1 /* $OpenBSD: packet.c,v 1.4 2021/06/16 16:55:02 dv Exp $ */
2
3 /* Packet assembly code, originally contributed by Archie Cobbs. */
4
5 /*
6 * Copyright (c) 1995, 1996, 1999 The Internet Software Consortium.
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
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.
21 *
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
34 * SUCH DAMAGE.
35 *
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''.
41 */
42
43 #include <sys/types.h>
44 #include <sys/socket.h>
45
46 #include <arpa/inet.h>
47
48 #include <net/if.h>
49 #include <net/if_enc.h>
50
51 #include <netinet/in.h>
52 #include <netinet/ip.h>
53 #include <netinet/udp.h>
54 #include <netinet/if_ether.h>
55
56 #include <string.h>
57
58 #include "dhcp.h"
59 #include "vmd.h"
60
61 u_int32_t checksum(unsigned char *, u_int32_t, u_int32_t);
62 u_int32_t wrapsum(u_int32_t);
63
64 u_int32_t
checksum(unsigned char * buf,u_int32_t nbytes,u_int32_t sum)65 checksum(unsigned char *buf, u_int32_t nbytes, u_int32_t sum)
66 {
67 u_int32_t i;
68
69 /* Checksum all the pairs of bytes first... */
70 for (i = 0; i < (nbytes & ~1U); i += 2) {
71 sum += (u_int16_t)ntohs(*((u_int16_t *)(buf + i)));
72 if (sum > 0xFFFF)
73 sum -= 0xFFFF;
74 }
75
76 /*
77 * If there's a single byte left over, checksum it, too.
78 * Network byte order is big-endian, so the remaining byte is
79 * the high byte.
80 */
81 if (i < nbytes) {
82 sum += buf[i] << 8;
83 if (sum > 0xFFFF)
84 sum -= 0xFFFF;
85 }
86
87 return (sum);
88 }
89
90 u_int32_t
wrapsum(u_int32_t sum)91 wrapsum(u_int32_t sum)
92 {
93 sum = ~sum & 0xFFFF;
94 return (htons(sum));
95 }
96
97 ssize_t
assemble_hw_header(unsigned char * buf,size_t buflen,size_t offset,struct packet_ctx * pc,unsigned int intfhtype)98 assemble_hw_header(unsigned char *buf, size_t buflen,
99 size_t offset, struct packet_ctx *pc, unsigned int intfhtype)
100 {
101 struct ether_header eh;
102
103 switch (intfhtype) {
104 case HTYPE_ETHER:
105 if (buflen < offset + ETHER_HDR_LEN)
106 return (-1);
107
108 /* Use the supplied address or let the kernel fill it. */
109 memcpy(eh.ether_shost, pc->pc_smac, ETHER_ADDR_LEN);
110 memcpy(eh.ether_dhost, pc->pc_dmac, ETHER_ADDR_LEN);
111
112 eh.ether_type = htons(ETHERTYPE_IP);
113
114 memcpy(&buf[offset], &eh, ETHER_HDR_LEN);
115 offset += ETHER_HDR_LEN;
116 break;
117 default:
118 return (-1);
119 }
120
121 return (offset);
122 }
123
124 ssize_t
assemble_udp_ip_header(unsigned char * buf,size_t buflen,size_t offset,struct packet_ctx * pc,unsigned char * data,size_t datalen)125 assemble_udp_ip_header(unsigned char *buf, size_t buflen, size_t offset,
126 struct packet_ctx *pc, unsigned char *data, size_t datalen)
127 {
128 struct ip ip;
129 struct udphdr udp;
130
131 if (buflen < offset + sizeof(ip) + sizeof(udp))
132 return (-1);
133
134 ip.ip_v = 4;
135 ip.ip_hl = 5;
136 ip.ip_tos = IPTOS_LOWDELAY;
137 ip.ip_len = htons(sizeof(ip) + sizeof(udp) + datalen);
138 ip.ip_id = 0;
139 ip.ip_off = 0;
140 ip.ip_ttl = 16;
141 ip.ip_p = IPPROTO_UDP;
142 ip.ip_sum = 0;
143 ip.ip_src.s_addr = ss2sin(&pc->pc_src)->sin_addr.s_addr;
144 ip.ip_dst.s_addr = ss2sin(&pc->pc_dst)->sin_addr.s_addr;
145
146 ip.ip_sum = wrapsum(checksum((unsigned char *)&ip, sizeof(ip), 0));
147 memcpy(&buf[offset], &ip, sizeof(ip));
148 offset += sizeof(ip);
149
150 udp.uh_sport = ss2sin(&pc->pc_src)->sin_port;
151 udp.uh_dport = ss2sin(&pc->pc_dst)->sin_port;
152 udp.uh_ulen = htons(sizeof(udp) + datalen);
153 memset(&udp.uh_sum, 0, sizeof(udp.uh_sum));
154
155 udp.uh_sum = wrapsum(checksum((unsigned char *)&udp, sizeof(udp),
156 checksum(data, datalen, checksum((unsigned char *)&ip.ip_src,
157 2 * sizeof(ip.ip_src),
158 IPPROTO_UDP + (u_int32_t)ntohs(udp.uh_ulen)))));
159
160 memcpy(&buf[offset], &udp, sizeof(udp));
161 offset += sizeof(udp);
162
163 return (offset);
164 }
165
166 ssize_t
decode_hw_header(unsigned char * buf,size_t buflen,size_t offset,struct packet_ctx * pc,unsigned int intfhtype)167 decode_hw_header(unsigned char *buf, size_t buflen,
168 size_t offset, struct packet_ctx *pc, unsigned int intfhtype)
169 {
170 u_int32_t ip_len;
171 u_int16_t ether_type;
172 struct ether_header *eh;
173 struct ip *ip;
174
175 switch (intfhtype) {
176 case HTYPE_IPSEC_TUNNEL:
177 if (buflen < offset + ENC_HDRLEN + sizeof(*ip))
178 return (-1);
179 offset += ENC_HDRLEN;
180 ip_len = (buf[offset] & 0xf) << 2;
181 if (buflen < offset + ip_len)
182 return (-1);
183
184 ip = (struct ip *)(buf + offset);
185
186 /* Encapsulated IP */
187 if (ip->ip_p != IPPROTO_IPIP)
188 return (-1);
189
190 memset(pc->pc_dmac, 0xff, ETHER_ADDR_LEN);
191 offset += ip_len;
192
193 pc->pc_htype = ARPHRD_ETHER;
194 pc->pc_hlen = ETHER_ADDR_LEN;
195 break;
196 case HTYPE_ETHER:
197 if (buflen < offset + ETHER_HDR_LEN)
198 return (-1);
199
200 eh = (struct ether_header *)(buf + offset);
201 memcpy(pc->pc_dmac, eh->ether_dhost, ETHER_ADDR_LEN);
202 memcpy(pc->pc_smac, eh->ether_shost, ETHER_ADDR_LEN);
203 memcpy(ðer_type, &eh->ether_type, sizeof(ether_type));
204
205 if (ether_type != htons(ETHERTYPE_IP))
206 return (-1);
207
208 offset += ETHER_HDR_LEN;
209
210 pc->pc_htype = ARPHRD_ETHER;
211 pc->pc_hlen = ETHER_ADDR_LEN;
212 break;
213 default:
214 return (-1);
215 }
216
217 return (offset);
218 }
219
220 ssize_t
decode_udp_ip_header(unsigned char * buf,size_t buflen,size_t offset,struct packet_ctx * pc)221 decode_udp_ip_header(unsigned char *buf, size_t buflen,
222 size_t offset, struct packet_ctx *pc)
223 {
224 struct ip *ip;
225 struct udphdr *udp;
226 unsigned char *data;
227 u_int32_t ip_len;
228 u_int32_t sum, usum;
229 int len;
230
231 /* Assure that an entire IP header is within the buffer. */
232 if (buflen < offset + sizeof(*ip))
233 return (-1);
234 ip = (struct ip *)(buf + offset);
235 if (ip->ip_v != IPVERSION)
236 return (-1);
237 ip_len = ip->ip_hl << 2;
238 if (ip_len < sizeof(struct ip) ||
239 buflen < offset + ip_len)
240 return (-1);
241
242 if (ip->ip_p != IPPROTO_UDP)
243 return (-1);
244
245 /* Check the IP header checksum - it should be zero. */
246 if (wrapsum(checksum(buf + offset, ip_len, 0)) != 0)
247 return (-1);
248
249 pc->pc_src.ss_len = sizeof(struct sockaddr_in);
250 pc->pc_src.ss_family = AF_INET;
251 memcpy(&ss2sin(&pc->pc_src)->sin_addr, &ip->ip_src,
252 sizeof(ss2sin(&pc->pc_src)->sin_addr));
253
254 pc->pc_dst.ss_len = sizeof(struct sockaddr_in);
255 pc->pc_dst.ss_family = AF_INET;
256 memcpy(&ss2sin(&pc->pc_dst)->sin_addr, &ip->ip_dst,
257 sizeof(ss2sin(&pc->pc_dst)->sin_addr));
258
259 #ifdef DEBUG
260 if (buflen != offset + ntohs(ip->ip_len))
261 log_debug("ip length %d disagrees with bytes received %zd.",
262 ntohs(ip->ip_len), buflen - offset);
263 #endif
264
265 /* Assure that the entire IP packet is within the buffer. */
266 if (buflen < offset + ntohs(ip->ip_len))
267 return (-1);
268
269 /* Assure that the UDP header is within the buffer. */
270 if (buflen < offset + ip_len + sizeof(*udp))
271 return (-1);
272 udp = (struct udphdr *)(buf + offset + ip_len);
273
274 /* Assure that the entire UDP packet is within the buffer. */
275 if (buflen < offset + ip_len + ntohs(udp->uh_ulen))
276 return (-1);
277 data = buf + offset + ip_len + sizeof(*udp);
278
279 /*
280 * Compute UDP checksums, including the ``pseudo-header'', the
281 * UDP header and the data. If the UDP checksum field is zero,
282 * we're not supposed to do a checksum.
283 */
284 len = ntohs(udp->uh_ulen) - sizeof(*udp);
285 if ((len < 0) || (len + data > buf + buflen)) {
286 return (-1);
287 }
288 if (len + data != buf + buflen)
289 log_debug("accepting packet with data after udp payload.");
290
291 usum = udp->uh_sum;
292 udp->uh_sum = 0;
293
294 sum = wrapsum(checksum((unsigned char *)udp, sizeof(*udp),
295 checksum(data, len, checksum((unsigned char *)&ip->ip_src,
296 2 * sizeof(ip->ip_src),
297 IPPROTO_UDP + (u_int32_t)ntohs(udp->uh_ulen)))));
298
299 if (usum && usum != sum)
300 return (-1);
301
302 ss2sin(&pc->pc_src)->sin_port = udp->uh_sport;
303 ss2sin(&pc->pc_dst)->sin_port = udp->uh_dport;
304
305 return (offset + ip_len + sizeof(*udp));
306 }
307