1 /* $OpenBSD: packet.c,v 1.11 2016/02/06 23:50:10 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 60 u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 61 u_int32_t wrapsum(u_int32_t); 62 63 u_int32_t 64 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 65 { 66 int i; 67 68 /* Checksum all the pairs of bytes first... */ 69 for (i = 0; i < (nbytes & ~1U); i += 2) { 70 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 71 if (sum > 0xFFFF) 72 sum -= 0xFFFF; 73 } 74 75 /* 76 * If there's a single byte left over, checksum it, too. 77 * Network byte order is big-endian, so the remaining byte is 78 * the high byte. 79 */ 80 if (i < nbytes) { 81 sum += buf[i] << 8; 82 if (sum > 0xFFFF) 83 sum -= 0xFFFF; 84 } 85 86 return (sum); 87 } 88 89 u_int32_t 90 wrapsum(u_int32_t sum) 91 { 92 sum = ~sum & 0xFFFF; 93 return (htons(sum)); 94 } 95 96 void 97 assemble_hw_header(struct interface_info *interface, unsigned char *buf, 98 int *bufix, struct hardware *to) 99 { 100 struct ether_header eh; 101 102 if (to != NULL && to->hlen == 6) /* XXX */ 103 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); 104 else 105 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 106 107 /* source address is filled in by the kernel */ 108 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 109 110 eh.ether_type = htons(ETHERTYPE_IP); 111 112 memcpy(&buf[*bufix], &eh, ETHER_HDR_LEN); 113 *bufix += ETHER_HDR_LEN; 114 } 115 116 void 117 assemble_udp_ip_header(struct interface_info *interface, unsigned char *buf, 118 int *bufix, u_int32_t from, u_int32_t to, unsigned int port, 119 unsigned char *data, int len) 120 { 121 struct ip ip; 122 struct udphdr udp; 123 124 ip.ip_v = 4; 125 ip.ip_hl = 5; 126 ip.ip_tos = IPTOS_LOWDELAY; 127 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len); 128 ip.ip_id = 0; 129 ip.ip_off = 0; 130 ip.ip_ttl = 16; 131 ip.ip_p = IPPROTO_UDP; 132 ip.ip_sum = 0; 133 ip.ip_src.s_addr = from; 134 ip.ip_dst.s_addr = to; 135 136 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); 137 memcpy(&buf[*bufix], &ip, sizeof(ip)); 138 *bufix += sizeof(ip); 139 140 udp.uh_sport = server_port; /* XXX */ 141 udp.uh_dport = port; /* XXX */ 142 udp.uh_ulen = htons(sizeof(udp) + len); 143 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 144 145 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 146 checksum(data, len, checksum((unsigned char *)&ip.ip_src, 147 2 * sizeof(ip.ip_src), 148 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 149 150 memcpy(&buf[*bufix], &udp, sizeof(udp)); 151 *bufix += sizeof(udp); 152 } 153 154 ssize_t 155 decode_hw_header(struct interface_info *interface, unsigned char *buf, 156 int bufix, struct hardware *from) 157 { 158 struct ether_header eh; 159 160 memcpy(&eh, buf + bufix, ETHER_HDR_LEN); 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(struct interface_info *interface, unsigned char *buf, 171 int bufix, struct sockaddr_in *from, int buflen) 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[bufix] & 0xf) << 2; 190 if (ip_len > buflen) 191 return (-1); 192 193 ip = (struct ip *)(buf + bufix); 194 ip_packets_seen++; 195 196 /* Check the IP header checksum - it should be zero. */ 197 if (wrapsum(checksum(buf + bufix, 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 note("%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 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 + bufix + 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 + bufix + 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 + bufix + 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 note("%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 + bufix + buflen) 254 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 note("%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