busybox/networking/dnsd.c

/* vi: set sw=4 ts=4: */
/*
 * Mini DNS server implementation for busybox
 *
 * Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name)
 * Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no)
 * Copyright (C) 2003 Paul Sheer
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 *
 * Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote
 * it into a shape which I believe is both easier to understand and maintain.
 * I also reused the input buffer for output and removed services he did not
 * need.  [1] http://threading.2038bug.com/sheerdns/
 *
 * Some bugfix and minor changes was applied by Roberto A. Foglietta who made
 * the first porting of oao' scdns to busybox also.
 */

#include "libbb.h"
#include <syslog.h>

//#define DEBUG 1
#define DEBUG 0

enum {
	MAX_HOST_LEN = 16,      // longest host name allowed is 15
	IP_STRING_LEN = 18,     // .xxx.xxx.xxx.xxx\0

//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
	MAX_NAME_LEN = (IP_STRING_LEN + 13),

/* Cannot get bigger packets than 512 per RFC1035
   In practice this can be set considerably smaller:
   Length of response packet is  header (12B) + 2*type(4B) + 2*class(4B) +
   ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
   2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
*/
	MAX_PACK_LEN = 512,

	DEFAULT_TTL = 30,       // increase this when not testing?

	REQ_A = 1,
	REQ_PTR = 12
};

struct dns_head {		// the message from client and first part of response mag
	uint16_t id;
	uint16_t flags;
	uint16_t nquer;		// accepts 0
	uint16_t nansw;		// 1 in response
	uint16_t nauth;		// 0
	uint16_t nadd;		// 0
};
struct dns_prop {
	uint16_t type;
	uint16_t class;
};
struct dns_entry {		// element of known name, ip address and reversed ip address
	struct dns_entry *next;
	char ip[IP_STRING_LEN];		// dotted decimal IP
	char rip[IP_STRING_LEN];	// length decimal reversed IP
	char name[MAX_HOST_LEN];
};

static struct dns_entry *dnsentry;
static uint32_t ttl = DEFAULT_TTL;

static const char *fileconf = "/etc/dnsd.conf";

// Must match getopt32 call
#define OPT_daemon  (option_mask32 & 0x10)
#define OPT_verbose (option_mask32 & 0x20)


/*
 * Convert host name from C-string to dns length/string.
 */
static void convname(char *a, uint8_t *q)
{
	int i = (q[0] == '.') ? 0 : 1;
	for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
		a[i] = tolower(*q);
	a[0] = i - 1;
	a[i] = 0;
}

/*
 * Insert length of substrings instead of dots
 */
static void undot(uint8_t * rip)
{
	int i = 0, s = 0;
	while (rip[i])
		i++;
	for (--i; i >= 0; i--) {
		if (rip[i] == '.') {
			rip[i] = s;
			s = 0;
		} else s++;
	}
}

/*
 * Read hostname/IP records from file
 */
static void dnsentryinit(void)
{
	char *token[2];
	parser_t *parser;
	struct dns_entry *m, *prev;

	prev = dnsentry = NULL;
	parser = config_open(fileconf);
	while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
		unsigned a, b, c, d;
		/*
		 * Assumes all host names are lower case only
		 * Hostnames with more than one label are not handled correctly.
		 * Presently the dot is copied into name without
		 * converting to a length/string substring for that label.
		 */
//		if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
		if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
			continue;

		m = xzalloc(sizeof(*m));
		/*m->next = NULL;*/
		sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
		sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
		undot((uint8_t*)m->rip);
		convname(m->name, (uint8_t*)token[0]);

		if (OPT_verbose)
			fprintf(stderr, "\tname:%s, ip:%s\n", &(m->name[1]), m->ip);

		if (prev == NULL)
			dnsentry = m;
		else
			prev->next = m;
		prev = m;
	}
	config_close(parser);
}

/*
 * Look query up in dns records and return answer if found
 * qs is the query string, first byte the string length
 */
static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
{
	int i;
	struct dns_entry *d = dnsentry;

	do {
#if DEBUG
		char *p,*q;
		q = (char *)&(qs[1]);
		p = &(d->name[1]);
		fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
			__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
			p, q, (int)strlen(q));
#endif
		if (type == REQ_A) { /* search by host name */
			for (i = 1; i <= (int)(d->name[0]); i++)
				if (tolower(qs[i]) != d->name[i])
					break;
			if (i > (int)(d->name[0]) ||
			    (d->name[0] == 1 && d->name[1] == '*')) {
				strcpy((char *)as, d->ip);
#if DEBUG
				fprintf(stderr, " OK as:%s\n", as);
#endif
				return 0;
			}
		} else if (type == REQ_PTR) { /* search by IP-address */
			if ((d->name[0] != 1 || d->name[1] != '*') &&
			    !strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) {
				strcpy((char *)as, d->name);
				return 0;
			}
		}
		d = d->next;
	} while (d);
	return -1;
}

/*
 * Decode message and generate answer
 */
static int process_packet(uint8_t *buf)
{
	uint8_t answstr[MAX_NAME_LEN + 1];
	struct dns_head *head;
	struct dns_prop *qprop;
	uint8_t *from, *answb;
	uint16_t outr_rlen;
	uint16_t outr_flags;
	uint16_t flags;
	int lookup_result, type, packet_len;
	int querystr_len;

	answstr[0] = '\0';

	head = (struct dns_head *)buf;
	if (head->nquer == 0) {
		bb_error_msg("no queries");
		return -1;
	}

	if (head->flags & 0x8000) {
		bb_error_msg("ignoring response packet");
		return -1;
	}

	from = (void *)&head[1];	//  start of query string
//FIXME: strlen of untrusted data??!
	querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
	answb = from + querystr_len;   // where to append answer block

	outr_rlen = 0;
	outr_flags = 0;

	qprop = (struct dns_prop *)(answb - 4);
	type = ntohs(qprop->type);

	// only let REQ_A and REQ_PTR pass
	if (!(type == REQ_A || type == REQ_PTR)) {
		goto empty_packet;	/* we can't handle the query type */
	}

	if (ntohs(qprop->class) != 1 /* class INET */ ) {
		outr_flags = 4; /* not supported */
		goto empty_packet;
	}
	/* we only support standard queries */

	if ((ntohs(head->flags) & 0x7800) != 0)
		goto empty_packet;

	// We have a standard query
	bb_info_msg("%s", (char *)from);
	lookup_result = table_lookup(type, answstr, from);
	if (lookup_result != 0) {
		outr_flags = 3 | 0x0400;	// name do not exist and auth
		goto empty_packet;
	}
	if (type == REQ_A) {    // return an address
		struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
		uint32_t v32;
		if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
			outr_flags = 1; /* Frmt err */
			goto empty_packet;
		}
		v32 = a.s_addr; /* in case long != int */
		memcpy(answstr, &v32, 4);
		outr_rlen = 4;			// uint32_t IP
	} else
		outr_rlen = strlen((char *)answstr) + 1;	// a host name
	outr_flags |= 0x0400;			/* authority-bit */
	// we have an answer
	head->nansw = htons(1);

	// copy query block to answer block
	memcpy(answb, from, querystr_len);
	answb += querystr_len;

	// and append answer rr
// FIXME: unaligned accesses??
	*(uint32_t *) answb = htonl(ttl);
	answb += 4;
	*(uint16_t *) answb = htons(outr_rlen);
	answb += 2;
	memcpy(answb, answstr, outr_rlen);
	answb += outr_rlen;

 empty_packet:

	flags = ntohs(head->flags);
	// clear rcode and RA, set responsebit and our new flags
	flags |= (outr_flags & 0xff80) | 0x8000;
	head->flags = htons(flags);
	head->nauth = head->nadd = 0;
	head->nquer = htons(1);

	packet_len = answb - buf;
	return packet_len;
}

/*
 * Exit on signal
 */
static void interrupt(int sig)
{
	/* unlink("/var/run/dnsd.lock"); */
	bb_error_msg("interrupt, exiting\n");
	kill_myself_with_sig(sig);
}

int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dnsd_main(int argc UNUSED_PARAM, char **argv)
{
	const char *listen_interface = "0.0.0.0";
	char *sttl, *sport;
	len_and_sockaddr *lsa, *from, *to;
	unsigned lsa_size;
	int udps;
	uint16_t port = 53;
	/* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */
	/* I'd rather see process_packet() fixed instead... */
	uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)];

	getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
	//if (option_mask32 & 0x1) // -i
	//if (option_mask32 & 0x2) // -c
	if (option_mask32 & 0x4) // -t
		ttl = xatou_range(sttl, 1, 0xffffffff);
	if (option_mask32 & 0x8) // -p
		port = xatou_range(sport, 1, 0xffff);

	if (OPT_verbose) {
		bb_info_msg("listen_interface: %s", listen_interface);
		bb_info_msg("ttl: %d, port: %d", ttl, port);
		bb_info_msg("fileconf: %s", fileconf);
	}

	if (OPT_daemon) {
		bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
		openlog(applet_name, LOG_PID, LOG_DAEMON);
		logmode = LOGMODE_SYSLOG;
	}

	dnsentryinit();

	signal(SIGINT, interrupt);
	bb_signals(0
		/* why? + (1 << SIGPIPE) */
		+ (1 << SIGHUP)
#ifdef SIGTSTP
		+ (1 << SIGTSTP)
#endif
#ifdef SIGURG
		+ (1 << SIGURG)
#endif
		, SIG_IGN);

	lsa = xdotted2sockaddr(listen_interface, port);
	udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
	xbind(udps, &lsa->u.sa, lsa->len);
	socket_want_pktinfo(udps); /* needed for recv_from_to to work */
	lsa_size = LSA_LEN_SIZE + lsa->len;
	from = xzalloc(lsa_size);
	to = xzalloc(lsa_size);

	bb_info_msg("Accepting UDP packets on %s",
			xmalloc_sockaddr2dotted(&lsa->u.sa));

	while (1) {
		int r;
		/* Try to get *DEST* address (to which of our addresses
		 * this query was directed), and reply from the same address.
		 * Or else we can exhibit usual UDP ugliness:
		 * [ip1.multihomed.ip2] <=  query to ip1  <= peer
		 * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
		memcpy(to, lsa, lsa_size);
		r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
		if (r < 12 || r > MAX_PACK_LEN) {
			bb_error_msg("invalid packet size");
			continue;
		}
		if (OPT_verbose)
			bb_info_msg("Got UDP packet");
		buf[r] = '\0'; /* paranoia */
		r = process_packet(buf);
		if (r <= 0)
			continue;
		send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len);
	}
	return 0;
}
1	/* vi: set sw=4 ts=4: */
2	/*
3	* Mini DNS server implementation for busybox
4	*
5	* Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name)
6	* Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no)
7	* Copyright (C) 2003 Paul Sheer
8	*
9	* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
10	*
11	* Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote
12	* it into a shape which I believe is both easier to understand and maintain.
13	* I also reused the input buffer for output and removed services he did not
14	* need. [1] http://threading.2038bug.com/sheerdns/
15	*
16	* Some bugfix and minor changes was applied by Roberto A. Foglietta who made
17	* the first porting of oao' scdns to busybox also.
18	*/
19
20	#include "libbb.h"
21	#include <syslog.h>
22
23	//#define DEBUG 1
24	#define DEBUG 0
25
26	enum {
27	MAX_HOST_LEN = 16, // longest host name allowed is 15
28	IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
29
30	//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
31	MAX_NAME_LEN = (IP_STRING_LEN + 13),
32
33	/* Cannot get bigger packets than 512 per RFC1035
34	In practice this can be set considerably smaller:
35	Length of response packet is header (12B) + 2type(4B) + 2class(4B) +
36	ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
37	2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
38	*/
39	MAX_PACK_LEN = 512,
40
41	DEFAULT_TTL = 30, // increase this when not testing?
42
43	REQ_A = 1,
44	REQ_PTR = 12
45	};
46
47	struct dns_head { // the message from client and first part of response mag
48	uint16_t id;
49	uint16_t flags;
50	uint16_t nquer; // accepts 0
51	uint16_t nansw; // 1 in response
52	uint16_t nauth; // 0
53	uint16_t nadd; // 0
54	};
55	struct dns_prop {
56	uint16_t type;
57	uint16_t class;
58	};
59	struct dns_entry { // element of known name, ip address and reversed ip address
60	struct dns_entry *next;
61	char ip[IP_STRING_LEN]; // dotted decimal IP
62	char rip[IP_STRING_LEN]; // length decimal reversed IP
63	char name[MAX_HOST_LEN];
64	};
65
66	static struct dns_entry *dnsentry;
67	static uint32_t ttl = DEFAULT_TTL;
68
69	static const char *fileconf = "/etc/dnsd.conf";
70
71	// Must match getopt32 call
72	#define OPT_daemon (option_mask32 & 0x10)
73	#define OPT_verbose (option_mask32 & 0x20)
74
75
76	/*
77	* Convert host name from C-string to dns length/string.
78	*/
79	static void convname(char a, uint8_t q)
80	{
81	int i = (q[0] == '.') ? 0 : 1;
82	for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
83	a[i] = tolower(*q);
84	a[0] = i - 1;
85	a[i] = 0;
86	}
87
88	/*
89	* Insert length of substrings instead of dots
90	*/
91	static void undot(uint8_t * rip)
92	{
93	int i = 0, s = 0;
94	while (rip[i])
95	i++;
96	for (--i; i >= 0; i--) {
97	if (rip[i] == '.') {
98	rip[i] = s;
99	s = 0;
100	} else s++;
101	}
102	}
103
104	/*
105	* Read hostname/IP records from file
106	*/
107	static void dnsentryinit(void)
108	{
109	char *token[2];
110	parser_t *parser;
111	struct dns_entry m, prev;
112
113	prev = dnsentry = NULL;
114	parser = config_open(fileconf);
115	while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
116	unsigned a, b, c, d;
117	/*
118	* Assumes all host names are lower case only
119	* Hostnames with more than one label are not handled correctly.
120	* Presently the dot is copied into name without
121	* converting to a length/string substring for that label.
122	*/
123	// if (!token[1] \|\| sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
124	if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
125	continue;
126
127	m = xzalloc(sizeof(*m));
128	/m->next = NULL;/
129	sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
130	sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
131	undot((uint8_t*)m->rip);
132	convname(m->name, (uint8_t*)token[0]);
133
134	if (OPT_verbose)
135	fprintf(stderr, "\tname:%s, ip:%s\n", &(m->name[1]), m->ip);
136
137	if (prev == NULL)
138	dnsentry = m;
139	else
140	prev->next = m;
141	prev = m;
142	}
143	config_close(parser);
144	}
145
146	/*
147	* Look query up in dns records and return answer if found
148	* qs is the query string, first byte the string length
149	*/
150	static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
151	{
152	int i;
153	struct dns_entry *d = dnsentry;
154
155	do {
156	#if DEBUG
157	char p,q;
158	q = (char *)&(qs[1]);
159	p = &(d->name[1]);
160	fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
161	__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
162	p, q, (int)strlen(q));
163	#endif
164	if (type == REQ_A) { /* search by host name */
165	for (i = 1; i <= (int)(d->name[0]); i++)
166	if (tolower(qs[i]) != d->name[i])
167	break;
168	if (i > (int)(d->name[0]) \|\|
169	(d->name[0] == 1 && d->name[1] == '*')) {
170	strcpy((char *)as, d->ip);
171	#if DEBUG
172	fprintf(stderr, " OK as:%s\n", as);
173	#endif
174	return 0;
175	}
176	} else if (type == REQ_PTR) { /* search by IP-address */
177	if ((d->name[0] != 1 \|\| d->name[1] != '*') &&
178	!strncmp((char)&d->rip[1], (char)&qs[1], strlen(d->rip)-1)) {
179	strcpy((char *)as, d->name);
180	return 0;
181	}
182	}
183	d = d->next;
184	} while (d);
185	return -1;
186	}
187
188	/*
189	* Decode message and generate answer
190	*/
191	static int process_packet(uint8_t *buf)
192	{
193	uint8_t answstr[MAX_NAME_LEN + 1];
194	struct dns_head *head;
195	struct dns_prop *qprop;
196	uint8_t from, answb;
197	uint16_t outr_rlen;
198	uint16_t outr_flags;
199	uint16_t flags;
200	int lookup_result, type, packet_len;
201	int querystr_len;
202
203	answstr[0] = '\0';
204
205	head = (struct dns_head *)buf;
206	if (head->nquer == 0) {
207	bb_error_msg("no queries");
208	return -1;
209	}
210
211	if (head->flags & 0x8000) {
212	bb_error_msg("ignoring response packet");
213	return -1;
214	}
215
216	from = (void *)&head[1]; // start of query string
217	//FIXME: strlen of untrusted data??!
218	querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
219	answb = from + querystr_len; // where to append answer block
220
221	outr_rlen = 0;
222	outr_flags = 0;
223
224	qprop = (struct dns_prop *)(answb - 4);
225	type = ntohs(qprop->type);
226
227	// only let REQ_A and REQ_PTR pass
228	if (!(type == REQ_A \|\| type == REQ_PTR)) {
229	goto empty_packet; /* we can't handle the query type */
230	}
231
232	if (ntohs(qprop->class) != 1 /* class INET */ ) {
233	outr_flags = 4; /* not supported */
234	goto empty_packet;
235	}
236	/* we only support standard queries */
237
238	if ((ntohs(head->flags) & 0x7800) != 0)
239	goto empty_packet;
240
241	// We have a standard query
242	bb_info_msg("%s", (char *)from);
243	lookup_result = table_lookup(type, answstr, from);
244	if (lookup_result != 0) {
245	outr_flags = 3 \| 0x0400; // name do not exist and auth
246	goto empty_packet;
247	}
248	if (type == REQ_A) { // return an address
249	struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
250	uint32_t v32;
251	if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
252	outr_flags = 1; /* Frmt err */
253	goto empty_packet;
254	}
255	v32 = a.s_addr; /* in case long != int */
256	memcpy(answstr, &v32, 4);
257	outr_rlen = 4; // uint32_t IP
258	} else
259	outr_rlen = strlen((char *)answstr) + 1; // a host name
260	outr_flags \|= 0x0400; /* authority-bit */
261	// we have an answer
262	head->nansw = htons(1);
263
264	// copy query block to answer block
265	memcpy(answb, from, querystr_len);
266	answb += querystr_len;
267
268	// and append answer rr
269	// FIXME: unaligned accesses??
270	(uint32_t ) answb = htonl(ttl);
271	answb += 4;
272	(uint16_t ) answb = htons(outr_rlen);
273	answb += 2;
274	memcpy(answb, answstr, outr_rlen);
275	answb += outr_rlen;
276
277	empty_packet:
278
279	flags = ntohs(head->flags);
280	// clear rcode and RA, set responsebit and our new flags
281	flags \|= (outr_flags & 0xff80) \| 0x8000;
282	head->flags = htons(flags);
283	head->nauth = head->nadd = 0;
284	head->nquer = htons(1);
285
286	packet_len = answb - buf;
287	return packet_len;
288	}
289
290	/*
291	* Exit on signal
292	*/
293	static void interrupt(int sig)
294	{
295	/* unlink("/var/run/dnsd.lock"); */
296	bb_error_msg("interrupt, exiting\n");
297	kill_myself_with_sig(sig);
298	}
299
300	int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
301	int dnsd_main(int argc UNUSED_PARAM, char **argv)
302	{
303	const char *listen_interface = "0.0.0.0";
304	char sttl, sport;
305	len_and_sockaddr lsa, from, *to;
306	unsigned lsa_size;
307	int udps;
308	uint16_t port = 53;
309	/* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */
310	/* I'd rather see process_packet() fixed instead... */
311	uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)];
312
313	getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
314	//if (option_mask32 & 0x1) // -i
315	//if (option_mask32 & 0x2) // -c
316	if (option_mask32 & 0x4) // -t
317	ttl = xatou_range(sttl, 1, 0xffffffff);
318	if (option_mask32 & 0x8) // -p
319	port = xatou_range(sport, 1, 0xffff);
320
321	if (OPT_verbose) {
322	bb_info_msg("listen_interface: %s", listen_interface);
323	bb_info_msg("ttl: %d, port: %d", ttl, port);
324	bb_info_msg("fileconf: %s", fileconf);
325	}
326
327	if (OPT_daemon) {
328	bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
329	openlog(applet_name, LOG_PID, LOG_DAEMON);
330	logmode = LOGMODE_SYSLOG;
331	}
332
333	dnsentryinit();
334
335	signal(SIGINT, interrupt);
336	bb_signals(0
337	/* why? + (1 << SIGPIPE) */
338	+ (1 << SIGHUP)
339	#ifdef SIGTSTP
340	+ (1 << SIGTSTP)
341	#endif
342	#ifdef SIGURG
343	+ (1 << SIGURG)
344	#endif
345	, SIG_IGN);
346
347	lsa = xdotted2sockaddr(listen_interface, port);
348	udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
349	xbind(udps, &lsa->u.sa, lsa->len);
350	socket_want_pktinfo(udps); /* needed for recv_from_to to work */
351	lsa_size = LSA_LEN_SIZE + lsa->len;
352	from = xzalloc(lsa_size);
353	to = xzalloc(lsa_size);
354
355	bb_info_msg("Accepting UDP packets on %s",
356	xmalloc_sockaddr2dotted(&lsa->u.sa));
357
358	while (1) {
359	int r;
360	/* Try to get DEST address (to which of our addresses
361	* this query was directed), and reply from the same address.
362	* Or else we can exhibit usual UDP ugliness:
363	* [ip1.multihomed.ip2] <= query to ip1 <= peer
364	* [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
365	memcpy(to, lsa, lsa_size);
366	r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
367	if (r < 12 \|\| r > MAX_PACK_LEN) {
368	bb_error_msg("invalid packet size");
369	continue;
370	}
371	if (OPT_verbose)
372	bb_info_msg("Got UDP packet");
373	buf[r] = '\0'; /* paranoia */
374	r = process_packet(buf);
375	if (r <= 0)
376	continue;
377	send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len);
378	}
379	return 0;
380	}