1 /* $OpenBSD: src/sbin/dhclient/packet.c,v 1.13 2009/06/06 04:02:42 krw 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''.
45 #include <netinet/if_ether.h>
46 #include <netinet/in_systm.h>
47 #include <netinet/ip.h>
48 #include <netinet/udp.h>
50 #define ETHER_HEADER_SIZE (ETHER_ADDR_LEN * 2 + sizeof(u_int16_t))
52 u_int32_t
checksum(unsigned char *, unsigned, u_int32_t
);
53 u_int32_t
wrapsum(u_int32_t
);
56 checksum(unsigned char *buf
, unsigned nbytes
, u_int32_t sum
)
60 /* Checksum all the pairs of bytes first... */
61 for (i
= 0; i
< (nbytes
& ~1U); i
+= 2) {
62 sum
+= (u_int16_t
)ntohs(*((u_int16_t
*)(buf
+ i
)));
68 * If there's a single byte left over, checksum it, too.
69 * Network byte order is big-endian, so the remaining byte is
82 wrapsum(u_int32_t sum
)
89 assemble_hw_header(unsigned char *buf
, int *bufix
, struct hardware
*to
)
91 struct ether_header eh
;
93 if (to
!= NULL
&& to
->hlen
== 6) /* XXX */
94 memcpy(eh
.ether_dhost
, to
->haddr
, sizeof(eh
.ether_dhost
));
96 memset(eh
.ether_dhost
, 0xff, sizeof(eh
.ether_dhost
));
97 if (ifi
->hw_address
.hlen
== sizeof(eh
.ether_shost
))
98 memcpy(eh
.ether_shost
, ifi
->hw_address
.haddr
,
99 sizeof(eh
.ether_shost
));
101 memset(eh
.ether_shost
, 0x00, sizeof(eh
.ether_shost
));
103 eh
.ether_type
= htons(ETHERTYPE_IP
);
105 memcpy(&buf
[*bufix
], &eh
, ETHER_HEADER_SIZE
);
106 *bufix
+= ETHER_HEADER_SIZE
;
110 assemble_udp_ip_header(unsigned char *buf
, int *bufix
, u_int32_t from
,
111 u_int32_t to
, unsigned int port
, unsigned char *data
, int len
)
118 ip
.ip_tos
= IPTOS_LOWDELAY
;
119 ip
.ip_len
= htons(sizeof(ip
) + sizeof(udp
) + len
);
123 ip
.ip_p
= IPPROTO_UDP
;
125 ip
.ip_src
.s_addr
= from
;
126 ip
.ip_dst
.s_addr
= to
;
128 ip
.ip_sum
= wrapsum(checksum((unsigned char *)&ip
, sizeof(ip
), 0));
129 memcpy(&buf
[*bufix
], &ip
, sizeof(ip
));
130 *bufix
+= sizeof(ip
);
132 udp
.uh_sport
= htons(LOCAL_PORT
); /* XXX */
133 udp
.uh_dport
= port
; /* XXX */
134 udp
.uh_ulen
= htons(sizeof(udp
) + len
);
135 memset(&udp
.uh_sum
, 0, sizeof(udp
.uh_sum
));
137 udp
.uh_sum
= wrapsum(checksum((unsigned char *)&udp
, sizeof(udp
),
138 checksum(data
, len
, checksum((unsigned char *)&ip
.ip_src
,
139 2 * sizeof(ip
.ip_src
),
140 IPPROTO_UDP
+ (u_int32_t
)ntohs(udp
.uh_ulen
)))));
142 memcpy(&buf
[*bufix
], &udp
, sizeof(udp
));
143 *bufix
+= sizeof(udp
);
147 decode_hw_header(unsigned char *buf
, int bufix
, struct hardware
*from
)
149 struct ether_header eh
;
151 memcpy(&eh
, buf
+ bufix
, ETHER_HEADER_SIZE
);
153 memcpy(from
->haddr
, eh
.ether_shost
, sizeof(eh
.ether_shost
));
154 from
->htype
= ARPHRD_ETHER
;
155 from
->hlen
= sizeof(eh
.ether_shost
);
161 decode_udp_ip_header(unsigned char *buf
, int bufix
, struct sockaddr_in
*from
,
162 unsigned char *data
, int buflen
)
166 u_int32_t ip_len
= (buf
[bufix
] & 0xf) << 2;
168 static int ip_packets_seen
;
169 static int ip_packets_bad_checksum
;
170 static int udp_packets_seen
;
171 static int udp_packets_bad_checksum
;
172 static int udp_packets_length_checked
;
173 static int udp_packets_length_overflow
;
176 ip
= (struct ip
*)(buf
+ bufix
);
177 udp
= (struct udphdr
*)(buf
+ bufix
+ ip_len
);
179 /* Check the IP header checksum - it should be zero. */
181 if (wrapsum(checksum(buf
+ bufix
, ip_len
, 0)) != 0) {
182 ip_packets_bad_checksum
++;
183 if (ip_packets_seen
> 4 &&
184 (ip_packets_seen
/ ip_packets_bad_checksum
) < 2) {
185 note("%d bad IP checksums seen in %d packets",
186 ip_packets_bad_checksum
, ip_packets_seen
);
187 ip_packets_seen
= ip_packets_bad_checksum
= 0;
193 if (ntohs(ip
->ip_len
) != buflen
)
194 debug("ip length %d disagrees with bytes received %d.",
195 ntohs(ip
->ip_len
), buflen
);
197 memcpy(&from
->sin_addr
, &ip
->ip_src
, 4);
200 * Compute UDP checksums, including the ``pseudo-header'', the
201 * UDP header and the data. If the UDP checksum field is zero,
202 * we're not supposed to do a checksum.
205 data
= buf
+ bufix
+ ip_len
+ sizeof(*udp
);
206 len
= ntohs(udp
->uh_ulen
) - sizeof(*udp
);
207 udp_packets_length_checked
++;
208 if (len
+ data
> buf
+ bufix
+ buflen
) {
209 udp_packets_length_overflow
++;
210 if (udp_packets_length_checked
> 4 &&
211 (udp_packets_length_checked
/
212 udp_packets_length_overflow
) < 2) {
213 note("%d udp packets in %d too long - dropped",
214 udp_packets_length_overflow
,
215 udp_packets_length_checked
);
216 udp_packets_length_overflow
=
217 udp_packets_length_checked
= 0;
222 if (len
+ data
!= buf
+ bufix
+ buflen
)
223 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
));