Contents of /tags/mkinitrd-6_1_1/busybox/networking/dnsd.c
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Mon May 4 16:31:54 2009 UTC (15 years, 4 months ago) by niro
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Mon May 4 16:31:54 2009 UTC (15 years, 4 months ago) by niro
File MIME type: text/plain
File size: 9893 byte(s)
tagged 'mkinitrd-6_1_1'
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) + 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 |
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 | } |