1 /* $OpenBSD: bpf.c,v 1.13 2004/05/05 14:28:58 deraadt Exp $ */ 2 /* $FreeBSD$ */ 3 4 /* BPF socket interface code, originally contributed by Archie Cobbs. */ 5 6 /* 7 * Copyright (c) 1995, 1996, 1998, 1999 8 * The Internet Software Consortium. All rights reserved. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. Neither the name of The Internet Software Consortium nor the names 20 * of its contributors may be used to endorse or promote products derived 21 * from this software without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND 24 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 25 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 26 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 27 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR 28 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 29 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 30 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 31 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 32 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 33 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 34 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35 * SUCH DAMAGE. 36 * 37 * This software has been written for the Internet Software Consortium 38 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie 39 * Enterprises. To learn more about the Internet Software Consortium, 40 * see ``http://www.vix.com/isc''. To learn more about Vixie 41 * Enterprises, see ``http://www.vix.com''. 42 */ 43 44 #include "dhcpd.h" 45 #include <sys/ioctl.h> 46 #include <sys/uio.h> 47 48 #include <net/bpf.h> 49 #include <netinet/in_systm.h> 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 < 0) { 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) < 0) 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... 100 * 101 * XXX: Changes to the filter program may require changes to the 102 * constant offsets used in if_register_send to patch the BPF program! 103 */ 104 struct bpf_insn dhcp_bpf_filter[] = { 105 /* Make sure this is an IP packet... */ 106 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 107 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8), 108 109 /* Make sure it's a UDP packet... */ 110 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 111 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6), 112 113 /* Make sure this isn't a fragment... */ 114 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 115 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0), 116 117 /* Get the IP header length... */ 118 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 119 120 /* Make sure it's to the right port... */ 121 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 122 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), /* patch */ 123 124 /* If we passed all the tests, ask for the whole packet. */ 125 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 126 127 /* Otherwise, drop it. */ 128 BPF_STMT(BPF_RET+BPF_K, 0), 129 }; 130 131 int dhcp_bpf_filter_len = sizeof(dhcp_bpf_filter) / sizeof(struct bpf_insn); 132 133 /* 134 * Packet write filter program: 135 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 136 */ 137 struct bpf_insn dhcp_bpf_wfilter[] = { 138 BPF_STMT(BPF_LD + BPF_B + BPF_IND, 14), 139 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (IPVERSION << 4) + 5, 0, 12), 140 141 /* Make sure this is an IP packet... */ 142 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 143 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 10), 144 145 /* Make sure it's a UDP packet... */ 146 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 147 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 8), 148 149 /* Make sure this isn't a fragment... */ 150 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 151 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 6, 0), /* patched */ 152 153 /* Get the IP header length... */ 154 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 155 156 /* Make sure it's from the right port... */ 157 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 158 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 68, 0, 3), 159 160 /* Make sure it is to the right ports ... */ 161 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 162 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 67, 0, 1), 163 164 /* If we passed all the tests, ask for the whole packet. */ 165 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 166 167 /* Otherwise, drop it. */ 168 BPF_STMT(BPF_RET+BPF_K, 0), 169 }; 170 171 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 172 173 void 174 if_register_receive(struct interface_info *info) 175 { 176 struct bpf_version v; 177 struct bpf_program p; 178 int flag = 1, sz; 179 180 /* Open a BPF device and hang it on this interface... */ 181 info->rfdesc = if_register_bpf(info); 182 183 /* Make sure the BPF version is in range... */ 184 if (ioctl(info->rfdesc, BIOCVERSION, &v) < 0) 185 error("Can't get BPF version: %m"); 186 187 if (v.bv_major != BPF_MAJOR_VERSION || 188 v.bv_minor < BPF_MINOR_VERSION) 189 error("Kernel BPF version out of range - recompile dhcpd!"); 190 191 /* 192 * Set immediate mode so that reads return as soon as a packet 193 * comes in, rather than waiting for the input buffer to fill 194 * with packets. 195 */ 196 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) < 0) 197 error("Can't set immediate mode on bpf device: %m"); 198 199 /* Get the required BPF buffer length from the kernel. */ 200 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) < 0) 201 error("Can't get bpf buffer length: %m"); 202 info->rbuf_max = sz; 203 info->rbuf = malloc(info->rbuf_max); 204 if (!info->rbuf) 205 error("Can't allocate %lu bytes for bpf input buffer.", 206 (unsigned long)info->rbuf_max); 207 info->rbuf_offset = 0; 208 info->rbuf_len = 0; 209 210 /* Set up the bpf filter program structure. */ 211 p.bf_len = dhcp_bpf_filter_len; 212 p.bf_insns = dhcp_bpf_filter; 213 214 /* Patch the server port into the BPF program... 215 * 216 * XXX: changes to filter program may require changes to the 217 * insn number(s) used below! 218 */ 219 dhcp_bpf_filter[8].k = LOCAL_PORT; 220 221 if (ioctl(info->rfdesc, BIOCSETF, &p) < 0) 222 error("Can't install packet filter program: %m"); 223 224 #ifdef BIOCSETWF 225 /* Set up the bpf write filter program structure. */ 226 p.bf_len = dhcp_bpf_wfilter_len; 227 p.bf_insns = dhcp_bpf_wfilter; 228 229 if (dhcp_bpf_wfilter[7].k == 0x1fff) 230 dhcp_bpf_wfilter[7].k = htons(IP_MF|IP_OFFMASK); 231 232 if (ioctl(info->rfdesc, BIOCSETWF, &p) < 0) 233 error("Can't install write filter program: %m"); 234 235 if (ioctl(info->rfdesc, BIOCLOCK, NULL) < 0) 236 error("Cannot lock bpf"); 237 #endif 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 /* 320 * If the captured data wasn't the whole packet, or if 321 * the packet won't fit in the input buffer, all we can 322 * do is drop it. 323 */ 324 if (hdr.bh_caplen != hdr.bh_datalen) { 325 interface->rbuf_offset += hdr.bh_hdrlen = hdr.bh_caplen; 326 continue; 327 } 328 329 /* Skip over the BPF header... */ 330 interface->rbuf_offset += hdr.bh_hdrlen; 331 332 /* Decode the physical header... */ 333 offset = decode_hw_header(interface->rbuf, 334 interface->rbuf_offset, hfrom); 335 336 /* 337 * If a physical layer checksum failed (dunno of any 338 * physical layer that supports this, but WTH), skip 339 * this packet. 340 */ 341 if (offset < 0) { 342 interface->rbuf_offset += hdr.bh_caplen; 343 continue; 344 } 345 interface->rbuf_offset += offset; 346 hdr.bh_caplen -= offset; 347 348 /* Decode the IP and UDP headers... */ 349 offset = decode_udp_ip_header(interface->rbuf, 350 interface->rbuf_offset, from, NULL, hdr.bh_caplen); 351 352 /* If the IP or UDP checksum was bad, skip the packet... */ 353 if (offset < 0) { 354 interface->rbuf_offset += hdr.bh_caplen; 355 continue; 356 } 357 interface->rbuf_offset += offset; 358 hdr.bh_caplen -= offset; 359 360 /* 361 * If there's not enough room to stash the packet data, 362 * we have to skip it (this shouldn't happen in real 363 * life, though). 364 */ 365 if (hdr.bh_caplen > len) { 366 interface->rbuf_offset += hdr.bh_caplen; 367 continue; 368 } 369 370 /* Copy out the data in the packet... */ 371 memcpy(buf, interface->rbuf + interface->rbuf_offset, 372 hdr.bh_caplen); 373 interface->rbuf_offset += hdr.bh_caplen; 374 return (hdr.bh_caplen); 375 } while (!length); 376 return (0); 377 } 378