1 /*- 2 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote 14 * products derived from this software without specific prior written 15 * permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 */ 29 30 /* 31 * ip_fastforward gets its speed from processing the forwarded packet to 32 * completion (if_output on the other side) without any queues or netisr's. 33 * The receiving interface DMAs the packet into memory, the upper half of 34 * driver calls ip_fastforward, we do our routing table lookup and directly 35 * send it off to the outgoing interface, which DMAs the packet to the 36 * network card. The only part of the packet we touch with the CPU is the 37 * IP header (unless there are complex firewall rules touching other parts 38 * of the packet, but that is up to you). We are essentially limited by bus 39 * bandwidth and how fast the network card/driver can set up receives and 40 * transmits. 41 * 42 * We handle basic errors, IP header errors, checksum errors, 43 * destination unreachable, fragmentation and fragmentation needed and 44 * report them via ICMP to the sender. 45 * 46 * Else if something is not pure IPv4 unicast forwarding we fall back to 47 * the normal ip_input processing path. We should only be called from 48 * interfaces connected to the outside world. 49 * 50 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 51 * ipnat and address rewrite. 52 * 53 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 54 * supported for connections to/from local host. 55 * 56 * We try to do the least expensive (in CPU ops) checks and operations 57 * first to catch junk with as little overhead as possible. 58 * 59 * We take full advantage of hardware support for IP checksum and 60 * fragmentation offloading. 61 * 62 * We don't do ICMP redirect in the fast forwarding path. I have had my own 63 * cases where two core routers with Zebra routing suite would send millions 64 * ICMP redirects to connected hosts if the destination router was not the 65 * default gateway. In one case it was filling the routing table of a host 66 * with approximately 300.000 cloned redirect entries until it ran out of 67 * kernel memory. However the networking code proved very robust and it didn't 68 * crash or fail in other ways. 69 */ 70 71 /* 72 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 73 * is being followed here. 74 */ 75 76 #include <sys/cdefs.h> 77 __FBSDID("$FreeBSD$"); 78 79 #include "opt_ipstealth.h" 80 81 #include <sys/param.h> 82 #include <sys/systm.h> 83 #include <sys/kernel.h> 84 #include <sys/malloc.h> 85 #include <sys/mbuf.h> 86 #include <sys/protosw.h> 87 #include <sys/sdt.h> 88 #include <sys/socket.h> 89 #include <sys/sysctl.h> 90 91 #include <net/pfil.h> 92 #include <net/if.h> 93 #include <net/if_types.h> 94 #include <net/if_var.h> 95 #include <net/if_dl.h> 96 #include <net/route.h> 97 #include <net/vnet.h> 98 99 #include <netinet/in.h> 100 #include <netinet/in_fib.h> 101 #include <netinet/in_kdtrace.h> 102 #include <netinet/in_systm.h> 103 #include <netinet/in_var.h> 104 #include <netinet/ip.h> 105 #include <netinet/ip_var.h> 106 #include <netinet/ip_icmp.h> 107 #include <netinet/ip_options.h> 108 109 #include <machine/in_cksum.h> 110 111 static int 112 ip_findroute(struct nhop4_basic *pnh, struct in_addr dest, struct mbuf *m) 113 { 114 115 bzero(pnh, sizeof(*pnh)); 116 if (fib4_lookup_nh_basic(M_GETFIB(m), dest, 0, 0, pnh) != 0) { 117 IPSTAT_INC(ips_noroute); 118 IPSTAT_INC(ips_cantforward); 119 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 120 return (EHOSTUNREACH); 121 } 122 /* 123 * Drop blackholed traffic and directed broadcasts. 124 */ 125 if ((pnh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 126 IPSTAT_INC(ips_cantforward); 127 m_freem(m); 128 return (EHOSTUNREACH); 129 } 130 131 if (pnh->nh_flags & NHF_REJECT) { 132 IPSTAT_INC(ips_cantforward); 133 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 134 return (EHOSTUNREACH); 135 } 136 137 return (0); 138 } 139 140 /* 141 * Try to forward a packet based on the destination address. 142 * This is a fast path optimized for the plain forwarding case. 143 * If the packet is handled (and consumed) here then we return NULL; 144 * otherwise mbuf is returned and the packet should be delivered 145 * to ip_input for full processing. 146 */ 147 struct mbuf * 148 ip_tryforward(struct mbuf *m) 149 { 150 struct ip *ip; 151 struct mbuf *m0 = NULL; 152 struct nhop4_basic nh; 153 struct sockaddr_in dst; 154 struct in_addr odest, dest; 155 uint16_t ip_len, ip_off; 156 int error = 0; 157 struct m_tag *fwd_tag = NULL; 158 159 /* 160 * Are we active and forwarding packets? 161 */ 162 163 M_ASSERTVALID(m); 164 M_ASSERTPKTHDR(m); 165 166 #ifdef ALTQ 167 /* 168 * Is packet dropped by traffic conditioner? 169 */ 170 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0) 171 goto drop; 172 #endif 173 174 /* 175 * Only IP packets without options 176 */ 177 ip = mtod(m, struct ip *); 178 179 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 180 if (V_ip_doopts == 1) 181 return m; 182 else if (V_ip_doopts == 2) { 183 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 184 0, 0); 185 return NULL; /* mbuf already free'd */ 186 } 187 /* else ignore IP options and continue */ 188 } 189 190 /* 191 * Only unicast IP, not from loopback, no L2 or IP broadcast, 192 * no multicast, no INADDR_ANY 193 * 194 * XXX: Probably some of these checks could be direct drop 195 * conditions. However it is not clear whether there are some 196 * hacks or obscure behaviours which make it necessary to 197 * let ip_input handle it. We play safe here and let ip_input 198 * deal with it until it is proven that we can directly drop it. 199 */ 200 if ((m->m_flags & (M_BCAST|M_MCAST)) || 201 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 202 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 203 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 204 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 205 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 206 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 207 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 208 ip->ip_src.s_addr == INADDR_ANY || 209 ip->ip_dst.s_addr == INADDR_ANY ) 210 return m; 211 212 /* 213 * Is it for a local address on this host? 214 */ 215 if (in_localip(ip->ip_dst)) 216 return m; 217 218 IPSTAT_INC(ips_total); 219 220 /* 221 * Step 3: incoming packet firewall processing 222 */ 223 224 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 225 226 /* 227 * Run through list of ipfilter hooks for input packets 228 */ 229 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 230 goto passin; 231 232 if (pfil_run_hooks( 233 &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) || 234 m == NULL) 235 goto drop; 236 237 M_ASSERTVALID(m); 238 M_ASSERTPKTHDR(m); 239 240 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 241 dest.s_addr = ip->ip_dst.s_addr; 242 243 /* 244 * Destination address changed? 245 */ 246 if (odest.s_addr != dest.s_addr) { 247 /* 248 * Is it now for a local address on this host? 249 */ 250 if (in_localip(dest)) 251 goto forwardlocal; 252 /* 253 * Go on with new destination address 254 */ 255 } 256 257 if (m->m_flags & M_FASTFWD_OURS) { 258 /* 259 * ipfw changed it for a local address on this host. 260 */ 261 goto forwardlocal; 262 } 263 264 passin: 265 /* 266 * Step 4: decrement TTL and look up route 267 */ 268 269 /* 270 * Check TTL 271 */ 272 #ifdef IPSTEALTH 273 if (!V_ipstealth) { 274 #endif 275 if (ip->ip_ttl <= IPTTLDEC) { 276 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 277 return NULL; /* mbuf already free'd */ 278 } 279 280 /* 281 * Decrement the TTL and incrementally change the IP header checksum. 282 * Don't bother doing this with hw checksum offloading, it's faster 283 * doing it right here. 284 */ 285 ip->ip_ttl -= IPTTLDEC; 286 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 287 ip->ip_sum -= ~htons(IPTTLDEC << 8); 288 else 289 ip->ip_sum += htons(IPTTLDEC << 8); 290 #ifdef IPSTEALTH 291 } 292 #endif 293 294 /* 295 * Find route to destination. 296 */ 297 if (ip_findroute(&nh, dest, m) != 0) 298 return (NULL); /* icmp unreach already sent */ 299 300 /* 301 * Step 5: outgoing firewall packet processing 302 */ 303 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 304 goto passout; 305 306 if (pfil_run_hooks(&V_inet_pfil_hook, &m, nh.nh_ifp, PFIL_OUT, NULL) || 307 m == NULL) { 308 goto drop; 309 } 310 311 M_ASSERTVALID(m); 312 M_ASSERTPKTHDR(m); 313 314 ip = mtod(m, struct ip *); 315 dest.s_addr = ip->ip_dst.s_addr; 316 317 /* 318 * Destination address changed? 319 */ 320 if (m->m_flags & M_IP_NEXTHOP) 321 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 322 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 323 /* 324 * Is it now for a local address on this host? 325 */ 326 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 327 forwardlocal: 328 /* 329 * Return packet for processing by ip_input(). 330 */ 331 m->m_flags |= M_FASTFWD_OURS; 332 return (m); 333 } 334 /* 335 * Redo route lookup with new destination address 336 */ 337 if (fwd_tag) { 338 dest.s_addr = ((struct sockaddr_in *) 339 (fwd_tag + 1))->sin_addr.s_addr; 340 m_tag_delete(m, fwd_tag); 341 m->m_flags &= ~M_IP_NEXTHOP; 342 } 343 if (ip_findroute(&nh, dest, m) != 0) 344 return (NULL); /* icmp unreach already sent */ 345 } 346 347 passout: 348 /* 349 * Step 6: send off the packet 350 */ 351 ip_len = ntohs(ip->ip_len); 352 ip_off = ntohs(ip->ip_off); 353 354 bzero(&dst, sizeof(dst)); 355 dst.sin_family = AF_INET; 356 dst.sin_len = sizeof(dst); 357 dst.sin_addr = nh.nh_addr; 358 359 /* 360 * Check if packet fits MTU or if hardware will fragment for us 361 */ 362 if (ip_len <= nh.nh_mtu) { 363 /* 364 * Avoid confusing lower layers. 365 */ 366 m_clrprotoflags(m); 367 /* 368 * Send off the packet via outgoing interface 369 */ 370 IP_PROBE(send, NULL, NULL, ip, nh.nh_ifp, ip, NULL); 371 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m, 372 (struct sockaddr *)&dst, NULL); 373 } else { 374 /* 375 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 376 */ 377 if (ip_off & IP_DF) { 378 IPSTAT_INC(ips_cantfrag); 379 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 380 0, nh.nh_mtu); 381 goto consumed; 382 } else { 383 /* 384 * We have to fragment the packet 385 */ 386 m->m_pkthdr.csum_flags |= CSUM_IP; 387 if (ip_fragment(ip, &m, nh.nh_mtu, 388 nh.nh_ifp->if_hwassist) != 0) 389 goto drop; 390 KASSERT(m != NULL, ("null mbuf and no error")); 391 /* 392 * Send off the fragments via outgoing interface 393 */ 394 error = 0; 395 do { 396 m0 = m->m_nextpkt; 397 m->m_nextpkt = NULL; 398 /* 399 * Avoid confusing lower layers. 400 */ 401 m_clrprotoflags(m); 402 403 IP_PROBE(send, NULL, NULL, 404 mtod(m, struct ip *), nh.nh_ifp, 405 mtod(m, struct ip *), NULL); 406 /* XXX: we can use cached route here */ 407 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m, 408 (struct sockaddr *)&dst, NULL); 409 if (error) 410 break; 411 } while ((m = m0) != NULL); 412 if (error) { 413 /* Reclaim remaining fragments */ 414 for (m = m0; m; m = m0) { 415 m0 = m->m_nextpkt; 416 m_freem(m); 417 } 418 } else 419 IPSTAT_INC(ips_fragmented); 420 } 421 } 422 423 if (error != 0) 424 IPSTAT_INC(ips_odropped); 425 else { 426 IPSTAT_INC(ips_forward); 427 IPSTAT_INC(ips_fastforward); 428 } 429 consumed: 430 return NULL; 431 drop: 432 if (m) 433 m_freem(m); 434 return NULL; 435 } 436