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97696d59 | 1 | /* $Cambridge: exim/src/src/dns.c,v 1.8 2005/06/10 13:38:06 tom Exp $ */ |
059ec3d9 PH |
2 | |
3 | /************************************************* | |
4 | * Exim - an Internet mail transport agent * | |
5 | *************************************************/ | |
6 | ||
c988f1f4 | 7 | /* Copyright (c) University of Cambridge 1995 - 2005 */ |
059ec3d9 PH |
8 | /* See the file NOTICE for conditions of use and distribution. */ |
9 | ||
10 | /* Functions for interfacing with the DNS. */ | |
11 | ||
12 | #include "exim.h" | |
13 | ||
14 | ||
15 | /* Function declaration needed for mutual recursion when A6 records | |
16 | are supported. */ | |
17 | ||
18 | #if HAVE_IPV6 | |
19 | #ifdef SUPPORT_A6 | |
20 | static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *, | |
21 | int, uschar *); | |
22 | #endif | |
23 | #endif | |
24 | ||
25 | ||
26 | ||
27 | /************************************************* | |
28 | * Initialize and configure resolver * | |
29 | *************************************************/ | |
30 | ||
31 | /* Initialize the resolver and the storage for holding DNS answers if this is | |
32 | the first time we have been here, and set the resolver options. | |
33 | ||
34 | Arguments: | |
35 | qualify_single TRUE to set the RES_DEFNAMES option | |
36 | search_parents TRUE to set the RES_DNSRCH option | |
37 | ||
38 | Returns: nothing | |
39 | */ | |
40 | ||
41 | void | |
42 | dns_init(BOOL qualify_single, BOOL search_parents) | |
43 | { | |
44 | if ((_res.options & RES_INIT) == 0) | |
45 | { | |
46 | DEBUG(D_resolver) _res.options |= RES_DEBUG; /* For Cygwin */ | |
47 | res_init(); | |
48 | DEBUG(D_resolver) _res.options |= RES_DEBUG; | |
49 | } | |
50 | ||
51 | _res.options &= ~(RES_DNSRCH | RES_DEFNAMES); | |
52 | _res.options |= (qualify_single? RES_DEFNAMES : 0) | | |
53 | (search_parents? RES_DNSRCH : 0); | |
54 | if (dns_retrans > 0) _res.retrans = dns_retrans; | |
55 | if (dns_retry > 0) _res.retry = dns_retry; | |
56 | } | |
57 | ||
58 | ||
59 | ||
60 | /************************************************* | |
61 | * Build key name for PTR records * | |
62 | *************************************************/ | |
63 | ||
64 | /* This function inverts an IP address and adds the relevant domain, to produce | |
65 | a name that can be used to look up PTR records. | |
66 | ||
67 | Arguments: | |
68 | string the IP address as a string | |
69 | buffer a suitable buffer, long enough to hold the result | |
70 | ||
71 | Returns: nothing | |
72 | */ | |
73 | ||
74 | void | |
75 | dns_build_reverse(uschar *string, uschar *buffer) | |
76 | { | |
77 | uschar *p = string + Ustrlen(string); | |
78 | uschar *pp = buffer; | |
79 | ||
80 | /* Handle IPv4 address */ | |
81 | ||
82 | #if HAVE_IPV6 | |
83 | if (Ustrchr(string, ':') == NULL) | |
84 | #endif | |
85 | { | |
86 | int i; | |
87 | for (i = 0; i < 4; i++) | |
88 | { | |
89 | uschar *ppp = p; | |
90 | while (ppp > string && ppp[-1] != '.') ppp--; | |
91 | Ustrncpy(pp, ppp, p - ppp); | |
92 | pp += p - ppp; | |
93 | *pp++ = '.'; | |
94 | p = ppp - 1; | |
95 | } | |
96 | Ustrcpy(pp, "in-addr.arpa"); | |
97 | } | |
98 | ||
99 | /* Handle IPv6 address; convert to binary so as to fill out any | |
100 | abbreviation in the textual form. */ | |
101 | ||
102 | #if HAVE_IPV6 | |
103 | else | |
104 | { | |
105 | int i; | |
106 | int v6[4]; | |
107 | (void)host_aton(string, v6); | |
108 | ||
109 | /* The original specification for IPv6 reverse lookup was to invert each | |
110 | nibble, and look in the ip6.int domain. The domain was subsequently | |
111 | changed to ip6.arpa. */ | |
112 | ||
113 | for (i = 3; i >= 0; i--) | |
114 | { | |
115 | int j; | |
116 | for (j = 0; j < 32; j += 4) | |
117 | { | |
118 | sprintf(CS pp, "%x.", (v6[i] >> j) & 15); | |
119 | pp += 2; | |
120 | } | |
121 | } | |
122 | Ustrcpy(pp, "ip6.arpa."); | |
123 | ||
124 | /* Another way of doing IPv6 reverse lookups was proposed in conjunction | |
125 | with A6 records. However, it fell out of favour when they did. The | |
126 | alternative was to construct a binary key, and look in ip6.arpa. I tried | |
127 | to make this code do that, but I could not make it work on Solaris 8. The | |
128 | resolver seems to lose the initial backslash somehow. However, now that | |
129 | this style of reverse lookup has been dropped, it doesn't matter. These | |
130 | lines are left here purely for historical interest. */ | |
131 | ||
132 | /************************************************** | |
133 | Ustrcpy(pp, "\\[x"); | |
134 | pp += 3; | |
135 | ||
136 | for (i = 0; i < 4; i++) | |
137 | { | |
138 | sprintf(pp, "%08X", v6[i]); | |
139 | pp += 8; | |
140 | } | |
141 | Ustrcpy(pp, "].ip6.arpa."); | |
142 | **************************************************/ | |
143 | ||
144 | } | |
145 | #endif | |
146 | } | |
147 | ||
148 | ||
149 | ||
150 | ||
151 | /************************************************* | |
152 | * Get next DNS record from answer block * | |
153 | *************************************************/ | |
154 | ||
155 | /* Call this with reset == RESET_ANSWERS to scan the answer block, reset == | |
e5a9dba6 PH |
156 | RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to |
157 | scan the additional records, and reset == RESET_NEXT to get the next record. | |
158 | The result is in static storage which must be copied if it is to be preserved. | |
059ec3d9 PH |
159 | |
160 | Arguments: | |
161 | dnsa pointer to dns answer block | |
162 | dnss pointer to dns scan block | |
163 | reset option specifing what portion to scan, as described above | |
164 | ||
165 | Returns: next dns record, or NULL when no more | |
166 | */ | |
167 | ||
168 | dns_record * | |
169 | dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset) | |
170 | { | |
171 | HEADER *h = (HEADER *)dnsa->answer; | |
172 | int namelen; | |
173 | ||
174 | /* Reset the saved data when requested to, and skip to the first required RR */ | |
175 | ||
176 | if (reset != RESET_NEXT) | |
177 | { | |
178 | dnss->rrcount = ntohs(h->qdcount); | |
179 | dnss->aptr = dnsa->answer + sizeof(HEADER); | |
180 | ||
181 | /* Skip over questions; failure to expand the name just gives up */ | |
182 | ||
183 | while (dnss->rrcount-- > 0) | |
184 | { | |
185 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, | |
186 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); | |
187 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } | |
188 | dnss->aptr += namelen + 4; /* skip name & type & class */ | |
189 | } | |
190 | ||
191 | /* Get the number of answer records. */ | |
192 | ||
193 | dnss->rrcount = ntohs(h->ancount); | |
194 | ||
e5a9dba6 PH |
195 | /* Skip over answers if we want to look at the authority section. Also skip |
196 | the NS records (i.e. authority section) if wanting to look at the additional | |
059ec3d9 PH |
197 | records. */ |
198 | ||
e5a9dba6 PH |
199 | if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount); |
200 | ||
201 | if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL) | |
059ec3d9 | 202 | { |
059ec3d9 PH |
203 | while (dnss->rrcount-- > 0) |
204 | { | |
205 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, | |
206 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); | |
207 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } | |
208 | dnss->aptr += namelen + 8; /* skip name, type, class & TTL */ | |
209 | GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */ | |
210 | dnss->aptr += dnss->srr.size; /* skip over it */ | |
211 | } | |
e5a9dba6 PH |
212 | dnss->rrcount = (reset == RESET_AUTHORITY) |
213 | ? ntohs(h->nscount) : ntohs(h->arcount); | |
059ec3d9 PH |
214 | } |
215 | } | |
216 | ||
059ec3d9 PH |
217 | /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount |
218 | contains the number of RR records left. */ | |
219 | ||
220 | if (dnss->rrcount-- <= 0) return NULL; | |
221 | ||
222 | /* If expanding the RR domain name fails, behave as if no more records | |
223 | (something safe). */ | |
224 | ||
225 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr, | |
226 | (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); | |
227 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } | |
228 | ||
229 | /* Move the pointer past the name and fill in the rest of the data structure | |
230 | from the following bytes. */ | |
231 | ||
232 | dnss->aptr += namelen; | |
233 | GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */ | |
234 | dnss->aptr += 6; /* Don't want class or TTL */ | |
235 | GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */ | |
236 | dnss->srr.data = dnss->aptr; /* The record's data follows */ | |
237 | dnss->aptr += dnss->srr.size; /* Advance to next RR */ | |
238 | ||
239 | /* Return a pointer to the dns_record structure within the dns_answer. This is | |
240 | for convenience so that the scans can use nice-looking for loops. */ | |
241 | ||
242 | return &(dnss->srr); | |
243 | } | |
244 | ||
245 | ||
246 | ||
247 | ||
248 | /************************************************* | |
249 | * Turn DNS type into text * | |
250 | *************************************************/ | |
251 | ||
252 | /* Turn the coded record type into a string for printing. | |
253 | ||
254 | Argument: record type | |
255 | Returns: pointer to string | |
256 | */ | |
257 | ||
258 | uschar * | |
259 | dns_text_type(int t) | |
260 | { | |
261 | switch(t) | |
262 | { | |
33397d19 PH |
263 | case T_A: return US"A"; |
264 | case T_MX: return US"MX"; | |
265 | case T_AAAA: return US"AAAA"; | |
266 | case T_A6: return US"A6"; | |
267 | case T_TXT: return US"TXT"; | |
268 | case T_PTR: return US"PTR"; | |
269 | case T_SRV: return US"SRV"; | |
270 | case T_NS: return US"NS"; | |
8e669ac1 | 271 | case T_CNAME: return US"CNAME"; |
33397d19 | 272 | default: return US"?"; |
059ec3d9 PH |
273 | } |
274 | } | |
275 | ||
276 | ||
277 | ||
278 | /************************************************* | |
279 | * Cache a failed DNS lookup result * | |
280 | *************************************************/ | |
281 | ||
282 | /* We cache failed lookup results so as not to experience timeouts many | |
283 | times for the same domain. We need to retain the resolver options because they | |
284 | may change. For successful lookups, we rely on resolver and/or name server | |
285 | caching. | |
286 | ||
287 | Arguments: | |
288 | name the domain name | |
289 | type the lookup type | |
290 | rc the return code | |
291 | ||
292 | Returns: the return code | |
293 | */ | |
294 | ||
295 | static int | |
296 | dns_return(uschar *name, int type, int rc) | |
297 | { | |
298 | tree_node *node = store_get_perm(sizeof(tree_node) + 290); | |
299 | sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type), | |
300 | _res.options); | |
301 | node->data.val = rc; | |
302 | (void)tree_insertnode(&tree_dns_fails, node); | |
303 | return rc; | |
304 | } | |
305 | ||
306 | ||
307 | ||
308 | /************************************************* | |
309 | * Do basic DNS lookup * | |
310 | *************************************************/ | |
311 | ||
312 | /* Call the resolver to look up the given domain name, using the given type, | |
313 | and check the result. The error code TRY_AGAIN is documented as meaning "non- | |
314 | Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set | |
315 | up nameservers that produce this error continually, so there is the option of | |
316 | providing a list of domains for which this is treated as a non-existent | |
317 | host. | |
318 | ||
319 | Arguments: | |
320 | dnsa pointer to dns_answer structure | |
321 | name name to look up | |
322 | type type of DNS record required (T_A, T_MX, etc) | |
323 | ||
324 | Returns: DNS_SUCCEED successful lookup | |
325 | DNS_NOMATCH name not found (NXDOMAIN) | |
326 | or name contains illegal characters (if checking) | |
327 | DNS_NODATA domain exists, but no data for this type (NODATA) | |
328 | DNS_AGAIN soft failure, try again later | |
329 | DNS_FAIL DNS failure | |
330 | */ | |
331 | ||
332 | int | |
333 | dns_basic_lookup(dns_answer *dnsa, uschar *name, int type) | |
334 | { | |
335 | #ifndef STAND_ALONE | |
336 | int rc; | |
337 | uschar *save; | |
338 | #endif | |
339 | ||
340 | tree_node *previous; | |
341 | uschar node_name[290]; | |
342 | ||
343 | /* DNS lookup failures of any kind are cached in a tree. This is mainly so that | |
344 | a timeout on one domain doesn't happen time and time again for messages that | |
345 | have many addresses in the same domain. We rely on the resolver and name server | |
346 | caching for successful lookups. */ | |
347 | ||
348 | sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type), | |
349 | _res.options); | |
350 | previous = tree_search(tree_dns_fails, node_name); | |
351 | if (previous != NULL) | |
352 | { | |
353 | DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n", | |
354 | name, dns_text_type(type), | |
355 | (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" : | |
356 | (previous->data.val == DNS_NODATA)? "DNS_NODATA" : | |
357 | (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" : | |
358 | (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??"); | |
359 | return previous->data.val; | |
360 | } | |
361 | ||
362 | /* If we are running in the test harness, recognize a couple of special | |
363 | names that always give error returns. This makes it straightforward to | |
364 | test the handling of DNS errors. */ | |
365 | ||
366 | if (running_in_test_harness) | |
367 | { | |
368 | uschar *endname = name + Ustrlen(name); | |
369 | if (Ustrcmp(endname - 14, "test.again.dns") == 0) | |
370 | { | |
371 | int delay = Uatoi(name); /* digits at the start of the name */ | |
372 | DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n", | |
373 | name, dns_text_type(type)); | |
374 | if (delay > 0) | |
375 | { | |
376 | DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay); | |
377 | sleep(delay); | |
378 | } | |
379 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); | |
380 | return dns_return(name, type, DNS_AGAIN); | |
381 | } | |
382 | if (Ustrcmp(endname - 13, "test.fail.dns") == 0) | |
383 | { | |
384 | DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n", | |
385 | name, dns_text_type(type)); | |
386 | DEBUG(D_dns) debug_printf("returning DNS_FAIL\n"); | |
387 | return dns_return(name, type, DNS_FAIL); | |
388 | } | |
389 | } | |
390 | ||
391 | /* If configured, check the hygene of the name passed to lookup. Otherwise, | |
392 | although DNS lookups may give REFUSED at the lower level, some resolvers | |
393 | turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such | |
394 | domains cannot be in the DNS. The check is now done by a regular expression; | |
395 | give it space for substring storage to save it having to get its own if the | |
396 | regex has substrings that are used - the default uses a conditional. | |
397 | ||
398 | This test is omitted for PTR records. These occur only in calls from the dnsdb | |
399 | lookup, which constructs the names itself, so they should be OK. Besides, | |
400 | bitstring labels don't conform to normal name syntax. (But the aren't used any | |
401 | more.) | |
402 | ||
403 | For SRV records, we omit the initial _smtp._tcp. components at the start. */ | |
404 | ||
405 | #ifndef STAND_ALONE /* Omit this for stand-alone tests */ | |
406 | ||
407 | if (check_dns_names_pattern[0] != 0 && type != T_PTR) | |
408 | { | |
409 | uschar *checkname = name; | |
410 | int ovector[3*(EXPAND_MAXN+1)]; | |
411 | ||
412 | if (regex_check_dns_names == NULL) | |
413 | regex_check_dns_names = | |
414 | regex_must_compile(check_dns_names_pattern, FALSE, TRUE); | |
415 | ||
416 | /* For an SRV lookup, skip over the first two components (the service and | |
417 | protocol names, which both start with an underscore). */ | |
418 | ||
419 | if (type == T_SRV) | |
420 | { | |
421 | while (*checkname++ != '.'); | |
422 | while (*checkname++ != '.'); | |
423 | } | |
424 | ||
425 | if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname), | |
426 | 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0) | |
427 | { | |
428 | DEBUG(D_dns) | |
429 | debug_printf("DNS name syntax check failed: %s (%s)\n", name, | |
430 | dns_text_type(type)); | |
431 | host_find_failed_syntax = TRUE; | |
432 | return DNS_NOMATCH; | |
433 | } | |
434 | } | |
435 | ||
436 | #endif /* STAND_ALONE */ | |
437 | ||
438 | /* Call the resolver; for an overlong response, res_search() will return the | |
439 | number of bytes the message would need, so we need to check for this case. | |
440 | The effect is to truncate overlong data. */ | |
441 | ||
442 | dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET); | |
443 | if (dnsa->answerlen > MAXPACKET) dnsa->answerlen = MAXPACKET; | |
444 | ||
445 | if (dnsa->answerlen < 0) switch (h_errno) | |
446 | { | |
447 | case HOST_NOT_FOUND: | |
448 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n" | |
449 | "returning DNS_NOMATCH\n", name, dns_text_type(type)); | |
450 | return dns_return(name, type, DNS_NOMATCH); | |
451 | ||
452 | case TRY_AGAIN: | |
453 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n", | |
454 | name, dns_text_type(type)); | |
455 | ||
456 | /* Cut this out for various test programs */ | |
457 | #ifndef STAND_ALONE | |
458 | save = deliver_domain; | |
459 | deliver_domain = name; /* set $domain */ | |
460 | rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL, | |
461 | MCL_DOMAIN, TRUE, NULL); | |
462 | deliver_domain = save; | |
463 | if (rc != OK) | |
464 | { | |
465 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); | |
466 | return dns_return(name, type, DNS_AGAIN); | |
467 | } | |
468 | DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning " | |
469 | "DNS_NOMATCH\n", name); | |
470 | return dns_return(name, type, DNS_NOMATCH); | |
471 | ||
472 | #else /* For stand-alone tests */ | |
473 | return dns_return(name, type, DNS_AGAIN); | |
474 | #endif | |
475 | ||
476 | case NO_RECOVERY: | |
477 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n" | |
478 | "returning DNS_FAIL\n", name, dns_text_type(type)); | |
479 | return dns_return(name, type, DNS_FAIL); | |
480 | ||
481 | case NO_DATA: | |
482 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n" | |
483 | "returning DNS_NODATA\n", name, dns_text_type(type)); | |
484 | return dns_return(name, type, DNS_NODATA); | |
485 | ||
486 | default: | |
487 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n" | |
488 | "returning DNS_FAIL\n", name, dns_text_type(type), h_errno); | |
489 | return dns_return(name, type, DNS_FAIL); | |
490 | } | |
491 | ||
492 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n", | |
493 | name, dns_text_type(type)); | |
494 | ||
495 | return DNS_SUCCEED; | |
496 | } | |
497 | ||
498 | ||
499 | ||
500 | ||
501 | /************************************************ | |
502 | * Do a DNS lookup and handle CNAMES * | |
503 | ************************************************/ | |
504 | ||
505 | /* Look up the given domain name, using the given type. Follow CNAMEs if | |
506 | necessary, but only so many times. There aren't supposed to be CNAME chains in | |
507 | the DNS, but you are supposed to cope with them if you find them. | |
508 | ||
509 | The assumption is made that if the resolver gives back records of the | |
510 | requested type *and* a CNAME, we don't need to make another call to look up | |
511 | the CNAME. I can't see how it could return only some of the right records. If | |
512 | it's done a CNAME lookup in the past, it will have all of them; if not, it | |
513 | won't return any. | |
514 | ||
515 | If fully_qualified_name is not NULL, set it to point to the full name | |
516 | returned by the resolver, if this is different to what it is given, unless | |
517 | the returned name starts with "*" as some nameservers seem to be returning | |
518 | wildcards in this form. | |
519 | ||
520 | Arguments: | |
521 | dnsa pointer to dns_answer structure | |
522 | name domain name to look up | |
523 | type DNS record type (T_A, T_MX, etc) | |
524 | fully_qualified_name if not NULL, return the returned name here if its | |
525 | contents are different (i.e. it must be preset) | |
526 | ||
527 | Returns: DNS_SUCCEED successful lookup | |
528 | DNS_NOMATCH name not found | |
529 | DNS_NODATA no data found | |
530 | DNS_AGAIN soft failure, try again later | |
531 | DNS_FAIL DNS failure | |
532 | */ | |
533 | ||
534 | int | |
535 | dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name) | |
536 | { | |
537 | int i; | |
538 | uschar *orig_name = name; | |
539 | ||
540 | /* Loop to follow CNAME chains so far, but no further... */ | |
541 | ||
542 | for (i = 0; i < 10; i++) | |
543 | { | |
544 | uschar data[256]; | |
545 | dns_record *rr, cname_rr, type_rr; | |
546 | dns_scan dnss; | |
547 | int datalen, rc; | |
548 | ||
549 | /* DNS lookup failures get passed straight back. */ | |
550 | ||
551 | if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc; | |
552 | ||
553 | /* We should have either records of the required type, or a CNAME record, | |
554 | or both. We need to know whether both exist for getting the fully qualified | |
555 | name, but avoid scanning more than necessary. Note that we must copy the | |
556 | contents of any rr blocks returned by dns_next_rr() as they use the same | |
557 | area in the dnsa block. */ | |
558 | ||
559 | cname_rr.data = type_rr.data = NULL; | |
560 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); | |
561 | rr != NULL; | |
562 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) | |
563 | { | |
564 | if (rr->type == type) | |
565 | { | |
566 | if (type_rr.data == NULL) type_rr = *rr; | |
567 | if (cname_rr.data != NULL) break; | |
568 | } | |
569 | else if (rr->type == T_CNAME) cname_rr = *rr; | |
570 | } | |
571 | ||
572 | /* If a CNAME was found, take the fully qualified name from it; otherwise | |
573 | from the first data record, if present. For testing, there is a magic name | |
574 | that gets its casing adjusted, because my resolver doesn't seem to pass back | |
575 | upper case letters in domain names. */ | |
576 | ||
577 | if (fully_qualified_name != NULL) | |
578 | { | |
579 | if (cname_rr.data != NULL) | |
580 | { | |
581 | if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 && | |
582 | cname_rr.name[0] != '*') | |
583 | *fully_qualified_name = string_copy_dnsdomain(cname_rr.name); | |
584 | } | |
585 | else if (type_rr.data != NULL) | |
586 | { | |
587 | if (running_in_test_harness && | |
588 | Ustrcmp(type_rr.name, "uppercase.test.ex") == 0) | |
589 | *fully_qualified_name = US"UpperCase.test.ex"; | |
590 | else | |
591 | { | |
592 | if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 && | |
593 | type_rr.name[0] != '*') | |
594 | *fully_qualified_name = string_copy_dnsdomain(type_rr.name); | |
595 | } | |
596 | } | |
597 | } | |
598 | ||
599 | /* If any data records of the correct type were found, we are done. */ | |
600 | ||
601 | if (type_rr.data != NULL) return DNS_SUCCEED; | |
602 | ||
603 | /* If there are no data records, we need to re-scan the DNS using the | |
604 | domain given in the CNAME record, which should exist (otherwise we should | |
605 | have had a failure from dns_lookup). However code against the possibility of | |
606 | its not existing. */ | |
607 | ||
608 | if (cname_rr.data == NULL) return DNS_FAIL; | |
609 | datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, | |
610 | cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256); | |
611 | if (datalen < 0) return DNS_FAIL; | |
612 | name = data; | |
613 | } /* Loop back to do another lookup */ | |
614 | ||
615 | /*Control reaches here after 10 times round the CNAME loop. Something isn't | |
616 | right... */ | |
617 | ||
618 | log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name); | |
619 | return DNS_FAIL; | |
620 | } | |
621 | ||
622 | ||
623 | ||
33397d19 PH |
624 | |
625 | ||
626 | ||
627 | /************************************************ | |
628 | * Do a DNS lookup and handle virtual types * | |
629 | ************************************************/ | |
630 | ||
8e669ac1 PH |
631 | /* This function handles some invented "lookup types" that synthesize feature |
632 | not available in the basic types. The special types all have negative values. | |
33397d19 PH |
633 | Positive type values are passed straight on to dns_lookup(). |
634 | ||
635 | Arguments: | |
636 | dnsa pointer to dns_answer structure | |
637 | name domain name to look up | |
638 | type DNS record type (T_A, T_MX, etc or a "special") | |
639 | fully_qualified_name if not NULL, return the returned name here if its | |
640 | contents are different (i.e. it must be preset) | |
641 | ||
642 | Returns: DNS_SUCCEED successful lookup | |
643 | DNS_NOMATCH name not found | |
644 | DNS_NODATA no data found | |
645 | DNS_AGAIN soft failure, try again later | |
646 | DNS_FAIL DNS failure | |
647 | */ | |
648 | ||
649 | int | |
8e669ac1 | 650 | dns_special_lookup(dns_answer *dnsa, uschar *name, int type, |
33397d19 PH |
651 | uschar **fully_qualified_name) |
652 | { | |
653 | if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name); | |
654 | ||
ea3bc19b PH |
655 | /* The "mx hosts only" type doesn't require any special action here */ |
656 | ||
657 | if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name); | |
658 | ||
8e669ac1 | 659 | /* Find nameservers for the domain or the nearest enclosing zone, excluding the |
33397d19 PH |
660 | root servers. */ |
661 | ||
662 | if (type == T_ZNS) | |
663 | { | |
664 | uschar *d = name; | |
665 | while (d != 0) | |
666 | { | |
667 | int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name); | |
668 | if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc; | |
669 | while (*d != 0 && *d != '.') d++; | |
8e669ac1 | 670 | if (*d++ == 0) break; |
33397d19 | 671 | } |
8e669ac1 PH |
672 | return DNS_NOMATCH; |
673 | } | |
33397d19 | 674 | |
e5a9dba6 PH |
675 | /* Try to look up the Client SMTP Authorization SRV record for the name. If |
676 | there isn't one, search from the top downwards for a CSA record in a parent | |
677 | domain, which might be making assertions about subdomains. If we find a record | |
678 | we set fully_qualified_name to whichever lookup succeeded, so that the caller | |
679 | can tell whether to look at the explicit authorization field or the subdomain | |
680 | assertion field. */ | |
681 | ||
682 | if (type == T_CSA) | |
683 | { | |
684 | uschar *srvname, *namesuff, *tld, *p; | |
685 | int priority, weight, port; | |
686 | int limit, rc, i; | |
687 | BOOL ipv6; | |
688 | dns_record *rr; | |
689 | dns_scan dnss; | |
690 | ||
691 | DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name); | |
692 | ||
693 | srvname = string_sprintf("_client._smtp.%s", name); | |
694 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); | |
695 | if (rc == DNS_SUCCEED || rc == DNS_AGAIN) | |
696 | { | |
697 | if (rc == DNS_SUCCEED) *fully_qualified_name = name; | |
698 | return rc; | |
699 | } | |
700 | ||
701 | /* Search for CSA subdomain assertion SRV records from the top downwards, | |
702 | starting with the 2nd level domain. This order maximizes cache-friendliness. | |
703 | We skip the top level domains to avoid loading their nameservers and because | |
704 | we know they'll never have CSA SRV records. */ | |
705 | ||
706 | namesuff = Ustrrchr(name, '.'); | |
707 | if (namesuff == NULL) return DNS_NOMATCH; | |
708 | tld = namesuff + 1; | |
709 | ipv6 = FALSE; | |
710 | limit = dns_csa_search_limit; | |
711 | ||
712 | /* Use more appropriate search parameters if we are in the reverse DNS. */ | |
713 | ||
714 | if (strcmpic(namesuff, US".arpa") == 0) | |
715 | { | |
716 | if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0) | |
717 | { | |
718 | namesuff -= 8; | |
719 | tld = namesuff + 1; | |
720 | limit = 3; | |
721 | } | |
722 | else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0) | |
723 | { | |
724 | namesuff -= 4; | |
725 | tld = namesuff + 1; | |
726 | ipv6 = TRUE; | |
727 | limit = 3; | |
728 | } | |
729 | } | |
730 | ||
731 | DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld); | |
732 | ||
733 | /* Do not perform the search if the top level or 2nd level domains do not | |
734 | exist. This is quite common, and when it occurs all the search queries would | |
735 | go to the root or TLD name servers, which is not friendly. So we check the | |
736 | AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then | |
737 | the TLD or the 2LD (respectively) doesn't exist and we can skip the search. | |
738 | If the TLD and the 2LD exist but the explicit CSA record lookup failed, then | |
739 | the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */ | |
740 | ||
741 | if (rc == DNS_NOMATCH) | |
742 | { | |
743 | /* This is really gross. The successful return value from res_search() is | |
744 | the packet length, which is stored in dnsa->answerlen. If we get a | |
745 | negative DNS reply then res_search() returns -1, which causes the bounds | |
746 | checks for name decompression to fail when it is treated as a packet | |
747 | length, which in turn causes the authority search to fail. The correct | |
748 | packet length has been lost inside libresolv, so we have to guess a | |
749 | replacement value. (The only way to fix this properly would be to | |
750 | re-implement res_search() and res_query() so that they don't muddle their | |
751 | success and packet length return values.) For added safety we only reset | |
752 | the packet length if the packet header looks plausible. */ | |
753 | ||
754 | HEADER *h = (HEADER *)dnsa->answer; | |
755 | if (h->qr == 1 && h->opcode == QUERY && h->tc == 0 | |
756 | && (h->rcode == NOERROR || h->rcode == NXDOMAIN) | |
757 | && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0 | |
758 | && ntohs(h->nscount) >= 1) | |
759 | dnsa->answerlen = MAXPACKET; | |
760 | ||
761 | for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); | |
762 | rr != NULL; | |
763 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) | |
764 | if (rr->type != T_SOA) continue; | |
765 | else if (strcmpic(rr->name, US"") == 0 || | |
766 | strcmpic(rr->name, tld) == 0) return DNS_NOMATCH; | |
767 | else break; | |
768 | } | |
769 | ||
770 | for (i = 0; i < limit; i++) | |
771 | { | |
772 | if (ipv6) | |
773 | { | |
774 | /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP | |
775 | address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */ | |
776 | namesuff -= 8; | |
777 | if (namesuff <= name) return DNS_NOMATCH; | |
778 | } | |
779 | else | |
780 | /* Find the start of the preceding domain name label. */ | |
781 | do | |
782 | if (--namesuff <= name) return DNS_NOMATCH; | |
783 | while (*namesuff != '.'); | |
784 | ||
785 | DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1); | |
786 | ||
787 | srvname = string_sprintf("_client._smtp.%s", namesuff + 1); | |
788 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); | |
789 | if (rc == DNS_AGAIN) return rc; | |
790 | if (rc != DNS_SUCCEED) continue; | |
791 | ||
792 | /* Check that the SRV record we have found is worth returning. We don't | |
793 | just return the first one we find, because some lower level SRV record | |
794 | might make stricter assertions than its parent domain. */ | |
795 | ||
796 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); | |
797 | rr != NULL; | |
798 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) | |
799 | { | |
800 | if (rr->type != T_SRV) continue; | |
801 | ||
802 | /* Extract the numerical SRV fields (p is incremented) */ | |
803 | p = rr->data; | |
804 | GETSHORT(priority, p); | |
805 | GETSHORT(weight, p); | |
806 | GETSHORT(port, p); | |
807 | ||
808 | /* Check the CSA version number */ | |
809 | if (priority != 1) continue; | |
810 | ||
811 | /* If it's making an interesting assertion, return this response. */ | |
812 | if (port & 1) | |
813 | { | |
814 | *fully_qualified_name = namesuff + 1; | |
815 | return DNS_SUCCEED; | |
816 | } | |
817 | } | |
818 | } | |
819 | return DNS_NOMATCH; | |
820 | } | |
821 | ||
33397d19 PH |
822 | /* Control should never reach here */ |
823 | ||
824 | return DNS_FAIL; | |
825 | } | |
826 | ||
827 | ||
828 | ||
059ec3d9 PH |
829 | /* Support for A6 records has been commented out since they were demoted to |
830 | experimental status at IETF 51. */ | |
831 | ||
832 | #if HAVE_IPV6 && defined(SUPPORT_A6) | |
833 | ||
834 | /************************************************* | |
835 | * Search DNS block for prefix RRs * | |
836 | *************************************************/ | |
837 | ||
838 | /* Called from dns_complete_a6() to search an additional section or a main | |
839 | answer section for required prefix records to complete an IPv6 address obtained | |
840 | from an A6 record. For each prefix record, a recursive call to dns_complete_a6 | |
841 | is made, with a new copy of the address so far. | |
842 | ||
843 | Arguments: | |
844 | dnsa the DNS answer block | |
845 | which RESET_ADDITIONAL or RESET_ANSWERS | |
846 | name name of prefix record | |
847 | yptrptr pointer to the pointer that points to where to hang the next | |
848 | dns_address structure | |
849 | bits number of bits we have already got | |
850 | bitvec the bits we have already got | |
851 | ||
852 | Returns: TRUE if any records were found | |
853 | */ | |
854 | ||
855 | static BOOL | |
856 | dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address | |
857 | ***yptrptr, int bits, uschar *bitvec) | |
858 | { | |
859 | BOOL yield = FALSE; | |
860 | dns_record *rr; | |
861 | dns_scan dnss; | |
862 | ||
863 | for (rr = dns_next_rr(dnsa, &dnss, which); | |
864 | rr != NULL; | |
865 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) | |
866 | { | |
867 | uschar cbitvec[16]; | |
868 | if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue; | |
869 | yield = TRUE; | |
870 | memcpy(cbitvec, bitvec, sizeof(cbitvec)); | |
871 | dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec); | |
872 | } | |
873 | ||
874 | return yield; | |
875 | } | |
876 | ||
877 | ||
878 | ||
879 | /************************************************* | |
880 | * Follow chains of A6 records * | |
881 | *************************************************/ | |
882 | ||
883 | /* A6 records may be incomplete, with pointers to other records containing more | |
884 | bits of the address. There can be a tree structure, leading to a number of | |
885 | addresses originating from a single initial A6 record. | |
886 | ||
887 | Arguments: | |
888 | yptrptr pointer to the pointer that points to where to hang the next | |
889 | dns_address structure | |
890 | dnsa the current DNS answer block | |
891 | rr the RR we have at present | |
892 | bits number of bits we have already got | |
893 | bitvec the bits we have already got | |
894 | ||
895 | Returns: nothing | |
896 | */ | |
897 | ||
898 | static void | |
899 | dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr, | |
900 | int bits, uschar *bitvec) | |
901 | { | |
902 | static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 }; | |
903 | uschar *p = (uschar *)(rr->data); | |
904 | int prefix_len, suffix_len; | |
905 | int i, j, k; | |
906 | uschar *chainptr; | |
907 | uschar chain[264]; | |
908 | dns_answer cdnsa; | |
909 | ||
910 | /* The prefix length is the first byte. It defines the prefix which is missing | |
911 | from the data in this record as a number of bits. Zero means this is the end of | |
912 | a chain. The suffix is the data in this record; only sufficient bytes to hold | |
913 | it are supplied. There may be zero bytes. We have to ignore trailing bits that | |
914 | we have already obtained from earlier RRs in the chain. */ | |
915 | ||
916 | prefix_len = *p++; /* bits */ | |
917 | suffix_len = (128 - prefix_len + 7)/8; /* bytes */ | |
918 | ||
919 | /* If the prefix in this record is greater than the prefix in the previous | |
920 | record in the chain, we have to ignore the record (RFC 2874). */ | |
921 | ||
922 | if (prefix_len > 128 - bits) return; | |
923 | ||
924 | /* In this little loop, the number of bits up to and including the current byte | |
925 | is held in k. If we have none of the bits in this byte, we can just or it into | |
926 | the current data. If we have all of the bits in this byte, we skip it. | |
927 | Otherwise, some masking has to be done. */ | |
928 | ||
929 | for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--) | |
930 | { | |
931 | int required = k - bits; | |
932 | if (required >= 8) bitvec[j] |= p[i]; | |
933 | else if (required > 0) bitvec[j] |= p[i] & bitmask[required]; | |
934 | j--; /* I tried putting these in the "for" statement, but gcc muttered */ | |
935 | k += 8; /* about computed values not being used. */ | |
936 | } | |
937 | ||
938 | /* If the prefix_length is zero, we are at the end of a chain. Build a | |
939 | dns_address item with the current data, hang it onto the end of the chain, | |
940 | adjust the hanging pointer, and we are done. */ | |
941 | ||
942 | if (prefix_len == 0) | |
943 | { | |
944 | dns_address *new = store_get(sizeof(dns_address) + 50); | |
945 | inet_ntop(AF_INET6, bitvec, CS new->address, 50); | |
946 | new->next = NULL; | |
947 | **yptrptr = new; | |
948 | *yptrptr = &(new->next); | |
949 | return; | |
950 | } | |
951 | ||
952 | /* Prefix length is not zero. Reset the number of bits that we have collected | |
953 | so far, and extract the chain name. */ | |
954 | ||
955 | bits = 128 - prefix_len; | |
956 | p += suffix_len; | |
957 | ||
958 | chainptr = chain; | |
959 | while ((i = *p++) != 0) | |
960 | { | |
961 | if (chainptr != chain) *chainptr++ = '.'; | |
962 | memcpy(chainptr, p, i); | |
963 | chainptr += i; | |
964 | p += i; | |
965 | } | |
966 | *chainptr = 0; | |
967 | chainptr = chain; | |
968 | ||
969 | /* Now scan the current DNS response record to see if the additional section | |
970 | contains the records we want. This processing can be cut out for testing | |
971 | purposes. */ | |
972 | ||
973 | if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec)) | |
974 | return; | |
975 | ||
976 | /* No chain records were found in the current DNS response block. Do a new DNS | |
977 | lookup to try to find these records. This opens up the possibility of DNS | |
978 | failures. We ignore them at this point; if all branches of the tree fail, there | |
979 | will be no addresses at the end. */ | |
980 | ||
981 | if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED) | |
982 | (void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec); | |
983 | } | |
984 | #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */ | |
985 | ||
986 | ||
987 | ||
988 | ||
989 | /************************************************* | |
990 | * Get address(es) from DNS record * | |
991 | *************************************************/ | |
992 | ||
993 | /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when | |
994 | supported) for an IPv6 address. In the A6 case, there may be several addresses, | |
995 | generated by following chains. A recursive function does all the hard work. A6 | |
996 | records now look like passing into history, so the code is only included when | |
997 | explicitly asked for. | |
998 | ||
999 | Argument: | |
1000 | dnsa the DNS answer block | |
1001 | rr the RR | |
1002 | ||
1003 | Returns: pointer a chain of dns_address items | |
1004 | */ | |
1005 | ||
1006 | dns_address * | |
1007 | dns_address_from_rr(dns_answer *dnsa, dns_record *rr) | |
1008 | { | |
1009 | dns_address *yield = NULL; | |
1010 | ||
1011 | #if HAVE_IPV6 && defined(SUPPORT_A6) | |
1012 | dns_address **yieldptr = &yield; | |
1013 | uschar bitvec[16]; | |
1014 | #else | |
1015 | dnsa = dnsa; /* Stop picky compilers warning */ | |
1016 | #endif | |
1017 | ||
1018 | if (rr->type == T_A) | |
1019 | { | |
1020 | uschar *p = (uschar *)(rr->data); | |
1021 | yield = store_get(sizeof(dns_address) + 20); | |
1022 | (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]); | |
1023 | yield->next = NULL; | |
1024 | } | |
1025 | ||
1026 | #if HAVE_IPV6 | |
1027 | ||
1028 | #ifdef SUPPORT_A6 | |
1029 | else if (rr->type == T_A6) | |
1030 | { | |
1031 | memset(bitvec, 0, sizeof(bitvec)); | |
1032 | dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec); | |
1033 | } | |
1034 | #endif /* SUPPORT_A6 */ | |
1035 | ||
1036 | else | |
1037 | { | |
1038 | yield = store_get(sizeof(dns_address) + 50); | |
1039 | inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50); | |
1040 | yield->next = NULL; | |
1041 | } | |
1042 | #endif /* HAVE_IPV6 */ | |
1043 | ||
1044 | return yield; | |
1045 | } | |
1046 | ||
1047 | /* End of dns.c */ |