1 /* $OpenBSD: bpf.c,v 1.14 2016/05/28 07:00:18 natano 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/ioctl.h> 44 #include <sys/types.h> 45 #include <sys/socket.h> 46 47 #include <arpa/inet.h> 48 49 #include <net/bpf.h> 50 #include <net/if.h> 51 52 #include <netinet/if_ether.h> 53 #include <netinet/in.h> 54 55 #include <errno.h> 56 #include <fcntl.h> 57 #include <stdio.h> 58 #include <stdlib.h> 59 #include <string.h> 60 #include <unistd.h> 61 62 #include "dhcp.h" 63 #include "tree.h" 64 #include "dhcpd.h" 65 66 ssize_t send_packet (struct interface_info *, struct dhcp_packet *, 67 size_t, struct in_addr, struct sockaddr_in *, struct hardware *); 68 69 /* 70 * Called by get_interface_list for each interface that's discovered. 71 * Opens a packet filter for each interface and adds it to the select 72 * mask. 73 */ 74 int 75 if_register_bpf(struct interface_info *info) 76 { 77 int sock; 78 79 if ((sock = open("/dev/bpf0", O_RDWR)) == -1) 80 error("Can't open bpf device: %m"); 81 82 /* Set the BPF device to point at this interface. */ 83 if (ioctl(sock, BIOCSETIF, info->ifp) == -1) 84 error("Can't attach interface %s to bpf device: %m", 85 info->name); 86 87 info->send_packet = send_packet; 88 return (sock); 89 } 90 91 void 92 if_register_send(struct interface_info *info) 93 { 94 /* 95 * If we're using the bpf API for sending and receiving, we 96 * don't need to register this interface twice. 97 */ 98 info->wfdesc = info->rfdesc; 99 } 100 101 /* 102 * Packet read filter program: 'ip and udp and dst port bootps' 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, SERVER_PORT, 0, 1), 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 /* 135 * Packet write filter program: 136 * 'ip and udp and src port bootps and dst port (bootps or bootpc)' 137 */ 138 struct bpf_insn dhcp_bpf_wfilter[] = { 139 /* Make sure this is an IP packet... */ 140 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12), 141 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 11), 142 143 /* Make sure it's a UDP packet... */ 144 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23), 145 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 9), 146 147 /* Make sure this isn't a fragment... */ 148 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20), 149 BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 7, 0), 150 151 /* Get the IP header length... */ 152 BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14), 153 154 /* Make sure it's from the right port... */ 155 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 14), 156 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 4), 157 158 /* Make sure it is to the right ports ... */ 159 BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16), 160 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, CLIENT_PORT, 1, 0), 161 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, SERVER_PORT, 0, 1), 162 163 /* If we passed all the tests, ask for the whole packet. */ 164 BPF_STMT(BPF_RET+BPF_K, (u_int)-1), 165 166 /* Otherwise, drop it. */ 167 BPF_STMT(BPF_RET+BPF_K, 0), 168 }; 169 170 int dhcp_bpf_wfilter_len = sizeof(dhcp_bpf_wfilter) / sizeof(struct bpf_insn); 171 172 void 173 if_register_receive(struct interface_info *info) 174 { 175 struct bpf_version v; 176 struct bpf_program p; 177 int flag = 1, sz, cmplt = 0; 178 179 /* Open a BPF device and hang it on this interface... */ 180 info->rfdesc = if_register_bpf(info); 181 182 /* Make sure the BPF version is in range... */ 183 if (ioctl(info->rfdesc, BIOCVERSION, &v) == -1) 184 error("Can't get BPF version: %m"); 185 186 if (v.bv_major != BPF_MAJOR_VERSION || 187 v.bv_minor < BPF_MINOR_VERSION) 188 error("Kernel BPF version out of range - recompile dhcpd!"); 189 190 /* 191 * Set immediate mode so that reads return as soon as a packet 192 * comes in, rather than waiting for the input buffer to fill 193 * with packets. 194 */ 195 if (ioctl(info->rfdesc, BIOCIMMEDIATE, &flag) == -1) 196 error("Can't set immediate mode on bpf device: %m"); 197 198 if (ioctl(info->rfdesc, BIOCSFILDROP, &flag) == -1) 199 error("Can't set filter-drop mode on bpf device: %m"); 200 201 /* make sure kernel fills in the source ethernet address */ 202 if (ioctl(info->rfdesc, BIOCSHDRCMPLT, &cmplt) == -1) 203 error("Can't set header complete flag on bpf device: %m"); 204 205 /* Get the required BPF buffer length from the kernel. */ 206 if (ioctl(info->rfdesc, BIOCGBLEN, &sz) == -1) 207 error("Can't get bpf buffer length: %m"); 208 info->rbuf_max = sz; 209 info->rbuf = malloc(info->rbuf_max); 210 if (!info->rbuf) 211 error("Can't allocate %lu bytes for bpf input buffer.", 212 (unsigned long)info->rbuf_max); 213 info->rbuf_offset = 0; 214 info->rbuf_len = 0; 215 216 /* Set up the bpf filter program structure. */ 217 p.bf_len = dhcp_bpf_filter_len; 218 p.bf_insns = dhcp_bpf_filter; 219 220 if (ioctl(info->rfdesc, BIOCSETF, &p) == -1) 221 error("Can't install packet filter program: %m"); 222 223 /* Set up the bpf write filter program structure. */ 224 p.bf_len = dhcp_bpf_wfilter_len; 225 p.bf_insns = dhcp_bpf_wfilter; 226 227 if (ioctl(info->rfdesc, BIOCSETWF, &p) == -1) 228 error("Can't install write filter program: %m"); 229 230 /* make sure these settings cannot be changed after dropping privs */ 231 if (ioctl(info->rfdesc, BIOCLOCK) == -1) 232 error("Failed to lock bpf descriptor: %m"); 233 } 234 235 ssize_t 236 send_packet(struct interface_info *interface, struct dhcp_packet *raw, 237 size_t len, struct in_addr from, struct sockaddr_in *to, 238 struct hardware *hto) 239 { 240 unsigned char buf[256]; 241 struct iovec iov[2]; 242 ssize_t result; 243 int bufp = 0; 244 245 /* Assemble the headers... */ 246 assemble_hw_header(interface, buf, &bufp, hto); 247 assemble_udp_ip_header(interface, buf, &bufp, from.s_addr, 248 to->sin_addr.s_addr, to->sin_port, (unsigned char *)raw, len); 249 250 /* Fire it off */ 251 iov[0].iov_base = (char *)buf; 252 iov[0].iov_len = bufp; 253 iov[1].iov_base = (char *)raw; 254 iov[1].iov_len = len; 255 256 result = writev(interface->wfdesc, iov, 2); 257 if (result == -1) 258 warning("send_packet: %m"); 259 return (result); 260 } 261 262 ssize_t 263 receive_packet(struct interface_info *interface, unsigned char *buf, 264 size_t len, struct sockaddr_in *from, struct hardware *hfrom) 265 { 266 int length = 0, offset = 0; 267 struct bpf_hdr hdr; 268 269 /* 270 * All this complexity is because BPF doesn't guarantee that 271 * only one packet will be returned at a time. We're getting 272 * what we deserve, though - this is a terrible abuse of the BPF 273 * interface. Sigh. 274 */ 275 276 /* Process packets until we get one we can return or until we've 277 * done a read and gotten nothing we can return... 278 */ 279 do { 280 /* If the buffer is empty, fill it. */ 281 if (interface->rbuf_offset == interface->rbuf_len) { 282 length = read(interface->rfdesc, interface->rbuf, 283 interface->rbuf_max); 284 if (length <= 0) 285 return (length); 286 interface->rbuf_offset = 0; 287 interface->rbuf_len = BPF_WORDALIGN(length); 288 } 289 290 /* 291 * If there isn't room for a whole bpf header, something 292 * went wrong, but we'll ignore it and hope it goes 293 * away... XXX 294 */ 295 if (interface->rbuf_len - interface->rbuf_offset < 296 sizeof(hdr)) { 297 interface->rbuf_offset = interface->rbuf_len; 298 continue; 299 } 300 301 /* Copy out a bpf header... */ 302 memcpy(&hdr, &interface->rbuf[interface->rbuf_offset], 303 sizeof(hdr)); 304 305 /* 306 * If the bpf header plus data doesn't fit in what's 307 * left of the buffer, stick head in sand yet again... 308 */ 309 if (interface->rbuf_offset + hdr.bh_hdrlen + hdr.bh_caplen > 310 interface->rbuf_len) { 311 interface->rbuf_offset = interface->rbuf_len; 312 continue; 313 } 314 315 /* 316 * If the captured data wasn't the whole packet, or if 317 * the packet won't fit in the input buffer, all we can 318 * do is drop it. 319 */ 320 if (hdr.bh_caplen != hdr.bh_datalen) { 321 interface->rbuf_offset = BPF_WORDALIGN( 322 interface->rbuf_offset + hdr.bh_hdrlen + 323 hdr.bh_caplen); 324 continue; 325 } 326 327 /* Skip over the BPF header... */ 328 interface->rbuf_offset += hdr.bh_hdrlen; 329 330 /* Decode the physical header... */ 331 offset = decode_hw_header(interface, 332 interface->rbuf, interface->rbuf_offset, hfrom); 333 334 /* 335 * If a physical layer checksum failed (dunno of any 336 * physical layer that supports this, but WTH), skip 337 * this packet. 338 */ 339 if (offset < 0) { 340 interface->rbuf_offset = BPF_WORDALIGN( 341 interface->rbuf_offset + hdr.bh_caplen); 342 continue; 343 } 344 interface->rbuf_offset += offset; 345 hdr.bh_caplen -= offset; 346 347 /* Decode the IP and UDP headers... */ 348 offset = decode_udp_ip_header(interface, interface->rbuf, 349 interface->rbuf_offset, from, hdr.bh_caplen); 350 351 /* If the IP or UDP checksum was bad, skip the packet... */ 352 if (offset < 0) { 353 interface->rbuf_offset = BPF_WORDALIGN( 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 = BPF_WORDALIGN( 367 interface->rbuf_offset + hdr.bh_caplen); 368 continue; 369 } 370 371 /* Copy out the data in the packet... */ 372 memcpy(buf, interface->rbuf + interface->rbuf_offset, 373 hdr.bh_caplen); 374 interface->rbuf_offset = BPF_WORDALIGN(interface->rbuf_offset + 375 hdr.bh_caplen); 376 return (hdr.bh_caplen); 377 } while (!length); 378 return (0); 379 } 380