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 * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
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.
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
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''.
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
48 #include <netinet/in_systm.h>
49 #include <netinet/ip.h>
50 #include <netinet/udp.h>
51 #include <netinet/if_ether.h>
53 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
55 u_int32_t checksum(unsigned char *, unsigned, u_int32_t);
56 u_int32_t wrapsum(u_int32_t);
59 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
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)));
71 * If there's a single byte left over, checksum it, too.
72 * Network byte order is big-endian, so the remaining byte is
85 wrapsum(u_int32_t sum)
92 assemble_hw_header(struct interface_info *interface, unsigned char *buf,
95 struct ether_header eh;
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));
102 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
104 eh.ether_type = htons(ETHERTYPE_IP);
106 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
107 *bufix += ETHER_HEADER_SIZE;
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)
119 ip.ip_tos = IPTOS_LOWDELAY;
120 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
124 ip.ip_p = IPPROTO_UDP;
126 ip.ip_src.s_addr = from;
127 ip.ip_dst.s_addr = to;
129 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
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.
138 if (to != INADDR_BROADCAST)
139 ip.ip_len = ntohs(ip.ip_len);
141 memcpy(&buf[*bufix], &ip, sizeof(ip));
142 *bufix += sizeof(ip);
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));
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)))));
154 memcpy(&buf[*bufix], &udp, sizeof(udp));
155 *bufix += sizeof(udp);
159 decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
161 struct ether_header eh;
163 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
165 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
166 from->htype = ARPHRD_ETHER;
167 from->hlen = sizeof(eh.ether_shost);
173 decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
174 unsigned char *data, int buflen)
178 u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
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;
188 ip = (struct ip *)(buf + bufix);
189 udp = (struct udphdr *)(buf + bufix + ip_len);
191 /* Check the IP header checksum - it should be zero. */
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;
204 if (ntohs(ip->ip_len) != buflen)
205 debug("ip length %d disagrees with bytes received %d.",
206 ntohs(ip->ip_len), buflen);
208 memcpy(&from->sin_addr, &ip->ip_src, 4);
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.
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;
232 if (len + data != buf + bufix + buflen)
233 debug("accepting packet with data after udp payload.");
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)))));
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;
256 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
258 return (ip_len + sizeof(*udp));