1 /* $OpenBSD: packet.c,v 1.1 2017/04/19 15:38:32 reyk Exp $ */ 2 3 /* Packet assembly code, originally contributed by Archie Cobbs. */ 4 5 /* 6 * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium. 7 * 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/types.h> 44 #include <sys/socket.h> 45 46 #include <arpa/inet.h> 47 48 #include <net/if.h> 49 #include <net/if_enc.h> 50 51 #include <netinet/in.h> 52 #include <netinet/ip.h> 53 #include <netinet/udp.h> 54 #include <netinet/if_ether.h> 55 56 #include <string.h> 57 58 #include "dhcp.h" 59 #include "vmd.h" 60 #include "proc.h" 61 62 u_int32_t checksum(unsigned char *, u_int32_t, u_int32_t); 63 u_int32_t wrapsum(u_int32_t); 64 65 u_int32_t 66 checksum(unsigned char *buf, u_int32_t nbytes, u_int32_t sum) 67 { 68 u_int32_t i; 69 70 /* Checksum all the pairs of bytes first... */ 71 for (i = 0; i < (nbytes & ~1U); i += 2) { 72 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 73 if (sum > 0xFFFF) 74 sum -= 0xFFFF; 75 } 76 77 /* 78 * If there's a single byte left over, checksum it, too. 79 * Network byte order is big-endian, so the remaining byte is 80 * the high byte. 81 */ 82 if (i < nbytes) { 83 sum += buf[i] << 8; 84 if (sum > 0xFFFF) 85 sum -= 0xFFFF; 86 } 87 88 return (sum); 89 } 90 91 u_int32_t 92 wrapsum(u_int32_t sum) 93 { 94 sum = ~sum & 0xFFFF; 95 return (htons(sum)); 96 } 97 98 ssize_t 99 assemble_hw_header(unsigned char *buf, size_t buflen, 100 size_t offset, struct packet_ctx *pc, unsigned int intfhtype) 101 { 102 struct ether_header eh; 103 104 switch (intfhtype) { 105 case HTYPE_ETHER: 106 if (buflen < offset + ETHER_HDR_LEN) 107 return (-1); 108 109 /* Use the supplied address or let the kernel fill it. */ 110 memcpy(eh.ether_shost, pc->pc_smac, ETHER_ADDR_LEN); 111 memcpy(eh.ether_dhost, pc->pc_dmac, ETHER_ADDR_LEN); 112 113 eh.ether_type = htons(ETHERTYPE_IP); 114 115 memcpy(&buf[offset], &eh, ETHER_HDR_LEN); 116 offset += ETHER_HDR_LEN; 117 break; 118 default: 119 return (-1); 120 } 121 122 return (offset); 123 } 124 125 ssize_t 126 assemble_udp_ip_header(unsigned char *buf, size_t buflen, size_t offset, 127 struct packet_ctx *pc, unsigned char *data, size_t datalen) 128 { 129 struct ip ip; 130 struct udphdr udp; 131 132 if (buflen < offset + sizeof(ip) + sizeof(udp)) 133 return (-1); 134 135 ip.ip_v = 4; 136 ip.ip_hl = 5; 137 ip.ip_tos = IPTOS_LOWDELAY; 138 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + datalen); 139 ip.ip_id = 0; 140 ip.ip_off = 0; 141 ip.ip_ttl = 16; 142 ip.ip_p = IPPROTO_UDP; 143 ip.ip_sum = 0; 144 ip.ip_src.s_addr = ss2sin(&pc->pc_src)->sin_addr.s_addr; 145 ip.ip_dst.s_addr = ss2sin(&pc->pc_dst)->sin_addr.s_addr; 146 147 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); 148 memcpy(&buf[offset], &ip, sizeof(ip)); 149 offset += sizeof(ip); 150 151 udp.uh_sport = ss2sin(&pc->pc_src)->sin_port; 152 udp.uh_dport = ss2sin(&pc->pc_dst)->sin_port; 153 udp.uh_ulen = htons(sizeof(udp) + datalen); 154 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 155 156 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 157 checksum(data, datalen, checksum((unsigned char *)&ip.ip_src, 158 2 * sizeof(ip.ip_src), 159 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 160 161 memcpy(&buf[offset], &udp, sizeof(udp)); 162 offset += sizeof(udp); 163 164 return (offset); 165 } 166 167 ssize_t 168 decode_hw_header(unsigned char *buf, size_t buflen, 169 size_t offset, struct packet_ctx *pc, unsigned int intfhtype) 170 { 171 u_int32_t ip_len; 172 struct ip *ip; 173 174 switch (intfhtype) { 175 case HTYPE_IPSEC_TUNNEL: 176 if (buflen < offset + ENC_HDRLEN + sizeof(*ip)) 177 return (-1); 178 offset += ENC_HDRLEN; 179 ip_len = (buf[offset] & 0xf) << 2; 180 if (buflen < offset + ip_len) 181 return (-1); 182 183 ip = (struct ip *)(buf + offset); 184 185 /* Encapsulated IP */ 186 if (ip->ip_p != IPPROTO_IPIP) 187 return (-1); 188 189 memset(pc->pc_dmac, 0xff, ETHER_ADDR_LEN); 190 offset += ip_len; 191 192 pc->pc_htype = ARPHRD_ETHER; 193 pc->pc_hlen = ETHER_ADDR_LEN; 194 break; 195 case HTYPE_ETHER: 196 if (buflen < offset + ETHER_HDR_LEN) 197 return (-1); 198 199 memcpy(pc->pc_dmac, buf + offset, ETHER_ADDR_LEN); 200 memcpy(pc->pc_smac, buf + offset + ETHER_ADDR_LEN, 201 ETHER_ADDR_LEN); 202 offset += ETHER_HDR_LEN; 203 204 pc->pc_htype = ARPHRD_ETHER; 205 pc->pc_hlen = ETHER_ADDR_LEN; 206 break; 207 default: 208 return (-1); 209 } 210 211 return (offset); 212 } 213 214 ssize_t 215 decode_udp_ip_header(unsigned char *buf, size_t buflen, 216 size_t offset, struct packet_ctx *pc) 217 { 218 struct ip *ip; 219 struct udphdr *udp; 220 unsigned char *data; 221 u_int32_t ip_len; 222 u_int32_t sum, usum; 223 static unsigned int ip_packets_seen; 224 static unsigned int ip_packets_bad_checksum; 225 static unsigned int udp_packets_seen; 226 static unsigned int udp_packets_bad_checksum; 227 static unsigned int udp_packets_length_checked; 228 static unsigned int udp_packets_length_overflow; 229 int len; 230 231 /* Assure that an entire IP header is within the buffer. */ 232 if (buflen < offset + sizeof(*ip)) 233 return (-1); 234 ip_len = (buf[offset] & 0xf) << 2; 235 if (buflen < offset + ip_len) 236 return (-1); 237 238 ip = (struct ip *)(buf + offset); 239 ip_packets_seen++; 240 241 /* Check the IP header checksum - it should be zero. */ 242 if (wrapsum(checksum(buf + offset, ip_len, 0)) != 0) { 243 ip_packets_bad_checksum++; 244 if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 && 245 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 246 log_info("%u bad IP checksums seen in %u packets", 247 ip_packets_bad_checksum, ip_packets_seen); 248 ip_packets_seen = ip_packets_bad_checksum = 0; 249 } 250 return (-1); 251 } 252 253 pc->pc_src.ss_len = sizeof(struct sockaddr_in); 254 pc->pc_src.ss_family = AF_INET; 255 memcpy(&ss2sin(&pc->pc_src)->sin_addr, &ip->ip_src, 256 sizeof(ss2sin(&pc->pc_src)->sin_addr)); 257 258 pc->pc_dst.ss_len = sizeof(struct sockaddr_in); 259 pc->pc_dst.ss_family = AF_INET; 260 memcpy(&ss2sin(&pc->pc_dst)->sin_addr, &ip->ip_dst, 261 sizeof(ss2sin(&pc->pc_dst)->sin_addr)); 262 263 #ifdef DEBUG 264 if (buflen != offset + ntohs(ip->ip_len)) 265 log_debug("ip length %d disagrees with bytes received %zd.", 266 ntohs(ip->ip_len), buflen - offset); 267 #endif 268 269 /* Assure that the entire IP packet is within the buffer. */ 270 if (buflen < offset + ntohs(ip->ip_len)) 271 return (-1); 272 273 /* Assure that the UDP header is within the buffer. */ 274 if (buflen < offset + ip_len + sizeof(*udp)) 275 return (-1); 276 udp = (struct udphdr *)(buf + offset + ip_len); 277 udp_packets_seen++; 278 279 /* Assure that the entire UDP packet is within the buffer. */ 280 if (buflen < offset + ip_len + ntohs(udp->uh_ulen)) 281 return (-1); 282 data = buf + offset + ip_len + sizeof(*udp); 283 284 /* 285 * Compute UDP checksums, including the ``pseudo-header'', the 286 * UDP header and the data. If the UDP checksum field is zero, 287 * we're not supposed to do a checksum. 288 */ 289 udp_packets_length_checked++; 290 len = ntohs(udp->uh_ulen) - sizeof(*udp); 291 if ((len < 0) || (len + data > buf + buflen)) { 292 udp_packets_length_overflow++; 293 if (udp_packets_length_checked > 4 && 294 udp_packets_length_overflow != 0 && 295 (udp_packets_length_checked / 296 udp_packets_length_overflow) < 2) { 297 log_info("%u udp packets in %u too long - dropped", 298 udp_packets_length_overflow, 299 udp_packets_length_checked); 300 udp_packets_length_overflow = 301 udp_packets_length_checked = 0; 302 } 303 return (-1); 304 } 305 if (len + data != buf + buflen) 306 log_debug("accepting packet with data after udp payload."); 307 308 usum = udp->uh_sum; 309 udp->uh_sum = 0; 310 311 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 312 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 313 2 * sizeof(ip->ip_src), 314 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 315 316 udp_packets_seen++; 317 if (usum && usum != sum) { 318 udp_packets_bad_checksum++; 319 if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 && 320 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 321 log_info("%u bad udp checksums in %u packets", 322 udp_packets_bad_checksum, udp_packets_seen); 323 udp_packets_seen = udp_packets_bad_checksum = 0; 324 } 325 return (-1); 326 } 327 328 ss2sin(&pc->pc_src)->sin_port = udp->uh_sport; 329 ss2sin(&pc->pc_dst)->sin_port = udp->uh_dport; 330 331 return (offset + ip_len + sizeof(*udp)); 332 } 333