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
60union 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
74struct 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 */
86struct 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 */
126static int
127name_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
146static char *
147name2str(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
176int __daemon2_detach_pipe[2];
177
178static int
179daemon2_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
232static int
233daemon2_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
273int 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