6) { 1742 #ifdef INET 1743 case 0: 1744 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1745 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1746 break; 1747 #endif 1748 #ifdef INET6 1749 case INC_ISIPV6: 1750 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1751 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1752 break; 1753 #endif 1754 } 1755 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1756 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1757 SipHash_Update(&ctx, &irs, sizeof(irs)); 1758 SipHash_Update(&ctx, &flags, sizeof(flags)); 1759 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1760 SipHash_Final((u_int8_t *)&siphash, &ctx); 1761 1762 return (siphash[0] ^ siphash[1]); 1763 } 1764 1765 static tcp_seq 1766 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1767 { 1768 u_int i, mss, secbit, wscale; 1769 uint32_t iss, hash; 1770 uint8_t *secbits; 1771 union syncookie cookie; 1772 1773 SCH_LOCK_ASSERT(sch); 1774 1775 cookie.cookie = 0; 1776 1777 /* Map our computed MSS into the 3-bit index. */ 1778 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1779 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1; 1780 tcp_sc_msstab[i] > mss && i > 0; 1781 i--) 1782 ; 1783 cookie.flags.mss_idx = i; 1784 1785 /* 1786 * Map the send window scale into the 3-bit index but only if 1787 * the wscale option was received. 1788 */ 1789 if (sc->sc_flags & SCF_WINSCALE) { 1790 wscale = sc->sc_requested_s_scale; 1791 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1; 1792 tcp_sc_wstab[i] > wscale && i > 0; 1793 i--) 1794 ; 1795 cookie.flags.wscale_idx = i; 1796 } 1797 1798 /* Can we do SACK? */ 1799 if (sc->sc_flags & SCF_SACK) 1800 cookie.flags.sack_ok = 1; 1801 1802 /* Which of the two secrets to use. */ 1803 secbit = sch->sch_sc->secret.oddeven & 0x1; 1804 cookie.flags.odd_even = secbit; 1805 1806 secbits = sch->sch_sc->secret.key[secbit]; 1807 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1808 (uintptr_t)sch); 1809 1810 /* 1811 * Put the flags into the hash and XOR them to get better ISS number 1812 * variance. This doesn't enhance the cryptographic strength and is 1813 * done to prevent the 8 cookie bits from showing up directly on the 1814 * wire. 1815 */ 1816 iss = hash & ~0xff; 1817 iss |= cookie.cookie ^ (hash >> 24); 1818 1819 /* Randomize the timestamp. */ 1820 if (sc->sc_flags & SCF_TIMESTAMP) { 1821 sc->sc_ts = arc4random(); 1822 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1823 } 1824 1825 TCPSTAT_INC(tcps_sc_sendcookie); 1826 return (iss); 1827 } 1828 1829 static struct syncache * 1830 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1831 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1832 struct socket *lso) 1833 { 1834 uint32_t hash; 1835 uint8_t *secbits; 1836 tcp_seq ack, seq; 1837 int wnd, wscale = 0; 1838 union syncookie cookie; 1839 1840 SCH_LOCK_ASSERT(sch); 1841 1842 /* 1843 * Pull information out of SYN-ACK/ACK and revert sequence number 1844 * advances. 1845 */ 1846 ack = th->th_ack - 1; 1847 seq = th->th_seq - 1; 1848 1849 /* 1850 * Unpack the flags containing enough information to restore the 1851 * connection. 1852 */ 1853 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 1854 1855 /* Which of the two secrets to use. */ 1856 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 1857 1858 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 1859 1860 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 1861 if ((ack & ~0xff) != (hash & ~0xff)) 1862 return (NULL); 1863 1864 /* Fill in the syncache values. */ 1865 sc->sc_flags = 0; 1866 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1867 sc->sc_ipopts = NULL; 1868 1869 sc->sc_irs = seq; 1870 sc->sc_iss = ack; 1871 1872 switch (inc->inc_flags & INC_ISIPV6) { 1873 #ifdef INET 1874 case 0: 1875 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 1876 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 1877 break; 1878 #endif 1879 #ifdef INET6 1880 case INC_ISIPV6: 1881 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 1882 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 1883 break; 1884 #endif 1885 } 1886 1887 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 1888 1889 /* We can simply recompute receive window scale we sent earlier. */ 1890 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 1891 wscale++; 1892 1893 /* Only use wscale if it was enabled in the orignal SYN. */ 1894 if (cookie.flags.wscale_idx > 0) { 1895 sc->sc_requested_r_scale = wscale; 1896 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 1897 sc->sc_flags |= SCF_WINSCALE; 1898 } 1899 1900 wnd = sbspace(&lso->so_rcv); 1901 wnd = imax(wnd, 0); 1902 wnd = imin(wnd, TCP_MAXWIN); 1903 sc->sc_wnd = wnd; 1904 1905 if (cookie.flags.sack_ok) 1906 sc->sc_flags |= SCF_SACK; 1907 1908 if (to->to_flags & TOF_TS) { 1909 sc->sc_flags |= SCF_TIMESTAMP; 1910 sc->sc_tsreflect = to->to_tsval; 1911 sc->sc_ts = to->to_tsecr; 1912 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 1913 } 1914 1915 if (to->to_flags & TOF_SIGNATURE) 1916 sc->sc_flags |= SCF_SIGNATURE; 1917 1918 sc->sc_rxmits = 0; 1919 1920 TCPSTAT_INC(tcps_sc_recvcookie); 1921 return (sc); 1922 } 1923 1924 #ifdef INVARIANTS 1925 static int 1926 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 1927 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1928 struct socket *lso) 1929 { 1930 struct syncache scs, *scx; 1931 char *s; 1932 1933 bzero(&scs, sizeof(scs)); 1934 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 1935 1936 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 1937 return (0); 1938 1939 if (scx != NULL) { 1940 if (sc->sc_peer_mss != scx->sc_peer_mss) 1941 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 1942 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 1943 1944 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 1945 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 1946 s, __func__, sc->sc_requested_r_scale, 1947 scx->sc_requested_r_scale); 1948 1949 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 1950 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 1951 s, __func__, sc->sc_requested_s_scale, 1952 scx->sc_requested_s_scale); 1953 1954 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 1955 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 1956 } 1957 1958 if (s != NULL) 1959 free(s, M_TCPLOG); 1960 return (0); 1961 } 1962 #endif /* INVARIANTS */ 1963 1964 static void 1965 syncookie_reseed(void *arg) 1966 { 1967 struct tcp_syncache *sc = arg; 1968 uint8_t *secbits; 1969 int secbit; 1970 1971 /* 1972 * Reseeding the secret doesn't have to be protected by a lock. 1973 * It only must be ensured that the new random values are visible 1974 * to all CPUs in a SMP environment. The atomic with release 1975 * semantics ensures that. 1976 */ 1977 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 1978 secbits = sc->secret.key[secbit]; 1979 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 1980 atomic_add_rel_int(&sc->secret.oddeven, 1); 1981 1982 /* Reschedule ourself. */ 1983 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 1984 } 1985 1986 /* 1987 * Returns the current number of syncache entries. This number 1988 * will probably change before you get around to calling 1989 * syncache_pcblist. 1990 */ 1991 int 1992 syncache_pcbcount(void) 1993 { 1994 struct syncache_head *sch; 1995 int count, i; 1996 1997 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 1998 /* No need to lock for a read. */ 1999 sch = &V_tcp_syncache.hashbase[i]; 2000 count += sch->sch_length; 2001 } 2002 return count; 2003 } 2004 2005 /* 2006 * Exports the syncache entries to userland so that netstat can display 2007 * them alongside the other sockets. This function is intended to be 2008 * called only from tcp_pcblist. 2009 * 2010 * Due to concurrency on an active system, the number of pcbs exported 2011 * may have no relation to max_pcbs. max_pcbs merely indicates the 2012 * amount of space the caller allocated for this function to use. 2013 */ 2014 int 2015 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2016 { 2017 struct xtcpcb xt; 2018 struct syncache *sc; 2019 struct syncache_head *sch; 2020 int count, error, i; 2021 2022 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2023 sch = &V_tcp_syncache.hashbase[i]; 2024 SCH_LOCK(sch); 2025 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2026 if (count >= max_pcbs) { 2027 SCH_UNLOCK(sch); 2028 goto exit; 2029 } 2030 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2031 continue; 2032 bzero(&xt, sizeof(xt)); 2033 xt.xt_len = sizeof(xt); 2034 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2035 xt.xt_inp.inp_vflag = INP_IPV6; 2036 else 2037 xt.xt_inp.inp_vflag = INP_IPV4; 2038 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2039 xt.xt_tp.t_inpcb = &xt.xt_inp; 2040 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2041 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2042 xt.xt_socket.xso_len = sizeof (struct xsocket); 2043 xt.xt_socket.so_type = SOCK_STREAM; 2044 xt.xt_socket.so_state = SS_ISCONNECTING; 2045 error = SYSCTL_OUT(req, &xt, sizeof xt); 2046 if (error) { 2047 SCH_UNLOCK(sch); 2048 goto exit; 2049 } 2050 count++; 2051 } 2052 SCH_UNLOCK(sch); 2053 } 2054 exit: 2055 *pcbs_exported = count; 2056 return error; 2057 } 2058