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.
27 MAX_HOST_LEN = 16, // longest host name allowed is 15
28 IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
30 //must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
31 MAX_NAME_LEN = (IP_STRING_LEN + 13),
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) + 2*type(4B) + 2*class(4B) +
36 ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
37 2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
41 DEFAULT_TTL = 30, // increase this when not testing?
47 struct dns_head { // the message from client and first part of response mag
50 uint16_t nquer; // accepts 0
51 uint16_t nansw; // 1 in response
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];
66 #define OPT_verbose (option_mask32)
70 * Convert host name from C-string to dns length/string.
72 static void convname(char *a, uint8_t *q)
74 int i = (q[0] == '.') ? 0 : 1;
75 for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
82 * Insert length of substrings instead of dots
84 static void undot(uint8_t *rip)
89 for (--i; i >= 0; i--) {
98 * Read hostname/IP records from file
100 static struct dns_entry *parse_conf_file(const char *fileconf)
104 struct dns_entry *m, *prev, *conf_data;
106 prev = conf_data = NULL;
107 parser = config_open(fileconf);
108 while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
111 * Assumes all host names are lower case only
112 * Hostnames with more than one label are not handled correctly.
113 * Presently the dot is copied into name without
114 * converting to a length/string substring for that label.
116 // if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
117 if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
120 m = xzalloc(sizeof(*m));
122 sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
123 sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
124 undot((uint8_t*)m->rip);
125 convname(m->name, (uint8_t*)token[0]);
128 bb_error_msg("name:%s, ip:%s", &(m->name[1]), m->ip);
136 config_close(parser);
141 * Look query up in dns records and return answer if found
142 * qs is the query string, first byte the string length
144 static int table_lookup(struct dns_entry *d, uint16_t type, uint8_t *as, uint8_t *qs)
151 q = (char *)&(qs[1]);
153 fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
154 __FUNCTION__, (int)strlen(p), (int)(d->name[0]),
155 p, q, (int)strlen(q));
158 /* search by host name */
159 for (i = 1; i <= (int)(d->name[0]); i++)
160 if (tolower(qs[i]) != d->name[i])
162 if (i > (int)(d->name[0])
163 || (d->name[0] == 1 && d->name[1] == '*')
165 strcpy((char *)as, d->ip);
167 fprintf(stderr, " OK as:%s\n", as);
171 } else if (type == REQ_PTR) {
172 /* search by IP-address */
173 if ((d->name[0] != 1 || d->name[1] != '*')
174 && !strncmp(d->rip + 1, (char*)qs + 1, strlen(d->rip)-1)
176 strcpy((char *)as, d->name);
186 * Decode message and generate answer
188 static int process_packet(struct dns_entry *conf_data, uint32_t conf_ttl, uint8_t *buf)
190 uint8_t answstr[MAX_NAME_LEN + 1];
191 struct dns_head *head;
192 struct dns_prop *qprop;
193 uint8_t *from, *answb;
197 int lookup_result, type, packet_len;
202 head = (struct dns_head *)buf;
203 if (head->nquer == 0) {
204 bb_error_msg("no queries");
208 if (head->flags & 0x8000) {
209 bb_error_msg("ignoring response packet");
213 from = (void *)&head[1]; // start of query string
214 //FIXME: strlen of untrusted data??!
215 querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
216 answb = from + querystr_len; // where to append answer block
221 qprop = (struct dns_prop *)(answb - 4);
222 type = ntohs(qprop->type);
224 // only let REQ_A and REQ_PTR pass
225 if (!(type == REQ_A || type == REQ_PTR)) {
226 goto empty_packet; /* we can't handle the query type */
229 if (ntohs(qprop->class) != 1 /* class INET */ ) {
230 outr_flags = 4; /* not supported */
233 /* we only support standard queries */
235 if ((ntohs(head->flags) & 0x7800) != 0)
238 // We have a standard query
239 bb_info_msg("%s", (char *)from);
240 lookup_result = table_lookup(conf_data, type, answstr, from);
241 if (lookup_result != 0) {
242 outr_flags = 3 | 0x0400; // name do not exist and auth
245 if (type == REQ_A) { // return an address
246 struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
248 if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
249 outr_flags = 1; /* Frmt err */
252 v32 = a.s_addr; /* in case long != int */
253 move_to_unaligned32(answstr, v32);
254 outr_rlen = 4; // uint32_t IP
256 outr_rlen = strlen((char *)answstr) + 1; // a host name
257 outr_flags |= 0x0400; /* authority-bit */
259 head->nansw = htons(1);
261 // copy query block to answer block
262 memcpy(answb, from, querystr_len);
263 answb += querystr_len;
265 // and append answer rr
266 // FIXME: unaligned accesses??
267 *(uint32_t *) answb = htonl(conf_ttl);
269 *(uint16_t *) answb = htons(outr_rlen);
271 memcpy(answb, answstr, outr_rlen);
276 flags = ntohs(head->flags);
277 // clear rcode and RA, set responsebit and our new flags
278 flags |= (outr_flags & 0xff80) | 0x8000;
279 head->flags = htons(flags);
280 head->nauth = head->nadd = 0;
281 head->nquer = htons(1);
283 packet_len = answb - buf;
290 //static void interrupt(int sig)
292 // /* unlink("/var/run/dnsd.lock"); */
293 // bb_error_msg("interrupt, exiting\n");
294 // kill_myself_with_sig(sig);
297 int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
298 int dnsd_main(int argc UNUSED_PARAM, char **argv)
300 const char *listen_interface = "0.0.0.0";
301 const char *fileconf = "/etc/dnsd.conf";
302 struct dns_entry *conf_data;
303 uint32_t conf_ttl = DEFAULT_TTL;
305 len_and_sockaddr *lsa, *from, *to;
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)];
313 opts = getopt32(argv, "vi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport);
314 //if (opts & 0x1) // -v
315 //if (opts & 0x2) // -i
316 //if (opts & 0x4) // -c
317 if (opts & 0x8) // -t
318 conf_ttl = xatou_range(sttl, 1, 0xffffffff);
319 if (opts & 0x10) // -p
320 port = xatou_range(sport, 1, 0xffff);
321 if (opts & 0x20) { // -d
322 bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
323 openlog(applet_name, LOG_PID, LOG_DAEMON);
324 logmode = LOGMODE_SYSLOG;
326 /* Clear all except "verbose" bit */
329 conf_data = parse_conf_file(fileconf);
331 // signal(SIGINT, interrupt); - just for one message?
333 /* why? + (1 << SIGPIPE) */
343 lsa = xdotted2sockaddr(listen_interface, port);
344 udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
345 xbind(udps, &lsa->u.sa, lsa->len);
346 socket_want_pktinfo(udps); /* needed for recv_from_to to work */
347 lsa_size = LSA_LEN_SIZE + lsa->len;
348 from = xzalloc(lsa_size);
349 to = xzalloc(lsa_size);
351 bb_info_msg("Accepting UDP packets on %s",
352 xmalloc_sockaddr2dotted(&lsa->u.sa));
356 /* Try to get *DEST* address (to which of our addresses
357 * this query was directed), and reply from the same address.
358 * Or else we can exhibit usual UDP ugliness:
359 * [ip1.multihomed.ip2] <= query to ip1 <= peer
360 * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
361 memcpy(to, lsa, lsa_size);
362 r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
363 if (r < 12 || r > MAX_PACK_LEN) {
364 bb_error_msg("invalid packet size");
368 bb_info_msg("Got UDP packet");
369 buf[r] = '\0'; /* paranoia */
370 r = process_packet(conf_data, conf_ttl, buf);
373 send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len);