1 /* $OpenBSD: packet.c,v 1.9 2004/05/04 18:58:50 deraadt Exp $ */
3 /* Packet assembly code, originally contributed by Archie Cobbs. */
6 * SPDX-License-Identifier: BSD-3-Clause
8 * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
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.
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
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''.
45 #include <sys/cdefs.h>
46 __FBSDID("$FreeBSD$");
50 #include <netinet/in_systm.h>
51 #include <netinet/ip.h>
52 #include <netinet/udp.h>
53 #include <netinet/if_ether.h>
55 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
57 u_int32_t checksum(unsigned char *, unsigned, u_int32_t);
58 u_int32_t wrapsum(u_int32_t);
61 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
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)));
73 * If there's a single byte left over, checksum it, too.
74 * Network byte order is big-endian, so the remaining byte is
87 wrapsum(u_int32_t sum)
94 assemble_hw_header(struct interface_info *interface, unsigned char *buf,
97 struct ether_header eh;
99 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
100 if (interface->hw_address.hlen == sizeof(eh.ether_shost))
101 memcpy(eh.ether_shost, interface->hw_address.haddr,
102 sizeof(eh.ether_shost));
104 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
106 eh.ether_type = htons(ETHERTYPE_IP);
108 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
109 *bufix += ETHER_HEADER_SIZE;
113 assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
114 u_int32_t to, unsigned int port, unsigned char *data, int len)
121 ip.ip_tos = IPTOS_LOWDELAY;
122 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
126 ip.ip_p = IPPROTO_UDP;
128 ip.ip_src.s_addr = from;
129 ip.ip_dst.s_addr = to;
131 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
132 memcpy(&buf[*bufix], &ip, sizeof(ip));
133 *bufix += sizeof(ip);
135 udp.uh_sport = htons(LOCAL_PORT); /* XXX */
136 udp.uh_dport = port; /* XXX */
137 udp.uh_ulen = htons(sizeof(udp) + len);
138 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
140 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
141 checksum(data, len, checksum((unsigned char *)&ip.ip_src,
142 2 * sizeof(ip.ip_src),
143 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
145 memcpy(&buf[*bufix], &udp, sizeof(udp));
146 *bufix += sizeof(udp);
150 decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
152 struct ether_header eh;
154 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
156 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
157 from->htype = ARPHRD_ETHER;
158 from->hlen = sizeof(eh.ether_shost);
164 decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
165 unsigned char *data, int buflen)
169 u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
171 static int ip_packets_seen;
172 static int ip_packets_bad_checksum;
173 static int udp_packets_seen;
174 static int udp_packets_bad_checksum;
175 static int udp_packets_length_checked;
176 static int udp_packets_length_overflow;
179 ip = (struct ip *)(buf + bufix);
180 udp = (struct udphdr *)(buf + bufix + ip_len);
182 /* Check the IP header checksum - it should be zero. */
184 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
185 ip_packets_bad_checksum++;
186 if (ip_packets_seen > 4 &&
187 (ip_packets_seen / ip_packets_bad_checksum) < 2) {
188 note("%d bad IP checksums seen in %d packets",
189 ip_packets_bad_checksum, ip_packets_seen);
190 ip_packets_seen = ip_packets_bad_checksum = 0;
195 if (ntohs(ip->ip_len) != buflen)
196 debug("ip length %d disagrees with bytes received %d.",
197 ntohs(ip->ip_len), buflen);
199 memcpy(&from->sin_addr, &ip->ip_src, 4);
202 * Compute UDP checksums, including the ``pseudo-header'', the
203 * UDP header and the data. If the UDP checksum field is zero,
204 * we're not supposed to do a checksum.
207 data = buf + bufix + ip_len + sizeof(*udp);
208 len = ntohs(udp->uh_ulen) - sizeof(*udp);
209 udp_packets_length_checked++;
210 if (len + data > buf + bufix + buflen) {
211 udp_packets_length_overflow++;
212 if (udp_packets_length_checked > 4 &&
213 (udp_packets_length_checked /
214 udp_packets_length_overflow) < 2) {
215 note("%d udp packets in %d too long - dropped",
216 udp_packets_length_overflow,
217 udp_packets_length_checked);
218 udp_packets_length_overflow =
219 udp_packets_length_checked = 0;
223 if (len + data != buf + bufix + buflen)
224 debug("accepting packet with data after udp payload.");
230 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
231 checksum(data, len, checksum((unsigned char *)&ip->ip_src,
232 2 * sizeof(ip->ip_src),
233 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
236 if (usum && usum != sum) {
237 udp_packets_bad_checksum++;
238 if (udp_packets_seen > 4 &&
239 (udp_packets_seen / udp_packets_bad_checksum) < 2) {
240 note("%d bad udp checksums in %d packets",
241 udp_packets_bad_checksum, udp_packets_seen);
242 udp_packets_seen = udp_packets_bad_checksum = 0;
247 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
249 return (ip_len + sizeof(*udp));