1 /* $OpenBSD: bpf.c,v 1.8 2014/10/25 03:23:49 lteo 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 "dhcpd.h" 44 #include <sys/ioctl.h> 45 #include <sys/uio.h> 46 47 #include <net/bpf.h> 48 #include <net/if_types.h> 49 50 #include <netinet/ip.h> 51 #include <netinet/udp.h> 52 #include <netinet/if_ether.h> 53 54 #define BPF_FORMAT "/dev/bpf%d" 55 56 /* 57 * Called by get_interface_list for each interface that's discovered. 58 * Opens a packet filter for each interface and adds it to the select 59 * mask. 60 */ 61 int 62 if_register_bpf(struct interface_info *info) 63 { 64 char filename[50]; 65 int sock, b; 66 67 /* Open a BPF device */ 68 for (b = 0; 1; b++) { 69 snprintf(filename, sizeof(filename), BPF_FORMAT, b); 70 sock = open(filename, O_RDWR, 0); 71 if (sock == -1) { 72 if (errno == EBUSY) 73 continue; 74 else 75 error("Can't find free bpf: %m"); 76 } else 77 break; 78 } 79 80 /* Set the BPF device to point at this interface. */ 81 if (ioctl(sock, BIOCSETIF, info->ifp) == -1) 82 error("Can't attach interface %s to bpf device %s: %m", 83 info->name, filename); 84 85 return (sock); 86 } 87 88 void 89 if_register_send(struct interface_info *info) 90 { 91 /* 92 * If we're using the bpf API for sending and receiving, we 93 * don't need to register this interface twice. 94 */ 95 info->wfdesc = info->rfdesc; 96 } 97 98 /* 99 * Packet filter program: 'ip and udp and dst port SERVER_PORT' 100 */ 101 struct bpf_insn dhcp_bpf_filter[] = { 102 /* Make sure this is an IP packet... */ 103 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 104 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 105 106 /* Make sure it's a UDP packet... */ 107 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 108 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 109 110 /* Make sure this isn't a fragment... */ 111 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 112 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 113 114 /* Get the IP header length... */ 115 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 116 117 /* Make sure it's to the right port... */ 118 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 119 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 120 121 /* If we passed all the tests, ask for the whole packet. */ 122 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 123 124 /* Otherwise, drop it. */ 125 BPF_STMT(BPF_RET+BPF_K, 0), 126 }; 127 128 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 129 130 /* 131 * Packet filter program: encapsulated 'ip and udp and dst port SERVER_PORT' 132 */ 133 struct bpf_insn dhcp_bpf_efilter[] = { 134 /* Make sure this is an encapsulated AF_INET packet... */ 135 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, 0), 136 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, AF_INET << 24, 0, 10), 137 138 /* Make sure it's an IPIP packet... */ 139 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 21), 140 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_IPIP, 0, 8), 141 142 /* Make sure it's an encapsulated UDP packet... */ 143 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 41), 144 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 145 146 /* Make sure this isn't a fragment... */ 147 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 38), 148 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 149 150 /* Get the IP header length... */ 151 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 32), 152 153 /* Make sure it's to the right port... */ 154 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 34), 155 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 156 157 /* If we passed all the tests, ask for the whole packet. */ 158 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 159 160 /* Otherwise, drop it. */ 161 BPF_STMT(BPF_RET+BPF_K, 0), 162 }; 163 164 int dhcp_bpf_efilter_len = sizeof(dhcp_bpf_efilter) / sizeof(struct bpf_insn); 165 166 /* 167 * Packet write filter program: 'ip and udp and src port SERVER_PORT' 168 */ 169 struct bpf_insn dhcp_bpf_wfilter[] = { 170 /* Make sure this is an IP packet... */ 171 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 172 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 173 174 /* Make sure it's a UDP packet... */ 175 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 176 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 177 178 /* Make sure this isn't a fragment... */ 179 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 180 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 181 182 /* Get the IP header length... */ 183 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 184 185 /* Make sure it's from the right port... */ 186 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 187 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 188 189 /* If we passed all the tests, ask for the whole packet. */ 190 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 191 192 /* Otherwise, drop it. */ 193 BPF_STMT(BPF_RET+BPF_K, 0), 194 }; 195 196 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 197 198 void 199 if_register_receive(struct interface_info *info) 200 { 201 struct bpf_version v; 202 struct bpf_program p; 203 int flag = 1, sz, cmplt = 0; 204 205 /* Open a BPF device and hang it on this interface... */ 206 info->rfdesc = if_register_bpf(info); 207 208 /* Make sure the BPF version is in range... */ 209 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1) 210 error("Can't get BPF version: %m"); 211 212 if (v.bv_major != BPF_MAJOR_VERSION || 213 v.bv_minor < BPF_MINOR_VERSION) 214 error("Kernel BPF version out of range - recompile dhcpd!"); 215 216 /* 217 * Set immediate mode so that reads return as soon as a packet 218 * comes in, rather than waiting for the input buffer to fill 219 * with packets. 220 */ 221 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1) 222 error("Can't set immediate mode on bpf device: %m"); 223 224 /* make sure kernel fills in the source ethernet address */ 225 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1) 226 error("Can't set header complete flag on bpf device: %m"); 227 228 /* Get the required BPF buffer length from the kernel. */ 229 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1) 230 error("Can't get bpf buffer length: %m"); 231 info->rbuf_max = sz; 232 info->rbuf = malloc(info->rbuf_max); 233 if (!info->rbuf) 234 error("Can't allocate %lu bytes for bpf input buffer.", 235 (unsigned long)info->rbuf_max); 236 info->rbuf_offset = 0; 237 info->rbuf_len = 0; 238 239 /* Set up the bpf filter program structure. */ 240 if (info->hw_address.htype == HTYPE_IPSEC_TUNNEL) { 241 p.bf_len = dhcp_bpf_efilter_len; 242 p.bf_insns = dhcp_bpf_efilter; 243 } else { 244 p.bf_len = dhcp_bpf_filter_len; 245 p.bf_insns = dhcp_bpf_filter; 246 } 247 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1) 248 error("Can't install packet filter program: %m"); 249 250 /* Set up the bpf write filter program structure. */ 251 p.bf_len = dhcp_bpf_wfilter_len; 252 p.bf_insns = dhcp_bpf_wfilter; 253 254 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1) 255 error("Can't install write filter program: %m"); 256 257 /* make sure these settings cannot be changed after dropping privs */ 258 if (ioctl(info->rfdesc, BIOCLOCK) == -1) 259 error("Failed to lock bpf descriptor: %m"); 260 } 261 262 ssize_t 263 send_packet(struct interface_info *interface, 264 struct dhcp_packet *raw, size_t len, struct in_addr from, 265 struct sockaddr_in *to, struct hardware *hto) 266 { 267 unsigned char buf[256]; 268 struct iovec iov[2]; 269 int result, bufp = 0; 270 271 if (interface->hw_address.htype == HTYPE_IPSEC_TUNNEL) { 272 socklen_t slen = sizeof(*to); 273 result = sendto(server_fd, raw, len, 0, 274 (struct sockaddr *)to, slen); 275 goto done; 276 } 277 278 /* Assemble the headers... */ 279 assemble_hw_header(interface, buf, &bufp, hto); 280 assemble_udp_ip_header(interface, buf, &bufp, from.s_addr, 281 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); 282 283 /* Fire it off */ 284 iov[0].iov_base = (char *)buf; 285 iov[0].iov_len = bufp; 286 iov[1].iov_base = (char *)raw; 287 iov[1].iov_len = len; 288 289 result = writev(interface->wfdesc, iov, 2); 290 done: 291 if (result == -1) 292 warning("send_packet: %m"); 293 return (result); 294 } 295 296 ssize_t 297 receive_packet(struct interface_info *interface, unsigned char *buf, 298 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 299 { 300 int length = 0, offset = 0; 301 struct bpf_hdr hdr; 302 303 /* 304 * All this complexity is because BPF doesn't guarantee that 305 * only one packet will be returned at a time. We're getting 306 * what we deserve, though - this is a terrible abuse of the BPF 307 * interface. Sigh. 308 */ 309 310 /* Process packets until we get one we can return or until we've 311 * done a read and gotten nothing we can return... 312 */ 313 do { 314 /* If the buffer is empty, fill it. */ 315 if (interface->rbuf_offset == interface->rbuf_len) { 316 length = read(interface->rfdesc, interface->rbuf, 317 interface->rbuf_max); 318 if (length <= 0) 319 return (length); 320 interface->rbuf_offset = 0; 321 interface->rbuf_len = length; 322 } 323 324 /* 325 * If there isn't room for a whole bpf header, something 326 * went wrong, but we'll ignore it and hope it goes 327 * away... XXX 328 */ 329 if (interface->rbuf_len - interface->rbuf_offset < 330 sizeof(hdr)) { 331 interface->rbuf_offset = interface->rbuf_len; 332 continue; 333 } 334 335 /* Copy out a bpf header... */ 336 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 337 sizeof(hdr)); 338 339 /* 340 * If the bpf header plus data doesn't fit in what's 341 * left of the buffer, stick head in sand yet again... 342 */ 343 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 344 interface->rbuf_len) { 345 interface->rbuf_offset = interface->rbuf_len; 346 continue; 347 } 348 349 /* 350 * If the captured data wasn't the whole packet, or if 351 * the packet won't fit in the input buffer, all we can 352 * do is drop it. 353 */ 354 if (hdr.bh_caplen != hdr.bh_datalen) { 355 interface->rbuf_offset += hdr.bh_hdrlen = hdr.bh_caplen; 356 continue; 357 } 358 359 /* Skip over the BPF header... */ 360 interface->rbuf_offset += hdr.bh_hdrlen; 361 362 /* Decode the physical header... */ 363 offset = decode_hw_header(interface, 364 interface->rbuf, interface->rbuf_offset, hfrom); 365 366 /* 367 * If a physical layer checksum failed (dunno of any 368 * physical layer that supports this, but WTH), skip 369 * this packet. 370 */ 371 if (offset < 0) { 372 interface->rbuf_offset += hdr.bh_caplen; 373 continue; 374 } 375 interface->rbuf_offset += offset; 376 hdr.bh_caplen -= offset; 377 378 /* Decode the IP and UDP headers... */ 379 offset = decode_udp_ip_header(interface, interface->rbuf, 380 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 381 382 /* If the IP or UDP checksum was bad, skip the packet... */ 383 if (offset < 0) { 384 interface->rbuf_offset += 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 += hdr.bh_caplen; 397 continue; 398 } 399 400 /* Copy out the data in the packet... */ 401 memcpy(buf, interface->rbuf + interface->rbuf_offset, 402 hdr.bh_caplen); 403 interface->rbuf_offset += hdr.bh_caplen; 404 return (hdr.bh_caplen); 405 } while (!length); 406 return (0); 407 } 408