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);
58 void assemble_ethernet_header(struct interface_info *, unsigned char *,
59 int *, struct hardware *);
60 ssize_t decode_ethernet_header(struct interface_info *, unsigned char *,
61 int bufix, struct hardware *);
64 checksum(unsigned char *buf, unsigned nbytes, u_int32_t sum)
68 /* Checksum all the pairs of bytes first... */
69 for (i = 0; i < (nbytes & ~1U); i += 2) {
70 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
76 * If there's a single byte left over, checksum it, too.
77 * Network byte order is big-endian, so the remaining byte is
90 wrapsum(u_int32_t sum)
97 assemble_hw_header(struct interface_info *interface, unsigned char *buf,
98 int *bufix, struct hardware *to)
100 struct ether_header eh;
102 if (to != NULL && to->hlen == 6) /* XXX */
103 memcpy(eh.ether_dhost, to->haddr, sizeof(eh.ether_dhost));
105 memset(eh.ether_dhost, 0xff, sizeof(eh.ether_dhost));
106 if (interface->hw_address.hlen == sizeof(eh.ether_shost))
107 memcpy(eh.ether_shost, interface->hw_address.haddr,
108 sizeof(eh.ether_shost));
110 memset(eh.ether_shost, 0x00, sizeof(eh.ether_shost));
112 eh.ether_type = htons(ETHERTYPE_IP);
114 memcpy(&buf[*bufix], &eh, ETHER_HEADER_SIZE);
115 *bufix += ETHER_HEADER_SIZE;
119 assemble_udp_ip_header(unsigned char *buf, int *bufix, u_int32_t from,
120 u_int32_t to, unsigned int port, unsigned char *data, int len)
127 ip.ip_tos = IPTOS_LOWDELAY;
128 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
132 ip.ip_p = IPPROTO_UDP;
134 ip.ip_src.s_addr = from;
135 ip.ip_dst.s_addr = to;
137 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
138 memcpy(&buf[*bufix], &ip, sizeof(ip));
139 *bufix += sizeof(ip);
141 udp.uh_sport = htons(LOCAL_PORT); /* XXX */
142 udp.uh_dport = port; /* XXX */
143 udp.uh_ulen = htons(sizeof(udp) + len);
144 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
146 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
147 checksum(data, len, checksum((unsigned char *)&ip.ip_src,
148 2 * sizeof(ip.ip_src),
149 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
151 memcpy(&buf[*bufix], &udp, sizeof(udp));
152 *bufix += sizeof(udp);
156 decode_hw_header(unsigned char *buf, int bufix, struct hardware *from)
158 struct ether_header eh;
160 memcpy(&eh, buf + bufix, ETHER_HEADER_SIZE);
162 memcpy(from->haddr, eh.ether_shost, sizeof(eh.ether_shost));
163 from->htype = ARPHRD_ETHER;
164 from->hlen = sizeof(eh.ether_shost);
170 decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
171 unsigned char *data, int buflen)
175 u_int32_t ip_len = (buf[bufix] & 0xf) << 2;
177 static int ip_packets_seen;
178 static int ip_packets_bad_checksum;
179 static int udp_packets_seen;
180 static int udp_packets_bad_checksum;
181 static int udp_packets_length_checked;
182 static int udp_packets_length_overflow;
185 ip = (struct ip *)(buf + bufix);
186 udp = (struct udphdr *)(buf + bufix + ip_len);
188 /* Check the IP header checksum - it should be zero. */
190 if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
191 ip_packets_bad_checksum++;
192 if (ip_packets_seen > 4 &&
193 (ip_packets_seen / ip_packets_bad_checksum) < 2) {
194 note("%d bad IP checksums seen in %d packets",
195 ip_packets_bad_checksum, ip_packets_seen);
196 ip_packets_seen = ip_packets_bad_checksum = 0;
201 if (ntohs(ip->ip_len) != buflen)
202 debug("ip length %d disagrees with bytes received %d.",
203 ntohs(ip->ip_len), buflen);
205 memcpy(&from->sin_addr, &ip->ip_src, 4);
208 * Compute UDP checksums, including the ``pseudo-header'', the
209 * UDP header and the data. If the UDP checksum field is zero,
210 * we're not supposed to do a checksum.
213 data = buf + bufix + ip_len + sizeof(*udp);
214 len = ntohs(udp->uh_ulen) - sizeof(*udp);
215 udp_packets_length_checked++;
216 if (len + data > buf + bufix + buflen) {
217 udp_packets_length_overflow++;
218 if (udp_packets_length_checked > 4 &&
219 (udp_packets_length_checked /
220 udp_packets_length_overflow) < 2) {
221 note("%d udp packets in %d too long - dropped",
222 udp_packets_length_overflow,
223 udp_packets_length_checked);
224 udp_packets_length_overflow =
225 udp_packets_length_checked = 0;
229 if (len + data != buf + bufix + buflen)
230 debug("accepting packet with data after udp payload.");
236 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
237 checksum(data, len, checksum((unsigned char *)&ip->ip_src,
238 2 * sizeof(ip->ip_src),
239 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
242 if (usum && usum != sum) {
243 udp_packets_bad_checksum++;
244 if (udp_packets_seen > 4 &&
245 (udp_packets_seen / udp_packets_bad_checksum) < 2) {
246 note("%d bad udp checksums in %d packets",
247 udp_packets_bad_checksum, udp_packets_seen);
248 udp_packets_seen = udp_packets_bad_checksum = 0;
253 memcpy(&from->sin_port, &udp->uh_sport, sizeof(udp->uh_sport));
255 return (ip_len + sizeof(*udp));