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 /* 94 * If we're using the bpf API for sending and receiving, we 95 * don't need to register this interface twice. 96 */ 97 info->wfdesc = info->rfdesc; 98 } 99 100 /* 101 * Packet filter program... 102 * 103 * XXX: Changes to the filter program may require changes to the 104 * constant offsets used in if_register_send to patch the BPF program! 105 */ 106 struct bpf_insn dhcp_bpf_filter[] = { 107 /* Make sure this is an IP packet... */ 108 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 109 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 110 111 /* Make sure it's a UDP packet... */ 112 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 113 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 114 115 /* Make sure this isn't a fragment... */ 116 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 117 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 118 119 /* Get the IP header length... */ 120 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 121 122 /* Make sure it's to the right port... */ 123 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 124 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */ 125 126 /* If we passed all the tests, ask for the whole packet. */ 127 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 128 129 /* Otherwise, drop it. */ 130 BPF_STMT(BPF_RET+BPF_K, 0), 131 }; 132 133 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 134 135 /* 136 * Packet write filter program: 137 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 138 */ 139 struct bpf_insn dhcp_bpf_wfilter[] = { 140 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), 141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), 142 143 /* Make sure this is an IP packet... */ 144 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 145 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10), 146 147 /* Make sure it's a UDP packet... */ 148 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 149 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8), 150 151 /* Make sure this isn't a fragment... */ 152 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 153 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */ 154 155 /* Get the IP header length... */ 156 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 157 158 /* Make sure it's from the right port... */ 159 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 160 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3), 161 162 /* Make sure it is to the right ports ... */ 163 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 164 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), 165 166 /* If we passed all the tests, ask for the whole packet. */ 167 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 168 169 /* Otherwise, drop it. */ 170 BPF_STMT(BPF_RET+BPF_K, 0), 171 }; 172 173 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 174 175 void 176 if_register_receive(struct interface_info *info) 177 { 178 struct bpf_version v; 179 struct bpf_program p; 180 int flag = 1, sz; 181 182 /* Open a BPF device and hang it on this interface... */ 183 info->rfdesc = if_register_bpf(info); 184 185 /* Make sure the BPF version is in range... */ 186 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0) 187 error("Can't get BPF version: %m"); 188 189 if (v.bv_major != BPF_MAJOR_VERSION || 190 v.bv_minor < BPF_MINOR_VERSION) 191 error("Kernel BPF version out of range - recompile dhcpd!"); 192 193 /* 194 * Set immediate mode so that reads return as soon as a packet 195 * comes in, rather than waiting for the input buffer to fill 196 * with packets. 197 */ 198 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) 199 error("Can't set immediate mode on bpf device: %m"); 200 201 /* Get the required BPF buffer length from the kernel. */ 202 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) 203 error("Can't get bpf buffer length: %m"); 204 info->rbuf_max = sz; 205 info->rbuf = malloc(info->rbuf_max); 206 if (!info->rbuf) 207 error("Can't allocate %lu bytes for bpf input buffer.", 208 (unsigned long)info->rbuf_max); 209 info->rbuf_offset = 0; 210 info->rbuf_len = 0; 211 212 /* Set up the bpf filter program structure. */ 213 p.bf_len = dhcp_bpf_filter_len; 214 p.bf_insns = dhcp_bpf_filter; 215 216 /* Patch the server port into the BPF program... 217 * 218 * XXX: changes to filter program may require changes to the 219 * insn number(s) used below! 220 */ 221 dhcp_bpf_filter[8].k = LOCAL_PORT; 222 223 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0) 224 error("Can't install packet filter program: %m"); 225 226 /* Set up the bpf write filter program structure. */ 227 p.bf_len = dhcp_bpf_wfilter_len; 228 p.bf_insns = dhcp_bpf_wfilter; 229 230 if (dhcp_bpf_wfilter[7].k == 0x1fff) 231 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK); 232 233 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0) 234 error("Can't install write filter program: %m"); 235 236 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0) 237 error("Cannot lock bpf"); 238 } 239 240 ssize_t 241 send_packet(struct interface_info *interface, struct dhcp_packet *raw, 242 size_t len, struct in_addr from, struct sockaddr_in *to, 243 struct hardware *hto) 244 { 245 unsigned char buf[256]; 246 struct iovec iov[2]; 247 int result, bufp = 0; 248 249 /* Assemble the headers... */ 250 assemble_hw_header(interface, buf, &bufp, hto); 251 assemble_udp_ip_header(buf, &bufp, from.s_addr, 252 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); 253 254 /* Fire it off */ 255 iov[0].iov_base = (char *)buf; 256 iov[0].iov_len = bufp; 257 iov[1].iov_base = (char *)raw; 258 iov[1].iov_len = len; 259 260 result = writev(interface->wfdesc, iov, 2); 261 if (result < 0) 262 warning("send_packet: %m"); 263 return (result); 264 } 265 266 ssize_t 267 receive_packet(struct interface_info *interface, unsigned char *buf, 268 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 269 { 270 int length = 0, offset = 0; 271 struct bpf_hdr hdr; 272 273 /* 274 * All this complexity is because BPF doesn't guarantee that 275 * only one packet will be returned at a time. We're getting 276 * what we deserve, though - this is a terrible abuse of the BPF 277 * interface. Sigh. 278 */ 279 280 /* Process packets until we get one we can return or until we've 281 * done a read and gotten nothing we can return... 282 */ 283 do { 284 /* If the buffer is empty, fill it. */ 285 if (interface->rbuf_offset >= interface->rbuf_len) { 286 length = read(interface->rfdesc, interface->rbuf, 287 interface->rbuf_max); 288 if (length <= 0) 289 return (length); 290 interface->rbuf_offset = 0; 291 interface->rbuf_len = length; 292 } 293 294 /* 295 * If there isn't room for a whole bpf header, something 296 * went wrong, but we'll ignore it and hope it goes 297 * away... XXX 298 */ 299 if (interface->rbuf_len - interface->rbuf_offset < 300 sizeof(hdr)) { 301 interface->rbuf_offset = interface->rbuf_len; 302 continue; 303 } 304 305 /* Copy out a bpf header... */ 306 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 307 sizeof(hdr)); 308 309 /* 310 * If the bpf header plus data doesn't fit in what's 311 * left of the buffer, stick head in sand yet again... 312 */ 313 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 314 interface->rbuf_len) { 315 interface->rbuf_offset = interface->rbuf_len; 316 continue; 317 } 318 319 /* Skip over the BPF header... */ 320 interface->rbuf_offset += hdr.bh_hdrlen; 321 322 /* 323 * If the captured data wasn't the whole packet, or if 324 * the packet won't fit in the input buffer, all we can 325 * do is drop it. 326 */ 327 if (hdr.bh_caplen != hdr.bh_datalen) { 328 interface->rbuf_offset = 329 BPF_WORDALIGN(interface->rbuf_offset + 330 hdr.bh_caplen); 331 continue; 332 } 333 334 /* Decode the physical header... */ 335 offset = decode_hw_header(interface->rbuf, 336 interface->rbuf_offset, hfrom); 337 338 /* 339 * If a physical layer checksum failed (dunno of any 340 * physical layer that supports this, but WTH), skip 341 * this packet. 342 */ 343 if (offset < 0) { 344 interface->rbuf_offset = 345 BPF_WORDALIGN(interface->rbuf_offset + 346 hdr.bh_caplen); 347 continue; 348 } 349 interface->rbuf_offset += offset; 350 hdr.bh_caplen -= offset; 351 352 /* Decode the IP and UDP headers... */ 353 offset = decode_udp_ip_header(interface->rbuf, 354 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 355 356 /* If the IP or UDP checksum was bad, skip the packet... */ 357 if (offset < 0) { 358 interface->rbuf_offset = 359 BPF_WORDALIGN(interface->rbuf_offset + 360 hdr.bh_caplen); 361 continue; 362 } 363 interface->rbuf_offset += offset; 364 hdr.bh_caplen -= offset; 365 366 /* 367 * If there's not enough room to stash the packet data, 368 * we have to skip it (this shouldn't happen in real 369 * life, though). 370 */ 371 if (hdr.bh_caplen > len) { 372 interface->rbuf_offset = 373 BPF_WORDALIGN(interface->rbuf_offset + 374 hdr.bh_caplen); 375 continue; 376 } 377 378 /* Copy out the data in the packet... */ 379 memcpy(buf, interface->rbuf + interface->rbuf_offset, 380 hdr.bh_caplen); 381 interface->rbuf_offset = 382 BPF_WORDALIGN(interface->rbuf_offset + 383 hdr.bh_caplen); 384 return (hdr.bh_caplen); 385 } while (!length); 386 return (0); 387 } 388