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 <sys/cdefs.h> 44__FBSDID("$FreeBSD$"); 45 46#include "dhcpd.h" 47 48#include <netinet/in_systm.h> 49#include <netinet/ip.h> 50#include <netinet/udp.h> 51#include <netinet/if_ether.h> 52 53#define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t)) 54 55u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 56u_int32_t wrapsum(u_int32_t); 57 58u_int32_t 59checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 60{ 61 int i; 62 63 /* Checksum all the pairs of bytes first... */ 64 for (i = 0; i < (nbytes & ~1U); i += 2) { 65 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i))); 66 if (sum > 0xFFFF) 67 sum -= 0xFFFF; 68 } 69 70 /* 71 * If there's a single byte left over, checksum it, too. 72 * Network byte order is big-endian, so the remaining byte is 73 * the high byte. 74 */ 75 if (i < nbytes) { 76 sum += buf[i] << 8; 77 if (sum > 0xFFFF) 78 sum -= 0xFFFF; 79 } 80 81 return (sum); 82} 83 84u_int32_t 85wrapsum(u_int32_t sum) 86{ 87 sum = ~sum & 0xFFFF; 88 return (htons(sum)); 89} 90 91void 92assemble_hw_header(struct interface_info *interface, unsigned char *buf, 93 int *bufix) 94{ 95 struct ether_header eh; 96 97 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost)); 98 if (interface->hw_address.hlen == sizeof(eh.ether_shost)) 99 memcpy(eh.ether_shost, interface->hw_address.haddr, 100 sizeof(eh.ether_shost)); 101 else 102 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost)); 103 104 eh.ether_type = htons(ETHERTYPE_IP); 105 106 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE); 107 *bufix += ETHER_HEADER_SIZE; 108} 109 110void 111assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from, 112 u_int32_t to, unsigned int port, 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 = 128; 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)); 130 131 /* 132 * While the BPF -- used for broadcasts -- expects a "true" IP header 133 * with all the bytes in network byte order, the raw socket interface 134 * which is used for unicasts expects the ip_len field to be in host 135 * byte order. In both cases, the checksum has to be correct, so this 136 * is as good a place as any to turn the bytes around again. 137 */ 138 if (to != INADDR_BROADCAST) 139 ip.ip_len = ntohs(ip.ip_len); 140 141 memcpy(&buf[*bufix], &ip, sizeof(ip)); 142 *bufix += sizeof(ip); 143 144 udp.uh_sport = htons(LOCAL_PORT); /* XXX */ 145 udp.uh_dport = port; /* XXX */ 146 udp.uh_ulen = htons(sizeof(udp) + len); 147 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum)); 148 149 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp), 150 checksum(data, len, checksum((unsigned char *)&ip.ip_src, 151 2 * sizeof(ip.ip_src), 152 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen))))); 153 154 memcpy(&buf[*bufix], &udp, sizeof(udp)); 155 *bufix += sizeof(udp); 156} 157 158ssize_t 159decode_hw_header(unsigned char *buf, int bufix, struct hardware *from) 160{ 161 struct ether_header eh; 162 163 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE); 164 165 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost)); 166 from->htype = ARPHRD_ETHER; 167 from->hlen = sizeof(eh.ether_shost); 168 169 return (sizeof(eh)); 170} 171 172ssize_t 173decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from, 174 unsigned char *data, int buflen) 175{ 176 struct ip *ip; 177 struct udphdr *udp; 178 u_int32_t ip_len = (buf[bufix] & 0xf) << 2; 179 u_int32_t sum, usum; 180 static int ip_packets_seen; 181 static int ip_packets_bad_checksum; 182 static int udp_packets_seen; 183 static int udp_packets_bad_checksum; 184 static int udp_packets_length_checked; 185 static int udp_packets_length_overflow; 186 int len = 0; 187 188 ip = (struct ip *)(buf + bufix); 189 udp = (struct udphdr *)(buf + bufix + ip_len); 190 191 /* Check the IP header checksum - it should be zero. */ 192 ip_packets_seen++; 193 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { 194 ip_packets_bad_checksum++; 195 if (ip_packets_seen > 4 && 196 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 197 note("%d bad IP checksums seen in %d packets", 198 ip_packets_bad_checksum, ip_packets_seen); 199 ip_packets_seen = ip_packets_bad_checksum = 0; 200 } 201 return (-1); 202 } 203 204 if (ntohs(ip->ip_len) != buflen) 205 debug("ip length %d disagrees with bytes received %d.", 206 ntohs(ip->ip_len), buflen); 207 208 memcpy(&from->sin_addr, &ip->ip_src, 4); 209 210 /* 211 * Compute UDP checksums, including the ``pseudo-header'', the 212 * UDP header and the data. If the UDP checksum field is zero, 213 * we're not supposed to do a checksum. 214 */ 215 if (!data) { 216 data = buf + bufix + ip_len + sizeof(*udp); 217 len = ntohs(udp->uh_ulen) - sizeof(*udp); 218 udp_packets_length_checked++; 219 if (len + data > buf + bufix + buflen) { 220 udp_packets_length_overflow++; 221 if (udp_packets_length_checked > 4 && 222 (udp_packets_length_checked / 223 udp_packets_length_overflow) < 2) { 224 note("%d udp packets in %d too long - dropped", 225 udp_packets_length_overflow, 226 udp_packets_length_checked); 227 udp_packets_length_overflow = 228 udp_packets_length_checked = 0; 229 } 230 return (-1); 231 } 232 if (len + data != buf + bufix + buflen) 233 debug("accepting packet with data after udp payload."); 234 } 235 236 usum = udp->uh_sum; 237 udp->uh_sum = 0; 238 239 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 240 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 241 2 * sizeof(ip->ip_src), 242 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 243 244 udp_packets_seen++; 245 if (usum && usum != sum) { 246 udp_packets_bad_checksum++; 247 if (udp_packets_seen > 4 && 248 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 249 note("%d bad udp checksums in %d packets", 250 udp_packets_bad_checksum, udp_packets_seen); 251 udp_packets_seen = udp_packets_bad_checksum = 0; 252 } 253 return (-1); 254 } 255 256 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 257 258 return (ip_len + sizeof(*udp)); 259} 260