95db526867029321275e247fbd986037247ef594
[exim.git] / src / src / dns.c
1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
4
5 /* Copyright (c) University of Cambridge 1995 - 2012 */
6 /* See the file NOTICE for conditions of use and distribution. */
7
8 /* Functions for interfacing with the DNS. */
9
10 #include "exim.h"
11
12
13 /* Function declaration needed for mutual recursion when A6 records
14 are supported. */
15
16 #if HAVE_IPV6
17 #ifdef SUPPORT_A6
18 static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *,
19 int, uschar *);
20 #endif
21 #endif
22
23
24 /*************************************************
25 * Fake DNS resolver *
26 *************************************************/
27
28 /* This function is called instead of res_search() when Exim is running in its
29 test harness. It recognizes some special domain names, and uses them to force
30 failure and retry responses (optionally with a delay). Otherwise, it calls an
31 external utility that mocks-up a nameserver, if it can find the utility.
32 If not, it passes its arguments on to res_search(). The fake nameserver may
33 also return a code specifying that the name should be passed on.
34
35 Background: the original test suite required a real nameserver to carry the
36 test zones, whereas the new test suit has the fake server for portability. This
37 code supports both.
38
39 Arguments:
40 domain the domain name
41 type the DNS record type
42 answerptr where to put the answer
43 size size of the answer area
44
45 Returns: length of returned data, or -1 on error (h_errno set)
46 */
47
48 static int
49 fakens_search(uschar *domain, int type, uschar *answerptr, int size)
50 {
51 int len = Ustrlen(domain);
52 int asize = size; /* Locally modified */
53 uschar *endname;
54 uschar name[256];
55 uschar utilname[256];
56 uschar *aptr = answerptr; /* Locally modified */
57 struct stat statbuf;
58
59 /* Remove terminating dot. */
60
61 if (domain[len - 1] == '.') len--;
62 Ustrncpy(name, domain, len);
63 name[len] = 0;
64 endname = name + len;
65
66 /* This code, for forcing TRY_AGAIN and NO_RECOVERY, is here so that it works
67 for the old test suite that uses a real nameserver. When the old test suite is
68 eventually abandoned, this code could be moved into the fakens utility. */
69
70 if (len >= 14 && Ustrcmp(endname - 14, "test.again.dns") == 0)
71 {
72 int delay = Uatoi(name); /* digits at the start of the name */
73 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
74 name, dns_text_type(type));
75 if (delay > 0)
76 {
77 DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay);
78 sleep(delay);
79 }
80 h_errno = TRY_AGAIN;
81 return -1;
82 }
83
84 if (len >= 13 && Ustrcmp(endname - 13, "test.fail.dns") == 0)
85 {
86 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
87 name, dns_text_type(type));
88 h_errno = NO_RECOVERY;
89 return -1;
90 }
91
92 /* Look for the fakens utility, and if it exists, call it. */
93
94 (void)string_format(utilname, sizeof(utilname), "%s/../bin/fakens",
95 spool_directory);
96
97 if (stat(CS utilname, &statbuf) >= 0)
98 {
99 pid_t pid;
100 int infd, outfd, rc;
101 uschar *argv[5];
102
103 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n",
104 name, dns_text_type(type));
105
106 argv[0] = utilname;
107 argv[1] = spool_directory;
108 argv[2] = name;
109 argv[3] = dns_text_type(type);
110 argv[4] = NULL;
111
112 pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
113 if (pid < 0)
114 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
115 strerror(errno));
116
117 len = 0;
118 rc = -1;
119 while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
120 {
121 len += rc;
122 aptr += rc; /* Don't modify the actual arguments, because they */
123 asize -= rc; /* may need to be passed on to res_search(). */
124 }
125
126 if (rc < 0)
127 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
128 strerror(errno));
129
130 switch(child_close(pid, 0))
131 {
132 case 0: return len;
133 case 1: h_errno = HOST_NOT_FOUND; return -1;
134 case 2: h_errno = TRY_AGAIN; return -1;
135 default:
136 case 3: h_errno = NO_RECOVERY; return -1;
137 case 4: h_errno = NO_DATA; return -1;
138 case 5: /* Pass on to res_search() */
139 DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
140 }
141 }
142
143 /* fakens utility not found, or it returned "pass on" */
144
145 DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain);
146
147 return res_search(CS domain, C_IN, type, answerptr, size);
148 }
149
150
151
152 /*************************************************
153 * Initialize and configure resolver *
154 *************************************************/
155
156 /* Initialize the resolver and the storage for holding DNS answers if this is
157 the first time we have been here, and set the resolver options.
158
159 Arguments:
160 qualify_single TRUE to set the RES_DEFNAMES option
161 search_parents TRUE to set the RES_DNSRCH option
162
163 Returns: nothing
164 */
165
166 void
167 dns_init(BOOL qualify_single, BOOL search_parents)
168 {
169 res_state resp = os_get_dns_resolver_res();
170
171 if ((resp->options & RES_INIT) == 0)
172 {
173 DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */
174 os_put_dns_resolver_res(resp);
175 res_init();
176 DEBUG(D_resolver) resp->options |= RES_DEBUG;
177 os_put_dns_resolver_res(resp);
178 }
179
180 resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
181 resp->options |= (qualify_single? RES_DEFNAMES : 0) |
182 (search_parents? RES_DNSRCH : 0);
183 if (dns_retrans > 0) resp->retrans = dns_retrans;
184 if (dns_retry > 0) resp->retry = dns_retry;
185
186 #ifdef RES_USE_EDNS0
187 if (dns_use_edns0 >= 0)
188 {
189 if (dns_use_edns0)
190 resp->options |= RES_USE_EDNS0;
191 else
192 resp->options &= ~RES_USE_EDNS0;
193 DEBUG(D_resolver)
194 debug_printf("Coerced resolver EDNS0 support %s.\n",
195 dns_use_edns0 ? "on" : "off");
196 }
197 #else
198 if (dns_use_edns0 >= 0)
199 DEBUG(D_resolver)
200 debug_printf("Unable to %sset EDNS0 without resolver support.\n",
201 dns_use_edns0 ? "" : "un");
202 #endif
203
204 #ifndef DISABLE_DNSSEC
205 # ifdef RES_USE_DNSSEC
206 # ifndef RES_USE_EDNS0
207 # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ...
208 # endif
209 if (dns_use_dnssec >= 0)
210 {
211 if (dns_use_edns0 == 0 && dns_use_dnssec != 0)
212 {
213 DEBUG(D_resolver)
214 debug_printf("CONFLICT: dns_use_edns0 forced false, dns_use_dnssec forced true!\n");
215 }
216 else
217 {
218 if (dns_use_dnssec)
219 resp->options |= RES_USE_DNSSEC;
220 else
221 resp->options &= ~RES_USE_DNSSEC;
222 DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n",
223 dns_use_dnssec ? "on" : "off");
224 }
225 }
226 # else
227 if (dns_use_dnssec >= 0)
228 DEBUG(D_resolver)
229 debug_printf("Unable to %sset DNSSEC without resolver support.\n",
230 dns_use_dnssec ? "" : "un");
231 # endif
232 #endif /* DISABLE_DNSSEC */
233
234 os_put_dns_resolver_res(resp);
235 }
236
237
238
239 /*************************************************
240 * Build key name for PTR records *
241 *************************************************/
242
243 /* This function inverts an IP address and adds the relevant domain, to produce
244 a name that can be used to look up PTR records.
245
246 Arguments:
247 string the IP address as a string
248 buffer a suitable buffer, long enough to hold the result
249
250 Returns: nothing
251 */
252
253 void
254 dns_build_reverse(uschar *string, uschar *buffer)
255 {
256 uschar *p = string + Ustrlen(string);
257 uschar *pp = buffer;
258
259 /* Handle IPv4 address */
260
261 #if HAVE_IPV6
262 if (Ustrchr(string, ':') == NULL)
263 #endif
264 {
265 int i;
266 for (i = 0; i < 4; i++)
267 {
268 uschar *ppp = p;
269 while (ppp > string && ppp[-1] != '.') ppp--;
270 Ustrncpy(pp, ppp, p - ppp);
271 pp += p - ppp;
272 *pp++ = '.';
273 p = ppp - 1;
274 }
275 Ustrcpy(pp, "in-addr.arpa");
276 }
277
278 /* Handle IPv6 address; convert to binary so as to fill out any
279 abbreviation in the textual form. */
280
281 #if HAVE_IPV6
282 else
283 {
284 int i;
285 int v6[4];
286 (void)host_aton(string, v6);
287
288 /* The original specification for IPv6 reverse lookup was to invert each
289 nibble, and look in the ip6.int domain. The domain was subsequently
290 changed to ip6.arpa. */
291
292 for (i = 3; i >= 0; i--)
293 {
294 int j;
295 for (j = 0; j < 32; j += 4)
296 {
297 sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
298 pp += 2;
299 }
300 }
301 Ustrcpy(pp, "ip6.arpa.");
302
303 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
304 with A6 records. However, it fell out of favour when they did. The
305 alternative was to construct a binary key, and look in ip6.arpa. I tried
306 to make this code do that, but I could not make it work on Solaris 8. The
307 resolver seems to lose the initial backslash somehow. However, now that
308 this style of reverse lookup has been dropped, it doesn't matter. These
309 lines are left here purely for historical interest. */
310
311 /**************************************************
312 Ustrcpy(pp, "\\[x");
313 pp += 3;
314
315 for (i = 0; i < 4; i++)
316 {
317 sprintf(pp, "%08X", v6[i]);
318 pp += 8;
319 }
320 Ustrcpy(pp, "].ip6.arpa.");
321 **************************************************/
322
323 }
324 #endif
325 }
326
327
328
329
330 /*************************************************
331 * Get next DNS record from answer block *
332 *************************************************/
333
334 /* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
335 RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
336 scan the additional records, and reset == RESET_NEXT to get the next record.
337 The result is in static storage which must be copied if it is to be preserved.
338
339 Arguments:
340 dnsa pointer to dns answer block
341 dnss pointer to dns scan block
342 reset option specifing what portion to scan, as described above
343
344 Returns: next dns record, or NULL when no more
345 */
346
347 dns_record *
348 dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset)
349 {
350 HEADER *h = (HEADER *)dnsa->answer;
351 int namelen;
352
353 /* Reset the saved data when requested to, and skip to the first required RR */
354
355 if (reset != RESET_NEXT)
356 {
357 dnss->rrcount = ntohs(h->qdcount);
358 dnss->aptr = dnsa->answer + sizeof(HEADER);
359
360 /* Skip over questions; failure to expand the name just gives up */
361
362 while (dnss->rrcount-- > 0)
363 {
364 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
365 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
366 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
367 dnss->aptr += namelen + 4; /* skip name & type & class */
368 }
369
370 /* Get the number of answer records. */
371
372 dnss->rrcount = ntohs(h->ancount);
373
374 /* Skip over answers if we want to look at the authority section. Also skip
375 the NS records (i.e. authority section) if wanting to look at the additional
376 records. */
377
378 if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
379
380 if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
381 {
382 while (dnss->rrcount-- > 0)
383 {
384 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
385 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
386 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
387 dnss->aptr += namelen + 8; /* skip name, type, class & TTL */
388 GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
389 dnss->aptr += dnss->srr.size; /* skip over it */
390 }
391 dnss->rrcount = (reset == RESET_AUTHORITY)
392 ? ntohs(h->nscount) : ntohs(h->arcount);
393 }
394 }
395
396 /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
397 contains the number of RR records left. */
398
399 if (dnss->rrcount-- <= 0) return NULL;
400
401 /* If expanding the RR domain name fails, behave as if no more records
402 (something safe). */
403
404 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
405 (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
406 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
407
408 /* Move the pointer past the name and fill in the rest of the data structure
409 from the following bytes. */
410
411 dnss->aptr += namelen;
412 GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
413 dnss->aptr += 6; /* Don't want class or TTL */
414 GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
415 dnss->srr.data = dnss->aptr; /* The record's data follows */
416 dnss->aptr += dnss->srr.size; /* Advance to next RR */
417
418 /* Return a pointer to the dns_record structure within the dns_answer. This is
419 for convenience so that the scans can use nice-looking for loops. */
420
421 return &(dnss->srr);
422 }
423
424
425
426
427 /*************************************************
428 * Return whether AD bit set in DNS result *
429 *************************************************/
430
431 /* We do not perform DNSSEC work ourselves; if the administrator has installed
432 a verifying resolver which sets AD as appropriate, though, we'll use that.
433 (AD = Authentic Data)
434
435 Argument: pointer to dns answer block
436 Returns: bool indicating presence of AD bit
437 */
438
439 BOOL
440 dns_is_secure(dns_answer *dnsa)
441 {
442 #ifdef DISABLE_DNSSEC
443 DEBUG(D_dns)
444 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
445 return FALSE;
446 #else
447 HEADER *h = (HEADER *)dnsa->answer;
448 return h->ad ? TRUE : FALSE;
449 #endif
450 }
451
452
453
454
455 /*************************************************
456 * Turn DNS type into text *
457 *************************************************/
458
459 /* Turn the coded record type into a string for printing. All those that Exim
460 uses should be included here.
461
462 Argument: record type
463 Returns: pointer to string
464 */
465
466 uschar *
467 dns_text_type(int t)
468 {
469 switch(t)
470 {
471 case T_A: return US"A";
472 case T_MX: return US"MX";
473 case T_AAAA: return US"AAAA";
474 case T_A6: return US"A6";
475 case T_TXT: return US"TXT";
476 case T_SPF: return US"SPF";
477 case T_PTR: return US"PTR";
478 case T_SOA: return US"SOA";
479 case T_SRV: return US"SRV";
480 case T_NS: return US"NS";
481 case T_CNAME: return US"CNAME";
482 default: return US"?";
483 }
484 }
485
486
487
488 /*************************************************
489 * Cache a failed DNS lookup result *
490 *************************************************/
491
492 /* We cache failed lookup results so as not to experience timeouts many
493 times for the same domain. We need to retain the resolver options because they
494 may change. For successful lookups, we rely on resolver and/or name server
495 caching.
496
497 Arguments:
498 name the domain name
499 type the lookup type
500 rc the return code
501
502 Returns: the return code
503 */
504
505 static int
506 dns_return(uschar *name, int type, int rc)
507 {
508 res_state resp = os_get_dns_resolver_res();
509 tree_node *node = store_get_perm(sizeof(tree_node) + 290);
510 sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
511 resp->options);
512 node->data.val = rc;
513 (void)tree_insertnode(&tree_dns_fails, node);
514 return rc;
515 }
516
517
518
519 /*************************************************
520 * Do basic DNS lookup *
521 *************************************************/
522
523 /* Call the resolver to look up the given domain name, using the given type,
524 and check the result. The error code TRY_AGAIN is documented as meaning "non-
525 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
526 up nameservers that produce this error continually, so there is the option of
527 providing a list of domains for which this is treated as a non-existent
528 host.
529
530 Arguments:
531 dnsa pointer to dns_answer structure
532 name name to look up
533 type type of DNS record required (T_A, T_MX, etc)
534
535 Returns: DNS_SUCCEED successful lookup
536 DNS_NOMATCH name not found (NXDOMAIN)
537 or name contains illegal characters (if checking)
538 or name is an IP address (for IP address lookup)
539 DNS_NODATA domain exists, but no data for this type (NODATA)
540 DNS_AGAIN soft failure, try again later
541 DNS_FAIL DNS failure
542 */
543
544 int
545 dns_basic_lookup(dns_answer *dnsa, uschar *name, int type)
546 {
547 #ifndef STAND_ALONE
548 int rc = -1;
549 uschar *save;
550 #endif
551 res_state resp = os_get_dns_resolver_res();
552
553 tree_node *previous;
554 uschar node_name[290];
555
556 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
557 a timeout on one domain doesn't happen time and time again for messages that
558 have many addresses in the same domain. We rely on the resolver and name server
559 caching for successful lookups. */
560
561 sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
562 resp->options);
563 previous = tree_search(tree_dns_fails, node_name);
564 if (previous != NULL)
565 {
566 DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
567 name, dns_text_type(type),
568 (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
569 (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
570 (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
571 (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
572 return previous->data.val;
573 }
574
575 /* If configured, check the hygene of the name passed to lookup. Otherwise,
576 although DNS lookups may give REFUSED at the lower level, some resolvers
577 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
578 domains cannot be in the DNS. The check is now done by a regular expression;
579 give it space for substring storage to save it having to get its own if the
580 regex has substrings that are used - the default uses a conditional.
581
582 This test is omitted for PTR records. These occur only in calls from the dnsdb
583 lookup, which constructs the names itself, so they should be OK. Besides,
584 bitstring labels don't conform to normal name syntax. (But the aren't used any
585 more.)
586
587 For SRV records, we omit the initial _smtp._tcp. components at the start. */
588
589 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
590
591 if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
592 {
593 uschar *checkname = name;
594 int ovector[3*(EXPAND_MAXN+1)];
595
596 if (regex_check_dns_names == NULL)
597 regex_check_dns_names =
598 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);
599
600 /* For an SRV lookup, skip over the first two components (the service and
601 protocol names, which both start with an underscore). */
602
603 if (type == T_SRV)
604 {
605 while (*checkname++ != '.');
606 while (*checkname++ != '.');
607 }
608
609 if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname),
610 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
611 {
612 DEBUG(D_dns)
613 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
614 dns_text_type(type));
615 host_find_failed_syntax = TRUE;
616 return DNS_NOMATCH;
617 }
618 }
619
620 #endif /* STAND_ALONE */
621
622 /* Call the resolver; for an overlong response, res_search() will return the
623 number of bytes the message would need, so we need to check for this case. The
624 effect is to truncate overlong data.
625
626 On some systems, res_search() will recognize "A-for-A" queries and return
627 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
628 nameservers are also believed to do this. It is, of course, contrary to the
629 specification of the DNS, so we lock it out. */
630
631 if ((
632 #ifdef SUPPORT_A6
633 type == T_A6 ||
634 #endif
635 type == T_A || type == T_AAAA) &&
636 string_is_ip_address(name, NULL) != 0)
637 return DNS_NOMATCH;
638
639 /* If we are running in the test harness, instead of calling the normal resolver
640 (res_search), we call fakens_search(), which recognizes certain special
641 domains, and interfaces to a fake nameserver for certain special zones. */
642
643 if (running_in_test_harness)
644 dnsa->answerlen = fakens_search(name, type, dnsa->answer, MAXPACKET);
645 else
646 dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET);
647
648 if (dnsa->answerlen > MAXPACKET)
649 {
650 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
651 name, dns_text_type(type), dnsa->answerlen, MAXPACKET);
652 dnsa->answerlen = MAXPACKET;
653 }
654
655 if (dnsa->answerlen < 0) switch (h_errno)
656 {
657 case HOST_NOT_FOUND:
658 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
659 "returning DNS_NOMATCH\n", name, dns_text_type(type));
660 return dns_return(name, type, DNS_NOMATCH);
661
662 case TRY_AGAIN:
663 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
664 name, dns_text_type(type));
665
666 /* Cut this out for various test programs */
667 #ifndef STAND_ALONE
668 save = deliver_domain;
669 deliver_domain = name; /* set $domain */
670 rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL,
671 MCL_DOMAIN, TRUE, NULL);
672 deliver_domain = save;
673 if (rc != OK)
674 {
675 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
676 return dns_return(name, type, DNS_AGAIN);
677 }
678 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
679 "DNS_NOMATCH\n", name);
680 return dns_return(name, type, DNS_NOMATCH);
681
682 #else /* For stand-alone tests */
683 return dns_return(name, type, DNS_AGAIN);
684 #endif
685
686 case NO_RECOVERY:
687 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
688 "returning DNS_FAIL\n", name, dns_text_type(type));
689 return dns_return(name, type, DNS_FAIL);
690
691 case NO_DATA:
692 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
693 "returning DNS_NODATA\n", name, dns_text_type(type));
694 return dns_return(name, type, DNS_NODATA);
695
696 default:
697 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
698 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
699 return dns_return(name, type, DNS_FAIL);
700 }
701
702 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
703 name, dns_text_type(type));
704
705 return DNS_SUCCEED;
706 }
707
708
709
710
711 /************************************************
712 * Do a DNS lookup and handle CNAMES *
713 ************************************************/
714
715 /* Look up the given domain name, using the given type. Follow CNAMEs if
716 necessary, but only so many times. There aren't supposed to be CNAME chains in
717 the DNS, but you are supposed to cope with them if you find them.
718
719 The assumption is made that if the resolver gives back records of the
720 requested type *and* a CNAME, we don't need to make another call to look up
721 the CNAME. I can't see how it could return only some of the right records. If
722 it's done a CNAME lookup in the past, it will have all of them; if not, it
723 won't return any.
724
725 If fully_qualified_name is not NULL, set it to point to the full name
726 returned by the resolver, if this is different to what it is given, unless
727 the returned name starts with "*" as some nameservers seem to be returning
728 wildcards in this form.
729
730 Arguments:
731 dnsa pointer to dns_answer structure
732 name domain name to look up
733 type DNS record type (T_A, T_MX, etc)
734 fully_qualified_name if not NULL, return the returned name here if its
735 contents are different (i.e. it must be preset)
736
737 Returns: DNS_SUCCEED successful lookup
738 DNS_NOMATCH name not found
739 DNS_NODATA no data found
740 DNS_AGAIN soft failure, try again later
741 DNS_FAIL DNS failure
742 */
743
744 int
745 dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name)
746 {
747 int i;
748 uschar *orig_name = name;
749
750 /* Loop to follow CNAME chains so far, but no further... */
751
752 for (i = 0; i < 10; i++)
753 {
754 uschar data[256];
755 dns_record *rr, cname_rr, type_rr;
756 dns_scan dnss;
757 int datalen, rc;
758
759 /* DNS lookup failures get passed straight back. */
760
761 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
762
763 /* We should have either records of the required type, or a CNAME record,
764 or both. We need to know whether both exist for getting the fully qualified
765 name, but avoid scanning more than necessary. Note that we must copy the
766 contents of any rr blocks returned by dns_next_rr() as they use the same
767 area in the dnsa block. */
768
769 cname_rr.data = type_rr.data = NULL;
770 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
771 rr != NULL;
772 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
773 {
774 if (rr->type == type)
775 {
776 if (type_rr.data == NULL) type_rr = *rr;
777 if (cname_rr.data != NULL) break;
778 }
779 else if (rr->type == T_CNAME) cname_rr = *rr;
780 }
781
782 /* For the first time round this loop, if a CNAME was found, take the fully
783 qualified name from it; otherwise from the first data record, if present. */
784
785 if (i == 0 && fully_qualified_name != NULL)
786 {
787 if (cname_rr.data != NULL)
788 {
789 if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 &&
790 cname_rr.name[0] != '*')
791 *fully_qualified_name = string_copy_dnsdomain(cname_rr.name);
792 }
793 else if (type_rr.data != NULL)
794 {
795 if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 &&
796 type_rr.name[0] != '*')
797 *fully_qualified_name = string_copy_dnsdomain(type_rr.name);
798 }
799 }
800
801 /* If any data records of the correct type were found, we are done. */
802
803 if (type_rr.data != NULL) return DNS_SUCCEED;
804
805 /* If there are no data records, we need to re-scan the DNS using the
806 domain given in the CNAME record, which should exist (otherwise we should
807 have had a failure from dns_lookup). However code against the possibility of
808 its not existing. */
809
810 if (cname_rr.data == NULL) return DNS_FAIL;
811 datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
812 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256);
813 if (datalen < 0) return DNS_FAIL;
814 name = data;
815
816 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
817 } /* Loop back to do another lookup */
818
819 /*Control reaches here after 10 times round the CNAME loop. Something isn't
820 right... */
821
822 log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
823 return DNS_FAIL;
824 }
825
826
827
828
829
830
831 /************************************************
832 * Do a DNS lookup and handle virtual types *
833 ************************************************/
834
835 /* This function handles some invented "lookup types" that synthesize feature
836 not available in the basic types. The special types all have negative values.
837 Positive type values are passed straight on to dns_lookup().
838
839 Arguments:
840 dnsa pointer to dns_answer structure
841 name domain name to look up
842 type DNS record type (T_A, T_MX, etc or a "special")
843 fully_qualified_name if not NULL, return the returned name here if its
844 contents are different (i.e. it must be preset)
845
846 Returns: DNS_SUCCEED successful lookup
847 DNS_NOMATCH name not found
848 DNS_NODATA no data found
849 DNS_AGAIN soft failure, try again later
850 DNS_FAIL DNS failure
851 */
852
853 int
854 dns_special_lookup(dns_answer *dnsa, uschar *name, int type,
855 uschar **fully_qualified_name)
856 {
857 if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name);
858
859 /* The "mx hosts only" type doesn't require any special action here */
860
861 if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
862
863 /* Find nameservers for the domain or the nearest enclosing zone, excluding the
864 root servers. */
865
866 if (type == T_ZNS)
867 {
868 uschar *d = name;
869 while (d != 0)
870 {
871 int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name);
872 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
873 while (*d != 0 && *d != '.') d++;
874 if (*d++ == 0) break;
875 }
876 return DNS_NOMATCH;
877 }
878
879 /* Try to look up the Client SMTP Authorization SRV record for the name. If
880 there isn't one, search from the top downwards for a CSA record in a parent
881 domain, which might be making assertions about subdomains. If we find a record
882 we set fully_qualified_name to whichever lookup succeeded, so that the caller
883 can tell whether to look at the explicit authorization field or the subdomain
884 assertion field. */
885
886 if (type == T_CSA)
887 {
888 uschar *srvname, *namesuff, *tld, *p;
889 int priority, weight, port;
890 int limit, rc, i;
891 BOOL ipv6;
892 dns_record *rr;
893 dns_scan dnss;
894
895 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
896
897 srvname = string_sprintf("_client._smtp.%s", name);
898 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
899 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
900 {
901 if (rc == DNS_SUCCEED) *fully_qualified_name = name;
902 return rc;
903 }
904
905 /* Search for CSA subdomain assertion SRV records from the top downwards,
906 starting with the 2nd level domain. This order maximizes cache-friendliness.
907 We skip the top level domains to avoid loading their nameservers and because
908 we know they'll never have CSA SRV records. */
909
910 namesuff = Ustrrchr(name, '.');
911 if (namesuff == NULL) return DNS_NOMATCH;
912 tld = namesuff + 1;
913 ipv6 = FALSE;
914 limit = dns_csa_search_limit;
915
916 /* Use more appropriate search parameters if we are in the reverse DNS. */
917
918 if (strcmpic(namesuff, US".arpa") == 0)
919 {
920 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
921 {
922 namesuff -= 8;
923 tld = namesuff + 1;
924 limit = 3;
925 }
926 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
927 {
928 namesuff -= 4;
929 tld = namesuff + 1;
930 ipv6 = TRUE;
931 limit = 3;
932 }
933 }
934
935 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
936
937 /* Do not perform the search if the top level or 2nd level domains do not
938 exist. This is quite common, and when it occurs all the search queries would
939 go to the root or TLD name servers, which is not friendly. So we check the
940 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
941 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
942 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
943 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
944
945 if (rc == DNS_NOMATCH)
946 {
947 /* This is really gross. The successful return value from res_search() is
948 the packet length, which is stored in dnsa->answerlen. If we get a
949 negative DNS reply then res_search() returns -1, which causes the bounds
950 checks for name decompression to fail when it is treated as a packet
951 length, which in turn causes the authority search to fail. The correct
952 packet length has been lost inside libresolv, so we have to guess a
953 replacement value. (The only way to fix this properly would be to
954 re-implement res_search() and res_query() so that they don't muddle their
955 success and packet length return values.) For added safety we only reset
956 the packet length if the packet header looks plausible. */
957
958 HEADER *h = (HEADER *)dnsa->answer;
959 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
960 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
961 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
962 && ntohs(h->nscount) >= 1)
963 dnsa->answerlen = MAXPACKET;
964
965 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
966 rr != NULL;
967 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
968 if (rr->type != T_SOA) continue;
969 else if (strcmpic(rr->name, US"") == 0 ||
970 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
971 else break;
972 }
973
974 for (i = 0; i < limit; i++)
975 {
976 if (ipv6)
977 {
978 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
979 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
980 namesuff -= 8;
981 if (namesuff <= name) return DNS_NOMATCH;
982 }
983 else
984 /* Find the start of the preceding domain name label. */
985 do
986 if (--namesuff <= name) return DNS_NOMATCH;
987 while (*namesuff != '.');
988
989 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
990
991 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
992 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
993 if (rc == DNS_AGAIN) return rc;
994 if (rc != DNS_SUCCEED) continue;
995
996 /* Check that the SRV record we have found is worth returning. We don't
997 just return the first one we find, because some lower level SRV record
998 might make stricter assertions than its parent domain. */
999
1000 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
1001 rr != NULL;
1002 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1003 {
1004 if (rr->type != T_SRV) continue;
1005
1006 /* Extract the numerical SRV fields (p is incremented) */
1007 p = rr->data;
1008 GETSHORT(priority, p);
1009 GETSHORT(weight, p);
1010 GETSHORT(port, p);
1011
1012 /* Check the CSA version number */
1013 if (priority != 1) continue;
1014
1015 /* If it's making an interesting assertion, return this response. */
1016 if (port & 1)
1017 {
1018 *fully_qualified_name = namesuff + 1;
1019 return DNS_SUCCEED;
1020 }
1021 }
1022 }
1023 return DNS_NOMATCH;
1024 }
1025
1026 /* Control should never reach here */
1027
1028 return DNS_FAIL;
1029 }
1030
1031
1032
1033 /* Support for A6 records has been commented out since they were demoted to
1034 experimental status at IETF 51. */
1035
1036 #if HAVE_IPV6 && defined(SUPPORT_A6)
1037
1038 /*************************************************
1039 * Search DNS block for prefix RRs *
1040 *************************************************/
1041
1042 /* Called from dns_complete_a6() to search an additional section or a main
1043 answer section for required prefix records to complete an IPv6 address obtained
1044 from an A6 record. For each prefix record, a recursive call to dns_complete_a6
1045 is made, with a new copy of the address so far.
1046
1047 Arguments:
1048 dnsa the DNS answer block
1049 which RESET_ADDITIONAL or RESET_ANSWERS
1050 name name of prefix record
1051 yptrptr pointer to the pointer that points to where to hang the next
1052 dns_address structure
1053 bits number of bits we have already got
1054 bitvec the bits we have already got
1055
1056 Returns: TRUE if any records were found
1057 */
1058
1059 static BOOL
1060 dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address
1061 ***yptrptr, int bits, uschar *bitvec)
1062 {
1063 BOOL yield = FALSE;
1064 dns_record *rr;
1065 dns_scan dnss;
1066
1067 for (rr = dns_next_rr(dnsa, &dnss, which);
1068 rr != NULL;
1069 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1070 {
1071 uschar cbitvec[16];
1072 if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue;
1073 yield = TRUE;
1074 memcpy(cbitvec, bitvec, sizeof(cbitvec));
1075 dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec);
1076 }
1077
1078 return yield;
1079 }
1080
1081
1082
1083 /*************************************************
1084 * Follow chains of A6 records *
1085 *************************************************/
1086
1087 /* A6 records may be incomplete, with pointers to other records containing more
1088 bits of the address. There can be a tree structure, leading to a number of
1089 addresses originating from a single initial A6 record.
1090
1091 Arguments:
1092 yptrptr pointer to the pointer that points to where to hang the next
1093 dns_address structure
1094 dnsa the current DNS answer block
1095 rr the RR we have at present
1096 bits number of bits we have already got
1097 bitvec the bits we have already got
1098
1099 Returns: nothing
1100 */
1101
1102 static void
1103 dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr,
1104 int bits, uschar *bitvec)
1105 {
1106 static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 };
1107 uschar *p = (uschar *)(rr->data);
1108 int prefix_len, suffix_len;
1109 int i, j, k;
1110 uschar *chainptr;
1111 uschar chain[264];
1112 dns_answer cdnsa;
1113
1114 /* The prefix length is the first byte. It defines the prefix which is missing
1115 from the data in this record as a number of bits. Zero means this is the end of
1116 a chain. The suffix is the data in this record; only sufficient bytes to hold
1117 it are supplied. There may be zero bytes. We have to ignore trailing bits that
1118 we have already obtained from earlier RRs in the chain. */
1119
1120 prefix_len = *p++; /* bits */
1121 suffix_len = (128 - prefix_len + 7)/8; /* bytes */
1122
1123 /* If the prefix in this record is greater than the prefix in the previous
1124 record in the chain, we have to ignore the record (RFC 2874). */
1125
1126 if (prefix_len > 128 - bits) return;
1127
1128 /* In this little loop, the number of bits up to and including the current byte
1129 is held in k. If we have none of the bits in this byte, we can just or it into
1130 the current data. If we have all of the bits in this byte, we skip it.
1131 Otherwise, some masking has to be done. */
1132
1133 for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--)
1134 {
1135 int required = k - bits;
1136 if (required >= 8) bitvec[j] |= p[i];
1137 else if (required > 0) bitvec[j] |= p[i] & bitmask[required];
1138 j--; /* I tried putting these in the "for" statement, but gcc muttered */
1139 k += 8; /* about computed values not being used. */
1140 }
1141
1142 /* If the prefix_length is zero, we are at the end of a chain. Build a
1143 dns_address item with the current data, hang it onto the end of the chain,
1144 adjust the hanging pointer, and we are done. */
1145
1146 if (prefix_len == 0)
1147 {
1148 dns_address *new = store_get(sizeof(dns_address) + 50);
1149 inet_ntop(AF_INET6, bitvec, CS new->address, 50);
1150 new->next = NULL;
1151 **yptrptr = new;
1152 *yptrptr = &(new->next);
1153 return;
1154 }
1155
1156 /* Prefix length is not zero. Reset the number of bits that we have collected
1157 so far, and extract the chain name. */
1158
1159 bits = 128 - prefix_len;
1160 p += suffix_len;
1161
1162 chainptr = chain;
1163 while ((i = *p++) != 0)
1164 {
1165 if (chainptr != chain) *chainptr++ = '.';
1166 memcpy(chainptr, p, i);
1167 chainptr += i;
1168 p += i;
1169 }
1170 *chainptr = 0;
1171 chainptr = chain;
1172
1173 /* Now scan the current DNS response record to see if the additional section
1174 contains the records we want. This processing can be cut out for testing
1175 purposes. */
1176
1177 if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec))
1178 return;
1179
1180 /* No chain records were found in the current DNS response block. Do a new DNS
1181 lookup to try to find these records. This opens up the possibility of DNS
1182 failures. We ignore them at this point; if all branches of the tree fail, there
1183 will be no addresses at the end. */
1184
1185 if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED)
1186 (void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec);
1187 }
1188 #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */
1189
1190
1191
1192
1193 /*************************************************
1194 * Get address(es) from DNS record *
1195 *************************************************/
1196
1197 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1198 supported) for an IPv6 address. In the A6 case, there may be several addresses,
1199 generated by following chains. A recursive function does all the hard work. A6
1200 records now look like passing into history, so the code is only included when
1201 explicitly asked for.
1202
1203 Argument:
1204 dnsa the DNS answer block
1205 rr the RR
1206
1207 Returns: pointer a chain of dns_address items
1208 */
1209
1210 dns_address *
1211 dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1212 {
1213 dns_address *yield = NULL;
1214
1215 #if HAVE_IPV6 && defined(SUPPORT_A6)
1216 dns_address **yieldptr = &yield;
1217 uschar bitvec[16];
1218 #else
1219 dnsa = dnsa; /* Stop picky compilers warning */
1220 #endif
1221
1222 if (rr->type == T_A)
1223 {
1224 uschar *p = (uschar *)(rr->data);
1225 yield = store_get(sizeof(dns_address) + 20);
1226 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1227 yield->next = NULL;
1228 }
1229
1230 #if HAVE_IPV6
1231
1232 #ifdef SUPPORT_A6
1233 else if (rr->type == T_A6)
1234 {
1235 memset(bitvec, 0, sizeof(bitvec));
1236 dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec);
1237 }
1238 #endif /* SUPPORT_A6 */
1239
1240 else
1241 {
1242 yield = store_get(sizeof(dns_address) + 50);
1243 inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50);
1244 yield->next = NULL;
1245 }
1246 #endif /* HAVE_IPV6 */
1247
1248 return yield;
1249 }
1250
1251 /* End of dns.c */