Contents of /tags/mkinitrd-6_2_3/busybox/networking/dnsd.c
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Mon May 31 20:54:44 2010 UTC (14 years, 3 months ago) by niro
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Mon May 31 20:54:44 2010 UTC (14 years, 3 months ago) by niro
File MIME type: text/plain
File size: 17184 byte(s)
tagged 'mkinitrd-6_2_3'
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 dns_prop { |
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) |
65 | |
66 | |
67 | /* |
68 | * Insert length of substrings instead of dots |
69 | */ |
70 | static void undot(char *rip) |
71 | { |
72 | int i = 0; |
73 | int s = 0; |
74 | |
75 | while (rip[i]) |
76 | i++; |
77 | for (--i; i >= 0; i--) { |
78 | if (rip[i] == '.') { |
79 | rip[i] = s; |
80 | s = 0; |
81 | } else { |
82 | s++; |
83 | } |
84 | } |
85 | } |
86 | |
87 | /* |
88 | * Read hostname/IP records from file |
89 | */ |
90 | static struct dns_entry *parse_conf_file(const char *fileconf) |
91 | { |
92 | char *token[2]; |
93 | parser_t *parser; |
94 | struct dns_entry *m, *conf_data; |
95 | struct dns_entry **nextp; |
96 | |
97 | conf_data = NULL; |
98 | nextp = &conf_data; |
99 | |
100 | parser = config_open(fileconf); |
101 | while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) { |
102 | struct in_addr ip; |
103 | uint32_t v32; |
104 | |
105 | if (inet_aton(token[1], &ip) == 0) { |
106 | bb_error_msg("error at line %u, skipping", parser->lineno); |
107 | continue; |
108 | } |
109 | |
110 | if (OPT_verbose) |
111 | bb_error_msg("name:%s, ip:%s", token[0], token[1]); |
112 | |
113 | /* sizeof(*m) includes 1 byte for m->name[0] */ |
114 | m = xzalloc(sizeof(*m) + strlen(token[0]) + 1); |
115 | /*m->next = NULL;*/ |
116 | *nextp = m; |
117 | nextp = &m->next; |
118 | |
119 | m->name[0] = '.'; |
120 | strcpy(m->name + 1, token[0]); |
121 | undot(m->name); |
122 | m->ip = ip.s_addr; /* in network order */ |
123 | v32 = ntohl(m->ip); |
124 | /* inverted order */ |
125 | sprintf(m->rip, ".%u.%u.%u.%u", |
126 | (uint8_t)(v32), |
127 | (uint8_t)(v32 >> 8), |
128 | (uint8_t)(v32 >> 16), |
129 | (v32 >> 24) |
130 | ); |
131 | undot(m->rip); |
132 | } |
133 | config_close(parser); |
134 | return conf_data; |
135 | } |
136 | |
137 | /* |
138 | * Look query up in dns records and return answer if found. |
139 | */ |
140 | static char *table_lookup(struct dns_entry *d, |
141 | uint16_t type, |
142 | char* query_string) |
143 | { |
144 | while (d) { |
145 | unsigned len = d->name[0]; |
146 | /* d->name[len] is the last (non NUL) char */ |
147 | #if DEBUG |
148 | char *p, *q; |
149 | q = query_string + 1; |
150 | p = d->name + 1; |
151 | fprintf(stderr, "%d/%d p:%s q:%s %d\n", |
152 | (int)strlen(p), len, |
153 | p, q, (int)strlen(q) |
154 | ); |
155 | #endif |
156 | if (type == htons(REQ_A)) { |
157 | /* search by host name */ |
158 | if (len != 1 || d->name[1] != '*') { |
159 | /* we are lax, hope no name component is ever >64 so that length |
160 | * (which will be represented as 'A','B'...) matches a lowercase letter. |
161 | * Actually, I think false matches are hard to construct. |
162 | * Example. |
163 | * [31] len is represented as '1', [65] as 'A', [65+32] as 'a'. |
164 | * [65] <65 same chars>[31]<31 same chars>NUL |
165 | * [65+32]<65 same chars>1 <31 same chars>NUL |
166 | * This example seems to be the minimal case when false match occurs. |
167 | */ |
168 | if (strcasecmp(d->name, query_string) != 0) |
169 | goto next; |
170 | } |
171 | return (char *)&d->ip; |
172 | #if DEBUG |
173 | fprintf(stderr, "Found IP:%x\n", (int)d->ip); |
174 | #endif |
175 | return 0; |
176 | } |
177 | /* search by IP-address */ |
178 | if ((len != 1 || d->name[1] != '*') |
179 | /* we assume (do not check) that query_string |
180 | * ends in ".in-addr.arpa" */ |
181 | && strncmp(d->rip, query_string, strlen(d->rip)) == 0 |
182 | ) { |
183 | #if DEBUG |
184 | fprintf(stderr, "Found name:%s\n", d->name); |
185 | #endif |
186 | return d->name; |
187 | } |
188 | next: |
189 | d = d->next; |
190 | } |
191 | |
192 | return NULL; |
193 | } |
194 | |
195 | /* |
196 | * Decode message and generate answer |
197 | */ |
198 | /* RFC 1035 |
199 | ... |
200 | Whenever an octet represents a numeric quantity, the left most bit |
201 | in the diagram is the high order or most significant bit. |
202 | That is, the bit labeled 0 is the most significant bit. |
203 | ... |
204 | |
205 | 4.1.1. Header section format |
206 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
207 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
208 | | ID | |
209 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
210 | |QR| OPCODE |AA|TC|RD|RA| 0 0 0| RCODE | |
211 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
212 | | QDCOUNT | |
213 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
214 | | ANCOUNT | |
215 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
216 | | NSCOUNT | |
217 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
218 | | ARCOUNT | |
219 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
220 | ID 16 bit random identifier assigned by querying peer. |
221 | Used to match query/response. |
222 | QR message is a query (0), or a response (1). |
223 | OPCODE 0 standard query (QUERY) |
224 | 1 inverse query (IQUERY) |
225 | 2 server status request (STATUS) |
226 | AA Authoritative Answer - this bit is valid in responses. |
227 | Responding name server is an authority for the domain name |
228 | in question section. Answer section may have multiple owner names |
229 | because of aliases. The AA bit corresponds to the name which matches |
230 | the query name, or the first owner name in the answer section. |
231 | TC TrunCation - this message was truncated. |
232 | RD Recursion Desired - this bit may be set in a query and |
233 | is copied into the response. If RD is set, it directs |
234 | the name server to pursue the query recursively. |
235 | Recursive query support is optional. |
236 | RA Recursion Available - this be is set or cleared in a |
237 | response, and denotes whether recursive query support is |
238 | available in the name server. |
239 | RCODE Response code. |
240 | 0 No error condition |
241 | 1 Format error |
242 | 2 Server failure - server was unable to process the query |
243 | due to a problem with the name server. |
244 | 3 Name Error - meaningful only for responses from |
245 | an authoritative name server. The referenced domain name |
246 | does not exist. |
247 | 4 Not Implemented. |
248 | 5 Refused. |
249 | QDCOUNT number of entries in the question section. |
250 | ANCOUNT number of records in the answer section. |
251 | NSCOUNT number of records in the authority records section. |
252 | ARCOUNT number of records in the additional records section. |
253 | |
254 | 4.1.2. Question section format |
255 | |
256 | The section contains QDCOUNT (usually 1) entries, each of this format: |
257 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
258 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
259 | / QNAME / |
260 | / / |
261 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
262 | | QTYPE | |
263 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
264 | | QCLASS | |
265 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
266 | QNAME a domain name represented as a sequence of labels, where |
267 | each label consists of a length octet followed by that |
268 | number of octets. The domain name terminates with the |
269 | zero length octet for the null label of the root. Note |
270 | that this field may be an odd number of octets; no |
271 | padding is used. |
272 | QTYPE a two octet type of the query. |
273 | 1 a host address [REQ_A const] |
274 | 2 an authoritative name server |
275 | 3 a mail destination (Obsolete - use MX) |
276 | 4 a mail forwarder (Obsolete - use MX) |
277 | 5 the canonical name for an alias |
278 | 6 marks the start of a zone of authority |
279 | 7 a mailbox domain name (EXPERIMENTAL) |
280 | 8 a mail group member (EXPERIMENTAL) |
281 | 9 a mail rename domain name (EXPERIMENTAL) |
282 | 10 a null RR (EXPERIMENTAL) |
283 | 11 a well known service description |
284 | 12 a domain name pointer [REQ_PTR const] |
285 | 13 host information |
286 | 14 mailbox or mail list information |
287 | 15 mail exchange |
288 | 16 text strings |
289 | 0x1c IPv6? |
290 | 252 a request for a transfer of an entire zone |
291 | 253 a request for mailbox-related records (MB, MG or MR) |
292 | 254 a request for mail agent RRs (Obsolete - see MX) |
293 | 255 a request for all records |
294 | QCLASS a two octet code that specifies the class of the query. |
295 | 1 the Internet |
296 | (others are historic only) |
297 | 255 any class |
298 | |
299 | 4.1.3. Resource record format |
300 | |
301 | The answer, authority, and additional sections all share the same format: |
302 | a variable number of resource records, where the number of records |
303 | is specified in the corresponding count field in the header. |
304 | Each resource record has this format: |
305 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
306 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
307 | / / |
308 | / NAME / |
309 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
310 | | TYPE | |
311 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
312 | | CLASS | |
313 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
314 | | TTL | |
315 | | | |
316 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
317 | | RDLENGTH | |
318 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| |
319 | / RDATA / |
320 | / / |
321 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
322 | NAME a domain name to which this resource record pertains. |
323 | TYPE two octets containing one of the RR type codes. This |
324 | field specifies the meaning of the data in the RDATA field. |
325 | CLASS two octets which specify the class of the data in the RDATA field. |
326 | TTL a 32 bit unsigned integer that specifies the time interval |
327 | (in seconds) that the record may be cached. |
328 | RDLENGTH a 16 bit integer, length in octets of the RDATA field. |
329 | RDATA a variable length string of octets that describes the resource. |
330 | The format of this information varies according to the TYPE |
331 | and CLASS of the resource record. |
332 | If the TYPE is A and the CLASS is IN, it's a 4 octet IP address. |
333 | |
334 | 4.1.4. Message compression |
335 | |
336 | In order to reduce the size of messages, domain names coan be compressed. |
337 | An entire domain name or a list of labels at the end of a domain name |
338 | is replaced with a pointer to a prior occurance of the same name. |
339 | |
340 | The pointer takes the form of a two octet sequence: |
341 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
342 | | 1 1| OFFSET | |
343 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
344 | The first two bits are ones. This allows a pointer to be distinguished |
345 | from a label, since the label must begin with two zero bits because |
346 | labels are restricted to 63 octets or less. The OFFSET field specifies |
347 | an offset from the start of the message (i.e., the first octet |
348 | of the ID field in the domain header). |
349 | A zero offset specifies the first byte of the ID field, etc. |
350 | Domain name in a message can be represented as either: |
351 | - a sequence of labels ending in a zero octet |
352 | - a pointer |
353 | - a sequence of labels ending with a pointer |
354 | */ |
355 | static int process_packet(struct dns_entry *conf_data, |
356 | uint32_t conf_ttl, |
357 | uint8_t *buf) |
358 | { |
359 | char *answstr; |
360 | struct dns_head *head; |
361 | struct dns_prop *unaligned_qprop; |
362 | char *query_string; |
363 | uint8_t *answb; |
364 | uint16_t outr_rlen; |
365 | uint16_t outr_flags; |
366 | uint16_t type; |
367 | uint16_t class; |
368 | int querystr_len; |
369 | |
370 | head = (struct dns_head *)buf; |
371 | if (head->nquer == 0) { |
372 | bb_error_msg("packet has 0 queries, ignored"); |
373 | return -1; |
374 | } |
375 | |
376 | if (head->flags & htons(0x8000)) { /* QR bit */ |
377 | bb_error_msg("response packet, ignored"); |
378 | return -1; |
379 | } |
380 | |
381 | /* start of query string */ |
382 | query_string = (void *)(head + 1); |
383 | /* caller guarantees strlen is <= MAX_PACK_LEN */ |
384 | querystr_len = strlen(query_string) + 1; |
385 | /* may be unaligned! */ |
386 | unaligned_qprop = (void *)(query_string + querystr_len); |
387 | querystr_len += sizeof(unaligned_qprop); |
388 | /* where to append answer block */ |
389 | answb = (void *)(unaligned_qprop + 1); |
390 | |
391 | /* QR = 1 "response", RCODE = 4 "Not Implemented" */ |
392 | outr_flags = htons(0x8000 | 4); |
393 | |
394 | move_from_unaligned16(type, &unaligned_qprop->type); |
395 | if (type != htons(REQ_A) && type != htons(REQ_PTR)) { |
396 | /* we can't handle the query type */ |
397 | goto empty_packet; |
398 | } |
399 | move_from_unaligned16(class, &unaligned_qprop->class); |
400 | if (class != htons(1)) { /* not class INET? */ |
401 | goto empty_packet; |
402 | } |
403 | /* OPCODE != 0 "standard query" ? */ |
404 | if ((head->flags & htons(0x7800)) != 0) { |
405 | goto empty_packet; |
406 | } |
407 | |
408 | /* look up the name */ |
409 | #if DEBUG |
410 | /* need to convert lengths to dots before we can use it in non-debug */ |
411 | bb_info_msg("%s", query_string); |
412 | #endif |
413 | answstr = table_lookup(conf_data, type, query_string); |
414 | outr_rlen = 4; |
415 | if (answstr && type == htons(REQ_PTR)) { |
416 | /* return a host name */ |
417 | outr_rlen = strlen(answstr) + 1; |
418 | } |
419 | if (!answstr |
420 | || (unsigned)(answb - buf) + querystr_len + 4 + 2 + outr_rlen > MAX_PACK_LEN |
421 | ) { |
422 | /* QR = 1 "response" |
423 | * AA = 1 "Authoritative Answer" |
424 | * RCODE = 3 "Name Error" */ |
425 | outr_flags = htons(0x8000 | 0x0400 | 3); |
426 | goto empty_packet; |
427 | } |
428 | |
429 | /* copy query block to answer block */ |
430 | memcpy(answb, query_string, querystr_len); |
431 | answb += querystr_len; |
432 | /* append answer Resource Record */ |
433 | move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl)); |
434 | answb += 4; |
435 | move_to_unaligned32((uint16_t *)answb, htons(outr_rlen)); |
436 | answb += 2; |
437 | memcpy(answb, answstr, outr_rlen); |
438 | answb += outr_rlen; |
439 | |
440 | /* QR = 1 "response", |
441 | * AA = 1 "Authoritative Answer", |
442 | * RCODE = 0 "success" */ |
443 | outr_flags = htons(0x8000 | 0x0400 | 0); |
444 | /* we have one answer */ |
445 | head->nansw = htons(1); |
446 | |
447 | empty_packet: |
448 | head->flags |= outr_flags; |
449 | head->nauth = head->nadd = 0; |
450 | head->nquer = htons(1); // why??? |
451 | |
452 | return answb - buf; |
453 | } |
454 | |
455 | int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
456 | int dnsd_main(int argc UNUSED_PARAM, char **argv) |
457 | { |
458 | const char *listen_interface = "0.0.0.0"; |
459 | const char *fileconf = "/etc/dnsd.conf"; |
460 | struct dns_entry *conf_data; |
461 | uint32_t conf_ttl = DEFAULT_TTL; |
462 | char *sttl, *sport; |
463 | len_and_sockaddr *lsa, *from, *to; |
464 | unsigned lsa_size; |
465 | int udps, opts; |
466 | uint16_t port = 53; |
467 | /* Ensure buf is 32bit aligned (we need 16bit, but 32bit can't hurt) */ |
468 | uint8_t buf[MAX_PACK_LEN + 1] ALIGN4; |
469 | |
470 | opts = getopt32(argv, "vi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport); |
471 | //if (opts & 0x1) // -v |
472 | //if (opts & 0x2) // -i |
473 | //if (opts & 0x4) // -c |
474 | if (opts & 0x8) // -t |
475 | conf_ttl = xatou_range(sttl, 1, 0xffffffff); |
476 | if (opts & 0x10) // -p |
477 | port = xatou_range(sport, 1, 0xffff); |
478 | if (opts & 0x20) { // -d |
479 | bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv); |
480 | openlog(applet_name, LOG_PID, LOG_DAEMON); |
481 | logmode = LOGMODE_SYSLOG; |
482 | } |
483 | /* Clear all except "verbose" bit */ |
484 | option_mask32 &= 1; |
485 | |
486 | conf_data = parse_conf_file(fileconf); |
487 | |
488 | lsa = xdotted2sockaddr(listen_interface, port); |
489 | udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0); |
490 | xbind(udps, &lsa->u.sa, lsa->len); |
491 | socket_want_pktinfo(udps); /* needed for recv_from_to to work */ |
492 | lsa_size = LSA_LEN_SIZE + lsa->len; |
493 | from = xzalloc(lsa_size); |
494 | to = xzalloc(lsa_size); |
495 | |
496 | { |
497 | char *p = xmalloc_sockaddr2dotted(&lsa->u.sa); |
498 | bb_info_msg("Accepting UDP packets on %s", p); |
499 | free(p); |
500 | } |
501 | |
502 | while (1) { |
503 | int r; |
504 | /* Try to get *DEST* address (to which of our addresses |
505 | * this query was directed), and reply from the same address. |
506 | * Or else we can exhibit usual UDP ugliness: |
507 | * [ip1.multihomed.ip2] <= query to ip1 <= peer |
508 | * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */ |
509 | memcpy(to, lsa, lsa_size); |
510 | r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len); |
511 | if (r < 12 || r > MAX_PACK_LEN) { |
512 | bb_error_msg("packet size %d, ignored", r); |
513 | continue; |
514 | } |
515 | if (OPT_verbose) |
516 | bb_info_msg("Got UDP packet"); |
517 | buf[r] = '\0'; /* paranoia */ |
518 | r = process_packet(conf_data, conf_ttl, buf); |
519 | if (r <= 0) |
520 | continue; |
521 | send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len); |
522 | } |
523 | return 0; |
524 | } |