1 /* $OpenBSD: packet.c,v 1.3 2009/09/03 11:56:49 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 "dhcpd.h" 44 45 #include <net/if_enc.h> 46 #include <netinet/in_systm.h> 47 #include <netinet/ip.h> 48 #include <netinet/udp.h> 49 #include <netinet/if_ether.h> 50 51 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t)) 52 53 u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 54 u_int32_t wrapsum(u_int32_t); 55 56 u_int32_t 57 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 58 { 59 int i; 60 61 /* Checksum all the pairs of bytes first... */ 62 for (i = 0; i < (nbytes & ~1U); i += 2) { 63 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 64 if (sum > 0xFFFF) 65 sum -= 0xFFFF; 66 } 67 68 /* 69 * If there's a single byte left over, checksum it, too. 70 * Network byte order is big-endian, so the remaining byte is 71 * the high byte. 72 */ 73 if (i < nbytes) { 74 sum += buf[i] << 8; 75 if (sum > 0xFFFF) 76 sum -= 0xFFFF; 77 } 78 79 return (sum); 80 } 81 82 u_int32_t 83 wrapsum(u_int32_t sum) 84 { 85 sum = ~sum & 0xFFFF; 86 return (htons(sum)); 87 } 88 89 void 90 assemble_hw_header(struct interface_info *interface, unsigned char *buf, 91 int *bufix, struct hardware *to) 92 { 93 struct ether_header eh; 94 95 if (to != NULL && to->hlen == 6) /* XXX */ 96 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); 97 else 98 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 99 100 /* source address is filled in by the kernel */ 101 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 102 103 eh.ether_type = htons(ETHERTYPE_IP); 104 105 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE); 106 *bufix += ETHER_HEADER_SIZE; 107 } 108 109 void 110 assemble_udp_ip_header(struct interface_info *interface, unsigned char *buf, 111 int *bufix, u_int32_t from, u_int32_t to, unsigned int port, 112 unsigned char *data, int len) 113 { 114 struct ip ip; 115 struct udphdr udp; 116 117 ip.ip_v = 4; 118 ip.ip_hl = 5; 119 ip.ip_tos = IPTOS_LOWDELAY; 120 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len); 121 ip.ip_id = 0; 122 ip.ip_off = 0; 123 ip.ip_ttl = 16; 124 ip.ip_p = IPPROTO_UDP; 125 ip.ip_sum = 0; 126 ip.ip_src.s_addr = from; 127 ip.ip_dst.s_addr = to; 128 129 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); 130 memcpy(&buf[*bufix], &ip, sizeof(ip)); 131 *bufix += sizeof(ip); 132 133 udp.uh_sport = server_port; /* XXX */ 134 udp.uh_dport = port; /* XXX */ 135 udp.uh_ulen = htons(sizeof(udp) + len); 136 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 137 138 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 139 checksum(data, len, checksum((unsigned char *)&ip.ip_src, 140 2 * sizeof(ip.ip_src), 141 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 142 143 memcpy(&buf[*bufix], &udp, sizeof(udp)); 144 *bufix += sizeof(udp); 145 } 146 147 ssize_t 148 decode_hw_header(struct interface_info *interface, unsigned char *buf, 149 int bufix, struct hardware *from) 150 { 151 struct ether_header eh; 152 size_t offset = 0; 153 154 if (interface->hw_address.htype == HTYPE_IPSEC_TUNNEL) { 155 u_int32_t ip_len; 156 struct ip *ip; 157 158 bufix += ENC_HDRLEN; 159 ip_len = (buf[bufix] & 0xf) << 2; 160 ip = (struct ip *)(buf + bufix); 161 162 /* Encapsulated IP */ 163 if (ip->ip_p != IPPROTO_IPIP) 164 return (-1); 165 166 bzero(&eh, sizeof(eh)); 167 offset = ENC_HDRLEN + ip_len; 168 } else { 169 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE); 170 offset = sizeof(eh); 171 } 172 173 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost)); 174 from->htype = ARPHRD_ETHER; 175 from->hlen = sizeof(eh.ether_shost); 176 177 return (offset); 178 } 179 180 ssize_t 181 decode_udp_ip_header(struct interface_info *interface, unsigned char *buf, 182 int bufix, struct sockaddr_in *from, unsigned char *data, int buflen) 183 { 184 struct ip *ip; 185 struct udphdr *udp; 186 u_int32_t ip_len = (buf[bufix] & 0xf) << 2; 187 u_int32_t sum, usum; 188 static int ip_packets_seen; 189 static int ip_packets_bad_checksum; 190 static int udp_packets_seen; 191 static int udp_packets_bad_checksum; 192 static int udp_packets_length_checked; 193 static int udp_packets_length_overflow; 194 int len = 0; 195 196 ip = (struct ip *)(buf + bufix); 197 udp = (struct udphdr *)(buf + bufix + ip_len); 198 199 /* Check the IP header checksum - it should be zero. */ 200 ip_packets_seen++; 201 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { 202 ip_packets_bad_checksum++; 203 if (ip_packets_seen > 4 && 204 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 205 note("%d bad IP checksums seen in %d packets", 206 ip_packets_bad_checksum, ip_packets_seen); 207 ip_packets_seen = ip_packets_bad_checksum = 0; 208 } 209 return (-1); 210 } 211 212 if (ntohs(ip->ip_len) != buflen) 213 debug("ip length %d disagrees with bytes received %d.", 214 ntohs(ip->ip_len), buflen); 215 216 memcpy(&from->sin_addr, &ip->ip_src, 4); 217 218 /* 219 * Compute UDP checksums, including the ``pseudo-header'', the 220 * UDP header and the data. If the UDP checksum field is zero, 221 * we're not supposed to do a checksum. 222 */ 223 if (!data) { 224 data = buf + bufix + ip_len + sizeof(*udp); 225 len = ntohs(udp->uh_ulen) - sizeof(*udp); 226 udp_packets_length_checked++; 227 if (len + data > buf + bufix + buflen) { 228 udp_packets_length_overflow++; 229 if (udp_packets_length_checked > 4 && 230 (udp_packets_length_checked / 231 udp_packets_length_overflow) < 2) { 232 note("%d udp packets in %d too long - dropped", 233 udp_packets_length_overflow, 234 udp_packets_length_checked); 235 udp_packets_length_overflow = 236 udp_packets_length_checked = 0; 237 } 238 return (-1); 239 } 240 if (len + data != buf + bufix + buflen) 241 debug("accepting packet with data after udp payload."); 242 } 243 244 usum = udp->uh_sum; 245 udp->uh_sum = 0; 246 247 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 248 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 249 2 * sizeof(ip->ip_src), 250 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 251 252 udp_packets_seen++; 253 if (usum && usum != sum) { 254 udp_packets_bad_checksum++; 255 if (udp_packets_seen > 4 && 256 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 257 note("%d bad udp checksums in %d packets", 258 udp_packets_bad_checksum, udp_packets_seen); 259 udp_packets_seen = udp_packets_bad_checksum = 0; 260 } 261 return (-1); 262 } 263 264 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 265 266 return (ip_len + sizeof(*udp)); 267 } 268