1 /* $OpenBSD: packet.c,v 1.2 2004/04/20 20:56:47 canacar 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 <netinet/in_systm.h> 46 #include <netinet/ip.h> 47 #include <netinet/udp.h> 48 #include <netinet/if_ether.h> 49 50 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t)) 51 52 u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 53 u_int32_t wrapsum(u_int32_t); 54 55 u_int32_t 56 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 57 { 58 int i; 59 60 /* Checksum all the pairs of bytes first... */ 61 for (i = 0; i < (nbytes & ~1U); i += 2) { 62 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 63 if (sum > 0xFFFF) 64 sum -= 0xFFFF; 65 } 66 67 /* 68 * If there's a single byte left over, checksum it, too. 69 * Network byte order is big-endian, so the remaining byte is 70 * the high byte. 71 */ 72 if (i < nbytes) { 73 sum += buf[i] << 8; 74 if (sum > 0xFFFF) 75 sum -= 0xFFFF; 76 } 77 78 return (sum); 79 } 80 81 u_int32_t 82 wrapsum(u_int32_t sum) 83 { 84 sum = ~sum & 0xFFFF; 85 return (htons(sum)); 86 } 87 88 void 89 assemble_hw_header(struct interface_info *interface, unsigned char *buf, 90 int *bufix, struct hardware *to) 91 { 92 struct ether_header eh; 93 94 if (to != NULL && to->hlen == 6) /* XXX */ 95 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); 96 else 97 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 98 99 /* source address is filled in by the kernel */ 100 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 101 102 eh.ether_type = htons(ETHERTYPE_IP); 103 104 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE); 105 *bufix += ETHER_HEADER_SIZE; 106 } 107 108 void 109 assemble_udp_ip_header(struct interface_info *interface, unsigned char *buf, 110 int *bufix, u_int32_t from, u_int32_t to, unsigned int port, 111 unsigned char *data, int len) 112 { 113 struct ip ip; 114 struct udphdr udp; 115 116 ip.ip_v = 4; 117 ip.ip_hl = 5; 118 ip.ip_tos = IPTOS_LOWDELAY; 119 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len); 120 ip.ip_id = 0; 121 ip.ip_off = 0; 122 ip.ip_ttl = 16; 123 ip.ip_p = IPPROTO_UDP; 124 ip.ip_sum = 0; 125 ip.ip_src.s_addr = from; 126 ip.ip_dst.s_addr = to; 127 128 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0)); 129 memcpy(&buf[*bufix], &ip, sizeof(ip)); 130 *bufix += sizeof(ip); 131 132 udp.uh_sport = server_port; /* XXX */ 133 udp.uh_dport = port; /* XXX */ 134 udp.uh_ulen = htons(sizeof(udp) + len); 135 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 136 137 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 138 checksum(data, len, checksum((unsigned char *)&ip.ip_src, 139 2 * sizeof(ip.ip_src), 140 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 141 142 memcpy(&buf[*bufix], &udp, sizeof(udp)); 143 *bufix += sizeof(udp); 144 } 145 146 ssize_t 147 decode_hw_header(struct interface_info *interface, unsigned char *buf, 148 int bufix, struct hardware *from) 149 { 150 struct ether_header eh; 151 152 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE); 153 154 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost)); 155 from->htype = ARPHRD_ETHER; 156 from->hlen = sizeof(eh.ether_shost); 157 158 return (sizeof(eh)); 159 } 160 161 ssize_t 162 decode_udp_ip_header(struct interface_info *interface, unsigned char *buf, 163 int bufix, struct sockaddr_in *from, unsigned char *data, int buflen) 164 { 165 struct ip *ip; 166 struct udphdr *udp; 167 u_int32_t ip_len = (buf[bufix] & 0xf) << 2; 168 u_int32_t sum, usum; 169 static int ip_packets_seen; 170 static int ip_packets_bad_checksum; 171 static int udp_packets_seen; 172 static int udp_packets_bad_checksum; 173 static int udp_packets_length_checked; 174 static int udp_packets_length_overflow; 175 int len = 0; 176 177 ip = (struct ip *)(buf + bufix); 178 udp = (struct udphdr *)(buf + bufix + ip_len); 179 180 /* Check the IP header checksum - it should be zero. */ 181 ip_packets_seen++; 182 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { 183 ip_packets_bad_checksum++; 184 if (ip_packets_seen > 4 && 185 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 186 note("%d bad IP checksums seen in %d packets", 187 ip_packets_bad_checksum, ip_packets_seen); 188 ip_packets_seen = ip_packets_bad_checksum = 0; 189 } 190 return (-1); 191 } 192 193 if (ntohs(ip->ip_len) != buflen) 194 debug("ip length %d disagrees with bytes received %d.", 195 ntohs(ip->ip_len), buflen); 196 197 memcpy(&from->sin_addr, &ip->ip_src, 4); 198 199 /* 200 * Compute UDP checksums, including the ``pseudo-header'', the 201 * UDP header and the data. If the UDP checksum field is zero, 202 * we're not supposed to do a checksum. 203 */ 204 if (!data) { 205 data = buf + bufix + ip_len + sizeof(*udp); 206 len = ntohs(udp->uh_ulen) - sizeof(*udp); 207 udp_packets_length_checked++; 208 if (len + data > buf + bufix + buflen) { 209 udp_packets_length_overflow++; 210 if (udp_packets_length_checked > 4 && 211 (udp_packets_length_checked / 212 udp_packets_length_overflow) < 2) { 213 note("%d udp packets in %d too long - dropped", 214 udp_packets_length_overflow, 215 udp_packets_length_checked); 216 udp_packets_length_overflow = 217 udp_packets_length_checked = 0; 218 } 219 return (-1); 220 } 221 if (len + data != buf + bufix + buflen) 222 debug("accepting packet with data after udp payload."); 223 } 224 225 usum = udp->uh_sum; 226 udp->uh_sum = 0; 227 228 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 229 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 230 2 * sizeof(ip->ip_src), 231 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 232 233 udp_packets_seen++; 234 if (usum && usum != sum) { 235 udp_packets_bad_checksum++; 236 if (udp_packets_seen > 4 && 237 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 238 note("%d bad udp checksums in %d packets", 239 udp_packets_bad_checksum, udp_packets_seen); 240 udp_packets_seen = udp_packets_bad_checksum = 0; 241 } 242 return (-1); 243 } 244 245 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 246 247 return (ip_len + sizeof(*udp)); 248 } 249