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 #ifdef __NetBSD__
53 #include <netinet6/in6.h>
54 #endif
55
56 #ifdef __FreeBSD__
57 #include <paths.h>
58 #endif
59
60 union sockaddr_either {
61 struct sockaddr s;
62 struct sockaddr_in sin;
63 struct sockaddr_in6 sin6;
64 };
65
66 #ifdef DEBUG
67 #define DPRINTF(...) fprintf(stderr, __VA_ARGS__)
68 #else
69 #define DPRINTF(...)
70 #endif
71
72 /* A DNS question and its corresponding answer */
73
74 struct dns_data {
75 size_t qname_size;
76 const char *qname; /* Wire-encode question name */
77 int qtype;
78 size_t answer_size;
79 const char *answer; /* One wire-encoded answer RDATA */
80 };
81
82 /* Convert C string constant to length + data pair */
83 #define STR_DATA(s) sizeof(s) - 1, s
84
85 /* Canned DNS queestion-answer pairs */
86 struct dns_data data[] = {
87 /* Forward mappings */
88 /* localhost IN A -> 127.0.0.1 */
89 { STR_DATA("\011localhost\000"), 1,
90 STR_DATA("\177\000\000\001") },
91 /* localhost IN AAAA -> ::1 */
92 { STR_DATA("\011localhost\000"), 28,
93 STR_DATA("\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001") },
94 /* sixthavenue.astron.com IN A -> 38.117.134.16 */
95 { STR_DATA("\013sixthavenue\006astron\003com\000"), 1,
96 STR_DATA("\046\165\206\020") },
97 /* sixthavenue.astron.com IN AAAA -> 2620:106:3003:1f00:3e4a:92ff:fef4:e180 */
98 { STR_DATA("\013sixthavenue\006astron\003com\000"), 28,
99 STR_DATA("\x26\x20\x01\x06\x30\x03\x1f\x00\x3e\x4a\x92\xff\xfe\xf4\xe1\x80") },
100 /* Reverse mappings */
101 { STR_DATA("\0011\0010\0010\003127\007in-addr\004arpa\000"), 12,
102 STR_DATA("\011localhost\000") },
103 { STR_DATA("\0011\0010\0010\0010\0010\0010\0010\0010"
104 "\0010\0010\0010\0010\0010\0010\0010\0010"
105 "\0010\0010\0010\0010\0010\0010\0010\0010"
106 "\0010\0010\0010\0010\0010\0010\0010\0010"
107 "\003ip6\004arpa\000"), 12,
108 STR_DATA("\011localhost\000") },
109 { STR_DATA("\00216\003134\003117\00238"
110 "\007in-addr\004arpa\000"), 12,
111 STR_DATA("\013sixthavenue\006astron\003com\000") },
112 { STR_DATA("\0010\0018\0011\001e\0014\001f\001e\001f"
113 "\001f\001f\0012\0019\001a\0014\001e\0013"
114 "\0010\0010\001f\0011\0013\0010\0010\0013"
115 "\0016\0010\0011\0010\0010\0012\0016\0012"
116 "\003ip6\004arpa\000"), 12,
117 STR_DATA("\013sixthavenue\006astron\003com\000") },
118 /* End marker */
119 { STR_DATA(""), 0, STR_DATA("") }
120 };
121
122 /*
123 * Compare two DNS names for equality. If equal, return their
124 * length, and if not, return zero. Does not handle compression.
125 */
126 static int
name_eq(const unsigned char * a,const unsigned char * b)127 name_eq(const unsigned char *a, const unsigned char *b) {
128 const unsigned char *a_save = a;
129 for (;;) {
130 int i;
131 int lena = *a++;
132 int lenb = *b++;
133 if (lena != lenb)
134 return 0;
135 if (lena == 0)
136 return a - a_save;
137 for (i = 0; i < lena; i++)
138 if (tolower(a[i]) != tolower(b[i]))
139 return 0;
140 a += lena;
141 b += lena;
142 }
143 }
144
145 #ifdef DEBUG
146 static char *
name2str(const void * v,char * buf,size_t buflen)147 name2str(const void *v, char *buf, size_t buflen) {
148 const unsigned char *a = v;
149 char *b = buf;
150 char *eb = buf + buflen;
151
152 #define ADDC(c) do { \
153 if (b < eb) \
154 *b++ = c; \
155 else \
156 return NULL; \
157 } while (/*CONSTCOND*/0)
158 for (int did = 0;; did++) {
159 int lena = *a++;
160 if (lena == 0) {
161 ADDC('\0');
162 return buf;
163 }
164 if (did)
165 ADDC('.');
166 for (int i = 0; i < lena; i++)
167 ADDC(a[i]);
168 a += lena;
169 }
170 }
171 #endif
172
173 #ifdef __FreeBSD__
174 /* XXX the daemon2_* functions should be in a library */
175
176 int __daemon2_detach_pipe[2];
177
178 static int
daemon2_fork(void)179 daemon2_fork(void)
180 {
181 int r;
182 int fd;
183 int i;
184
185 /*
186 * Set up the pipe, making sure the write end does not
187 * get allocated one of the file descriptors that will
188 * be closed in daemon2_detach().
189 */
190 for (i = 0; i < 3; i++) {
191 r = pipe(__daemon2_detach_pipe);
192 if (r < 0)
193 return -1;
194 if (__daemon2_detach_pipe[1] <= STDERR_FILENO &&
195 (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
196 (void)dup2(fd, __daemon2_detach_pipe[0]);
197 (void)dup2(fd, __daemon2_detach_pipe[1]);
198 if (fd > STDERR_FILENO)
199 (void)close(fd);
200 continue;
201 }
202 break;
203 }
204
205 r = fork();
206 if (r < 0) {
207 return -1;
208 } else if (r == 0) {
209 /* child */
210 close(__daemon2_detach_pipe[0]);
211 return 0;
212 }
213 /* Parent */
214
215 (void) close(__daemon2_detach_pipe[1]);
216
217 for (;;) {
218 char dummy;
219 r = read(__daemon2_detach_pipe[0], &dummy, 1);
220 if (r < 0) {
221 if (errno == EINTR)
222 continue;
223 _exit(1);
224 } else if (r == 0) {
225 _exit(1);
226 } else { /* r > 0 */
227 _exit(0);
228 }
229 }
230 }
231
232 static int
daemon2_detach(int nochdir,int noclose)233 daemon2_detach(int nochdir, int noclose)
234 {
235 int r;
236 int fd;
237
238 if (setsid() == -1)
239 return -1;
240
241 if (!nochdir)
242 (void)chdir("/");
243
244 if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
245 (void)dup2(fd, STDIN_FILENO);
246 (void)dup2(fd, STDOUT_FILENO);
247 (void)dup2(fd, STDERR_FILENO);
248 if (fd > STDERR_FILENO)
249 (void)close(fd);
250 }
251
252 while (1) {
253 r = write(__daemon2_detach_pipe[1], "", 1);
254 if (r < 0) {
255 if (errno == EINTR)
256 continue;
257 /* May get "broken pipe" here if parent is killed */
258 return -1;
259 } else if (r == 0) {
260 /* Should not happen */
261 return -1;
262 } else {
263 break;
264 }
265 }
266
267 (void) close(__daemon2_detach_pipe[1]);
268
269 return 0;
270 }
271 #endif
272
main(int argc,char ** argv)273 int main(int argc, char **argv) {
274 int s, r, protocol;
275 union sockaddr_either saddr;
276 struct dns_data *dp;
277 unsigned char *p;
278 char pidfile_name[40];
279 FILE *f;
280 int one = 1;
281 #ifdef DEBUG
282 char buf1[1024], buf2[1024];
283 #endif
284
285 #ifdef __FreeBSD__
286 daemon2_fork();
287 #endif
288 if (argc < 2 || ((protocol = argv[1][0]) != '4' && protocol != '6'))
289 errx(1, "usage: dns_server 4 | 6");
290 s = socket(protocol == '4' ? PF_INET : PF_INET6, SOCK_DGRAM, IPPROTO_UDP);
291 if (s < 0)
292 err(1, "socket");
293 if (protocol == '4') {
294 memset(&saddr.sin, 0, sizeof(saddr.sin));
295 saddr.sin.sin_family = AF_INET;
296 saddr.sin.sin_len = sizeof(saddr.sin);
297 saddr.sin.sin_port = htons(53);
298 saddr.sin.sin_addr.s_addr = INADDR_ANY;
299 } else {
300 static struct in6_addr loopback = IN6ADDR_LOOPBACK_INIT;
301 memset(&saddr.sin6, 0, sizeof(saddr.sin6));
302 saddr.sin6.sin6_family = AF_INET6;
303 saddr.sin6.sin6_len = sizeof(saddr.sin6);
304 saddr.sin6.sin6_port = htons(53);
305 saddr.sin6.sin6_addr = loopback;
306 }
307
308 r = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one);
309 if (r < 0)
310 err(1, "setsockopt");
311
312 r = bind(s,
313 (struct sockaddr *) &saddr,
314 protocol == '4' ? sizeof(struct sockaddr_in) :
315 sizeof(struct sockaddr_in6));
316 if (r < 0)
317 err(1, "bind");
318
319 snprintf(pidfile_name, sizeof pidfile_name,
320 "dns_server_%c.pid", protocol);
321 f = fopen(pidfile_name, "w");
322 fprintf(f, "%d", getpid());
323 fclose(f);
324 #ifdef __FreeBSD__
325 #ifdef DEBUG
326 daemon2_detach(0, 1);
327 #else
328 daemon2_detach(0, 0);
329 #endif
330 #else
331 #ifdef DEBUG
332 daemon(0, 1);
333 #else
334 daemon(0, 0);
335 #endif
336 #endif
337
338 for (;;) {
339 unsigned char buf[512];
340 union sockaddr_either from;
341 ssize_t nrecv, nsent;
342 socklen_t fromlen =
343 protocol == '4' ? sizeof(struct sockaddr_in) :
344 sizeof(struct sockaddr_in6);
345 memset(buf, 0, sizeof buf);
346 nrecv = recvfrom(s, buf, sizeof buf, 0, &from.s, &fromlen);
347 if (nrecv < 0)
348 err(1, "recvfrom");
349 if (nrecv < 12) {
350 DPRINTF("Too short %zd\n", nrecv);
351 continue;
352 }
353 if ((buf[2] & 0x80) != 0) {
354 DPRINTF("Not a query 0x%x\n", buf[2]);
355 continue;
356 }
357 if (!(buf[4] == 0 && buf[5] == 1)) {
358 DPRINTF("QCOUNT is not 1 0x%x 0x%x\n", buf[4], buf[5]);
359 continue; /* QDCOUNT is not 1 */
360 }
361
362 for (dp = data; dp->qname_size != 0; dp++) {
363 int qtype, qclass;
364 p = buf + 12; /* Point to QNAME */
365 int n = name_eq(p, (const unsigned char *) dp->qname);
366 if (n == 0) {
367 DPRINTF("no match name %s != %s\n",
368 name2str(p, buf1, sizeof(buf1)),
369 name2str(dp->qname, buf2, sizeof(buf2)));
370 continue; /* Name does not match */
371 }
372 DPRINTF("match name %s\n",
373 name2str(p, buf1, sizeof(buf1)));
374 p += n; /* Skip QNAME */
375 qtype = *p++ << 8;
376 qtype |= *p++;
377 if (qtype != dp->qtype) {
378 DPRINTF("no match name 0x%x != 0x%x\n",
379 qtype, dp->qtype);
380 continue;
381 }
382 DPRINTF("match type 0x%x\n", qtype);
383 qclass = *p++ << 8;
384 qclass |= *p++;
385 if (qclass != 1) { /* IN */
386 DPRINTF("no match class %d != 1\n", qclass);
387 continue;
388 }
389 DPRINTF("match class %d\n", qclass);
390 goto found;
391 }
392 continue;
393 found:
394 buf[2] |= 0x80; /* QR */
395 buf[3] |= 0x80; /* RA */
396 memset(buf + 6, 0, 6); /* Clear ANCOUNT, NSCOUNT, ARCOUNT */
397 buf[7] = 1; /* ANCOUNT */
398 memcpy(p, dp->qname, dp->qname_size);
399 p += dp->qname_size;
400 *p++ = dp->qtype >> 8;
401 *p++ = dp->qtype & 0xFF;
402 *p++ = 0;
403 *p++ = 1; /* IN */
404 memset(p, 0, 4); /* TTL = 0 */
405 p += 4;
406 *p++ = 0; /* RDLENGTH MSB */
407 *p++ = dp->answer_size; /* RDLENGTH LSB */
408 memcpy(p, dp->answer, dp->answer_size);
409 p += dp->answer_size;
410 nsent = sendto(s, buf, p - buf, 0, &from.s, fromlen);
411 DPRINTF("sent %zd\n", nsent);
412 if (nsent != p - buf)
413 warn("sendto");
414 }
415 }
416