1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
|
/* $OpenBSD: packet.c,v 1.2 2004/02/04 12:16:56 henning Exp $ */
/* Packet assembly code, originally contributed by Archie Cobbs. */
/*
* Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of The Internet Software Consortium nor the names
* of its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
* CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This software has been written for the Internet Software Consortium
* by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
* Enterprises. To learn more about the Internet Software Consortium,
* see ``http://www.vix.com/isc''. To learn more about Vixie
* Enterprises, see ``http://www.vix.com''.
*/
#include "dhcpd.h"
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
/* Compute the easy part of the checksum on a range of bytes. */
u_int32_t checksum (buf, nbytes, sum)
unsigned char *buf;
unsigned nbytes;
u_int32_t sum;
{
int i;
#ifdef DEBUG_CHECKSUM
debug ("checksum (%x %d %x)", buf, nbytes, sum);
#endif
/* Checksum all the pairs of bytes first... */
for (i = 0; i < (nbytes & ~1U); i += 2) {
#ifdef DEBUG_CHECKSUM_VERBOSE
debug ("sum = %x", sum);
#endif
sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
/* Add carry. */
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
/* If there's a single byte left over, checksum it, too. Network
byte order is big-endian, so the remaining byte is the high byte. */
if (i < nbytes) {
#ifdef DEBUG_CHECKSUM_VERBOSE
debug ("sum = %x", sum);
#endif
sum += buf [i] << 8;
/* Add carry. */
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
return sum;
}
/* Finish computing the sum, and then put it into network byte order. */
u_int32_t wrapsum (sum)
u_int32_t sum;
{
#ifdef DEBUG_CHECKSUM
debug ("wrapsum (%x)", sum);
#endif
sum = ~sum & 0xFFFF;
#ifdef DEBUG_CHECKSUM_VERBOSE
debug ("sum = %x", sum);
#endif
#ifdef DEBUG_CHECKSUM
debug ("wrapsum returns %x", htons (sum));
#endif
return htons(sum);
}
/* Assemble an hardware header... */
/* XXX currently only supports ethernet; doesn't check for other types. */
void assemble_hw_header (interface, buf, bufix, to)
struct interface_info *interface;
unsigned char *buf;
int *bufix;
struct hardware *to;
{
#if defined (HAVE_TR_SUPPORT)
if (interface -> hw_address.htype == HTYPE_IEEE802)
assemble_tr_header (interface, buf, bufix, to);
else
#endif
assemble_ethernet_header (interface, buf, bufix, to);
}
/* UDP header and IP header assembled together for convenience. */
void assemble_udp_ip_header (interface, buf, bufix,
from, to, port, data, len)
struct interface_info *interface;
unsigned char *buf;
int *bufix;
u_int32_t from;
u_int32_t to;
unsigned int port;
unsigned char *data;
int len;
{
struct ip ip;
struct udphdr udp;
/* Fill out the IP header */
ip.ip_v = 4;
ip.ip_hl = 5;
ip.ip_tos = IPTOS_LOWDELAY;
ip.ip_len = htons(sizeof(ip) + sizeof(udp) + len);
ip.ip_id = 0;
ip.ip_off = 0;
ip.ip_ttl = 16;
ip.ip_p = IPPROTO_UDP;
ip.ip_sum = 0;
ip.ip_src.s_addr = from;
ip.ip_dst.s_addr = to;
/* Checksum the IP header... */
ip.ip_sum = wrapsum (checksum ((unsigned char *)&ip, sizeof ip, 0));
/* Copy the ip header into the buffer... */
memcpy (&buf [*bufix], &ip, sizeof ip);
*bufix += sizeof ip;
/* Fill out the UDP header */
udp.uh_sport = local_port; /* XXX */
udp.uh_dport = port; /* XXX */
udp.uh_ulen = htons(sizeof(udp) + len);
memset (&udp.uh_sum, 0, sizeof udp.uh_sum);
/* Compute UDP checksums, including the ``pseudo-header'', the UDP
header and the data. */
udp.uh_sum =
wrapsum (checksum ((unsigned char *)&udp, sizeof udp,
checksum (data, len,
checksum ((unsigned char *)
&ip.ip_src,
2 * sizeof ip.ip_src,
IPPROTO_UDP +
(u_int32_t)
ntohs (udp.uh_ulen)))));
/* Copy the udp header into the buffer... */
memcpy (&buf [*bufix], &udp, sizeof udp);
*bufix += sizeof udp;
}
/* Decode a hardware header... */
ssize_t decode_hw_header (interface, buf, bufix, from)
struct interface_info *interface;
unsigned char *buf;
int bufix;
struct hardware *from;
{
#if defined (HAVE_TR_SUPPORT)
if (interface -> hw_address.htype == HTYPE_IEEE802)
return decode_tr_header (interface, buf, bufix, from);
else
#endif
return decode_ethernet_header (interface, buf, bufix, from);
}
/* UDP header and IP header decoded together for convenience. */
ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
struct interface_info *interface;
unsigned char *buf;
int bufix;
struct sockaddr_in *from;
unsigned char *data;
int buflen;
{
struct ip *ip;
struct udphdr *udp;
u_int32_t ip_len = (buf [bufix] & 0xf) << 2;
u_int32_t sum, usum;
static int ip_packets_seen;
static int ip_packets_bad_checksum;
static int udp_packets_seen;
static int udp_packets_bad_checksum;
static int udp_packets_length_checked;
static int udp_packets_length_overflow;
int len = 0;
ip = (struct ip *)(buf + bufix);
udp = (struct udphdr *)(buf + bufix + ip_len);
/* Check the IP header checksum - it should be zero. */
++ip_packets_seen;
if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
++ip_packets_bad_checksum;
if (ip_packets_seen > 4 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) {
note ("%d bad IP checksums seen in %d packets",
ip_packets_bad_checksum, ip_packets_seen);
ip_packets_seen = ip_packets_bad_checksum = 0;
}
return -1;
}
/* Check the IP packet length. */
if (ntohs (ip -> ip_len) != buflen)
debug ("ip length %d disagrees with bytes received %d.",
ntohs (ip -> ip_len), buflen);
/* Copy out the IP source address... */
memcpy (&from -> sin_addr, &ip -> ip_src, 4);
/* Compute UDP checksums, including the ``pseudo-header'', the UDP
header and the data. If the UDP checksum field is zero, we're
not supposed to do a checksum. */
if (!data) {
data = buf + bufix + ip_len + sizeof *udp;
len = ntohs (udp -> uh_ulen) - sizeof *udp;
++udp_packets_length_checked;
if (len + data > buf + bufix + buflen) {
++udp_packets_length_overflow;
if (udp_packets_length_checked > 4 &&
(udp_packets_length_checked /
udp_packets_length_overflow) < 2) {
note ("%d udp packets in %d too long - dropped",
udp_packets_length_overflow,
udp_packets_length_checked);
udp_packets_length_overflow =
udp_packets_length_checked = 0;
}
return -1;
}
if (len + data != buf + bufix + buflen)
debug ("accepting packet with data after udp payload.");
}
usum = udp -> uh_sum;
udp -> uh_sum = 0;
sum = wrapsum (checksum ((unsigned char *)udp, sizeof *udp,
checksum (data, len,
checksum ((unsigned char *)
&ip -> ip_src,
2 * sizeof ip -> ip_src,
IPPROTO_UDP +
(u_int32_t)
ntohs (udp -> uh_ulen)))));
udp_packets_seen++;
if (usum && usum != sum) {
udp_packets_bad_checksum++;
if (udp_packets_seen > 4 &&
(udp_packets_seen / udp_packets_bad_checksum) < 2) {
note ("%d bad udp checksums in %d packets",
udp_packets_bad_checksum, udp_packets_seen);
udp_packets_seen = udp_packets_bad_checksum = 0;
}
return -1;
}
/* Copy out the port... */
memcpy (&from -> sin_port, &udp -> uh_sport, sizeof udp -> uh_sport);
return ip_len + sizeof *udp;
}
|
