1 /* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */ 2 3 /* BPF socket interface code, originally contributed by Archie Cobbs. */ 4 5 /* 6 * Copyright (c) 1995, 1996, 1998, 1999 7 * The Internet Software Consortium. All rights reserved. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of The Internet Software Consortium nor the names 19 * of its contributors may be used to endorse or promote products derived 20 * from this software without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND 23 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 24 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 25 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 26 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR 27 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 29 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 30 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 31 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 32 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 33 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * This software has been written for the Internet Software Consortium 37 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie 38 * Enterprises. To learn more about the Internet Software Consortium, 39 * see ``http://www.vix.com/isc''. To learn more about Vixie 40 * Enterprises, see ``http://www.vix.com''. 41 */ 42 43 #include <sys/cdefs.h> 44 __FBSDID("$FreeBSD$"); 45 46 #include "dhcpd.h" 47 #include <sys/ioctl.h> 48 #include <sys/uio.h> 49 50 #include <net/bpf.h> 51 #include <netinet/in_systm.h> 52 #include <netinet/ip.h> 53 #include <netinet/udp.h> 54 #include <netinet/if_ether.h> 55 56 #define BPF_FORMAT "/dev/bpf%d" 57 58 /* 59 * Called by get_interface_list for each interface that's discovered. 60 * Opens a packet filter for each interface and adds it to the select 61 * mask. 62 */ 63 int 64 if_register_bpf(struct interface_info *info) 65 { 66 char filename[50]; 67 int sock, b; 68 69 /* Open a BPF device */ 70 for (b = 0; 1; b++) { 71 snprintf(filename, sizeof(filename), BPF_FORMAT, b); 72 sock = open(filename, O_RDWR, 0); 73 if (sock < 0) { 74 if (errno == EBUSY) 75 continue; 76 else 77 error("Can't find free bpf: %m"); 78 } else 79 break; 80 } 81 82 /* Set the BPF device to point at this interface. */ 83 if (ioctl(sock, BIOCSETIF, info->ifp) < 0) 84 error("Can't attach interface %s to bpf device %s: %m", 85 info->name, filename); 86 87 return (sock); 88 } 89 90 void 91 if_register_send(struct interface_info *info) 92 { 93 int sock, on = 1; 94 95 /* 96 * If we're using the bpf API for sending and receiving, we 97 * don't need to register this interface twice. 98 */ 99 info->wfdesc = info->rfdesc; 100 101 /* 102 * Use raw socket for unicast send. 103 */ 104 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1) 105 error("socket(SOCK_RAW): %m"); 106 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, 107 sizeof(on)) == -1) 108 error("setsockopt(IP_HDRINCL): %m"); 109 info->ufdesc = sock; 110 } 111 112 /* 113 * Packet filter program... 114 * 115 * XXX: Changes to the filter program may require changes to the 116 * constant offsets used in if_register_send to patch the BPF program! 117 */ 118 struct bpf_insn dhcp_bpf_filter[] = { 119 /* Make sure this is an IP packet... */ 120 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 121 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 122 123 /* Make sure it's a UDP packet... */ 124 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 125 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 126 127 /* Make sure this isn't a fragment... */ 128 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 129 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 130 131 /* Get the IP header length... */ 132 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 133 134 /* Make sure it's to the right port... */ 135 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 136 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */ 137 138 /* If we passed all the tests, ask for the whole packet. */ 139 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 140 141 /* Otherwise, drop it. */ 142 BPF_STMT(BPF_RET+BPF_K, 0), 143 }; 144 145 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 146 147 /* 148 * Packet write filter program: 149 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 150 */ 151 struct bpf_insn dhcp_bpf_wfilter[] = { 152 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), 153 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), 154 155 /* Make sure this is an IP packet... */ 156 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 157 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10), 158 159 /* Make sure it's a UDP packet... */ 160 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 161 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8), 162 163 /* Make sure this isn't a fragment... */ 164 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 165 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */ 166 167 /* Get the IP header length... */ 168 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 169 170 /* Make sure it's from the right port... */ 171 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 172 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3), 173 174 /* Make sure it is to the right ports ... */ 175 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 176 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), 177 178 /* If we passed all the tests, ask for the whole packet. */ 179 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 180 181 /* Otherwise, drop it. */ 182 BPF_STMT(BPF_RET+BPF_K, 0), 183 }; 184 185 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 186 187 void 188 if_register_receive(struct interface_info *info) 189 { 190 struct bpf_version v; 191 struct bpf_program p; 192 int flag = 1, sz; 193 194 /* Open a BPF device and hang it on this interface... */ 195 info->rfdesc = if_register_bpf(info); 196 197 /* Make sure the BPF version is in range... */ 198 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0) 199 error("Can't get BPF version: %m"); 200 201 if (v.bv_major != BPF_MAJOR_VERSION || 202 v.bv_minor < BPF_MINOR_VERSION) 203 error("Kernel BPF version out of range - recompile dhcpd!"); 204 205 /* 206 * Set immediate mode so that reads return as soon as a packet 207 * comes in, rather than waiting for the input buffer to fill 208 * with packets. 209 */ 210 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) 211 error("Can't set immediate mode on bpf device: %m"); 212 213 /* Get the required BPF buffer length from the kernel. */ 214 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) 215 error("Can't get bpf buffer length: %m"); 216 info->rbuf_max = sz; 217 info->rbuf = malloc(info->rbuf_max); 218 if (!info->rbuf) 219 error("Can't allocate %lu bytes for bpf input buffer.", 220 (unsigned long)info->rbuf_max); 221 info->rbuf_offset = 0; 222 info->rbuf_len = 0; 223 224 /* Set up the bpf filter program structure. */ 225 p.bf_len = dhcp_bpf_filter_len; 226 p.bf_insns = dhcp_bpf_filter; 227 228 /* Patch the server port into the BPF program... 229 * 230 * XXX: changes to filter program may require changes to the 231 * insn number(s) used below! 232 */ 233 dhcp_bpf_filter[8].k = LOCAL_PORT; 234 235 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0) 236 error("Can't install packet filter program: %m"); 237 238 /* Set up the bpf write filter program structure. */ 239 p.bf_len = dhcp_bpf_wfilter_len; 240 p.bf_insns = dhcp_bpf_wfilter; 241 242 if (dhcp_bpf_wfilter[7].k == 0x1fff) 243 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK); 244 245 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0) 246 error("Can't install write filter program: %m"); 247 248 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0) 249 error("Cannot lock bpf"); 250 } 251 252 ssize_t 253 send_packet(struct interface_info *interface, struct dhcp_packet *raw, 254 size_t len, struct in_addr from, struct sockaddr_in *to, 255 struct hardware *hto) 256 { 257 unsigned char buf[256]; 258 struct iovec iov[2]; 259 struct msghdr msg; 260 int result, bufp = 0; 261 262 /* Assemble the headers... */ 263 if (to->sin_addr.s_addr == INADDR_BROADCAST) 264 assemble_hw_header(interface, buf, &bufp, hto); 265 assemble_udp_ip_header(buf, &bufp, from.s_addr, 266 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); 267 268 iov[0].iov_base = (char *)buf; 269 iov[0].iov_len = bufp; 270 iov[1].iov_base = (char *)raw; 271 iov[1].iov_len = len; 272 273 /* Fire it off */ 274 if (to->sin_addr.s_addr == INADDR_BROADCAST) 275 result = writev(interface->wfdesc, iov, 2); 276 else { 277 memset(&msg, 0, sizeof(msg)); 278 msg.msg_name = (struct sockaddr *)to; 279 msg.msg_namelen = sizeof(*to); 280 msg.msg_iov = iov; 281 msg.msg_iovlen = 2; 282 result = sendmsg(interface->ufdesc, &msg, 0); 283 } 284 285 if (result < 0) 286 warning("send_packet: %m"); 287 return (result); 288 } 289 290 ssize_t 291 receive_packet(struct interface_info *interface, unsigned char *buf, 292 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 293 { 294 int length = 0, offset = 0; 295 struct bpf_hdr hdr; 296 297 /* 298 * All this complexity is because BPF doesn't guarantee that 299 * only one packet will be returned at a time. We're getting 300 * what we deserve, though - this is a terrible abuse of the BPF 301 * interface. Sigh. 302 */ 303 304 /* Process packets until we get one we can return or until we've 305 * done a read and gotten nothing we can return... 306 */ 307 do { 308 /* If the buffer is empty, fill it. */ 309 if (interface->rbuf_offset >= interface->rbuf_len) { 310 length = read(interface->rfdesc, interface->rbuf, 311 interface->rbuf_max); 312 if (length <= 0) 313 return (length); 314 interface->rbuf_offset = 0; 315 interface->rbuf_len = length; 316 } 317 318 /* 319 * If there isn't room for a whole bpf header, something 320 * went wrong, but we'll ignore it and hope it goes 321 * away... XXX 322 */ 323 if (interface->rbuf_len - interface->rbuf_offset < 324 sizeof(hdr)) { 325 interface->rbuf_offset = interface->rbuf_len; 326 continue; 327 } 328 329 /* Copy out a bpf header... */ 330 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 331 sizeof(hdr)); 332 333 /* 334 * If the bpf header plus data doesn't fit in what's 335 * left of the buffer, stick head in sand yet again... 336 */ 337 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 338 interface->rbuf_len) { 339 interface->rbuf_offset = interface->rbuf_len; 340 continue; 341 } 342 343 /* Skip over the BPF header... */ 344 interface->rbuf_offset += hdr.bh_hdrlen; 345 346 /* 347 * If the captured data wasn't the whole packet, or if 348 * the packet won't fit in the input buffer, all we can 349 * do is drop it. 350 */ 351 if (hdr.bh_caplen != hdr.bh_datalen) { 352 interface->rbuf_offset = 353 BPF_WORDALIGN(interface->rbuf_offset + 354 hdr.bh_caplen); 355 continue; 356 } 357 358 /* Decode the physical header... */ 359 offset = decode_hw_header(interface->rbuf, 360 interface->rbuf_offset, hfrom); 361 362 /* 363 * If a physical layer checksum failed (dunno of any 364 * physical layer that supports this, but WTH), skip 365 * this packet. 366 */ 367 if (offset < 0) { 368 interface->rbuf_offset = 369 BPF_WORDALIGN(interface->rbuf_offset + 370 hdr.bh_caplen); 371 continue; 372 } 373 interface->rbuf_offset += offset; 374 hdr.bh_caplen -= offset; 375 376 /* Decode the IP and UDP headers... */ 377 offset = decode_udp_ip_header(interface->rbuf, 378 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 379 380 /* If the IP or UDP checksum was bad, skip the packet... */ 381 if (offset < 0) { 382 interface->rbuf_offset = 383 BPF_WORDALIGN(interface->rbuf_offset + 384 hdr.bh_caplen); 385 continue; 386 } 387 interface->rbuf_offset += offset; 388 hdr.bh_caplen -= offset; 389 390 /* 391 * If there's not enough room to stash the packet data, 392 * we have to skip it (this shouldn't happen in real 393 * life, though). 394 */ 395 if (hdr.bh_caplen > len) { 396 interface->rbuf_offset = 397 BPF_WORDALIGN(interface->rbuf_offset + 398 hdr.bh_caplen); 399 continue; 400 } 401 402 /* Copy out the data in the packet... */ 403 memcpy(buf, interface->rbuf + interface->rbuf_offset, 404 hdr.bh_caplen); 405 interface->rbuf_offset = 406 BPF_WORDALIGN(interface->rbuf_offset + 407 hdr.bh_caplen); 408 return (hdr.bh_caplen); 409 } while (!length); 410 return (0); 411 } 412