bpf.c revision 252626
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: head/sbin/dhclient/bpf.c 252626 2013-07-03 22:12:54Z pjd $"); 45 46#include "dhcpd.h" 47#include "privsep.h" 48#include <sys/ioctl.h> 49#include <sys/uio.h> 50 51#include <net/bpf.h> 52#include <netinet/in_systm.h> 53#include <netinet/ip.h> 54#include <netinet/udp.h> 55#include <netinet/if_ether.h> 56 57#define BPF_FORMAT "/dev/bpf%d" 58 59/* 60 * Called by get_interface_list for each interface that's discovered. 61 * Opens a packet filter for each interface and adds it to the select 62 * mask. 63 */ 64int 65if_register_bpf(struct interface_info *info, int flags) 66{ 67 char filename[50]; 68 int sock, b; 69 70 /* Open a BPF device */ 71 for (b = 0;; b++) { 72 snprintf(filename, sizeof(filename), BPF_FORMAT, b); 73 sock = open(filename, flags); 74 if (sock < 0) { 75 if (errno == EBUSY) 76 continue; 77 else 78 error("Can't find free bpf: %m"); 79 } else 80 break; 81 } 82 83 /* Set the BPF device to point at this interface. */ 84 if (ioctl(sock, BIOCSETIF, info->ifp) < 0) 85 error("Can't attach interface %s to bpf device %s: %m", 86 info->name, filename); 87 88 return (sock); 89} 90 91/* 92 * Packet write filter program: 93 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 94 */ 95struct bpf_insn dhcp_bpf_wfilter[] = { 96 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), 97 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), 98 99 /* Make sure this is an IP packet... */ 100 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 101 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10), 102 103 /* Make sure it's a UDP packet... */ 104 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 105 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8), 106 107 /* Make sure this isn't a fragment... */ 108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 109 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */ 110 111 /* Get the IP header length... */ 112 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 113 114 /* Make sure it's from the right port... */ 115 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 116 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3), 117 118 /* Make sure it is to the right ports ... */ 119 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 120 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), 121 122 /* If we passed all the tests, ask for the whole packet. */ 123 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 124 125 /* Otherwise, drop it. */ 126 BPF_STMT(BPF_RET+BPF_K, 0), 127}; 128 129int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 130 131void 132if_register_send(struct interface_info *info) 133{ 134 struct bpf_version v; 135 struct bpf_program p; 136 int sock, on = 1; 137 138 /* Open a BPF device and hang it on this interface... */ 139 info->wfdesc = if_register_bpf(info, O_WRONLY); 140 141 /* Make sure the BPF version is in range... */ 142 if (ioctl(info->wfdesc, BIOCVERSION, &v) < 0) 143 error("Can't get BPF version: %m"); 144 145 if (v.bv_major != BPF_MAJOR_VERSION || 146 v.bv_minor < BPF_MINOR_VERSION) 147 error("Kernel BPF version out of range - recompile dhcpd!"); 148 149 /* Set up the bpf write filter program structure. */ 150 p.bf_len = dhcp_bpf_wfilter_len; 151 p.bf_insns = dhcp_bpf_wfilter; 152 153 if (dhcp_bpf_wfilter[7].k == 0x1fff) 154 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK); 155 156 if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0) 157 error("Can't install write filter program: %m"); 158 159 if (ioctl(info->wfdesc, BIOCLOCK, NULL) < 0) 160 error("Cannot lock bpf"); 161 162 /* 163 * Use raw socket for unicast send. 164 */ 165 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1) 166 error("socket(SOCK_RAW): %m"); 167 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, 168 sizeof(on)) == -1) 169 error("setsockopt(IP_HDRINCL): %m"); 170 info->ufdesc = sock; 171} 172 173/* 174 * Packet filter program... 175 * 176 * XXX: Changes to the filter program may require changes to the 177 * constant offsets used in if_register_send to patch the BPF program! 178 */ 179struct bpf_insn dhcp_bpf_filter[] = { 180 /* Make sure this is an IP packet... */ 181 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 182 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 183 184 /* Make sure it's a UDP packet... */ 185 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 186 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 187 188 /* Make sure this isn't a fragment... */ 189 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 190 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 191 192 /* Get the IP header length... */ 193 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 194 195 /* Make sure it's to the right port... */ 196 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 197 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */ 198 199 /* If we passed all the tests, ask for the whole packet. */ 200 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 201 202 /* Otherwise, drop it. */ 203 BPF_STMT(BPF_RET+BPF_K, 0), 204}; 205 206int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 207 208void 209if_register_receive(struct interface_info *info) 210{ 211 struct bpf_version v; 212 struct bpf_program p; 213 int flag = 1, sz; 214 215 /* Open a BPF device and hang it on this interface... */ 216 info->rfdesc = if_register_bpf(info, O_RDONLY); 217 218 /* Make sure the BPF version is in range... */ 219 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0) 220 error("Can't get BPF version: %m"); 221 222 if (v.bv_major != BPF_MAJOR_VERSION || 223 v.bv_minor < BPF_MINOR_VERSION) 224 error("Kernel BPF version out of range - recompile dhcpd!"); 225 226 /* 227 * Set immediate mode so that reads return as soon as a packet 228 * comes in, rather than waiting for the input buffer to fill 229 * with packets. 230 */ 231 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) 232 error("Can't set immediate mode on bpf device: %m"); 233 234 /* Get the required BPF buffer length from the kernel. */ 235 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) 236 error("Can't get bpf buffer length: %m"); 237 info->rbuf_max = sz; 238 info->rbuf = malloc(info->rbuf_max); 239 if (!info->rbuf) 240 error("Can't allocate %lu bytes for bpf input buffer.", 241 (unsigned long)info->rbuf_max); 242 info->rbuf_offset = 0; 243 info->rbuf_len = 0; 244 245 /* Set up the bpf filter program structure. */ 246 p.bf_len = dhcp_bpf_filter_len; 247 p.bf_insns = dhcp_bpf_filter; 248 249 /* Patch the server port into the BPF program... 250 * 251 * XXX: changes to filter program may require changes to the 252 * insn number(s) used below! 253 */ 254 dhcp_bpf_filter[8].k = LOCAL_PORT; 255 256 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0) 257 error("Can't install packet filter program: %m"); 258 259 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0) 260 error("Cannot lock bpf"); 261} 262 263void 264send_packet_unpriv(int privfd, struct dhcp_packet *raw, size_t len, 265 struct in_addr from, struct in_addr to) 266{ 267 struct imsg_hdr hdr; 268 struct buf *buf; 269 int errs; 270 271 hdr.code = IMSG_SEND_PACKET; 272 hdr.len = sizeof(hdr) + 273 sizeof(size_t) + len + 274 sizeof(from) + sizeof(to); 275 276 if ((buf = buf_open(hdr.len)) == NULL) 277 error("buf_open: %m"); 278 279 errs = 0; 280 errs += buf_add(buf, &hdr, sizeof(hdr)); 281 errs += buf_add(buf, &len, sizeof(len)); 282 errs += buf_add(buf, raw, len); 283 errs += buf_add(buf, &from, sizeof(from)); 284 errs += buf_add(buf, &to, sizeof(to)); 285 if (errs) 286 error("buf_add: %m"); 287 288 if (buf_close(privfd, buf) == -1) 289 error("buf_close: %m"); 290} 291 292void 293send_packet_priv(struct interface_info *interface, struct imsg_hdr *hdr, int fd) 294{ 295 unsigned char buf[256]; 296 struct iovec iov[2]; 297 struct msghdr msg; 298 struct dhcp_packet raw; 299 size_t len; 300 struct in_addr from, to; 301 int result, bufp = 0; 302 303 if (hdr->len < sizeof(*hdr) + sizeof(size_t)) 304 error("corrupted message received"); 305 buf_read(fd, &len, sizeof(len)); 306 if (hdr->len != sizeof(*hdr) + sizeof(size_t) + len + 307 sizeof(from) + sizeof(to)) { 308 error("corrupted message received"); 309 } 310 if (len > sizeof(raw)) 311 error("corrupted message received"); 312 buf_read(fd, &raw, len); 313 buf_read(fd, &from, sizeof(from)); 314 buf_read(fd, &to, sizeof(to)); 315 316 /* Assemble the headers... */ 317 if (to.s_addr == INADDR_BROADCAST) 318 assemble_hw_header(interface, buf, &bufp); 319 assemble_udp_ip_header(buf, &bufp, from.s_addr, to.s_addr, 320 htons(REMOTE_PORT), (unsigned char *)&raw, len); 321 322 iov[0].iov_base = buf; 323 iov[0].iov_len = bufp; 324 iov[1].iov_base = &raw; 325 iov[1].iov_len = len; 326 327 /* Fire it off */ 328 if (to.s_addr == INADDR_BROADCAST) 329 result = writev(interface->wfdesc, iov, 2); 330 else { 331 struct sockaddr_in sato; 332 333 sato.sin_addr = to; 334 sato.sin_port = htons(REMOTE_PORT); 335 sato.sin_family = AF_INET; 336 sato.sin_len = sizeof(sato); 337 338 memset(&msg, 0, sizeof(msg)); 339 msg.msg_name = (struct sockaddr *)&sato; 340 msg.msg_namelen = sizeof(sato); 341 msg.msg_iov = iov; 342 msg.msg_iovlen = 2; 343 result = sendmsg(interface->ufdesc, &msg, 0); 344 } 345 346 if (result < 0) 347 warning("send_packet: %m"); 348} 349 350ssize_t 351receive_packet(struct interface_info *interface, unsigned char *buf, 352 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 353{ 354 int length = 0, offset = 0; 355 struct bpf_hdr hdr; 356 357 /* 358 * All this complexity is because BPF doesn't guarantee that 359 * only one packet will be returned at a time. We're getting 360 * what we deserve, though - this is a terrible abuse of the BPF 361 * interface. Sigh. 362 */ 363 364 /* Process packets until we get one we can return or until we've 365 * done a read and gotten nothing we can return... 366 */ 367 do { 368 /* If the buffer is empty, fill it. */ 369 if (interface->rbuf_offset >= interface->rbuf_len) { 370 length = read(interface->rfdesc, interface->rbuf, 371 interface->rbuf_max); 372 if (length <= 0) 373 return (length); 374 interface->rbuf_offset = 0; 375 interface->rbuf_len = length; 376 } 377 378 /* 379 * If there isn't room for a whole bpf header, something 380 * went wrong, but we'll ignore it and hope it goes 381 * away... XXX 382 */ 383 if (interface->rbuf_len - interface->rbuf_offset < 384 sizeof(hdr)) { 385 interface->rbuf_offset = interface->rbuf_len; 386 continue; 387 } 388 389 /* Copy out a bpf header... */ 390 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 391 sizeof(hdr)); 392 393 /* 394 * If the bpf header plus data doesn't fit in what's 395 * left of the buffer, stick head in sand yet again... 396 */ 397 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 398 interface->rbuf_len) { 399 interface->rbuf_offset = interface->rbuf_len; 400 continue; 401 } 402 403 /* Skip over the BPF header... */ 404 interface->rbuf_offset += hdr.bh_hdrlen; 405 406 /* 407 * If the captured data wasn't the whole packet, or if 408 * the packet won't fit in the input buffer, all we can 409 * do is drop it. 410 */ 411 if (hdr.bh_caplen != hdr.bh_datalen) { 412 interface->rbuf_offset = 413 BPF_WORDALIGN(interface->rbuf_offset + 414 hdr.bh_caplen); 415 continue; 416 } 417 418 /* Decode the physical header... */ 419 offset = decode_hw_header(interface->rbuf, 420 interface->rbuf_offset, hfrom); 421 422 /* 423 * If a physical layer checksum failed (dunno of any 424 * physical layer that supports this, but WTH), skip 425 * this packet. 426 */ 427 if (offset < 0) { 428 interface->rbuf_offset = 429 BPF_WORDALIGN(interface->rbuf_offset + 430 hdr.bh_caplen); 431 continue; 432 } 433 interface->rbuf_offset += offset; 434 hdr.bh_caplen -= offset; 435 436 /* Decode the IP and UDP headers... */ 437 offset = decode_udp_ip_header(interface->rbuf, 438 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 439 440 /* If the IP or UDP checksum was bad, skip the packet... */ 441 if (offset < 0) { 442 interface->rbuf_offset = 443 BPF_WORDALIGN(interface->rbuf_offset + 444 hdr.bh_caplen); 445 continue; 446 } 447 interface->rbuf_offset += offset; 448 hdr.bh_caplen -= offset; 449 450 /* 451 * If there's not enough room to stash the packet data, 452 * we have to skip it (this shouldn't happen in real 453 * life, though). 454 */ 455 if (hdr.bh_caplen > len) { 456 interface->rbuf_offset = 457 BPF_WORDALIGN(interface->rbuf_offset + 458 hdr.bh_caplen); 459 continue; 460 } 461 462 /* Copy out the data in the packet... */ 463 memcpy(buf, interface->rbuf + interface->rbuf_offset, 464 hdr.bh_caplen); 465 interface->rbuf_offset = 466 BPF_WORDALIGN(interface->rbuf_offset + 467 hdr.bh_caplen); 468 return (hdr.bh_caplen); 469 } while (!length); 470 return (0); 471} 472