1 /* vi: set sw=4 ts=4: */
3 * Mini DNS server implementation for busybox
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
9 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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/
16 * Some bugfix and minor changes was applied by Roberto A. Foglietta who made
17 * the first porting of oao' scdns to busybox also.
22 static const char *fileconf = "/etc/dnsd.conf";
23 #define LOCK_FILE "/var/run/dnsd.lock"
25 // Must match getopt32 call
26 #define OPT_daemon (option_mask32 & 0x10)
27 #define OPT_verbose (option_mask32 & 0x20)
33 MAX_HOST_LEN = 16, // longest host name allowed is 15
34 IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
36 //must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
37 MAX_NAME_LEN = (IP_STRING_LEN + 13),
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) + 2*type(4B) + 2*class(4B) +
42 ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
43 2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
45 MAX_PACK_LEN = 512 + 1,
47 DEFAULT_TTL = 30, // increase this when not testing?
53 struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
55 uint8_t *r; // resource
59 struct dns_head { // the message from client and first part of response mag
62 uint16_t nquer; // accepts 0
63 uint16_t nansw; // 1 in response
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];
78 static struct dns_entry *dnsentry = NULL;
79 static uint32_t ttl = DEFAULT_TTL;
82 * Convert host name from C-string to dns length/string.
84 static void convname(char *a, uint8_t *q)
86 int i = (q[0] == '.') ? 0 : 1;
87 for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
94 * Insert length of substrings instead of dots
96 static void undot(uint8_t * rip)
101 for (--i; i >= 0; i--) {
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 are not handled correctly.
114 * Presently the dot is copied into name without
115 * converting to a length/string substring for that label.
118 static int getfileentry(FILE * fp, struct dns_entry *s)
120 unsigned int a,b,c,d;
121 char *line, *r, *name;
124 line = r = xmalloc_fgets(fp);
127 while (*r == ' ' || *r == '\t') {
129 if (!*r || *r == '#' || *r == '\n') {
131 goto restart; /* skipping empty/blank and commented lines */
135 while (*r != ' ' && *r != '\t')
138 if (sscanf(r, "%u.%u.%u.%u", &a, &b, &c, &d) != 4) {
140 goto restart; /* skipping wrong lines */
143 sprintf(s->ip, "%u.%u.%u.%u", a, b, c, d);
144 sprintf(s->rip, ".%u.%u.%u.%u", d, c, b, a);
145 undot((uint8_t*)s->rip);
146 convname(s->name, (uint8_t*)name);
149 fprintf(stderr, "\tname:%s, ip:%s\n", &(s->name[1]),s->ip);
156 * Read hostname/IP records from file
158 static void dnsentryinit(void)
161 struct dns_entry *m, *prev;
163 prev = dnsentry = NULL;
164 fp = xfopen(fileconf, "r");
167 m = xzalloc(sizeof(*m));
169 if (getfileentry(fp, m))
182 * Look query up in dns records and return answer if found
183 * qs is the query string, first byte the string length
185 static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
188 struct dns_entry *d=dnsentry;
193 q = (char *)&(qs[1]);
195 fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
196 __FUNCTION__, (int)strlen(p), (int)(d->name[0]),
197 p, q, (int)strlen(q));
199 if (type == REQ_A) { /* search by host name */
200 for (i = 1; i <= (int)(d->name[0]); i++)
201 if (tolower(qs[i]) != d->name[i])
203 if (i > (int)(d->name[0])) {
205 fprintf(stderr, " OK");
207 strcpy((char *)as, d->ip);
209 fprintf(stderr, " as:%s\n", as);
214 if (type == REQ_PTR) { /* search by IP-address */
215 if (!strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) {
216 strcpy((char *)as, d->name);
227 * Decode message and generate answer
229 #define eret(s) do { fputs(s, stderr); return -1; } while (0)
230 static int process_packet(uint8_t * buf)
232 struct dns_head *head;
233 struct dns_prop *qprop;
234 struct dns_repl outr;
235 void *next, *from, *answb;
237 uint8_t answstr[MAX_NAME_LEN + 1];
238 int lookup_result, type, len, packet_len;
243 head = (struct dns_head *)buf;
244 if (head->nquer == 0)
245 eret("no queries\n");
247 if (head->flags & 0x8000)
248 eret("ignoring response packet\n");
250 from = (void *)&head[1]; // start of query string
251 next = answb = from + strlen((char *)from) + 1 + sizeof(struct dns_prop); // where to append answer block
253 outr.rlen = 0; // may change later
257 qprop = (struct dns_prop *)(answb - 4);
258 type = ntohs(qprop->type);
260 // only let REQ_A and REQ_PTR pass
261 if (!(type == REQ_A || type == REQ_PTR)) {
262 goto empty_packet; /* we can't handle the query type */
265 if (ntohs(qprop->class) != 1 /* class INET */ ) {
266 outr.flags = 4; /* not supported */
269 /* we only support standard queries */
271 if ((ntohs(head->flags) & 0x7800) != 0)
274 // We have a standard query
275 bb_info_msg("%s", (char *)from);
276 lookup_result = table_lookup(type, answstr, (uint8_t*)from);
277 if (lookup_result != 0) {
278 outr.flags = 3 | 0x0400; //name do not exist and auth
281 if (type == REQ_A) { // return an address
283 if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
284 outr.flags = 1; /* Frmt err */
287 memcpy(answstr, &a.s_addr, 4); // save before a disappears
288 outr.rlen = 4; // uint32_t IP
291 outr.rlen = strlen((char *)answstr) + 1; // a host name
292 outr.r = answstr; // 32 bit ip or a host name
293 outr.flags |= 0x0400; /* authority-bit */
295 head->nansw = htons(1);
297 // copy query block to answer block
299 memcpy(answb, from, len);
302 // and append answer rr
303 *(uint32_t *) next = htonl(ttl);
305 *(uint16_t *) next = htons(outr.rlen);
307 memcpy(next, (void *)answstr, outr.rlen);
312 flags = ntohs(head->flags);
313 // clear rcode and RA, set responsebit and our new flags
314 flags |= (outr.flags & 0xff80) | 0x8000;
315 head->flags = htons(flags);
316 head->nauth = head->nadd = htons(0);
317 head->nquer = htons(1);
319 packet_len = next - (void *)buf;
326 static void interrupt(int x)
329 bb_error_msg("interrupt, exiting\n");
333 int dnsd_main(int argc, char **argv)
335 char *listen_interface = NULL;
337 len_and_sockaddr *lsa;
340 uint8_t buf[MAX_PACK_LEN];
342 getopt32(argc, argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
343 //if (option_mask32 & 0x1) // -i
344 //if (option_mask32 & 0x2) // -c
345 if (option_mask32 & 0x4) // -t
346 ttl = xatou_range(sttl, 1, 0xffffffff);
347 if (option_mask32 & 0x8) // -p
348 port = xatou_range(sttl, 1, 0xffff);
351 bb_info_msg("listen_interface: %s", listen_interface);
352 bb_info_msg("ttl: %d, port: %d", ttl, port);
353 bb_info_msg("fileconf: %s", fileconf);
357 //FIXME: NOMMU will NOT set LOGMODE_SYSLOG!
359 /* reexec for vfork() do continue parent */
360 vfork_daemon_rexec(1, 0, argc, argv, "-d");
364 logmode = LOGMODE_SYSLOG;
369 signal(SIGINT, interrupt);
370 signal(SIGPIPE, SIG_IGN);
371 signal(SIGHUP, SIG_IGN);
373 signal(SIGTSTP, SIG_IGN);
376 signal(SIGURG, SIG_IGN);
379 lsa = host2sockaddr(listen_interface, port);
380 udps = xsocket(lsa->sa.sa_family, SOCK_DGRAM, 0);
381 xbind(udps, &lsa->sa, lsa->len);
382 // xlisten(udps, 50); - ?!! DGRAM sockets are never listened on I think?
383 bb_info_msg("Accepting UDP packets on %s",
384 xmalloc_sockaddr2dotted(&lsa->sa, lsa->len));
391 FD_SET(udps, &fdset);
392 // Block until a message arrives
393 // FIXME: Fantastic. select'ing on just one fd??
394 // Why no just block on it doing recvfrom() ?
395 r = select(udps + 1, &fdset, NULL, NULL, NULL);
397 bb_perror_msg_and_die("select error");
399 bb_perror_msg_and_die("select spurious return");
401 /* Can this test ever be false? - yes */
402 if (FD_ISSET(udps, &fdset)) {
403 socklen_t fromlen = lsa->len;
404 // FIXME: need to get *DEST* address (to which of our addresses
405 // this query was directed), and reply from the same address.
406 // Or else we can exhibit usual UDP ugliness:
407 // [ip1.multihomed.ip2] <= query to ip1 <= peer
408 // [ip1.multihomed.ip2] => reply from ip2 => peer (confused)
409 r = recvfrom(udps, buf, sizeof(buf), 0, &lsa->sa, &fromlen);
411 bb_info_msg("Got UDP packet");
413 if (r < 12 || r > 512) {
414 bb_error_msg("invalid packet size");
419 r = process_packet(buf);
422 sendto(udps, buf, r, 0, &lsa->sa, fromlen);