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 * SPDX-License-Identifier: BSD-3-Clause 7 * 8 * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium. 9 * All rights reserved. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of The Internet Software Consortium nor the names 21 * of its contributors may be used to endorse or promote products derived 22 * from this software without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND 25 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 26 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 27 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 28 * DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR 29 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 32 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 33 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 34 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 35 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * This software has been written for the Internet Software Consortium 39 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie 40 * Enterprises. To learn more about the Internet Software Consortium, 41 * see ``http://www.vix.com/isc''. To learn more about Vixie 42 * Enterprises, see ``http://www.vix.com''. 43 */ 44 45 #include <sys/cdefs.h> 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 55 u_int32_t checksum(unsigned char *, unsigned, u_int32_t); 56 u_int32_t wrapsum(u_int32_t); 57 58 u_int32_t 59 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum) 60 { 61 unsigned 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 84 u_int32_t 85 wrapsum(u_int32_t sum) 86 { 87 sum = ~sum & 0xFFFF; 88 return (htons(sum)); 89 } 90 91 void 92 assemble_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 } 109 110 void 111 assemble_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 memcpy(&buf[*bufix], &ip, sizeof(ip)); 131 *bufix += sizeof(ip); 132 133 udp.uh_sport = htons(LOCAL_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(unsigned char *buf, 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) + (ntohs(eh.ether_type) == ETHERTYPE_VLAN ? 159 ETHER_VLAN_ENCAP_LEN : 0)); 160 } 161 162 ssize_t 163 decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from, 164 unsigned char *data, int buflen) 165 { 166 struct ip *ip; 167 struct udphdr *udp; 168 u_int32_t ip_len = (buf[bufix] & 0xf) << 2; 169 u_int32_t sum, usum; 170 static int ip_packets_seen; 171 static int ip_packets_bad_checksum; 172 static int udp_packets_seen; 173 static int udp_packets_bad_checksum; 174 static int udp_packets_length_checked; 175 static int udp_packets_length_overflow; 176 int len = 0; 177 178 ip = (struct ip *)(buf + bufix); 179 udp = (struct udphdr *)(buf + bufix + ip_len); 180 181 /* Check the IP header checksum - it should be zero. */ 182 ip_packets_seen++; 183 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { 184 ip_packets_bad_checksum++; 185 if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 && 186 (ip_packets_seen / ip_packets_bad_checksum) < 2) { 187 note("%d bad IP checksums seen in %d packets", 188 ip_packets_bad_checksum, ip_packets_seen); 189 ip_packets_seen = ip_packets_bad_checksum = 0; 190 } 191 return (-1); 192 } 193 194 if (ntohs(ip->ip_len) != buflen) 195 debug("ip length %d disagrees with bytes received %d.", 196 ntohs(ip->ip_len), buflen); 197 198 memcpy(&from->sin_addr, &ip->ip_src, 4); 199 200 /* 201 * Compute UDP checksums, including the ``pseudo-header'', the 202 * UDP header and the data. If the UDP checksum field is zero, 203 * we're not supposed to do a checksum. 204 */ 205 if (!data) { 206 data = buf + bufix + ip_len + sizeof(*udp); 207 len = ntohs(udp->uh_ulen) - sizeof(*udp); 208 udp_packets_length_checked++; 209 if (len + data > buf + bufix + buflen) { 210 udp_packets_length_overflow++; 211 if (udp_packets_length_checked > 4 && 212 (udp_packets_length_checked / 213 udp_packets_length_overflow) < 2) { 214 note("%d udp packets in %d too long - dropped", 215 udp_packets_length_overflow, 216 udp_packets_length_checked); 217 udp_packets_length_overflow = 218 udp_packets_length_checked = 0; 219 } 220 return (-1); 221 } 222 if (len + data != buf + bufix + buflen) 223 debug("accepting packet with data after udp payload."); 224 } 225 226 usum = udp->uh_sum; 227 udp->uh_sum = 0; 228 229 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp), 230 checksum(data, len, checksum((unsigned char *)&ip->ip_src, 231 2 * sizeof(ip->ip_src), 232 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen))))); 233 234 udp_packets_seen++; 235 if (usum && usum != sum) { 236 udp_packets_bad_checksum++; 237 if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 && 238 (udp_packets_seen / udp_packets_bad_checksum) < 2) { 239 note("%d bad udp checksums in %d packets", 240 udp_packets_bad_checksum, udp_packets_seen); 241 udp_packets_seen = udp_packets_bad_checksum = 0; 242 } 243 return (-1); 244 } 245 246 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport)); 247 248 return (ip_len + sizeof(*udp)); 249 } 250