Contents of /trunk/mkinitrd-magellan/busybox/networking/dnsd.c
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Wed Aug 18 21:56:57 2010 UTC (14 years, 1 month ago) by niro
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Wed Aug 18 21:56:57 2010 UTC (14 years, 1 month ago) by niro
File MIME type: text/plain
File size: 17984 byte(s)
-updated to busybox-1.17.1
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 | /* can tweak this */ |
28 | DEFAULT_TTL = 120, |
29 | |
30 | /* cannot get bigger packets than 512 per RFC1035. */ |
31 | MAX_PACK_LEN = 512, |
32 | IP_STRING_LEN = sizeof(".xxx.xxx.xxx.xxx"), |
33 | MAX_NAME_LEN = IP_STRING_LEN - 1 + sizeof(".in-addr.arpa"), |
34 | REQ_A = 1, |
35 | REQ_PTR = 12, |
36 | }; |
37 | |
38 | /* the message from client and first part of response msg */ |
39 | struct dns_head { |
40 | uint16_t id; |
41 | uint16_t flags; |
42 | uint16_t nquer; |
43 | uint16_t nansw; |
44 | uint16_t nauth; |
45 | uint16_t nadd; |
46 | }; |
47 | /* Structure used to access type and class fields. |
48 | * They are totally unaligned, but gcc 4.3.4 thinks that pointer of type uint16_t* |
49 | * is 16-bit aligned and replaces 16-bit memcpy (in move_from_unaligned16 macro) |
50 | * with aligned halfword access on arm920t! |
51 | * Oh well. Slapping PACKED everywhere seems to help: */ |
52 | struct type_and_class { |
53 | uint16_t type PACKED; |
54 | uint16_t class PACKED; |
55 | } PACKED; |
56 | /* element of known name, ip address and reversed ip address */ |
57 | struct dns_entry { |
58 | struct dns_entry *next; |
59 | uint32_t ip; |
60 | char rip[IP_STRING_LEN]; /* length decimal reversed IP */ |
61 | char name[1]; |
62 | }; |
63 | |
64 | #define OPT_verbose (option_mask32 & 1) |
65 | #define OPT_silent (option_mask32 & 2) |
66 | |
67 | |
68 | /* |
69 | * Insert length of substrings instead of dots |
70 | */ |
71 | static void undot(char *rip) |
72 | { |
73 | int i = 0; |
74 | int s = 0; |
75 | |
76 | while (rip[i]) |
77 | i++; |
78 | for (--i; i >= 0; i--) { |
79 | if (rip[i] == '.') { |
80 | rip[i] = s; |
81 | s = 0; |
82 | } else { |
83 | s++; |
84 | } |
85 | } |
86 | } |
87 | |
88 | /* |
89 | * Read hostname/IP records from file |
90 | */ |
91 | static struct dns_entry *parse_conf_file(const char *fileconf) |
92 | { |
93 | char *token[2]; |
94 | parser_t *parser; |
95 | struct dns_entry *m, *conf_data; |
96 | struct dns_entry **nextp; |
97 | |
98 | conf_data = NULL; |
99 | nextp = &conf_data; |
100 | |
101 | parser = config_open(fileconf); |
102 | while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) { |
103 | struct in_addr ip; |
104 | uint32_t v32; |
105 | |
106 | if (inet_aton(token[1], &ip) == 0) { |
107 | bb_error_msg("error at line %u, skipping", parser->lineno); |
108 | continue; |
109 | } |
110 | |
111 | if (OPT_verbose) |
112 | bb_error_msg("name:%s, ip:%s", token[0], token[1]); |
113 | |
114 | /* sizeof(*m) includes 1 byte for m->name[0] */ |
115 | m = xzalloc(sizeof(*m) + strlen(token[0]) + 1); |
116 | /*m->next = NULL;*/ |
117 | *nextp = m; |
118 | nextp = &m->next; |
119 | |
120 | m->name[0] = '.'; |
121 | strcpy(m->name + 1, token[0]); |
122 | undot(m->name); |
123 | m->ip = ip.s_addr; /* in network order */ |
124 | v32 = ntohl(m->ip); |
125 | /* inverted order */ |
126 | sprintf(m->rip, ".%u.%u.%u.%u", |
127 | (uint8_t)(v32), |
128 | (uint8_t)(v32 >> 8), |
129 | (uint8_t)(v32 >> 16), |
130 | (v32 >> 24) |
131 | ); |
132 | undot(m->rip); |
133 | } |
134 | config_close(parser); |
135 | return conf_data; |
136 | } |
137 | |
138 | /* |
139 | * Look query up in dns records and return answer if found. |
140 | */ |
141 | static char *table_lookup(struct dns_entry *d, |
142 | uint16_t type, |
143 | char* query_string) |
144 | { |
145 | while (d) { |
146 | unsigned len = d->name[0]; |
147 | /* d->name[len] is the last (non NUL) char */ |
148 | #if DEBUG |
149 | char *p, *q; |
150 | q = query_string + 1; |
151 | p = d->name + 1; |
152 | fprintf(stderr, "%d/%d p:%s q:%s %d\n", |
153 | (int)strlen(p), len, |
154 | p, q, (int)strlen(q) |
155 | ); |
156 | #endif |
157 | if (type == htons(REQ_A)) { |
158 | /* search by host name */ |
159 | if (len != 1 || d->name[1] != '*') { |
160 | /* we are lax, hope no name component is ever >64 so that length |
161 | * (which will be represented as 'A','B'...) matches a lowercase letter. |
162 | * Actually, I think false matches are hard to construct. |
163 | * Example. |
164 | * [31] len is represented as '1', [65] as 'A', [65+32] as 'a'. |
165 | * [65] <65 same chars>[31]<31 same chars>NUL |
166 | * [65+32]<65 same chars>1 <31 same chars>NUL |
167 | * This example seems to be the minimal case when false match occurs. |
168 | */ |
169 | if (strcasecmp(d->name, query_string) != 0) |
170 | goto next; |
171 | } |
172 | return (char *)&d->ip; |
173 | #if DEBUG |
174 | fprintf(stderr, "Found IP:%x\n", (int)d->ip); |
175 | #endif |
176 | return 0; |
177 | } |
178 | /* search by IP-address */ |
179 | if ((len != 1 || d->name[1] != '*') |
180 | /* we assume (do not check) that query_string |
181 | * ends in ".in-addr.arpa" */ |
182 | && strncmp(d->rip, query_string, strlen(d->rip)) == 0 |
183 | ) { |
184 | #if DEBUG |
185 | fprintf(stderr, "Found name:%s\n", d->name); |
186 | #endif |
187 | return d->name; |
188 | } |
189 | next: |
190 | d = d->next; |
191 | } |
192 | |
193 | return NULL; |
194 | } |
195 | |
196 | /* |
197 | * Decode message and generate answer |
198 | */ |
199 | /* RFC 1035 |
200 | ... |
201 | Whenever an octet represents a numeric quantity, the left most bit |
202 | in the diagram is the high order or most significant bit. |
203 | That is, the bit labeled 0 is the most significant bit. |
204 | ... |
205 | |
206 | 4.1.1. Header section format |
207 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
208 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
209 | | ID | |
210 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
211 | |QR| OPCODE |AA|TC|RD|RA| 0 0 0| RCODE | |
212 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
213 | | QDCOUNT | |
214 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
215 | | ANCOUNT | |
216 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
217 | | NSCOUNT | |
218 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
219 | | ARCOUNT | |
220 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
221 | ID 16 bit random identifier assigned by querying peer. |
222 | Used to match query/response. |
223 | QR message is a query (0), or a response (1). |
224 | OPCODE 0 standard query (QUERY) |
225 | 1 inverse query (IQUERY) |
226 | 2 server status request (STATUS) |
227 | AA Authoritative Answer - this bit is valid in responses. |
228 | Responding name server is an authority for the domain name |
229 | in question section. Answer section may have multiple owner names |
230 | because of aliases. The AA bit corresponds to the name which matches |
231 | the query name, or the first owner name in the answer section. |
232 | TC TrunCation - this message was truncated. |
233 | RD Recursion Desired - this bit may be set in a query and |
234 | is copied into the response. If RD is set, it directs |
235 | the name server to pursue the query recursively. |
236 | Recursive query support is optional. |
237 | RA Recursion Available - this be is set or cleared in a |
238 | response, and denotes whether recursive query support is |
239 | available in the name server. |
240 | RCODE Response code. |
241 | 0 No error condition |
242 | 1 Format error |
243 | 2 Server failure - server was unable to process the query |
244 | due to a problem with the name server. |
245 | 3 Name Error - meaningful only for responses from |
246 | an authoritative name server. The referenced domain name |
247 | does not exist. |
248 | 4 Not Implemented. |
249 | 5 Refused. |
250 | QDCOUNT number of entries in the question section. |
251 | ANCOUNT number of records in the answer section. |
252 | NSCOUNT number of records in the authority records section. |
253 | ARCOUNT number of records in the additional records section. |
254 | |
255 | 4.1.2. Question section format |
256 | |
257 | The section contains QDCOUNT (usually 1) entries, each of this format: |
258 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
259 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
260 | / QNAME / |
261 | / / |
262 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
263 | | QTYPE | |
264 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
265 | | QCLASS | |
266 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
267 | QNAME a domain name represented as a sequence of labels, where |
268 | each label consists of a length octet followed by that |
269 | number of octets. The domain name terminates with the |
270 | zero length octet for the null label of the root. Note |
271 | that this field may be an odd number of octets; no |
272 | padding is used. |
273 | QTYPE a two octet type of the query. |
274 | 1 a host address [REQ_A const] |
275 | 2 an authoritative name server |
276 | 3 a mail destination (Obsolete - use MX) |
277 | 4 a mail forwarder (Obsolete - use MX) |
278 | 5 the canonical name for an alias |
279 | 6 marks the start of a zone of authority |
280 | 7 a mailbox domain name (EXPERIMENTAL) |
281 | 8 a mail group member (EXPERIMENTAL) |
282 | 9 a mail rename domain name (EXPERIMENTAL) |
283 | 10 a null RR (EXPERIMENTAL) |
284 | 11 a well known service description |
285 | 12 a domain name pointer [REQ_PTR const] |
286 | 13 host information |
287 | 14 mailbox or mail list information |
288 | 15 mail exchange |
289 | 16 text strings |
290 | 0x1c IPv6? |
291 | 252 a request for a transfer of an entire zone |
292 | 253 a request for mailbox-related records (MB, MG or MR) |
293 | 254 a request for mail agent RRs (Obsolete - see MX) |
294 | 255 a request for all records |
295 | QCLASS a two octet code that specifies the class of the query. |
296 | 1 the Internet |
297 | (others are historic only) |
298 | 255 any class |
299 | |
300 | 4.1.3. Resource Record format |
301 | |
302 | The answer, authority, and additional sections all share the same format: |
303 | a variable number of resource records, where the number of records |
304 | is specified in the corresponding count field in the header. |
305 | Each resource record has this format: |
306 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
307 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
308 | / / |
309 | / NAME / |
310 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
311 | | TYPE | |
312 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
313 | | CLASS | |
314 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
315 | | TTL | |
316 | | | |
317 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
318 | | RDLENGTH | |
319 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| |
320 | / RDATA / |
321 | / / |
322 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
323 | NAME a domain name to which this resource record pertains. |
324 | TYPE two octets containing one of the RR type codes. This |
325 | field specifies the meaning of the data in the RDATA field. |
326 | CLASS two octets which specify the class of the data in the RDATA field. |
327 | TTL a 32 bit unsigned integer that specifies the time interval |
328 | (in seconds) that the record may be cached. |
329 | RDLENGTH a 16 bit integer, length in octets of the RDATA field. |
330 | RDATA a variable length string of octets that describes the resource. |
331 | The format of this information varies according to the TYPE |
332 | and CLASS of the resource record. |
333 | If the TYPE is A and the CLASS is IN, it's a 4 octet IP address. |
334 | |
335 | 4.1.4. Message compression |
336 | |
337 | In order to reduce the size of messages, domain names coan be compressed. |
338 | An entire domain name or a list of labels at the end of a domain name |
339 | is replaced with a pointer to a prior occurance of the same name. |
340 | |
341 | The pointer takes the form of a two octet sequence: |
342 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
343 | | 1 1| OFFSET | |
344 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
345 | The first two bits are ones. This allows a pointer to be distinguished |
346 | from a label, since the label must begin with two zero bits because |
347 | labels are restricted to 63 octets or less. The OFFSET field specifies |
348 | an offset from the start of the message (i.e., the first octet |
349 | of the ID field in the domain header). |
350 | A zero offset specifies the first byte of the ID field, etc. |
351 | Domain name in a message can be represented as either: |
352 | - a sequence of labels ending in a zero octet |
353 | - a pointer |
354 | - a sequence of labels ending with a pointer |
355 | */ |
356 | static int process_packet(struct dns_entry *conf_data, |
357 | uint32_t conf_ttl, |
358 | uint8_t *buf) |
359 | { |
360 | struct dns_head *head; |
361 | struct type_and_class *unaligned_type_class; |
362 | const char *err_msg; |
363 | char *query_string; |
364 | char *answstr; |
365 | uint8_t *answb; |
366 | uint16_t outr_rlen; |
367 | uint16_t outr_flags; |
368 | uint16_t type; |
369 | uint16_t class; |
370 | int query_len; |
371 | |
372 | head = (struct dns_head *)buf; |
373 | if (head->nquer == 0) { |
374 | bb_error_msg("packet has 0 queries, ignored"); |
375 | return 0; /* don't reply */ |
376 | } |
377 | if (head->flags & htons(0x8000)) { /* QR bit */ |
378 | bb_error_msg("response packet, ignored"); |
379 | return 0; /* don't reply */ |
380 | } |
381 | /* QR = 1 "response", RCODE = 4 "Not Implemented" */ |
382 | outr_flags = htons(0x8000 | 4); |
383 | err_msg = NULL; |
384 | |
385 | /* start of query string */ |
386 | query_string = (void *)(head + 1); |
387 | /* caller guarantees strlen is <= MAX_PACK_LEN */ |
388 | query_len = strlen(query_string) + 1; |
389 | /* may be unaligned! */ |
390 | unaligned_type_class = (void *)(query_string + query_len); |
391 | query_len += sizeof(unaligned_type_class); |
392 | /* where to append answer block */ |
393 | answb = (void *)(unaligned_type_class + 1); |
394 | |
395 | /* OPCODE != 0 "standard query"? */ |
396 | if ((head->flags & htons(0x7800)) != 0) { |
397 | err_msg = "opcode != 0"; |
398 | goto empty_packet; |
399 | } |
400 | move_from_unaligned16(class, &unaligned_type_class->class); |
401 | if (class != htons(1)) { /* not class INET? */ |
402 | err_msg = "class != 1"; |
403 | goto empty_packet; |
404 | } |
405 | move_from_unaligned16(type, &unaligned_type_class->type); |
406 | if (type != htons(REQ_A) && type != htons(REQ_PTR)) { |
407 | /* we can't handle this query type */ |
408 | //TODO: happens all the time with REQ_AAAA (0x1c) requests - implement those? |
409 | err_msg = "type is !REQ_A and !REQ_PTR"; |
410 | goto empty_packet; |
411 | } |
412 | |
413 | /* look up the name */ |
414 | answstr = table_lookup(conf_data, type, query_string); |
415 | #if DEBUG |
416 | /* Shows lengths instead of dots, unusable for !DEBUG */ |
417 | bb_error_msg("'%s'->'%s'", query_string, answstr); |
418 | #endif |
419 | outr_rlen = 4; |
420 | if (answstr && type == htons(REQ_PTR)) { |
421 | /* returning a host name */ |
422 | outr_rlen = strlen(answstr) + 1; |
423 | } |
424 | if (!answstr |
425 | || (unsigned)(answb - buf) + query_len + 4 + 2 + outr_rlen > MAX_PACK_LEN |
426 | ) { |
427 | /* QR = 1 "response" |
428 | * AA = 1 "Authoritative Answer" |
429 | * RCODE = 3 "Name Error" */ |
430 | err_msg = "name is not found"; |
431 | outr_flags = htons(0x8000 | 0x0400 | 3); |
432 | goto empty_packet; |
433 | } |
434 | |
435 | /* Append answer Resource Record */ |
436 | memcpy(answb, query_string, query_len); /* name, type, class */ |
437 | answb += query_len; |
438 | move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl)); |
439 | answb += 4; |
440 | move_to_unaligned16((uint16_t *)answb, htons(outr_rlen)); |
441 | answb += 2; |
442 | memcpy(answb, answstr, outr_rlen); |
443 | answb += outr_rlen; |
444 | |
445 | /* QR = 1 "response", |
446 | * AA = 1 "Authoritative Answer", |
447 | * TODO: need to set RA bit 0x80? One user says nslookup complains |
448 | * "Got recursion not available from SERVER, trying next server" |
449 | * "** server can't find HOSTNAME" |
450 | * RCODE = 0 "success" |
451 | */ |
452 | if (OPT_verbose) |
453 | bb_error_msg("returning positive reply"); |
454 | outr_flags = htons(0x8000 | 0x0400 | 0); |
455 | /* we have one answer */ |
456 | head->nansw = htons(1); |
457 | |
458 | empty_packet: |
459 | if ((outr_flags & htons(0xf)) != 0) { /* not a positive response */ |
460 | if (OPT_verbose) { |
461 | bb_error_msg("%s, %s", |
462 | err_msg, |
463 | OPT_silent ? "dropping query" : "sending error reply" |
464 | ); |
465 | } |
466 | if (OPT_silent) |
467 | return 0; |
468 | } |
469 | head->flags |= outr_flags; |
470 | head->nauth = head->nadd = 0; |
471 | head->nquer = htons(1); // why??? |
472 | |
473 | return answb - buf; |
474 | } |
475 | |
476 | int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
477 | int dnsd_main(int argc UNUSED_PARAM, char **argv) |
478 | { |
479 | const char *listen_interface = "0.0.0.0"; |
480 | const char *fileconf = "/etc/dnsd.conf"; |
481 | struct dns_entry *conf_data; |
482 | uint32_t conf_ttl = DEFAULT_TTL; |
483 | char *sttl, *sport; |
484 | len_and_sockaddr *lsa, *from, *to; |
485 | unsigned lsa_size; |
486 | int udps, opts; |
487 | uint16_t port = 53; |
488 | /* Ensure buf is 32bit aligned (we need 16bit, but 32bit can't hurt) */ |
489 | uint8_t buf[MAX_PACK_LEN + 1] ALIGN4; |
490 | |
491 | opts = getopt32(argv, "vsi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport); |
492 | //if (opts & (1 << 0)) // -v |
493 | //if (opts & (1 << 1)) // -s |
494 | //if (opts & (1 << 2)) // -i |
495 | //if (opts & (1 << 3)) // -c |
496 | if (opts & (1 << 4)) // -t |
497 | conf_ttl = xatou_range(sttl, 1, 0xffffffff); |
498 | if (opts & (1 << 5)) // -p |
499 | port = xatou_range(sport, 1, 0xffff); |
500 | if (opts & (1 << 6)) { // -d |
501 | bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv); |
502 | openlog(applet_name, LOG_PID, LOG_DAEMON); |
503 | logmode = LOGMODE_SYSLOG; |
504 | } |
505 | |
506 | conf_data = parse_conf_file(fileconf); |
507 | |
508 | lsa = xdotted2sockaddr(listen_interface, port); |
509 | udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0); |
510 | xbind(udps, &lsa->u.sa, lsa->len); |
511 | socket_want_pktinfo(udps); /* needed for recv_from_to to work */ |
512 | lsa_size = LSA_LEN_SIZE + lsa->len; |
513 | from = xzalloc(lsa_size); |
514 | to = xzalloc(lsa_size); |
515 | |
516 | { |
517 | char *p = xmalloc_sockaddr2dotted(&lsa->u.sa); |
518 | bb_error_msg("accepting UDP packets on %s", p); |
519 | free(p); |
520 | } |
521 | |
522 | while (1) { |
523 | int r; |
524 | /* Try to get *DEST* address (to which of our addresses |
525 | * this query was directed), and reply from the same address. |
526 | * Or else we can exhibit usual UDP ugliness: |
527 | * [ip1.multihomed.ip2] <= query to ip1 <= peer |
528 | * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */ |
529 | memcpy(to, lsa, lsa_size); |
530 | r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len); |
531 | if (r < 12 || r > MAX_PACK_LEN) { |
532 | bb_error_msg("packet size %d, ignored", r); |
533 | continue; |
534 | } |
535 | if (OPT_verbose) |
536 | bb_error_msg("got UDP packet"); |
537 | buf[r] = '\0'; /* paranoia */ |
538 | r = process_packet(conf_data, conf_ttl, buf); |
539 | if (r <= 0) |
540 | continue; |
541 | send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len); |
542 | } |
543 | return 0; |
544 | } |