1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior written 17 * permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * ip_fastforward gets its speed from processing the forwarded packet to 34 * completion (if_output on the other side) without any queues or netisr's. 35 * The receiving interface DMAs the packet into memory, the upper half of 36 * driver calls ip_fastforward, we do our routing table lookup and directly 37 * send it off to the outgoing interface, which DMAs the packet to the 38 * network card. The only part of the packet we touch with the CPU is the 39 * IP header (unless there are complex firewall rules touching other parts 40 * of the packet, but that is up to you). We are essentially limited by bus 41 * bandwidth and how fast the network card/driver can set up receives and 42 * transmits. 43 * 44 * We handle basic errors, IP header errors, checksum errors, 45 * destination unreachable, fragmentation and fragmentation needed and 46 * report them via ICMP to the sender. 47 * 48 * Else if something is not pure IPv4 unicast forwarding we fall back to 49 * the normal ip_input processing path. We should only be called from 50 * interfaces connected to the outside world. 51 * 52 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 53 * ipnat and address rewrite. 54 * 55 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 56 * supported for connections to/from local host. 57 * 58 * We try to do the least expensive (in CPU ops) checks and operations 59 * first to catch junk with as little overhead as possible. 60 * 61 * We take full advantage of hardware support for IP checksum and 62 * fragmentation offloading. 63 * 64 * We don't do ICMP redirect in the fast forwarding path. I have had my own 65 * cases where two core routers with Zebra routing suite would send millions 66 * ICMP redirects to connected hosts if the destination router was not the 67 * default gateway. In one case it was filling the routing table of a host 68 * with approximately 300.000 cloned redirect entries until it ran out of 69 * kernel memory. However the networking code proved very robust and it didn't 70 * crash or fail in other ways. 71 */ 72 73 /* 74 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 75 * is being followed here. 76 */ 77 78 #include <sys/cdefs.h> 79 __FBSDID("$FreeBSD$"); 80 81 #include "opt_ipstealth.h" 82 83 #include <sys/param.h> 84 #include <sys/systm.h> 85 #include <sys/kernel.h> 86 #include <sys/malloc.h> 87 #include <sys/mbuf.h> 88 #include <sys/protosw.h> 89 #include <sys/sdt.h> 90 #include <sys/socket.h> 91 #include <sys/sysctl.h> 92 93 #include <net/if.h> 94 #include <net/if_types.h> 95 #include <net/if_var.h> 96 #include <net/if_dl.h> 97 #include <net/pfil.h> 98 #include <net/route.h> 99 #include <net/route/nhop.h> 100 #include <net/vnet.h> 101 102 #include <netinet/in.h> 103 #include <netinet/in_fib.h> 104 #include <netinet/in_kdtrace.h> 105 #include <netinet/in_systm.h> 106 #include <netinet/in_var.h> 107 #include <netinet/ip.h> 108 #include <netinet/ip_var.h> 109 #include <netinet/ip_icmp.h> 110 #include <netinet/ip_options.h> 111 112 #include <machine/in_cksum.h> 113 114 #define V_ipsendredirects VNET(ipsendredirects) 115 116 static struct mbuf * 117 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, 118 struct ip *ip, in_addr_t *addr) 119 { 120 struct mbuf *mcopy = m_gethdr(M_NOWAIT, m->m_type); 121 122 if (mcopy == NULL) 123 return (NULL); 124 125 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { 126 /* 127 * It's probably ok if the pkthdr dup fails (because 128 * the deep copy of the tag chain failed), but for now 129 * be conservative and just discard the copy since 130 * code below may some day want the tags. 131 */ 132 m_free(mcopy); 133 return (NULL); 134 } 135 mcopy->m_len = min(ntohs(ip->ip_len), M_TRAILINGSPACE(mcopy)); 136 mcopy->m_pkthdr.len = mcopy->m_len; 137 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); 138 139 if (nh != NULL && 140 ((nh->nh_flags & (NHF_REDIRECT|NHF_DEFAULT)) == 0)) { 141 struct in_ifaddr *nh_ia = (struct in_ifaddr *)(nh->nh_ifa); 142 u_long src = ntohl(ip->ip_src.s_addr); 143 144 if (nh_ia != NULL && 145 (src & nh_ia->ia_subnetmask) == nh_ia->ia_subnet) { 146 if (nh->nh_flags & NHF_GATEWAY) 147 *addr = nh->gw4_sa.sin_addr.s_addr; 148 else 149 *addr = ip->ip_dst.s_addr; 150 } 151 } 152 return (mcopy); 153 } 154 155 156 static int 157 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) 158 { 159 struct nhop_object *nh; 160 161 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, 162 m->m_pkthdr.flowid); 163 if (nh == NULL) { 164 IPSTAT_INC(ips_noroute); 165 IPSTAT_INC(ips_cantforward); 166 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 167 return (EHOSTUNREACH); 168 } 169 /* 170 * Drop blackholed traffic and directed broadcasts. 171 */ 172 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 173 IPSTAT_INC(ips_cantforward); 174 m_freem(m); 175 return (EHOSTUNREACH); 176 } 177 178 if (nh->nh_flags & NHF_REJECT) { 179 IPSTAT_INC(ips_cantforward); 180 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 181 return (EHOSTUNREACH); 182 } 183 184 *pnh = nh; 185 186 return (0); 187 } 188 189 /* 190 * Try to forward a packet based on the destination address. 191 * This is a fast path optimized for the plain forwarding case. 192 * If the packet is handled (and consumed) here then we return NULL; 193 * otherwise mbuf is returned and the packet should be delivered 194 * to ip_input for full processing. 195 */ 196 struct mbuf * 197 ip_tryforward(struct mbuf *m) 198 { 199 struct ip *ip; 200 struct mbuf *m0 = NULL; 201 struct nhop_object *nh = NULL; 202 struct route ro; 203 struct sockaddr_in *dst; 204 const struct sockaddr *gw; 205 struct in_addr dest, odest, rtdest; 206 uint16_t ip_len, ip_off; 207 int error = 0; 208 struct m_tag *fwd_tag = NULL; 209 struct mbuf *mcopy = NULL; 210 struct in_addr redest; 211 /* 212 * Are we active and forwarding packets? 213 */ 214 215 M_ASSERTVALID(m); 216 M_ASSERTPKTHDR(m); 217 218 #ifdef ALTQ 219 /* 220 * Is packet dropped by traffic conditioner? 221 */ 222 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0) 223 goto drop; 224 #endif 225 226 /* 227 * Only IP packets without options 228 */ 229 ip = mtod(m, struct ip *); 230 231 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 232 if (V_ip_doopts == 1) 233 return m; 234 else if (V_ip_doopts == 2) { 235 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 236 0, 0); 237 return NULL; /* mbuf already free'd */ 238 } 239 /* else ignore IP options and continue */ 240 } 241 242 /* 243 * Only unicast IP, not from loopback, no L2 or IP broadcast, 244 * no multicast, no INADDR_ANY 245 * 246 * XXX: Probably some of these checks could be direct drop 247 * conditions. However it is not clear whether there are some 248 * hacks or obscure behaviours which make it necessary to 249 * let ip_input handle it. We play safe here and let ip_input 250 * deal with it until it is proven that we can directly drop it. 251 */ 252 if ((m->m_flags & (M_BCAST|M_MCAST)) || 253 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 254 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 255 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 256 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 257 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 258 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 259 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 260 ip->ip_src.s_addr == INADDR_ANY || 261 ip->ip_dst.s_addr == INADDR_ANY ) 262 return m; 263 264 /* 265 * Is it for a local address on this host? 266 */ 267 if (in_localip(ip->ip_dst)) 268 return m; 269 270 IPSTAT_INC(ips_total); 271 272 /* 273 * Step 3: incoming packet firewall processing 274 */ 275 276 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 277 278 /* 279 * Run through list of ipfilter hooks for input packets 280 */ 281 if (!PFIL_HOOKED_IN(V_inet_pfil_head)) 282 goto passin; 283 284 if (pfil_run_hooks(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, PFIL_IN, 285 NULL) != PFIL_PASS) 286 goto drop; 287 288 M_ASSERTVALID(m); 289 M_ASSERTPKTHDR(m); 290 291 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 292 dest.s_addr = ip->ip_dst.s_addr; 293 294 /* 295 * Destination address changed? 296 */ 297 if (odest.s_addr != dest.s_addr) { 298 /* 299 * Is it now for a local address on this host? 300 */ 301 if (in_localip(dest)) 302 goto forwardlocal; 303 /* 304 * Go on with new destination address 305 */ 306 } 307 308 if (m->m_flags & M_FASTFWD_OURS) { 309 /* 310 * ipfw changed it for a local address on this host. 311 */ 312 goto forwardlocal; 313 } 314 315 passin: 316 /* 317 * Step 4: decrement TTL and look up route 318 */ 319 320 /* 321 * Check TTL 322 */ 323 #ifdef IPSTEALTH 324 if (!V_ipstealth) { 325 #endif 326 if (ip->ip_ttl <= IPTTLDEC) { 327 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 328 return NULL; /* mbuf already free'd */ 329 } 330 331 /* 332 * Decrement the TTL and incrementally change the IP header checksum. 333 * Don't bother doing this with hw checksum offloading, it's faster 334 * doing it right here. 335 */ 336 ip->ip_ttl -= IPTTLDEC; 337 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 338 ip->ip_sum -= ~htons(IPTTLDEC << 8); 339 else 340 ip->ip_sum += htons(IPTTLDEC << 8); 341 #ifdef IPSTEALTH 342 } 343 #endif 344 345 /* 346 * Next hop forced by pfil(9) hook? 347 */ 348 if ((m->m_flags & M_IP_NEXTHOP) && 349 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { 350 /* 351 * Now we will find route to forced destination. 352 */ 353 dest.s_addr = ((struct sockaddr_in *) 354 (fwd_tag + 1))->sin_addr.s_addr; 355 m_tag_delete(m, fwd_tag); 356 m->m_flags &= ~M_IP_NEXTHOP; 357 } 358 359 /* 360 * Find route to destination. 361 */ 362 if (ip_findroute(&nh, dest, m) != 0) 363 return (NULL); /* icmp unreach already sent */ 364 365 /* 366 * Avoid second route lookup by caching destination. 367 */ 368 rtdest.s_addr = dest.s_addr; 369 370 /* 371 * Step 5: outgoing firewall packet processing 372 */ 373 if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) 374 goto passout; 375 376 if (pfil_run_hooks(V_inet_pfil_head, &m, nh->nh_ifp, 377 PFIL_OUT | PFIL_FWD, NULL) != PFIL_PASS) 378 goto drop; 379 380 M_ASSERTVALID(m); 381 M_ASSERTPKTHDR(m); 382 383 ip = mtod(m, struct ip *); 384 dest.s_addr = ip->ip_dst.s_addr; 385 386 /* 387 * Destination address changed? 388 */ 389 if (m->m_flags & M_IP_NEXTHOP) 390 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 391 else 392 fwd_tag = NULL; 393 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 394 /* 395 * Is it now for a local address on this host? 396 */ 397 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 398 forwardlocal: 399 /* 400 * Return packet for processing by ip_input(). 401 */ 402 m->m_flags |= M_FASTFWD_OURS; 403 return (m); 404 } 405 /* 406 * Redo route lookup with new destination address 407 */ 408 if (fwd_tag) { 409 dest.s_addr = ((struct sockaddr_in *) 410 (fwd_tag + 1))->sin_addr.s_addr; 411 m_tag_delete(m, fwd_tag); 412 m->m_flags &= ~M_IP_NEXTHOP; 413 } 414 if (dest.s_addr != rtdest.s_addr && 415 ip_findroute(&nh, dest, m) != 0) 416 return (NULL); /* icmp unreach already sent */ 417 } 418 419 passout: 420 /* 421 * Step 6: send off the packet 422 */ 423 ip_len = ntohs(ip->ip_len); 424 ip_off = ntohs(ip->ip_off); 425 426 bzero(&ro, sizeof(ro)); 427 dst = (struct sockaddr_in *)&ro.ro_dst; 428 dst->sin_family = AF_INET; 429 dst->sin_len = sizeof(*dst); 430 dst->sin_addr = dest; 431 if (nh->nh_flags & NHF_GATEWAY) { 432 gw = &nh->gw_sa; 433 ro.ro_flags |= RT_HAS_GW; 434 } else 435 gw = (const struct sockaddr *)dst; 436 437 /* 438 * Handle redirect case. 439 */ 440 redest.s_addr = 0; 441 if (V_ipsendredirects && (nh->nh_ifp == m->m_pkthdr.rcvif) && 442 gw->sa_family == AF_INET) 443 mcopy = ip_redir_alloc(m, nh, ip, &redest.s_addr); 444 445 /* 446 * Check if packet fits MTU or if hardware will fragment for us 447 */ 448 if (ip_len <= nh->nh_mtu) { 449 /* 450 * Avoid confusing lower layers. 451 */ 452 m_clrprotoflags(m); 453 /* 454 * Send off the packet via outgoing interface 455 */ 456 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); 457 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); 458 } else { 459 /* 460 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 461 */ 462 if (ip_off & IP_DF) { 463 IPSTAT_INC(ips_cantfrag); 464 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 465 0, nh->nh_mtu); 466 goto consumed; 467 } else { 468 /* 469 * We have to fragment the packet 470 */ 471 m->m_pkthdr.csum_flags |= CSUM_IP; 472 if (ip_fragment(ip, &m, nh->nh_mtu, 473 nh->nh_ifp->if_hwassist) != 0) 474 goto drop; 475 KASSERT(m != NULL, ("null mbuf and no error")); 476 /* 477 * Send off the fragments via outgoing interface 478 */ 479 error = 0; 480 do { 481 m0 = m->m_nextpkt; 482 m->m_nextpkt = NULL; 483 /* 484 * Avoid confusing lower layers. 485 */ 486 m_clrprotoflags(m); 487 488 IP_PROBE(send, NULL, NULL, 489 mtod(m, struct ip *), nh->nh_ifp, 490 mtod(m, struct ip *), NULL); 491 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, 492 gw, &ro); 493 if (error) 494 break; 495 } while ((m = m0) != NULL); 496 if (error) { 497 /* Reclaim remaining fragments */ 498 for (m = m0; m; m = m0) { 499 m0 = m->m_nextpkt; 500 m_freem(m); 501 } 502 } else 503 IPSTAT_INC(ips_fragmented); 504 } 505 } 506 507 if (error != 0) 508 IPSTAT_INC(ips_odropped); 509 else { 510 IPSTAT_INC(ips_forward); 511 IPSTAT_INC(ips_fastforward); 512 } 513 514 /* Send required redirect */ 515 if (mcopy != NULL) { 516 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); 517 mcopy = NULL; /* Freed by caller */ 518 } 519 520 consumed: 521 if (mcopy != NULL) 522 m_freem(mcopy); 523 return NULL; 524 drop: 525 if (m) 526 m_freem(m); 527 return NULL; 528 } 529