1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006 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. 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 * $FreeBSD$ 33 */ 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 #include "opt_mac.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/kernel.h> 43 #include <sys/sysctl.h> 44 #include <sys/lock.h> 45 #include <sys/mutex.h> 46 #include <sys/malloc.h> 47 #include <sys/mbuf.h> 48 #include <sys/md5.h> 49 #include <sys/proc.h> /* for proc0 declaration */ 50 #include <sys/random.h> 51 #include <sys/socket.h> 52 #include <sys/socketvar.h> 53 #include <sys/syslog.h> 54 55 #include <vm/uma.h> 56 57 #include <net/if.h> 58 #include <net/route.h> 59 60 #include <netinet/in.h> 61 #include <netinet/in_systm.h> 62 #include <netinet/ip.h> 63 #include <netinet/in_var.h> 64 #include <netinet/in_pcb.h> 65 #include <netinet/ip_var.h> 66 #include <netinet/ip_options.h> 67 #ifdef INET6 68 #include <netinet/ip6.h> 69 #include <netinet/icmp6.h> 70 #include <netinet6/nd6.h> 71 #include <netinet6/ip6_var.h> 72 #include <netinet6/in6_pcb.h> 73 #endif 74 #include <netinet/tcp.h> 75 #include <netinet/tcp_fsm.h> 76 #include <netinet/tcp_seq.h> 77 #include <netinet/tcp_timer.h> 78 #include <netinet/tcp_var.h> 79 #ifdef INET6 80 #include <netinet6/tcp6_var.h> 81 #endif 82 83 #ifdef IPSEC 84 #include <netipsec/ipsec.h> 85 #ifdef INET6 86 #include <netipsec/ipsec6.h> 87 #endif 88 #include <netipsec/key.h> 89 #endif /*IPSEC*/ 90 91 #include <machine/in_cksum.h> 92 93 #include <security/mac/mac_framework.h> 94 95 static int tcp_syncookies = 1; 96 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 97 &tcp_syncookies, 0, 98 "Use TCP SYN cookies if the syncache overflows"); 99 100 static int tcp_syncookiesonly = 0; 101 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 102 &tcp_syncookiesonly, 0, 103 "Use only TCP SYN cookies"); 104 105 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 106 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 107 108 struct syncache { 109 TAILQ_ENTRY(syncache) sc_hash; 110 struct in_conninfo sc_inc; /* addresses */ 111 u_long sc_rxttime; /* retransmit time */ 112 u_int16_t sc_rxmits; /* retransmit counter */ 113 114 u_int32_t sc_tsreflect; /* timestamp to reflect */ 115 u_int32_t sc_ts; /* our timestamp to send */ 116 u_int32_t sc_tsoff; /* ts offset w/ syncookies */ 117 u_int32_t sc_flowlabel; /* IPv6 flowlabel */ 118 tcp_seq sc_irs; /* seq from peer */ 119 tcp_seq sc_iss; /* our ISS */ 120 struct mbuf *sc_ipopts; /* source route */ 121 122 u_int16_t sc_peer_mss; /* peer's MSS */ 123 u_int16_t sc_wnd; /* advertised window */ 124 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 125 u_int8_t sc_ip_tos; /* IPv4 TOS */ 126 u_int8_t sc_requested_s_scale:4, 127 sc_requested_r_scale:4; 128 u_int8_t sc_flags; 129 #define SCF_NOOPT 0x01 /* no TCP options */ 130 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 131 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 132 /* MSS is implicit */ 133 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 134 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 135 #define SCF_SACK 0x80 /* send SACK option */ 136 #ifdef MAC 137 struct label *sc_label; /* MAC label reference */ 138 #endif 139 }; 140 141 struct syncache_head { 142 struct mtx sch_mtx; 143 TAILQ_HEAD(sch_head, syncache) sch_bucket; 144 struct callout sch_timer; 145 int sch_nextc; 146 u_int sch_length; 147 u_int sch_oddeven; 148 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 149 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 150 u_int sch_reseed; /* time_uptime, seconds */ 151 }; 152 153 static void syncache_drop(struct syncache *, struct syncache_head *); 154 static void syncache_free(struct syncache *); 155 static void syncache_insert(struct syncache *, struct syncache_head *); 156 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 157 static int syncache_respond(struct syncache *); 158 static struct socket *syncache_socket(struct syncache *, struct socket *, 159 struct mbuf *m); 160 static void syncache_timer(void *); 161 static void syncookie_generate(struct syncache_head *, struct syncache *, 162 u_int32_t *); 163 static struct syncache 164 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 165 struct syncache *, struct tcpopt *, struct tcphdr *, 166 struct socket *); 167 168 /* 169 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 170 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 171 * the odds are that the user has given up attempting to connect by then. 172 */ 173 #define SYNCACHE_MAXREXMTS 3 174 175 /* Arbitrary values */ 176 #define TCP_SYNCACHE_HASHSIZE 512 177 #define TCP_SYNCACHE_BUCKETLIMIT 30 178 179 struct tcp_syncache { 180 struct syncache_head *hashbase; 181 uma_zone_t zone; 182 u_int hashsize; 183 u_int hashmask; 184 u_int bucket_limit; 185 u_int cache_count; /* XXX: unprotected */ 186 u_int cache_limit; 187 u_int rexmt_limit; 188 u_int hash_secret; 189 }; 190 static struct tcp_syncache tcp_syncache; 191 192 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 193 194 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 195 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 196 197 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 198 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 199 200 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 201 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 202 203 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 204 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 205 206 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 207 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 208 209 int tcp_sc_rst_sock_fail = 1; 210 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW, 211 &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure"); 212 213 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 214 215 #define SYNCACHE_HASH(inc, mask) \ 216 ((tcp_syncache.hash_secret ^ \ 217 (inc)->inc_faddr.s_addr ^ \ 218 ((inc)->inc_faddr.s_addr >> 16) ^ \ 219 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 220 221 #define SYNCACHE_HASH6(inc, mask) \ 222 ((tcp_syncache.hash_secret ^ \ 223 (inc)->inc6_faddr.s6_addr32[0] ^ \ 224 (inc)->inc6_faddr.s6_addr32[3] ^ \ 225 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 226 227 #define ENDPTS_EQ(a, b) ( \ 228 (a)->ie_fport == (b)->ie_fport && \ 229 (a)->ie_lport == (b)->ie_lport && \ 230 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 231 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 232 ) 233 234 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 235 236 #define SYNCACHE_TIMEOUT(sc, sch, co) do { \ 237 (sc)->sc_rxmits++; \ 238 (sc)->sc_rxttime = ticks + \ 239 TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \ 240 if ((sch)->sch_nextc > (sc)->sc_rxttime) \ 241 (sch)->sch_nextc = (sc)->sc_rxttime; \ 242 if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \ 243 callout_reset(&(sch)->sch_timer, \ 244 (sch)->sch_nextc - ticks, \ 245 syncache_timer, (void *)(sch)); \ 246 } while (0) 247 248 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 249 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 250 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 251 252 /* 253 * Requires the syncache entry to be already removed from the bucket list. 254 */ 255 static void 256 syncache_free(struct syncache *sc) 257 { 258 if (sc->sc_ipopts) 259 (void) m_free(sc->sc_ipopts); 260 #ifdef MAC 261 mac_destroy_syncache(&sc->sc_label); 262 #endif 263 264 uma_zfree(tcp_syncache.zone, sc); 265 } 266 267 void 268 syncache_init(void) 269 { 270 int i; 271 272 tcp_syncache.cache_count = 0; 273 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 274 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 275 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 276 tcp_syncache.hash_secret = arc4random(); 277 278 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 279 &tcp_syncache.hashsize); 280 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 281 &tcp_syncache.bucket_limit); 282 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 283 printf("WARNING: syncache hash size is not a power of 2.\n"); 284 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 285 } 286 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 287 288 /* Set limits. */ 289 tcp_syncache.cache_limit = 290 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 291 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 292 &tcp_syncache.cache_limit); 293 294 /* Allocate the hash table. */ 295 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 296 tcp_syncache.hashsize * sizeof(struct syncache_head), 297 M_SYNCACHE, M_WAITOK | M_ZERO); 298 299 /* Initialize the hash buckets. */ 300 for (i = 0; i < tcp_syncache.hashsize; i++) { 301 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 302 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 303 NULL, MTX_DEF); 304 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 305 &tcp_syncache.hashbase[i].sch_mtx, 0); 306 tcp_syncache.hashbase[i].sch_length = 0; 307 } 308 309 /* Create the syncache entry zone. */ 310 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 311 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 312 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 313 } 314 315 /* 316 * Inserts a syncache entry into the specified bucket row. 317 * Locks and unlocks the syncache_head autonomously. 318 */ 319 static void 320 syncache_insert(struct syncache *sc, struct syncache_head *sch) 321 { 322 struct syncache *sc2; 323 324 SCH_LOCK(sch); 325 326 /* 327 * Make sure that we don't overflow the per-bucket limit. 328 * If the bucket is full, toss the oldest element. 329 */ 330 if (sch->sch_length >= tcp_syncache.bucket_limit) { 331 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 332 ("sch->sch_length incorrect")); 333 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 334 syncache_drop(sc2, sch); 335 tcpstat.tcps_sc_bucketoverflow++; 336 } 337 338 /* Put it into the bucket. */ 339 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 340 sch->sch_length++; 341 342 /* Reinitialize the bucket row's timer. */ 343 SYNCACHE_TIMEOUT(sc, sch, 1); 344 345 SCH_UNLOCK(sch); 346 347 tcp_syncache.cache_count++; 348 tcpstat.tcps_sc_added++; 349 } 350 351 /* 352 * Remove and free entry from syncache bucket row. 353 * Expects locked syncache head. 354 */ 355 static void 356 syncache_drop(struct syncache *sc, struct syncache_head *sch) 357 { 358 359 SCH_LOCK_ASSERT(sch); 360 361 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 362 sch->sch_length--; 363 364 syncache_free(sc); 365 tcp_syncache.cache_count--; 366 } 367 368 /* 369 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 370 * If we have retransmitted an entry the maximum number of times, expire it. 371 * One separate timer for each bucket row. 372 */ 373 static void 374 syncache_timer(void *xsch) 375 { 376 struct syncache_head *sch = (struct syncache_head *)xsch; 377 struct syncache *sc, *nsc; 378 int tick = ticks; 379 char *s; 380 381 /* NB: syncache_head has already been locked by the callout. */ 382 SCH_LOCK_ASSERT(sch); 383 384 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 385 /* 386 * We do not check if the listen socket still exists 387 * and accept the case where the listen socket may be 388 * gone by the time we resend the SYN/ACK. We do 389 * not expect this to happens often. If it does, 390 * then the RST will be sent by the time the remote 391 * host does the SYN/ACK->ACK. 392 */ 393 if (sc->sc_rxttime >= tick) { 394 if (sc->sc_rxttime < sch->sch_nextc) 395 sch->sch_nextc = sc->sc_rxttime; 396 continue; 397 } 398 399 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 400 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 401 log(LOG_DEBUG, "%s; %s: Response timeout\n", 402 s, __func__); 403 free(s, M_TCPLOG); 404 } 405 syncache_drop(sc, sch); 406 tcpstat.tcps_sc_stale++; 407 continue; 408 } 409 410 (void) syncache_respond(sc); 411 tcpstat.tcps_sc_retransmitted++; 412 SYNCACHE_TIMEOUT(sc, sch, 0); 413 } 414 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 415 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 416 syncache_timer, (void *)(sch)); 417 } 418 419 /* 420 * Find an entry in the syncache. 421 * Returns always with locked syncache_head plus a matching entry or NULL. 422 */ 423 struct syncache * 424 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 425 { 426 struct syncache *sc; 427 struct syncache_head *sch; 428 429 #ifdef INET6 430 if (inc->inc_isipv6) { 431 sch = &tcp_syncache.hashbase[ 432 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 433 *schp = sch; 434 435 SCH_LOCK(sch); 436 437 /* Circle through bucket row to find matching entry. */ 438 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 439 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 440 return (sc); 441 } 442 } else 443 #endif 444 { 445 sch = &tcp_syncache.hashbase[ 446 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 447 *schp = sch; 448 449 SCH_LOCK(sch); 450 451 /* Circle through bucket row to find matching entry. */ 452 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 453 #ifdef INET6 454 if (sc->sc_inc.inc_isipv6) 455 continue; 456 #endif 457 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 458 return (sc); 459 } 460 } 461 SCH_LOCK_ASSERT(*schp); 462 return (NULL); /* always returns with locked sch */ 463 } 464 465 /* 466 * This function is called when we get a RST for a 467 * non-existent connection, so that we can see if the 468 * connection is in the syn cache. If it is, zap it. 469 */ 470 void 471 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 472 { 473 struct syncache *sc; 474 struct syncache_head *sch; 475 476 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 477 SCH_LOCK_ASSERT(sch); 478 if (sc == NULL) 479 goto done; 480 481 /* 482 * If the RST bit is set, check the sequence number to see 483 * if this is a valid reset segment. 484 * RFC 793 page 37: 485 * In all states except SYN-SENT, all reset (RST) segments 486 * are validated by checking their SEQ-fields. A reset is 487 * valid if its sequence number is in the window. 488 * 489 * The sequence number in the reset segment is normally an 490 * echo of our outgoing acknowlegement numbers, but some hosts 491 * send a reset with the sequence number at the rightmost edge 492 * of our receive window, and we have to handle this case. 493 */ 494 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 495 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 496 syncache_drop(sc, sch); 497 tcpstat.tcps_sc_reset++; 498 } 499 done: 500 SCH_UNLOCK(sch); 501 } 502 503 void 504 syncache_badack(struct in_conninfo *inc) 505 { 506 struct syncache *sc; 507 struct syncache_head *sch; 508 509 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 510 SCH_LOCK_ASSERT(sch); 511 if (sc != NULL) { 512 syncache_drop(sc, sch); 513 tcpstat.tcps_sc_badack++; 514 } 515 SCH_UNLOCK(sch); 516 } 517 518 void 519 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 520 { 521 struct syncache *sc; 522 struct syncache_head *sch; 523 524 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 525 SCH_LOCK_ASSERT(sch); 526 if (sc == NULL) 527 goto done; 528 529 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 530 if (ntohl(th->th_seq) != sc->sc_iss) 531 goto done; 532 533 /* 534 * If we've rertransmitted 3 times and this is our second error, 535 * we remove the entry. Otherwise, we allow it to continue on. 536 * This prevents us from incorrectly nuking an entry during a 537 * spurious network outage. 538 * 539 * See tcp_notify(). 540 */ 541 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 542 sc->sc_flags |= SCF_UNREACH; 543 goto done; 544 } 545 syncache_drop(sc, sch); 546 tcpstat.tcps_sc_unreach++; 547 done: 548 SCH_UNLOCK(sch); 549 } 550 551 /* 552 * Build a new TCP socket structure from a syncache entry. 553 */ 554 static struct socket * 555 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 556 { 557 struct inpcb *inp = NULL; 558 struct socket *so; 559 struct tcpcb *tp; 560 char *s; 561 562 NET_ASSERT_GIANT(); 563 INP_INFO_WLOCK_ASSERT(&tcbinfo); 564 565 /* 566 * Ok, create the full blown connection, and set things up 567 * as they would have been set up if we had created the 568 * connection when the SYN arrived. If we can't create 569 * the connection, abort it. 570 */ 571 so = sonewconn(lso, SS_ISCONNECTED); 572 if (so == NULL) { 573 /* 574 * Drop the connection; we will either send a RST or 575 * have the peer retransmit its SYN again after its 576 * RTO and try again. 577 */ 578 tcpstat.tcps_listendrop++; 579 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 580 log(LOG_DEBUG, "%s; %s: Socket create failed " 581 "due to limits or memory shortage\n", 582 s, __func__); 583 free(s, M_TCPLOG); 584 } 585 goto abort2; 586 } 587 #ifdef MAC 588 SOCK_LOCK(so); 589 mac_set_socket_peer_from_mbuf(m, so); 590 SOCK_UNLOCK(so); 591 #endif 592 593 inp = sotoinpcb(so); 594 INP_LOCK(inp); 595 596 /* Insert new socket into PCB hash list. */ 597 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 598 #ifdef INET6 599 if (sc->sc_inc.inc_isipv6) { 600 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 601 } else { 602 inp->inp_vflag &= ~INP_IPV6; 603 inp->inp_vflag |= INP_IPV4; 604 #endif 605 inp->inp_laddr = sc->sc_inc.inc_laddr; 606 #ifdef INET6 607 } 608 #endif 609 inp->inp_lport = sc->sc_inc.inc_lport; 610 if (in_pcbinshash(inp) != 0) { 611 /* 612 * Undo the assignments above if we failed to 613 * put the PCB on the hash lists. 614 */ 615 #ifdef INET6 616 if (sc->sc_inc.inc_isipv6) 617 inp->in6p_laddr = in6addr_any; 618 else 619 #endif 620 inp->inp_laddr.s_addr = INADDR_ANY; 621 inp->inp_lport = 0; 622 goto abort; 623 } 624 #ifdef IPSEC 625 /* Copy old policy into new socket's. */ 626 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 627 printf("syncache_socket: could not copy policy\n"); 628 #endif 629 #ifdef INET6 630 if (sc->sc_inc.inc_isipv6) { 631 struct inpcb *oinp = sotoinpcb(lso); 632 struct in6_addr laddr6; 633 struct sockaddr_in6 sin6; 634 /* 635 * Inherit socket options from the listening socket. 636 * Note that in6p_inputopts are not (and should not be) 637 * copied, since it stores previously received options and is 638 * used to detect if each new option is different than the 639 * previous one and hence should be passed to a user. 640 * If we copied in6p_inputopts, a user would not be able to 641 * receive options just after calling the accept system call. 642 */ 643 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 644 if (oinp->in6p_outputopts) 645 inp->in6p_outputopts = 646 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 647 648 sin6.sin6_family = AF_INET6; 649 sin6.sin6_len = sizeof(sin6); 650 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 651 sin6.sin6_port = sc->sc_inc.inc_fport; 652 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 653 laddr6 = inp->in6p_laddr; 654 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 655 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 656 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 657 thread0.td_ucred)) { 658 inp->in6p_laddr = laddr6; 659 goto abort; 660 } 661 /* Override flowlabel from in6_pcbconnect. */ 662 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 663 inp->in6p_flowinfo |= sc->sc_flowlabel; 664 } else 665 #endif 666 { 667 struct in_addr laddr; 668 struct sockaddr_in sin; 669 670 inp->inp_options = ip_srcroute(m); 671 if (inp->inp_options == NULL) { 672 inp->inp_options = sc->sc_ipopts; 673 sc->sc_ipopts = NULL; 674 } 675 676 sin.sin_family = AF_INET; 677 sin.sin_len = sizeof(sin); 678 sin.sin_addr = sc->sc_inc.inc_faddr; 679 sin.sin_port = sc->sc_inc.inc_fport; 680 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 681 laddr = inp->inp_laddr; 682 if (inp->inp_laddr.s_addr == INADDR_ANY) 683 inp->inp_laddr = sc->sc_inc.inc_laddr; 684 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 685 thread0.td_ucred)) { 686 inp->inp_laddr = laddr; 687 goto abort; 688 } 689 } 690 tp = intotcpcb(inp); 691 tp->t_state = TCPS_SYN_RECEIVED; 692 tp->iss = sc->sc_iss; 693 tp->irs = sc->sc_irs; 694 tcp_rcvseqinit(tp); 695 tcp_sendseqinit(tp); 696 tp->snd_wl1 = sc->sc_irs; 697 tp->snd_max = tp->iss + 1; 698 tp->snd_nxt = tp->iss + 1; 699 tp->rcv_up = sc->sc_irs + 1; 700 tp->rcv_wnd = sc->sc_wnd; 701 tp->rcv_adv += tp->rcv_wnd; 702 tp->last_ack_sent = tp->rcv_nxt; 703 704 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 705 if (sc->sc_flags & SCF_NOOPT) 706 tp->t_flags |= TF_NOOPT; 707 else { 708 if (sc->sc_flags & SCF_WINSCALE) { 709 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 710 tp->snd_scale = sc->sc_requested_s_scale; 711 tp->request_r_scale = sc->sc_requested_r_scale; 712 } 713 if (sc->sc_flags & SCF_TIMESTAMP) { 714 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 715 tp->ts_recent = sc->sc_tsreflect; 716 tp->ts_recent_age = ticks; 717 tp->ts_offset = sc->sc_tsoff; 718 } 719 #ifdef TCP_SIGNATURE 720 if (sc->sc_flags & SCF_SIGNATURE) 721 tp->t_flags |= TF_SIGNATURE; 722 #endif 723 if (sc->sc_flags & SCF_SACK) 724 tp->t_flags |= TF_SACK_PERMIT; 725 } 726 727 /* 728 * Set up MSS and get cached values from tcp_hostcache. 729 * This might overwrite some of the defaults we just set. 730 */ 731 tcp_mss(tp, sc->sc_peer_mss); 732 733 /* 734 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 735 */ 736 if (sc->sc_rxmits > 1) 737 tp->snd_cwnd = tp->t_maxseg; 738 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); 739 740 INP_UNLOCK(inp); 741 742 tcpstat.tcps_accepts++; 743 return (so); 744 745 abort: 746 INP_UNLOCK(inp); 747 abort2: 748 if (so != NULL) 749 soabort(so); 750 return (NULL); 751 } 752 753 /* 754 * This function gets called when we receive an ACK for a 755 * socket in the LISTEN state. We look up the connection 756 * in the syncache, and if its there, we pull it out of 757 * the cache and turn it into a full-blown connection in 758 * the SYN-RECEIVED state. 759 */ 760 int 761 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 762 struct socket **lsop, struct mbuf *m) 763 { 764 struct syncache *sc; 765 struct syncache_head *sch; 766 struct syncache scs; 767 char *s; 768 769 /* 770 * Global TCP locks are held because we manipulate the PCB lists 771 * and create a new socket. 772 */ 773 INP_INFO_WLOCK_ASSERT(&tcbinfo); 774 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 775 ("%s: can handle only ACK", __func__)); 776 777 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 778 SCH_LOCK_ASSERT(sch); 779 if (sc == NULL) { 780 /* 781 * There is no syncache entry, so see if this ACK is 782 * a returning syncookie. To do this, first: 783 * A. See if this socket has had a syncache entry dropped in 784 * the past. We don't want to accept a bogus syncookie 785 * if we've never received a SYN. 786 * B. check that the syncookie is valid. If it is, then 787 * cobble up a fake syncache entry, and return. 788 */ 789 if (!tcp_syncookies) { 790 SCH_UNLOCK(sch); 791 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 792 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 793 "segment rejected (syncookies disabled)\n", 794 s, __func__); 795 goto failed; 796 } 797 bzero(&scs, sizeof(scs)); 798 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 799 SCH_UNLOCK(sch); 800 if (sc == NULL) { 801 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 802 log(LOG_DEBUG, "%s; %s: Segment failed " 803 "SYNCOOKIE authentication, segment rejected " 804 "(probably spoofed)\n", s, __func__); 805 goto failed; 806 } 807 tcpstat.tcps_sc_recvcookie++; 808 } else { 809 /* Pull out the entry to unlock the bucket row. */ 810 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 811 sch->sch_length--; 812 tcp_syncache.cache_count--; 813 SCH_UNLOCK(sch); 814 } 815 816 /* 817 * Segment validation: 818 * ACK must match our initial sequence number + 1 (the SYN|ACK). 819 */ 820 if (th->th_ack != sc->sc_iss + 1) { 821 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 822 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 823 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 824 goto failed; 825 } 826 /* 827 * The SEQ must match the received initial receive sequence 828 * number + 1 (the SYN) because we didn't ACK any data that 829 * may have come with the SYN. 830 */ 831 if (th->th_seq != sc->sc_irs + 1) { 832 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 833 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 834 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 835 goto failed; 836 } 837 /* 838 * If timestamps were present in the SYN and we accepted 839 * them in our SYN|ACK we require them to be present from 840 * now on. And vice versa. 841 */ 842 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 843 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 844 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 845 "segment rejected\n", s, __func__); 846 goto failed; 847 } 848 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 849 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 850 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 851 "segment rejected\n", s, __func__); 852 goto failed; 853 } 854 /* 855 * If timestamps were negotiated the reflected timestamp 856 * must be equal to what we actually sent in the SYN|ACK. 857 */ 858 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 859 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 860 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 861 "segment rejected\n", 862 s, __func__, to->to_tsecr, sc->sc_ts); 863 goto failed; 864 } 865 866 *lsop = syncache_socket(sc, *lsop, m); 867 868 if (*lsop == NULL) 869 tcpstat.tcps_sc_aborted++; 870 else 871 tcpstat.tcps_sc_completed++; 872 873 if (sc != &scs) 874 syncache_free(sc); 875 return (1); 876 failed: 877 if (sc != NULL && sc != &scs) 878 syncache_free(sc); 879 if (s != NULL) 880 free(s, M_TCPLOG); 881 *lsop = NULL; 882 return (0); 883 } 884 885 /* 886 * Given a LISTEN socket and an inbound SYN request, add 887 * this to the syn cache, and send back a segment: 888 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 889 * to the source. 890 * 891 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 892 * Doing so would require that we hold onto the data and deliver it 893 * to the application. However, if we are the target of a SYN-flood 894 * DoS attack, an attacker could send data which would eventually 895 * consume all available buffer space if it were ACKed. By not ACKing 896 * the data, we avoid this DoS scenario. 897 */ 898 void 899 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 900 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 901 { 902 struct tcpcb *tp; 903 struct socket *so; 904 struct syncache *sc = NULL; 905 struct syncache_head *sch; 906 struct mbuf *ipopts = NULL; 907 u_int32_t flowtmp; 908 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 909 #ifdef INET6 910 int autoflowlabel = 0; 911 #endif 912 #ifdef MAC 913 struct label *maclabel; 914 #endif 915 struct syncache scs; 916 917 INP_INFO_WLOCK_ASSERT(&tcbinfo); 918 INP_LOCK_ASSERT(inp); /* listen socket */ 919 920 /* 921 * Combine all so/tp operations very early to drop the INP lock as 922 * soon as possible. 923 */ 924 so = *lsop; 925 tp = sototcpcb(so); 926 927 #ifdef INET6 928 if (inc->inc_isipv6 && 929 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 930 autoflowlabel = 1; 931 #endif 932 ip_ttl = inp->inp_ip_ttl; 933 ip_tos = inp->inp_ip_tos; 934 win = sbspace(&so->so_rcv); 935 sb_hiwat = so->so_rcv.sb_hiwat; 936 noopt = (tp->t_flags & TF_NOOPT); 937 938 so = NULL; 939 tp = NULL; 940 941 #ifdef MAC 942 if (mac_init_syncache(&maclabel) != 0) { 943 INP_UNLOCK(inp); 944 INP_INFO_WUNLOCK(&tcbinfo); 945 goto done; 946 } else 947 mac_init_syncache_from_inpcb(maclabel, inp); 948 #endif 949 INP_UNLOCK(inp); 950 INP_INFO_WUNLOCK(&tcbinfo); 951 952 /* 953 * Remember the IP options, if any. 954 */ 955 #ifdef INET6 956 if (!inc->inc_isipv6) 957 #endif 958 ipopts = ip_srcroute(m); 959 960 /* 961 * See if we already have an entry for this connection. 962 * If we do, resend the SYN,ACK, and reset the retransmit timer. 963 * 964 * XXX: should the syncache be re-initialized with the contents 965 * of the new SYN here (which may have different options?) 966 */ 967 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 968 SCH_LOCK_ASSERT(sch); 969 if (sc != NULL) { 970 tcpstat.tcps_sc_dupsyn++; 971 if (ipopts) { 972 /* 973 * If we were remembering a previous source route, 974 * forget it and use the new one we've been given. 975 */ 976 if (sc->sc_ipopts) 977 (void) m_free(sc->sc_ipopts); 978 sc->sc_ipopts = ipopts; 979 } 980 /* 981 * Update timestamp if present. 982 */ 983 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 984 sc->sc_tsreflect = to->to_tsval; 985 else 986 sc->sc_flags &= ~SCF_TIMESTAMP; 987 #ifdef MAC 988 /* 989 * Since we have already unconditionally allocated label 990 * storage, free it up. The syncache entry will already 991 * have an initialized label we can use. 992 */ 993 mac_destroy_syncache(&maclabel); 994 KASSERT(sc->sc_label != NULL, 995 ("%s: label not initialized", __func__)); 996 #endif 997 if (syncache_respond(sc) == 0) { 998 SYNCACHE_TIMEOUT(sc, sch, 1); 999 tcpstat.tcps_sndacks++; 1000 tcpstat.tcps_sndtotal++; 1001 } 1002 SCH_UNLOCK(sch); 1003 goto done; 1004 } 1005 1006 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1007 if (sc == NULL) { 1008 /* 1009 * The zone allocator couldn't provide more entries. 1010 * Treat this as if the cache was full; drop the oldest 1011 * entry and insert the new one. 1012 */ 1013 tcpstat.tcps_sc_zonefail++; 1014 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1015 syncache_drop(sc, sch); 1016 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1017 if (sc == NULL) { 1018 if (tcp_syncookies) { 1019 bzero(&scs, sizeof(scs)); 1020 sc = &scs; 1021 } else { 1022 SCH_UNLOCK(sch); 1023 if (ipopts) 1024 (void) m_free(ipopts); 1025 goto done; 1026 } 1027 } 1028 } 1029 1030 /* 1031 * Fill in the syncache values. 1032 */ 1033 #ifdef MAC 1034 sc->sc_label = maclabel; 1035 #endif 1036 sc->sc_ipopts = ipopts; 1037 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1038 #ifdef INET6 1039 if (!inc->inc_isipv6) 1040 #endif 1041 { 1042 sc->sc_ip_tos = ip_tos; 1043 sc->sc_ip_ttl = ip_ttl; 1044 } 1045 1046 sc->sc_irs = th->th_seq; 1047 sc->sc_iss = arc4random(); 1048 sc->sc_flags = 0; 1049 sc->sc_flowlabel = 0; 1050 1051 /* 1052 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1053 * win was derived from socket earlier in the function. 1054 */ 1055 win = imax(win, 0); 1056 win = imin(win, TCP_MAXWIN); 1057 sc->sc_wnd = win; 1058 1059 if (tcp_do_rfc1323) { 1060 /* 1061 * A timestamp received in a SYN makes 1062 * it ok to send timestamp requests and replies. 1063 */ 1064 if (to->to_flags & TOF_TS) { 1065 sc->sc_tsreflect = to->to_tsval; 1066 sc->sc_ts = ticks; 1067 sc->sc_flags |= SCF_TIMESTAMP; 1068 } 1069 if (to->to_flags & TOF_SCALE) { 1070 int wscale = 0; 1071 1072 /* 1073 * Compute proper scaling value from buffer space. 1074 * Leave enough room for the socket buffer to grow 1075 * with auto sizing. This allows us to scale the 1076 * receive buffer over a wide range while not losing 1077 * any efficiency or fine granularity. 1078 * 1079 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1080 * or <SYN,ACK>) segment itself is never scaled. 1081 */ 1082 while (wscale < TCP_MAX_WINSHIFT && 1083 (0x1 << wscale) < tcp_minmss) 1084 wscale++; 1085 sc->sc_requested_r_scale = wscale; 1086 sc->sc_requested_s_scale = to->to_wscale; 1087 sc->sc_flags |= SCF_WINSCALE; 1088 } 1089 } 1090 #ifdef TCP_SIGNATURE 1091 /* 1092 * If listening socket requested TCP digests, and received SYN 1093 * contains the option, flag this in the syncache so that 1094 * syncache_respond() will do the right thing with the SYN+ACK. 1095 * XXX: Currently we always record the option by default and will 1096 * attempt to use it in syncache_respond(). 1097 */ 1098 if (to->to_flags & TOF_SIGNATURE) 1099 sc->sc_flags |= SCF_SIGNATURE; 1100 #endif 1101 if (to->to_flags & TOF_SACK) 1102 sc->sc_flags |= SCF_SACK; 1103 if (to->to_flags & TOF_MSS) 1104 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1105 if (noopt) 1106 sc->sc_flags |= SCF_NOOPT; 1107 1108 if (tcp_syncookies) { 1109 syncookie_generate(sch, sc, &flowtmp); 1110 #ifdef INET6 1111 if (autoflowlabel) 1112 sc->sc_flowlabel = flowtmp; 1113 #endif 1114 } else { 1115 #ifdef INET6 1116 if (autoflowlabel) 1117 sc->sc_flowlabel = 1118 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1119 #endif 1120 } 1121 SCH_UNLOCK(sch); 1122 1123 /* 1124 * Do a standard 3-way handshake. 1125 */ 1126 if (syncache_respond(sc) == 0) { 1127 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1128 syncache_free(sc); 1129 else if (sc != &scs) 1130 syncache_insert(sc, sch); /* locks and unlocks sch */ 1131 tcpstat.tcps_sndacks++; 1132 tcpstat.tcps_sndtotal++; 1133 } else { 1134 if (sc != &scs) 1135 syncache_free(sc); 1136 tcpstat.tcps_sc_dropped++; 1137 } 1138 1139 done: 1140 #ifdef MAC 1141 if (sc == &scs) 1142 mac_destroy_syncache(&maclabel); 1143 #endif 1144 *lsop = NULL; 1145 m_freem(m); 1146 return; 1147 } 1148 1149 static int 1150 syncache_respond(struct syncache *sc) 1151 { 1152 struct ip *ip = NULL; 1153 struct mbuf *m; 1154 struct tcphdr *th; 1155 int optlen, error; 1156 u_int16_t hlen, tlen, mssopt; 1157 struct tcpopt to; 1158 #ifdef INET6 1159 struct ip6_hdr *ip6 = NULL; 1160 #endif 1161 1162 hlen = 1163 #ifdef INET6 1164 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1165 #endif 1166 sizeof(struct ip); 1167 tlen = hlen + sizeof(struct tcphdr); 1168 1169 /* Determine MSS we advertize to other end of connection. */ 1170 mssopt = tcp_mssopt(&sc->sc_inc); 1171 if (sc->sc_peer_mss) 1172 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1173 1174 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1175 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1176 ("syncache: mbuf too small")); 1177 1178 /* Create the IP+TCP header from scratch. */ 1179 m = m_gethdr(M_DONTWAIT, MT_DATA); 1180 if (m == NULL) 1181 return (ENOBUFS); 1182 #ifdef MAC 1183 mac_create_mbuf_from_syncache(sc->sc_label, m); 1184 #endif 1185 m->m_data += max_linkhdr; 1186 m->m_len = tlen; 1187 m->m_pkthdr.len = tlen; 1188 m->m_pkthdr.rcvif = NULL; 1189 1190 #ifdef INET6 1191 if (sc->sc_inc.inc_isipv6) { 1192 ip6 = mtod(m, struct ip6_hdr *); 1193 ip6->ip6_vfc = IPV6_VERSION; 1194 ip6->ip6_nxt = IPPROTO_TCP; 1195 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1196 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1197 ip6->ip6_plen = htons(tlen - hlen); 1198 /* ip6_hlim is set after checksum */ 1199 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1200 ip6->ip6_flow |= sc->sc_flowlabel; 1201 1202 th = (struct tcphdr *)(ip6 + 1); 1203 } else 1204 #endif 1205 { 1206 ip = mtod(m, struct ip *); 1207 ip->ip_v = IPVERSION; 1208 ip->ip_hl = sizeof(struct ip) >> 2; 1209 ip->ip_len = tlen; 1210 ip->ip_id = 0; 1211 ip->ip_off = 0; 1212 ip->ip_sum = 0; 1213 ip->ip_p = IPPROTO_TCP; 1214 ip->ip_src = sc->sc_inc.inc_laddr; 1215 ip->ip_dst = sc->sc_inc.inc_faddr; 1216 ip->ip_ttl = sc->sc_ip_ttl; 1217 ip->ip_tos = sc->sc_ip_tos; 1218 1219 /* 1220 * See if we should do MTU discovery. Route lookups are 1221 * expensive, so we will only unset the DF bit if: 1222 * 1223 * 1) path_mtu_discovery is disabled 1224 * 2) the SCF_UNREACH flag has been set 1225 */ 1226 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1227 ip->ip_off |= IP_DF; 1228 1229 th = (struct tcphdr *)(ip + 1); 1230 } 1231 th->th_sport = sc->sc_inc.inc_lport; 1232 th->th_dport = sc->sc_inc.inc_fport; 1233 1234 th->th_seq = htonl(sc->sc_iss); 1235 th->th_ack = htonl(sc->sc_irs + 1); 1236 th->th_off = sizeof(struct tcphdr) >> 2; 1237 th->th_x2 = 0; 1238 th->th_flags = TH_SYN|TH_ACK; 1239 th->th_win = htons(sc->sc_wnd); 1240 th->th_urp = 0; 1241 1242 /* Tack on the TCP options. */ 1243 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1244 to.to_flags = 0; 1245 1246 to.to_mss = mssopt; 1247 to.to_flags = TOF_MSS; 1248 if (sc->sc_flags & SCF_WINSCALE) { 1249 to.to_wscale = sc->sc_requested_r_scale; 1250 to.to_flags |= TOF_SCALE; 1251 } 1252 if (sc->sc_flags & SCF_TIMESTAMP) { 1253 /* Virgin timestamp or TCP cookie enhanced one. */ 1254 to.to_tsval = sc->sc_ts; 1255 to.to_tsecr = sc->sc_tsreflect; 1256 to.to_flags |= TOF_TS; 1257 } 1258 if (sc->sc_flags & SCF_SACK) 1259 to.to_flags |= TOF_SACKPERM; 1260 #ifdef TCP_SIGNATURE 1261 if (sc->sc_flags & SCF_SIGNATURE) 1262 to.to_flags |= TOF_SIGNATURE; 1263 #endif 1264 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1265 1266 #ifdef TCP_SIGNATURE 1267 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1268 to.to_signature, IPSEC_DIR_OUTBOUND); 1269 #endif 1270 1271 /* Adjust headers by option size. */ 1272 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1273 m->m_len += optlen; 1274 m->m_pkthdr.len += optlen; 1275 #ifdef INET6 1276 if (sc->sc_inc.inc_isipv6) 1277 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1278 else 1279 #endif 1280 ip->ip_len += optlen; 1281 } else 1282 optlen = 0; 1283 1284 #ifdef INET6 1285 if (sc->sc_inc.inc_isipv6) { 1286 th->th_sum = 0; 1287 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, 1288 tlen + optlen - hlen); 1289 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1290 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1291 } else 1292 #endif 1293 { 1294 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1295 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1296 m->m_pkthdr.csum_flags = CSUM_TCP; 1297 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1298 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1299 } 1300 return (error); 1301 } 1302 1303 /* 1304 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1305 * receive and to be able to handle SYN floods from bogus source addresses 1306 * (where we will never receive any reply). SYN floods try to exhaust all 1307 * our memory and available slots in the SYN cache table to cause a denial 1308 * of service to legitimate users of the local host. 1309 * 1310 * The idea of SYN cookies is to encode and include all necessary information 1311 * about the connection setup state within the SYN-ACK we send back and thus 1312 * to get along without keeping any local state until the ACK to the SYN-ACK 1313 * arrives (if ever). Everything we need to know should be available from 1314 * the information we encoded in the SYN-ACK. 1315 * 1316 * More information about the theory behind SYN cookies and its first 1317 * discussion and specification can be found at: 1318 * http://cr.yp.to/syncookies.html (overview) 1319 * http://cr.yp.to/syncookies/archive (gory details) 1320 * 1321 * This implementation extends the orginal idea and first implementation 1322 * of FreeBSD by using not only the initial sequence number field to store 1323 * information but also the timestamp field if present. This way we can 1324 * keep track of the entire state we need to know to recreate the session in 1325 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1326 * these days. For those that do not we still have to live with the known 1327 * shortcomings of the ISN only SYN cookies. 1328 * 1329 * Cookie layers: 1330 * 1331 * Initial sequence number we send: 1332 * 31|................................|0 1333 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1334 * D = MD5 Digest (first dword) 1335 * M = MSS index 1336 * R = Rotation of secret 1337 * P = Odd or Even secret 1338 * 1339 * The MD5 Digest is computed with over following parameters: 1340 * a) randomly rotated secret 1341 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1342 * c) the received initial sequence number from remote host 1343 * d) the rotation offset and odd/even bit 1344 * 1345 * Timestamp we send: 1346 * 31|................................|0 1347 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1348 * D = MD5 Digest (third dword) (only as filler) 1349 * S = Requested send window scale 1350 * R = Requested receive window scale 1351 * A = SACK allowed 1352 * 5 = TCP-MD5 enabled (not implemented yet) 1353 * XORed with MD5 Digest (forth dword) 1354 * 1355 * The timestamp isn't cryptographically secure and doesn't need to be. 1356 * The double use of the MD5 digest dwords ties it to a specific remote/ 1357 * local host/port, remote initial sequence number and our local time 1358 * limited secret. A received timestamp is reverted (XORed) and then 1359 * the contained MD5 dword is compared to the computed one to ensure the 1360 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1361 * have been tampered with but this isn't different from supplying bogus 1362 * values in the SYN in the first place. 1363 * 1364 * Some problems with SYN cookies remain however: 1365 * Consider the problem of a recreated (and retransmitted) cookie. If the 1366 * original SYN was accepted, the connection is established. The second 1367 * SYN is inflight, and if it arrives with an ISN that falls within the 1368 * receive window, the connection is killed. 1369 * 1370 * Notes: 1371 * A heuristic to determine when to accept syn cookies is not necessary. 1372 * An ACK flood would cause the syncookie verification to be attempted, 1373 * but a SYN flood causes syncookies to be generated. Both are of equal 1374 * cost, so there's no point in trying to optimize the ACK flood case. 1375 * Also, if you don't process certain ACKs for some reason, then all someone 1376 * would have to do is launch a SYN and ACK flood at the same time, which 1377 * would stop cookie verification and defeat the entire purpose of syncookies. 1378 */ 1379 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1380 1381 static void 1382 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1383 u_int32_t *flowlabel) 1384 { 1385 MD5_CTX ctx; 1386 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1387 u_int32_t data; 1388 u_int32_t *secbits; 1389 u_int off, pmss, mss; 1390 int i; 1391 1392 SCH_LOCK_ASSERT(sch); 1393 1394 /* Which of the two secrets to use. */ 1395 secbits = sch->sch_oddeven ? 1396 sch->sch_secbits_odd : sch->sch_secbits_even; 1397 1398 /* Reseed secret if too old. */ 1399 if (sch->sch_reseed < time_uptime) { 1400 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1401 secbits = sch->sch_oddeven ? 1402 sch->sch_secbits_odd : sch->sch_secbits_even; 1403 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1404 secbits[i] = arc4random(); 1405 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1406 } 1407 1408 /* Secret rotation offset. */ 1409 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1410 1411 /* Maximum segment size calculation. */ 1412 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1413 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1414 if (tcp_sc_msstab[mss] <= pmss) 1415 break; 1416 1417 /* Fold parameters and MD5 digest into the ISN we will send. */ 1418 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1419 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1420 data |= mss << 4; /* mss, 3 bits */ 1421 1422 MD5Init(&ctx); 1423 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1424 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1425 MD5Update(&ctx, secbits, off); 1426 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1427 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1428 MD5Update(&ctx, &data, sizeof(data)); 1429 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1430 1431 data |= (md5_buffer[0] << 7); 1432 sc->sc_iss = data; 1433 1434 #ifdef INET6 1435 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1436 #endif 1437 1438 /* Additional parameters are stored in the timestamp if present. */ 1439 if (sc->sc_flags & SCF_TIMESTAMP) { 1440 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1441 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1442 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1443 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1444 data |= md5_buffer[2] << 10; /* more digest bits */ 1445 data ^= md5_buffer[3]; 1446 sc->sc_ts = data; 1447 sc->sc_tsoff = data - ticks; /* after XOR */ 1448 } 1449 1450 return; 1451 } 1452 1453 static struct syncache * 1454 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1455 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1456 struct socket *so) 1457 { 1458 MD5_CTX ctx; 1459 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1460 u_int32_t data = 0; 1461 u_int32_t *secbits; 1462 tcp_seq ack, seq; 1463 int off, mss, wnd, flags; 1464 1465 SCH_LOCK_ASSERT(sch); 1466 1467 /* 1468 * Pull information out of SYN-ACK/ACK and 1469 * revert sequence number advances. 1470 */ 1471 ack = th->th_ack - 1; 1472 seq = th->th_seq - 1; 1473 off = (ack >> 1) & 0x7; 1474 mss = (ack >> 4) & 0x7; 1475 flags = ack & 0x7f; 1476 1477 /* Which of the two secrets to use. */ 1478 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1479 1480 /* 1481 * The secret wasn't updated for the lifetime of a syncookie, 1482 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1483 */ 1484 if (sch->sch_reseed < time_uptime) { 1485 return (NULL); 1486 } 1487 1488 /* Recompute the digest so we can compare it. */ 1489 MD5Init(&ctx); 1490 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1491 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1492 MD5Update(&ctx, secbits, off); 1493 MD5Update(&ctx, inc, sizeof(*inc)); 1494 MD5Update(&ctx, &seq, sizeof(seq)); 1495 MD5Update(&ctx, &flags, sizeof(flags)); 1496 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1497 1498 /* Does the digest part of or ACK'ed ISS match? */ 1499 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1500 return (NULL); 1501 1502 /* Does the digest part of our reflected timestamp match? */ 1503 if (to->to_flags & TOF_TS) { 1504 data = md5_buffer[3] ^ to->to_tsecr; 1505 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1506 return (NULL); 1507 } 1508 1509 /* Fill in the syncache values. */ 1510 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1511 sc->sc_ipopts = NULL; 1512 1513 sc->sc_irs = seq; 1514 sc->sc_iss = ack; 1515 1516 #ifdef INET6 1517 if (inc->inc_isipv6) { 1518 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1519 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1520 } else 1521 #endif 1522 { 1523 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1524 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1525 } 1526 1527 /* Additional parameters that were encoded in the timestamp. */ 1528 if (data) { 1529 sc->sc_flags |= SCF_TIMESTAMP; 1530 sc->sc_tsreflect = to->to_tsval; 1531 sc->sc_ts = to->to_tsecr; 1532 sc->sc_tsoff = to->to_tsecr - ticks; 1533 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1534 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1535 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1536 TCP_MAX_WINSHIFT); 1537 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1538 TCP_MAX_WINSHIFT); 1539 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1540 sc->sc_flags |= SCF_WINSCALE; 1541 } else 1542 sc->sc_flags |= SCF_NOOPT; 1543 1544 wnd = sbspace(&so->so_rcv); 1545 wnd = imax(wnd, 0); 1546 wnd = imin(wnd, TCP_MAXWIN); 1547 sc->sc_wnd = wnd; 1548 1549 sc->sc_rxmits = 0; 1550 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1551 1552 return (sc); 1553 } 1554