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 * SPDX-License-Identifier: BSD-3-Clause 7 * 8 * Copyright (c) 1995, 1996, 1998, 1999 9 * The Internet Software Consortium. All rights reserved. 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 * 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of The Internet Software Consortium nor the names 21 * of its contributors may be used to endorse or promote products derived 22 * from this software without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND 25 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 26 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 27 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 28 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR 29 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 32 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 33 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 34 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 35 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * This software has been written for the Internet Software Consortium 39 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie 40 * Enterprises. To learn more about the Internet Software Consortium, 41 * see ``http://www.vix.com/isc''. To learn more about Vixie 42 * Enterprises, see ``http://www.vix.com''. 43 */ 44 45 #include <sys/cdefs.h> 46 __FBSDID("$FreeBSD$"); 47 48 #include "dhcpd.h" 49 #include "privsep.h" 50 #include <sys/capsicum.h> 51 #include <sys/ioctl.h> 52 #include <sys/uio.h> 53 54 #include <net/bpf.h> 55 #include <netinet/in_systm.h> 56 #include <netinet/ip.h> 57 #include <netinet/udp.h> 58 #include <netinet/if_ether.h> 59 60 #include <capsicum_helpers.h> 61 62 #define BPF_FORMAT "/dev/bpf%d" 63 64 /* 65 * Called by get_interface_list for each interface that's discovered. 66 * Opens a packet filter for each interface and adds it to the select 67 * mask. 68 */ 69 int 70 if_register_bpf(struct interface_info *info, int flags) 71 { 72 char filename[50]; 73 int sock, b; 74 75 /* Open a BPF device */ 76 for (b = 0;; b++) { 77 snprintf(filename, sizeof(filename), BPF_FORMAT, b); 78 sock = open(filename, flags); 79 if (sock < 0) { 80 if (errno == EBUSY) 81 continue; 82 else 83 error("Can't find free bpf: %m"); 84 } else 85 break; 86 } 87 88 /* Set the BPF device to point at this interface. */ 89 if (ioctl(sock, BIOCSETIF, info->ifp) < 0) 90 error("Can't attach interface %s to bpf device %s: %m", 91 info->name, filename); 92 93 /* Tag the packets with the proper VLAN PCP setting. */ 94 if (info->client->config->vlan_pcp != 0) { 95 if (ioctl(sock, BIOCSETVLANPCP, 96 &info->client->config->vlan_pcp) < 0) 97 error( "Can't set the VLAN PCP tag on interface %s: %m", 98 info->name); 99 } 100 101 return (sock); 102 } 103 104 /* 105 * Packet write filter program: 106 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 107 */ 108 static const struct bpf_insn dhcp_bpf_wfilter[] = { 109 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), 110 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), 111 112 /* Make sure this is an IP packet... */ 113 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 114 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10), 115 116 /* Make sure it's a UDP packet... */ 117 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 118 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8), 119 120 /* Make sure this isn't a fragment... */ 121 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 122 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 6, 0), 123 124 /* Get the IP header length... */ 125 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 126 127 /* Make sure it's from the right port... */ 128 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 129 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 3), 130 131 /* Make sure it is to the right ports ... */ 132 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 133 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, REMOTE_PORT, 0, 1), 134 135 /* If we passed all the tests, ask for the whole packet. */ 136 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 137 138 /* Otherwise, drop it. */ 139 BPF_STMT(BPF_RET+BPF_K, 0), 140 }; 141 142 void 143 if_register_send(struct interface_info *info) 144 { 145 cap_rights_t rights; 146 struct bpf_version v; 147 struct bpf_program p; 148 int sock, on = 1; 149 150 /* Open a BPF device and hang it on this interface... */ 151 info->wfdesc = if_register_bpf(info, O_WRONLY); 152 153 /* Make sure the BPF version is in range... */ 154 if (ioctl(info->wfdesc, BIOCVERSION, &v) < 0) 155 error("Can't get BPF version: %m"); 156 157 if (v.bv_major != BPF_MAJOR_VERSION || 158 v.bv_minor < BPF_MINOR_VERSION) 159 error("Kernel BPF version out of range - recompile dhcpd!"); 160 161 /* Set up the bpf write filter program structure. */ 162 p.bf_insns = __DECONST(struct bpf_insn *, dhcp_bpf_wfilter); 163 p.bf_len = nitems(dhcp_bpf_wfilter); 164 165 if (ioctl(info->wfdesc, BIOCSETWF, &p) < 0) 166 error("Can't install write filter program: %m"); 167 168 if (ioctl(info->wfdesc, BIOCLOCK, NULL) < 0) 169 error("Cannot lock bpf"); 170 171 cap_rights_init(&rights, CAP_WRITE); 172 if (caph_rights_limit(info->wfdesc, &rights) < 0) 173 error("Can't limit bpf descriptor: %m"); 174 175 /* 176 * Use raw socket for unicast send. 177 */ 178 if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_UDP)) == -1) 179 error("socket(SOCK_RAW): %m"); 180 if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, 181 sizeof(on)) == -1) 182 error("setsockopt(IP_HDRINCL): %m"); 183 info->ufdesc = sock; 184 } 185 186 /* 187 * Packet filter program... 188 */ 189 static const struct bpf_insn dhcp_bpf_filter[] = { 190 /* Make sure this is an IP packet... */ 191 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 192 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 193 194 /* Make sure it's a UDP packet... */ 195 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 196 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 197 198 /* Make sure this isn't a fragment... */ 199 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 200 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, IP_MF|IP_OFFMASK, 4, 0), 201 202 /* Get the IP header length... */ 203 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 204 205 /* Make sure it's to the right port... */ 206 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 207 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, LOCAL_PORT, 0, 1), 208 209 /* If we passed all the tests, ask for the whole packet. */ 210 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 211 212 /* Otherwise, drop it. */ 213 BPF_STMT(BPF_RET+BPF_K, 0), 214 }; 215 216 void 217 if_register_receive(struct interface_info *info) 218 { 219 static const unsigned long cmds[2] = { SIOCGIFFLAGS, SIOCGIFMEDIA }; 220 cap_rights_t rights; 221 struct bpf_version v; 222 struct bpf_program p; 223 int flag = 1, sz; 224 225 /* Open a BPF device and hang it on this interface... */ 226 info->rfdesc = if_register_bpf(info, O_RDONLY); 227 228 /* Make sure the BPF version is in range... */ 229 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0) 230 error("Can't get BPF version: %m"); 231 232 if (v.bv_major != BPF_MAJOR_VERSION || 233 v.bv_minor < BPF_MINOR_VERSION) 234 error("Kernel BPF version out of range - recompile dhcpd!"); 235 236 /* 237 * Set immediate mode so that reads return as soon as a packet 238 * comes in, rather than waiting for the input buffer to fill 239 * with packets. 240 */ 241 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) 242 error("Can't set immediate mode on bpf device: %m"); 243 244 /* Get the required BPF buffer length from the kernel. */ 245 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) 246 error("Can't get bpf buffer length: %m"); 247 info->rbuf_max = sz; 248 info->rbuf = malloc(info->rbuf_max); 249 if (!info->rbuf) 250 error("Can't allocate %lu bytes for bpf input buffer.", 251 (unsigned long)info->rbuf_max); 252 info->rbuf_offset = 0; 253 info->rbuf_len = 0; 254 255 /* Set up the bpf filter program structure. */ 256 p.bf_insns = __DECONST(struct bpf_insn *, dhcp_bpf_filter); 257 p.bf_len = nitems(dhcp_bpf_filter); 258 259 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0) 260 error("Can't install packet filter program: %m"); 261 262 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0) 263 error("Cannot lock bpf"); 264 265 cap_rights_init(&rights, CAP_IOCTL, CAP_EVENT, CAP_READ); 266 if (caph_rights_limit(info->rfdesc, &rights) < 0) 267 error("Can't limit bpf descriptor: %m"); 268 if (caph_ioctls_limit(info->rfdesc, cmds, 2) < 0) 269 error("Can't limit ioctls for bpf descriptor: %m"); 270 } 271 272 void 273 send_packet_unpriv(int privfd, struct dhcp_packet *raw, size_t len, 274 struct in_addr from, struct in_addr to) 275 { 276 struct imsg_hdr hdr; 277 struct buf *buf; 278 int errs; 279 280 hdr.code = IMSG_SEND_PACKET; 281 hdr.len = sizeof(hdr) + 282 sizeof(size_t) + len + 283 sizeof(from) + sizeof(to); 284 285 if ((buf = buf_open(hdr.len)) == NULL) 286 error("buf_open: %m"); 287 288 errs = 0; 289 errs += buf_add(buf, &hdr, sizeof(hdr)); 290 errs += buf_add(buf, &len, sizeof(len)); 291 errs += buf_add(buf, raw, len); 292 errs += buf_add(buf, &from, sizeof(from)); 293 errs += buf_add(buf, &to, sizeof(to)); 294 if (errs) 295 error("buf_add: %m"); 296 297 if (buf_close(privfd, buf) == -1) 298 error("buf_close: %m"); 299 } 300 301 void 302 send_packet_priv(struct interface_info *interface, struct imsg_hdr *hdr, int fd) 303 { 304 unsigned char buf[256]; 305 struct iovec iov[2]; 306 struct msghdr msg; 307 struct dhcp_packet raw; 308 size_t len; 309 struct in_addr from, to; 310 int result, bufp = 0; 311 312 if (hdr->len < sizeof(*hdr) + sizeof(size_t)) 313 error("corrupted message received"); 314 buf_read(fd, &len, sizeof(len)); 315 if (hdr->len != sizeof(*hdr) + sizeof(size_t) + len + 316 sizeof(from) + sizeof(to)) { 317 error("corrupted message received"); 318 } 319 if (len > sizeof(raw)) 320 error("corrupted message received"); 321 buf_read(fd, &raw, len); 322 buf_read(fd, &from, sizeof(from)); 323 buf_read(fd, &to, sizeof(to)); 324 325 /* Assemble the headers... */ 326 if (to.s_addr == INADDR_BROADCAST) 327 assemble_hw_header(interface, buf, &bufp); 328 assemble_udp_ip_header(buf, &bufp, from.s_addr, to.s_addr, 329 htons(REMOTE_PORT), (unsigned char *)&raw, len); 330 331 iov[0].iov_base = buf; 332 iov[0].iov_len = bufp; 333 iov[1].iov_base = &raw; 334 iov[1].iov_len = len; 335 336 /* Fire it off */ 337 if (to.s_addr == INADDR_BROADCAST) 338 result = writev(interface->wfdesc, iov, 2); 339 else { 340 struct sockaddr_in sato; 341 342 sato.sin_addr = to; 343 sato.sin_port = htons(REMOTE_PORT); 344 sato.sin_family = AF_INET; 345 sato.sin_len = sizeof(sato); 346 347 memset(&msg, 0, sizeof(msg)); 348 msg.msg_name = (struct sockaddr *)&sato; 349 msg.msg_namelen = sizeof(sato); 350 msg.msg_iov = iov; 351 msg.msg_iovlen = 2; 352 result = sendmsg(interface->ufdesc, &msg, 0); 353 } 354 355 if (result < 0) 356 warning("send_packet: %m"); 357 } 358 359 ssize_t 360 receive_packet(struct interface_info *interface, unsigned char *buf, 361 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 362 { 363 int length = 0, offset = 0; 364 struct bpf_hdr hdr; 365 366 /* 367 * All this complexity is because BPF doesn't guarantee that 368 * only one packet will be returned at a time. We're getting 369 * what we deserve, though - this is a terrible abuse of the BPF 370 * interface. Sigh. 371 */ 372 373 /* Process packets until we get one we can return or until we've 374 * done a read and gotten nothing we can return... 375 */ 376 do { 377 /* If the buffer is empty, fill it. */ 378 if (interface->rbuf_offset >= interface->rbuf_len) { 379 length = read(interface->rfdesc, interface->rbuf, 380 interface->rbuf_max); 381 if (length <= 0) 382 return (length); 383 interface->rbuf_offset = 0; 384 interface->rbuf_len = length; 385 } 386 387 /* 388 * If there isn't room for a whole bpf header, something 389 * went wrong, but we'll ignore it and hope it goes 390 * away... XXX 391 */ 392 if (interface->rbuf_len - interface->rbuf_offset < 393 sizeof(hdr)) { 394 interface->rbuf_offset = interface->rbuf_len; 395 continue; 396 } 397 398 /* Copy out a bpf header... */ 399 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 400 sizeof(hdr)); 401 402 /* 403 * If the bpf header plus data doesn't fit in what's 404 * left of the buffer, stick head in sand yet again... 405 */ 406 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 407 interface->rbuf_len) { 408 interface->rbuf_offset = interface->rbuf_len; 409 continue; 410 } 411 412 /* Skip over the BPF header... */ 413 interface->rbuf_offset += hdr.bh_hdrlen; 414 415 /* 416 * If the captured data wasn't the whole packet, or if 417 * the packet won't fit in the input buffer, all we can 418 * do is drop it. 419 */ 420 if (hdr.bh_caplen != hdr.bh_datalen) { 421 interface->rbuf_offset = 422 BPF_WORDALIGN(interface->rbuf_offset + 423 hdr.bh_caplen); 424 continue; 425 } 426 427 /* Decode the physical header... */ 428 offset = decode_hw_header(interface->rbuf, 429 interface->rbuf_offset, hfrom); 430 431 /* 432 * If a physical layer checksum failed (dunno of any 433 * physical layer that supports this, but WTH), skip 434 * this packet. 435 */ 436 if (offset < 0) { 437 interface->rbuf_offset = 438 BPF_WORDALIGN(interface->rbuf_offset + 439 hdr.bh_caplen); 440 continue; 441 } 442 interface->rbuf_offset += offset; 443 hdr.bh_caplen -= offset; 444 445 /* Decode the IP and UDP headers... */ 446 offset = decode_udp_ip_header(interface->rbuf, 447 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 448 449 /* If the IP or UDP checksum was bad, skip the packet... */ 450 if (offset < 0) { 451 interface->rbuf_offset = 452 BPF_WORDALIGN(interface->rbuf_offset + 453 hdr.bh_caplen); 454 continue; 455 } 456 interface->rbuf_offset += offset; 457 hdr.bh_caplen -= offset; 458 459 /* 460 * If there's not enough room to stash the packet data, 461 * we have to skip it (this shouldn't happen in real 462 * life, though). 463 */ 464 if (hdr.bh_caplen > len) { 465 interface->rbuf_offset = 466 BPF_WORDALIGN(interface->rbuf_offset + 467 hdr.bh_caplen); 468 continue; 469 } 470 471 /* Copy out the data in the packet... */ 472 memcpy(buf, interface->rbuf + interface->rbuf_offset, 473 hdr.bh_caplen); 474 interface->rbuf_offset = 475 BPF_WORDALIGN(interface->rbuf_offset + 476 hdr.bh_caplen); 477 return (hdr.bh_caplen); 478 } while (!length); 479 return (0); 480 } 481