1 /* $OpenBSD: packet.c,v 1.14 2017/04/18 13:59:09 krw 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 <net/if.h> 47 48 #include <netinet/in.h> 49 #include <netinet/ip.h> 50 #include <netinet/udp.h> 51 #include <netinet/if_ether.h> 52 53 #include <stdio.h> 54 #include <string.h> 55 56 #include "dhcp.h" 57 #include "tree.h" 58 #include "dhcpd.h" 59 #include "log.h" 60 61 u_int32_t 62 checksum(unsigned char *buf, u_int32_t nbytes, u_int32_t sum) 63 { 64 unsigned int i; 65 66 /* Checksum all the pairs of bytes first... */ 67 for (i = 0; i < (nbytes & ~1U); i += 2) { 68 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 69 if (sum > 0xFFFF) 70 sum -= 0xFFFF; 71 } 72 73 /* 74 * If there's a single byte left over, checksum it, too. 75 * Network byte order is big-endian, so the remaining byte is 76 * the high byte. 77 */ 78 if (i < nbytes) { 79 sum += buf[i] << 8; 80 if (sum > 0xFFFF) 81 sum -= 0xFFFF; 82 } 83 84 return (sum); 85 } 86 87 u_int32_t 88 wrapsum(u_int32_t sum) 89 { 90 sum = ~sum & 0xFFFF; 91 return (htons(sum)); 92 } 93 94 void 95 assemble_hw_header(struct interface_info *interface, unsigned char *buf, 96 int *bufix, struct hardware *to) 97 { 98 struct ether_header eh; 99 100 if (to != NULL && to->hlen == 6) /* XXX */ 101 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); 102 else 103 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 104 105 /* source address is filled in by the kernel */ 106 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 107 108 eh.ether_type = htons(ETHERTYPE_IP); 109 110 memcpy(&buf[*bufix], &eh, ETHER_HDR_LEN); 111 *bufix += ETHER_HDR_LEN; 112 } 113 114 void 115 assemble_udp_ip_header(struct interface_info *interface, unsigned char *buf, 116 int *bufix, u_int32_t from, u_int32_t to, unsigned int port, 117 unsigned char *data, int len) 118 { 119 struct ip ip; 120 struct udphdr udp; 121 122 ip.ip_v = 4; 123 ip.ip_hl = 5; 124 ip.ip_tos = IPTOS_LOWDELAY; 125 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len); 126 ip.ip_id = 0; 127 ip.ip_off = 0; 128 ip.ip_ttl = 16; 129 ip.ip_p = IPPROTO_UDP; 130 ip.ip_sum = 0; 131 ip.ip_src.s_addr = from; 132 ip.ip_dst.s_addr = to; 133 134 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); 135 memcpy(&buf[*bufix], &ip, sizeof(ip)); 136 *bufix += sizeof(ip); 137 138 udp.uh_sport = server_port; /* XXX */ 139 udp.uh_dport = port; /* XXX */ 140 udp.uh_ulen = htons(sizeof(udp) + len); 141 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 142 143 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 144 checksum(data, len, checksum((unsigned char *)&ip.ip_src, 145 2 * sizeof(ip.ip_src), 146 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 147 148 memcpy(&buf[*bufix], &udp, sizeof(udp)); 149 *bufix += sizeof(udp); 150 } 151 152 ssize_t 153 decode_hw_header(unsigned char *buf, u_int32_t buflen, struct hardware *from) 154 { 155 struct ether_header eh; 156 157 if (buflen < sizeof(eh)) 158 return (-1); 159 160 memcpy(&eh, buf, sizeof(eh)); 161 162 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost)); 163 from->htype = ARPHRD_ETHER; 164 from->hlen = sizeof(eh.ether_shost); 165 166 return (sizeof(eh)); 167 } 168 169 ssize_t 170 decode_udp_ip_header(unsigned char *buf, u_int32_t buflen, 171 struct sockaddr_in *from) 172 { 173 struct ip *ip; 174 struct udphdr *udp; 175 unsigned char *data; 176 u_int32_t ip_len; 177 u_int32_t sum, usum; 178 static unsigned int ip_packets_seen; 179 static unsigned int ip_packets_bad_checksum; 180 static unsigned int udp_packets_seen; 181 static unsigned int udp_packets_bad_checksum; 182 static unsigned int udp_packets_length_checked; 183 static unsigned int udp_packets_length_overflow; 184 int len; 185 186 /* Assure that an entire IP header is within the buffer. */ 187 if (sizeof(*ip) > buflen) 188 return (-1); 189 ip_len = (*buf & 0xf) << 2; 190 if (ip_len > buflen) 191 return (-1); 192 193 ip = (struct ip *)buf; 194 ip_packets_seen++; 195 196 /* Check the IP header checksum - it should be zero. */ 197 if (wrapsum(checksum((unsigned char *)ip, ip_len, 0)) != 0) { 198 ip_packets_bad_checksum++; 199 if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 && 200 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 201 log_info("%u bad IP checksums seen in %u packets", 202 ip_packets_bad_checksum, ip_packets_seen); 203 ip_packets_seen = ip_packets_bad_checksum = 0; 204 } 205 return (-1); 206 } 207 208 memcpy(&from->sin_addr, &ip->ip_src, sizeof(from->sin_addr)); 209 210 #ifdef DEBUG 211 if (ntohs(ip->ip_len) != buflen) 212 log_debug("ip length %d disagrees with bytes received %d.", 213 ntohs(ip->ip_len), buflen); 214 #endif 215 216 217 /* Assure that the entire IP packet is within the buffer. */ 218 if (ntohs(ip->ip_len) > buflen) 219 return (-1); 220 221 /* Assure that the UDP header is within the buffer. */ 222 if (ip_len + sizeof(*udp) > buflen) 223 return (-1); 224 udp = (struct udphdr *)(buf + ip_len); 225 udp_packets_seen++; 226 227 /* Assure that the entire UDP packet is within the buffer. */ 228 if (ip_len + ntohs(udp->uh_ulen) > buflen) 229 return (-1); 230 data = buf + ip_len + sizeof(*udp); 231 232 /* 233 * Compute UDP checksums, including the ``pseudo-header'', the 234 * UDP header and the data. If the UDP checksum field is zero, 235 * we're not supposed to do a checksum. 236 */ 237 udp_packets_length_checked++; 238 len = ntohs(udp->uh_ulen) - sizeof(*udp); 239 if ((len < 0) || (len + data > buf + buflen)) { 240 udp_packets_length_overflow++; 241 if (udp_packets_length_checked > 4 && 242 udp_packets_length_overflow != 0 && 243 (udp_packets_length_checked / 244 udp_packets_length_overflow) < 2) { 245 log_info("%u udp packets in %u too long - dropped", 246 udp_packets_length_overflow, 247 udp_packets_length_checked); 248 udp_packets_length_overflow = 249 udp_packets_length_checked = 0; 250 } 251 return (-1); 252 } 253 if (len + data != buf + buflen) 254 log_debug("accepting packet with data after udp payload."); 255 256 usum = udp->uh_sum; 257 udp->uh_sum = 0; 258 259 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 260 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 261 2 * sizeof(ip->ip_src), 262 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 263 264 udp_packets_seen++; 265 if (usum && usum != sum) { 266 udp_packets_bad_checksum++; 267 if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 && 268 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 269 log_info("%u bad udp checksums in %u packets", 270 udp_packets_bad_checksum, udp_packets_seen); 271 udp_packets_seen = udp_packets_bad_checksum = 0; 272 } 273 return (-1); 274 } 275 276 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 277 278 return (ip_len + sizeof(*udp)); 279 } 280