packet.c revision 147073
1/* $OpenBSD: packet.c,v 1.9 2004/05/04 18:58:50 deraadt 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 52u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 53u_int32_t wrapsum(u_int32_t); 54 55void assemble_ethernet_header(struct interface_info *, unsigned char *, 56 int *, struct hardware *); 57ssize_t decode_ethernet_header(struct interface_info *, unsigned char *, 58 int bufix, struct hardware *); 59 60u_int32_t 61checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 62{ 63 int i; 64 65 /* Checksum all the pairs of bytes first... */ 66 for (i = 0; i < (nbytes & ~1U); i += 2) { 67 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 68 if (sum > 0xFFFF) 69 sum -= 0xFFFF; 70 } 71 72 /* 73 * If there's a single byte left over, checksum it, too. 74 * Network byte order is big-endian, so the remaining byte is 75 * the high byte. 76 */ 77 if (i < nbytes) { 78 sum += buf[i] << 8; 79 if (sum > 0xFFFF) 80 sum -= 0xFFFF; 81 } 82 83 return (sum); 84} 85 86u_int32_t 87wrapsum(u_int32_t sum) 88{ 89 sum = ~sum & 0xFFFF; 90 return (htons(sum)); 91} 92 93void 94assemble_hw_header(struct interface_info *interface, unsigned char *buf, 95 int *bufix, struct hardware *to) 96{ 97 struct ether_header eh; 98 99 if (to != NULL && to->hlen == 6) /* XXX */ 100 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost)); 101 else 102 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 103 if (interface->hw_address.hlen == sizeof(eh.ether_shost)) 104 memcpy(eh.ether_shost, interface->hw_address.haddr, 105 sizeof(eh.ether_shost)); 106 else 107 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 108 109 eh.ether_type = htons(ETHERTYPE_IP); 110 111 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE); 112 *bufix += ETHER_HEADER_SIZE; 113} 114 115void 116assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from, 117 u_int32_t to, unsigned int port, 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 = htons(LOCAL_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 152ssize_t 153decode_hw_header(unsigned char *buf, int bufix, struct hardware *from) 154{ 155 struct ether_header eh; 156 157 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE); 158 159 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost)); 160 from->htype = ARPHRD_ETHER; 161 from->hlen = sizeof(eh.ether_shost); 162 163 return (sizeof(eh)); 164} 165 166ssize_t 167decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from, 168 unsigned char *data, int buflen) 169{ 170 struct ip *ip; 171 struct udphdr *udp; 172 u_int32_t ip_len = (buf[bufix] & 0xf) << 2; 173 u_int32_t sum, usum; 174 static int ip_packets_seen; 175 static int ip_packets_bad_checksum; 176 static int udp_packets_seen; 177 static int udp_packets_bad_checksum; 178 static int udp_packets_length_checked; 179 static int udp_packets_length_overflow; 180 int len = 0; 181 182 ip = (struct ip *)(buf + bufix); 183 udp = (struct udphdr *)(buf + bufix + ip_len); 184 185 /* Check the IP header checksum - it should be zero. */ 186 ip_packets_seen++; 187 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { 188 ip_packets_bad_checksum++; 189 if (ip_packets_seen > 4 && 190 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 191 note("%d bad IP checksums seen in %d packets", 192 ip_packets_bad_checksum, ip_packets_seen); 193 ip_packets_seen = ip_packets_bad_checksum = 0; 194 } 195 return (-1); 196 } 197 198 if (ntohs(ip->ip_len) != buflen) 199 debug("ip length %d disagrees with bytes received %d.", 200 ntohs(ip->ip_len), buflen); 201 202 memcpy(&from->sin_addr, &ip->ip_src, 4); 203 204 /* 205 * Compute UDP checksums, including the ``pseudo-header'', the 206 * UDP header and the data. If the UDP checksum field is zero, 207 * we're not supposed to do a checksum. 208 */ 209 if (!data) { 210 data = buf + bufix + ip_len + sizeof(*udp); 211 len = ntohs(udp->uh_ulen) - sizeof(*udp); 212 udp_packets_length_checked++; 213 if (len + data > buf + bufix + buflen) { 214 udp_packets_length_overflow++; 215 if (udp_packets_length_checked > 4 && 216 (udp_packets_length_checked / 217 udp_packets_length_overflow) < 2) { 218 note("%d udp packets in %d too long - dropped", 219 udp_packets_length_overflow, 220 udp_packets_length_checked); 221 udp_packets_length_overflow = 222 udp_packets_length_checked = 0; 223 } 224 return (-1); 225 } 226 if (len + data != buf + bufix + buflen) 227 debug("accepting packet with data after udp payload."); 228 } 229 230 usum = udp->uh_sum; 231 udp->uh_sum = 0; 232 233 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 234 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 235 2 * sizeof(ip->ip_src), 236 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 237 238 udp_packets_seen++; 239 if (usum && usum != sum) { 240 udp_packets_bad_checksum++; 241 if (udp_packets_seen > 4 && 242 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 243 note("%d bad udp checksums in %d packets", 244 udp_packets_bad_checksum, udp_packets_seen); 245 udp_packets_seen = udp_packets_bad_checksum = 0; 246 } 247 return (-1); 248 } 249 250 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 251 252 return (ip_len + sizeof(*udp)); 253} 254