1 /* $NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $ */
2
3 /*-
4 * Copyright (c) 2013 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Andreas Gustafsson.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
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 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 /*
33 * A minimal DNS server capable of providing canned answers to the
34 * specific queries issued by t_hostent.sh and nothing more.
35 */
36
37 #include <sys/cdefs.h>
38 __RCSID("$NetBSD: h_dns_server.c,v 1.4 2014/03/29 16:10:54 gson Exp $");
39
40 #include <ctype.h>
41 #include <err.h>
42 #include <errno.h>
43 #include <fcntl.h>
44 #include <memory.h>
45 #include <stdio.h>
46 #include <stdlib.h>
47 #include <unistd.h>
48
49 #include <sys/socket.h>
50
51 #include <netinet/in.h>
52 #include <netinet6/in6.h>
53
54 union sockaddr_either {
55 struct sockaddr s;
56 struct sockaddr_in sin;
57 struct sockaddr_in6 sin6;
58 };
59
60 #ifdef DEBUG
61 #define DPRINTF(...) fprintf(stderr, __VA_ARGS__)
62 #else
63 #define DPRINTF(...)
64 #endif
65
66 /* A DNS question and its corresponding answer */
67
68 struct dns_data {
69 size_t qname_size;
70 const char *qname; /* Wire-encode question name */
71 int qtype;
72 size_t answer_size;
73 const char *answer; /* One wire-encoded answer RDATA */
74 };
75
76 /* Convert C string constant to length + data pair */
77 #define STR_DATA(s) sizeof(s) - 1, s
78
79 /* Canned DNS queestion-answer pairs */
80 struct dns_data data[] = {
81 /* Forward mappings */
82 /* localhost IN A -> 127.0.0.1 */
83 { STR_DATA("\011localhost\000"), 1,
84 STR_DATA("\177\000\000\001") },
85 /* localhost IN AAAA -> ::1 */
86 { STR_DATA("\011localhost\000"), 28,
87 STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") },
88 /* sixthavenue.astron.com IN A -> 38.117.134.16 */
89 { STR_DATA("\013sixthavenue\006astron\003com\000"), 1,
90 STR_DATA("\046\165\206\020") },
91 /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */
92 { STR_DATA("\013sixthavenue\006astron\003com\000"), 28,
93 STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") },
94 /* Reverse mappings */
95 { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12,
96 STR_DATA("\011localhost\000") },
97 { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010"
98 "\0010\0010\0010\0010\0010\0010\0010\0010"
99 "\0010\0010\0010\0010\0010\0010\0010\0010"
100 "\0010\0010\0010\0010\0010\0010\0010\0010"
101 "\003ip6\004arpa\000"), 12,
102 STR_DATA("\011localhost\000") },
103 { STR_DATA("\00216\003134\003117\00238"
104 "\007in-addr\004arpa\000"), 12,
105 STR_DATA("\013sixthavenue\006astron\003com\000") },
106 { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f"
107 "\001f\001f\0012\0019\001a\0014\001e\0013"
108 "\0010\0010\001f\0011\0013\0010\0010\0013"
109 "\0016\0010\0011\0010\0010\0012\0016\0012"
110 "\003ip6\004arpa\000"), 12,
111 STR_DATA("\013sixthavenue\006astron\003com\000") },
112 /* End marker */
113 { STR_DATA(""), 0, STR_DATA("") }
114 };
115
116 /*
117 * Compare two DNS names for equality. If equal, return their
118 * length, and if not, return zero. Does not handle compression.
119 */
120 static int
name_eq(const unsigned char * a,const unsigned char * b)121 name_eq(const unsigned char *a, const unsigned char *b) {
122 const unsigned char *a_save = a;
123 for (;;) {
124 int i;
125 int lena = *a++;
126 int lenb = *b++;
127 if (lena != lenb)
128 return 0;
129 if (lena == 0)
130 return a - a_save;
131 for (i = 0; i < lena; i++)
132 if (tolower(a[i]) != tolower(b[i]))
133 return 0;
134 a += lena;
135 b += lena;
136 }
137 }
138
139 #ifdef DEBUG
140 static char *
name2str(const void * v,char * buf,size_t buflen)141 name2str(const void *v, char *buf, size_t buflen) {
142 const unsigned char *a = v;
143 char *b = buf;
144 char *eb = buf + buflen;
145
146 #define ADDC(c) do { \
147 if (b < eb) \
148 *b++ = c; \
149 else \
150 return NULL; \
151 } while (/*CONSTCOND*/0)
152 for (int did = 0;; did++) {
153 int lena = *a++;
154 if (lena == 0) {
155 ADDC('\0');
156 return buf;
157 }
158 if (did)
159 ADDC('.');
160 for (int i = 0; i < lena; i++)
161 ADDC(a[i]);
162 a += lena;
163 }
164 }
165 #endif
166
main(int argc,char ** argv)167 int main(int argc, char **argv) {
168 int s, r, protocol;
169 union sockaddr_either saddr;
170 struct dns_data *dp;
171 unsigned char *p;
172 char pidfile_name[40];
173 FILE *f;
174 int one = 1;
175 #ifdef DEBUG
176 char buf1[1024], buf2[1024];
177 #endif
178
179 if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6'))
180 errx(1, "usage: dns_server 4 | 6");
181 s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP);
182 if (s < 0)
183 err(1, "socket");
184 if (protocol == '4') {
185 memset(&saddr.sin, 0, sizeof(saddr.sin));
186 saddr.sin.sin_family = AF_INET;
187 saddr.sin.sin_len = sizeof(saddr.sin);
188 saddr.sin.sin_port = htons(53);
189 saddr.sin.sin_addr.s_addr = INADDR_ANY;
190 } else {
191 static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT;
192 memset(&saddr.sin6, 0, sizeof(saddr.sin6));
193 saddr.sin6.sin6_family = AF_INET6;
194 saddr.sin6.sin6_len = sizeof(saddr.sin6);
195 saddr.sin6.sin6_port = htons(53);
196 saddr.sin6.sin6_addr = loopback;
197 }
198
199 r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one);
200 if (r < 0)
201 err(1, "setsockopt");
202
203 r = bind(s,
204 (struct sockaddr *) &saddr,
205 protocol == '4' ? sizeof(struct sockaddr_in) :
206 sizeof(struct sockaddr_in6));
207 if (r < 0)
208 err(1, "bind");
209
210 snprintf(pidfile_name, sizeof pidfile_name,
211 "dns_server_%c.pid", protocol);
212 f = fopen(pidfile_name, "w");
213 fprintf(f, "%d", getpid());
214 fclose(f);
215 #ifdef DEBUG
216 daemon(0, 1);
217 #else
218 daemon(0, 0);
219 #endif
220
221 for (;;) {
222 unsigned char buf[512];
223 union sockaddr_either from;
224 ssize_t nrecv, nsent;
225 socklen_t fromlen =
226 protocol == '4' ? sizeof(struct sockaddr_in) :
227 sizeof(struct sockaddr_in6);
228 memset(buf, 0, sizeof buf);
229 nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen);
230 if (nrecv < 0)
231 err(1, "recvfrom");
232 if (nrecv < 12) {
233 DPRINTF("Too short %zd\n", nrecv);
234 continue;
235 }
236 if ((buf[2] & 0x80) != 0) {
237 DPRINTF("Not a query 0x%x\n", buf[2]);
238 continue;
239 }
240 if (!(buf[4] == 0 && buf[5] == 1)) {
241 DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]);
242 continue; /* QDCOUNT is not 1 */
243 }
244
245 for (dp = data; dp->qname_size != 0; dp++) {
246 int qtype, qclass;
247 p = buf + 12; /* Point to QNAME */
248 int n = name_eq(p, (const unsigned char *) dp->qname);
249 if (n == 0) {
250 DPRINTF("no match name %s != %s\n",
251 name2str(p, buf1, sizeof(buf1)),
252 name2str(dp->qname, buf2, sizeof(buf2)));
253 continue; /* Name does not match */
254 }
255 DPRINTF("match name %s\n",
256 name2str(p, buf1, sizeof(buf1)));
257 p += n; /* Skip QNAME */
258 qtype = *p++ << 8;
259 qtype |= *p++;
260 if (qtype != dp->qtype) {
261 DPRINTF("no match name 0x%x != 0x%x\n",
262 qtype, dp->qtype);
263 continue;
264 }
265 DPRINTF("match type 0x%x\n", qtype);
266 qclass = *p++ << 8;
267 qclass |= *p++;
268 if (qclass != 1) { /* IN */
269 DPRINTF("no match class %d != 1\n", qclass);
270 continue;
271 }
272 DPRINTF("match class %d\n", qclass);
273 goto found;
274 }
275 continue;
276 found:
277 buf[2] |= 0x80; /* QR */
278 buf[3] |= 0x80; /* RA */
279 memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */
280 buf[7] = 1; /* ANCOUNT */
281 memcpy(p, dp->qname, dp->qname_size);
282 p += dp->qname_size;
283 *p++ = dp->qtype >> 8;
284 *p++ = dp->qtype & 0xFF;
285 *p++ = 0;
286 *p++ = 1; /* IN */
287 memset(p, 0, 4); /* TTL = 0 */
288 p += 4;
289 *p++ = 0; /* RDLENGTH MSB */
290 *p++ = dp->answer_size; /* RDLENGTH LSB */
291 memcpy(p, dp->answer, dp->answer_size);
292 p += dp->answer_size;
293 nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen);
294 DPRINTF("sent %zd\n", nsent);
295 if (nsent != p - buf)
296 warn("sendto");
297 }
298 }
299