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 "busybox.h"

static const char *fileconf = "/etc/dnsd.conf";
#define LOCK_FILE       "/var/run/dnsd.lock"

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

//#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 + 1,

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

	REQ_A = 1,
	REQ_PTR = 12
};

struct dns_repl {		// resource record, add 0 or 1 to accepted dns_msg in resp
	uint16_t rlen;
	uint8_t *r;		// resource
	uint16_t flags;
};

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 = NULL;
static uint32_t ttl = DEFAULT_TTL;

/*
 * 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 one line of hostname/IP from file
 * Returns 0 for each valid entry read, -1 at EOF
 * Assumes all host names are lower case only
 * Hostnames with more than one label is not handled correctly.
 * Presently the dot is copied into name without
 * converting to a length/string substring for that label.
 */

static int getfileentry(FILE * fp, struct dns_entry *s)
{
	unsigned int a,b,c,d;
	char *r, *name;

 restart:
	r = xmalloc_fgets(fp);
	if (!r)
		return -1;
	while (*r == ' ' || *r == '\t') {
		r++;
		if (!*r || *r == '#' || *r == '\n')
			goto restart; /* skipping empty/blank and commented lines  */
	}
	name = r;
	while (*r != ' ' && *r != '\t')
		r++;
	*r++ = 0;
	if (sscanf(r, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
		goto restart; /* skipping wrong lines */

	sprintf(s->ip, "%u.%u.%u.%u", a, b, c, d);
	sprintf(s->rip, ".%u.%u.%u.%u", d, c, b, a);
	undot((uint8_t*)s->rip);
	convname(s->name,(uint8_t*)name);

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

	return 0;
}

/*
 * Read hostname/IP records from file
 */
static void dnsentryinit(void)
{
	FILE *fp;
	struct dns_entry *m, *prev;
	prev = dnsentry = NULL;

	fp = xfopen(fileconf, "r");

	while (1) {
		m = xmalloc(sizeof(struct dns_entry));

		m->next = NULL;
		if (getfileentry(fp, m))
			break;

		if (prev == NULL)
			dnsentry = m;
		else
			prev->next = m;
		prev = m;
	}
	fclose(fp);
}

/*
 * 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])) {
#if DEBUG
				fprintf(stderr, " OK");
#endif
				strcpy((char *)as, d->ip);
#if DEBUG
				fprintf(stderr, " as:%s\n", as);
#endif
					return 0;
			}
		} else
		if (type == REQ_PTR) { /* search by IP-address */
			if (!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
 */
#define eret(s) do { fputs(s, stderr); return -1; } while (0)
static int process_packet(uint8_t * buf)
{
	struct dns_head *head;
	struct dns_prop *qprop;
	struct dns_repl outr;
	void *next, *from, *answb;

	uint8_t answstr[MAX_NAME_LEN + 1];
	int lookup_result, type, len, packet_len;
	uint16_t flags;

	answstr[0] = '\0';

	head = (struct dns_head *)buf;
	if (head->nquer == 0)
		eret("no queries\n");

	if (head->flags & 0x8000)
		eret("ignoring response packet\n");

	from = (void *)&head[1];	//  start of query string
	next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop);   // where to append answer block

	outr.rlen = 0;			// may change later
	outr.r = NULL;
	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, (uint8_t*)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;
		if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
			outr.flags = 1; /* Frmt err */
			goto empty_packet;
		}
		memcpy(answstr, &a.s_addr, 4);	// save before a disappears
		outr.rlen = 4;			// uint32_t IP
	}
	else
		outr.rlen = strlen((char *)answstr) + 1;	// a host name
	outr.r = answstr;			// 32 bit ip or a host name
	outr.flags |= 0x0400;			/* authority-bit */
	// we have an answer
	head->nansw = htons(1);

	// copy query block to answer block
	len = answb - from;
	memcpy(answb, from, len);
	next += len;

	// and append answer rr
	*(uint32_t *) next = htonl(ttl);
	next += 4;
	*(uint16_t *) next = htons(outr.rlen);
	next += 2;
	memcpy(next, (void *)answstr, outr.rlen);
	next += 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 = htons(0);
	head->nquer = htons(1);

	packet_len = next - (void *)buf;
	return packet_len;
}

/*
 * Exit on signal
 */
static void interrupt(int x)
{
	unlink(LOCK_FILE);
	bb_error_msg("interrupt, exiting\n");
	exit(2);
}

int dnsd_main(int argc, char **argv)
{
	char *listen_interface = NULL;
	char *sttl, *sport;
	len_and_sockaddr *lsa;
	int udps;
	uint16_t port = 53;
	uint8_t buf[MAX_PACK_LEN];

	getopt32(argc, 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(sttl, 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) {
//FIXME: NOMMU will NOT set LOGMODE_SYSLOG!
#ifdef BB_NOMMU
		/* reexec for vfork() do continue parent */
		vfork_daemon_rexec(1, 0, argc, argv, "-d");
#else
		xdaemon(1, 0);
#endif
		logmode = LOGMODE_SYSLOG;
	}

	dnsentryinit();

	signal(SIGINT, interrupt);
	signal(SIGPIPE, SIG_IGN);
	signal(SIGHUP, SIG_IGN);
#ifdef SIGTSTP
	signal(SIGTSTP, SIG_IGN);
#endif
#ifdef SIGURG
	signal(SIGURG, SIG_IGN);
#endif

	lsa = host2sockaddr(listen_interface, port);
	udps = xsocket(lsa->sa.sa_family, SOCK_DGRAM, 0);
	xbind(udps, &lsa->sa, lsa->len);
	// xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think?
	bb_info_msg("Accepting UDP packets on %s",
			xmalloc_sockaddr2dotted(&lsa->sa, lsa->len));

	while (1) {
		fd_set fdset;
		int r;

		FD_ZERO(&fdset);
		FD_SET(udps, &fdset);
		// Block until a message arrives
// FIXME: Fantastic. select'ing on just one fd??
// Why no just block on it doing recvfrom() ?
		r = select(udps + 1, &fdset, NULL, NULL, NULL);
		if (r < 0)
			bb_perror_msg_and_die("select error");
		if (r == 0)
			bb_perror_msg_and_die("select spurious return");

		/* Can this test ever be false? - yes */
		if (FD_ISSET(udps, &fdset)) {
			socklen_t fromlen = lsa->len;
// FIXME: need 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)
			r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->sa, &fromlen);
			if (OPT_verbose)
				bb_info_msg("Got UDP packet");

			if (r < 12 || r > 512) {
				bb_error_msg("invalid packet size");
				continue;
			}
			if (r <= 0)
				continue;
			r = process_packet(buf);
			if (r <= 0)
				continue;
			sendto(udps, buf, r, 0, &lsa->sa, fromlen);
		}
	}
}
1	niro	532	/* 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 "busybox.h"
21
22			static const char *fileconf = "/etc/dnsd.conf";
23			#define LOCK_FILE "/var/run/dnsd.lock"
24
25			// Must match getopt32 call
26			#define OPT_daemon (option_mask32 & 0x10)
27			#define OPT_verbose (option_mask32 & 0x20)
28
29			//#define DEBUG 1
30			#define DEBUG 0
31
32			enum {
33			MAX_HOST_LEN = 16, // longest host name allowed is 15
34			IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
35
36			//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
37			MAX_NAME_LEN = (IP_STRING_LEN + 13),
38
39			/* Cannot get bigger packets than 512 per RFC1035
40			In practice this can be set considerably smaller:
41			Length of response packet is header (12B) + 2type(4B) + 2class(4B) +
42			ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
43			2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
44			*/
45			MAX_PACK_LEN = 512 + 1,
46
47			DEFAULT_TTL = 30, // increase this when not testing?
48
49			REQ_A = 1,
50			REQ_PTR = 12
51			};
52
53			struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
54			uint16_t rlen;
55			uint8_t *r; // resource
56			uint16_t flags;
57			};
58
59			struct dns_head { // the message from client and first part of response mag
60			uint16_t id;
61			uint16_t flags;
62			uint16_t nquer; // accepts 0
63			uint16_t nansw; // 1 in response
64			uint16_t nauth; // 0
65			uint16_t nadd; // 0
66			};
67			struct dns_prop {
68			uint16_t type;
69			uint16_t class;
70			};
71			struct dns_entry { // element of known name, ip address and reversed ip address
72			struct dns_entry *next;
73			char ip[IP_STRING_LEN]; // dotted decimal IP
74			char rip[IP_STRING_LEN]; // length decimal reversed IP
75			char name[MAX_HOST_LEN];
76			};
77
78			static struct dns_entry *dnsentry = NULL;
79			static uint32_t ttl = DEFAULT_TTL;
80
81			/*
82			* Convert host name from C-string to dns length/string.
83			*/
84			static void convname(char a, uint8_t q)
85			{
86			int i = (q[0] == '.') ? 0 : 1;
87			for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
88			a[i] = tolower(*q);
89			a[0] = i - 1;
90			a[i] = 0;
91			}
92
93			/*
94			* Insert length of substrings instead of dots
95			*/
96			static void undot(uint8_t * rip)
97			{
98			int i = 0, s = 0;
99			while (rip[i])
100			i++;
101			for (--i; i >= 0; i--) {
102			if (rip[i] == '.') {
103			rip[i] = s;
104			s = 0;
105			} else s++;
106			}
107			}
108
109			/*
110			* Read one line of hostname/IP from file
111			* Returns 0 for each valid entry read, -1 at EOF
112			* Assumes all host names are lower case only
113			* Hostnames with more than one label is not handled correctly.
114			* Presently the dot is copied into name without
115			* converting to a length/string substring for that label.
116			*/
117
118			static int getfileentry(FILE * fp, struct dns_entry *s)
119			{
120			unsigned int a,b,c,d;
121			char r, name;
122
123			restart:
124			r = xmalloc_fgets(fp);
125			if (!r)
126			return -1;
127			while (r == ' ' \|\| r == '\t') {
128			r++;
129			if (!r \|\| r == '#' \|\| *r == '\n')
130			goto restart; /* skipping empty/blank and commented lines */
131			}
132			name = r;
133			while (r != ' ' && r != '\t')
134			r++;
135			*r++ = 0;
136			if (sscanf(r, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
137			goto restart; /* skipping wrong lines */
138
139			sprintf(s->ip, "%u.%u.%u.%u", a, b, c, d);
140			sprintf(s->rip, ".%u.%u.%u.%u", d, c, b, a);
141			undot((uint8_t*)s->rip);
142			convname(s->name,(uint8_t*)name);
143
144			if (OPT_verbose)
145			fprintf(stderr, "\tname:%s, ip:%s\n", &(s->name[1]),s->ip);
146
147			return 0;
148			}
149
150			/*
151			* Read hostname/IP records from file
152			*/
153			static void dnsentryinit(void)
154			{
155			FILE *fp;
156			struct dns_entry m, prev;
157			prev = dnsentry = NULL;
158
159			fp = xfopen(fileconf, "r");
160
161			while (1) {
162			m = xmalloc(sizeof(struct dns_entry));
163
164			m->next = NULL;
165			if (getfileentry(fp, m))
166			break;
167
168			if (prev == NULL)
169			dnsentry = m;
170			else
171			prev->next = m;
172			prev = m;
173			}
174			fclose(fp);
175			}
176
177			/*
178			* Look query up in dns records and return answer if found
179			* qs is the query string, first byte the string length
180			*/
181			static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
182			{
183			int i;
184			struct dns_entry *d=dnsentry;
185
186			do {
187			#if DEBUG
188			char p,q;
189			q = (char *)&(qs[1]);
190			p = &(d->name[1]);
191			fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
192			__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
193			p, q, (int)strlen(q));
194			#endif
195			if (type == REQ_A) { /* search by host name */
196			for (i = 1; i <= (int)(d->name[0]); i++)
197			if (tolower(qs[i]) != d->name[i])
198			break;
199			if (i > (int)(d->name[0])) {
200			#if DEBUG
201			fprintf(stderr, " OK");
202			#endif
203			strcpy((char *)as, d->ip);
204			#if DEBUG
205			fprintf(stderr, " as:%s\n", as);
206			#endif
207			return 0;
208			}
209			} else
210			if (type == REQ_PTR) { /* search by IP-address */
211			if (!strncmp((char)&d->rip[1], (char)&qs[1], strlen(d->rip)-1)) {
212			strcpy((char *)as, d->name);
213			return 0;
214			}
215			}
216			d = d->next;
217			} while (d);
218			return -1;
219			}
220
221
222			/*
223			* Decode message and generate answer
224			*/
225			#define eret(s) do { fputs(s, stderr); return -1; } while (0)
226			static int process_packet(uint8_t * buf)
227			{
228			struct dns_head *head;
229			struct dns_prop *qprop;
230			struct dns_repl outr;
231			void next, from, *answb;
232
233			uint8_t answstr[MAX_NAME_LEN + 1];
234			int lookup_result, type, len, packet_len;
235			uint16_t flags;
236
237			answstr[0] = '\0';
238
239			head = (struct dns_head *)buf;
240			if (head->nquer == 0)
241			eret("no queries\n");
242
243			if (head->flags & 0x8000)
244			eret("ignoring response packet\n");
245
246			from = (void *)&head[1]; // start of query string
247			next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop); // where to append answer block
248
249			outr.rlen = 0; // may change later
250			outr.r = NULL;
251			outr.flags = 0;
252
253			qprop = (struct dns_prop *)(answb - 4);
254			type = ntohs(qprop->type);
255
256			// only let REQ_A and REQ_PTR pass
257			if (!(type == REQ_A \|\| type == REQ_PTR)) {
258			goto empty_packet; /* we can't handle the query type */
259			}
260
261			if (ntohs(qprop->class) != 1 /* class INET */ ) {
262			outr.flags = 4; /* not supported */
263			goto empty_packet;
264			}
265			/* we only support standard queries */
266
267			if ((ntohs(head->flags) & 0x7800) != 0)
268			goto empty_packet;
269
270			// We have a standard query
271			bb_info_msg("%s", (char *)from);
272			lookup_result = table_lookup(type, answstr, (uint8_t*)from);
273			if (lookup_result != 0) {
274			outr.flags = 3 \| 0x0400; //name do not exist and auth
275			goto empty_packet;
276			}
277			if (type == REQ_A) { // return an address
278			struct in_addr a;
279			if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
280			outr.flags = 1; /* Frmt err */
281			goto empty_packet;
282			}
283			memcpy(answstr, &a.s_addr, 4); // save before a disappears
284			outr.rlen = 4; // uint32_t IP
285			}
286			else
287			outr.rlen = strlen((char *)answstr) + 1; // a host name
288			outr.r = answstr; // 32 bit ip or a host name
289			outr.flags \|= 0x0400; /* authority-bit */
290			// we have an answer
291			head->nansw = htons(1);
292
293			// copy query block to answer block
294			len = answb - from;
295			memcpy(answb, from, len);
296			next += len;
297
298			// and append answer rr
299			(uint32_t ) next = htonl(ttl);
300			next += 4;
301			(uint16_t ) next = htons(outr.rlen);
302			next += 2;
303			memcpy(next, (void *)answstr, outr.rlen);
304			next += outr.rlen;
305
306			empty_packet:
307
308			flags = ntohs(head->flags);
309			// clear rcode and RA, set responsebit and our new flags
310			flags \|= (outr.flags & 0xff80) \| 0x8000;
311			head->flags = htons(flags);
312			head->nauth = head->nadd = htons(0);
313			head->nquer = htons(1);
314
315			packet_len = next - (void *)buf;
316			return packet_len;
317			}
318
319			/*
320			* Exit on signal
321			*/
322			static void interrupt(int x)
323			{
324			unlink(LOCK_FILE);
325			bb_error_msg("interrupt, exiting\n");
326			exit(2);
327			}
328
329			int dnsd_main(int argc, char **argv)
330			{
331			char *listen_interface = NULL;
332			char sttl, sport;
333			len_and_sockaddr *lsa;
334			int udps;
335			uint16_t port = 53;
336			uint8_t buf[MAX_PACK_LEN];
337
338			getopt32(argc, argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
339			//if (option_mask32 & 0x1) // -i
340			//if (option_mask32 & 0x2) // -c
341			if (option_mask32 & 0x4) // -t
342			ttl = xatou_range(sttl, 1, 0xffffffff);
343			if (option_mask32 & 0x8) // -p
344			port = xatou_range(sttl, 1, 0xffff);
345
346			if (OPT_verbose) {
347			bb_info_msg("listen_interface: %s", listen_interface);
348			bb_info_msg("ttl: %d, port: %d", ttl, port);
349			bb_info_msg("fileconf: %s", fileconf);
350			}
351
352			if (OPT_daemon) {
353			//FIXME: NOMMU will NOT set LOGMODE_SYSLOG!
354			#ifdef BB_NOMMU
355			/* reexec for vfork() do continue parent */
356			vfork_daemon_rexec(1, 0, argc, argv, "-d");
357			#else
358			xdaemon(1, 0);
359			#endif
360			logmode = LOGMODE_SYSLOG;
361			}
362
363			dnsentryinit();
364
365			signal(SIGINT, interrupt);
366			signal(SIGPIPE, SIG_IGN);
367			signal(SIGHUP, SIG_IGN);
368			#ifdef SIGTSTP
369			signal(SIGTSTP, SIG_IGN);
370			#endif
371			#ifdef SIGURG
372			signal(SIGURG, SIG_IGN);
373			#endif
374
375			lsa = host2sockaddr(listen_interface, port);
376			udps = xsocket(lsa->sa.sa_family, SOCK_DGRAM, 0);
377			xbind(udps, &lsa->sa, lsa->len);
378			// xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think?
379			bb_info_msg("Accepting UDP packets on %s",
380			xmalloc_sockaddr2dotted(&lsa->sa, lsa->len));
381
382			while (1) {
383			fd_set fdset;
384			int r;
385
386			FD_ZERO(&fdset);
387			FD_SET(udps, &fdset);
388			// Block until a message arrives
389			// FIXME: Fantastic. select'ing on just one fd??
390			// Why no just block on it doing recvfrom() ?
391			r = select(udps + 1, &fdset, NULL, NULL, NULL);
392			if (r < 0)
393			bb_perror_msg_and_die("select error");
394			if (r == 0)
395			bb_perror_msg_and_die("select spurious return");
396
397			/* Can this test ever be false? - yes */
398			if (FD_ISSET(udps, &fdset)) {
399			socklen_t fromlen = lsa->len;
400			// FIXME: need to get DEST address (to which of our addresses
401			// this query was directed), and reply from the same address.
402			// Or else we can exhibit usual UDP ugliness:
403			// [ip1.multihomed.ip2] <= query to ip1 <= peer
404			// [ip1.multihomed.ip2] => reply from ip2 => peer (confused)
405			r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->sa, &fromlen);
406			if (OPT_verbose)
407			bb_info_msg("Got UDP packet");
408
409			if (r < 12 \|\| r > 512) {
410			bb_error_msg("invalid packet size");
411			continue;
412			}
413			if (r <= 0)
414			continue;
415			r = process_packet(buf);
416			if (r <= 0)
417			continue;
418			sendto(udps, buf, r, 0, &lsa->sa, fromlen);
419			}
420			}
421			}