1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2015 */
6 /* See the file NOTICE for conditions of use and distribution. */
8 /* Functions for interfacing with the DNS. */
14 /*************************************************
16 *************************************************/
18 /* This function is called instead of res_search() when Exim is running in its
19 test harness. It recognizes some special domain names, and uses them to force
20 failure and retry responses (optionally with a delay). Otherwise, it calls an
21 external utility that mocks-up a nameserver, if it can find the utility.
22 If not, it passes its arguments on to res_search(). The fake nameserver may
23 also return a code specifying that the name should be passed on.
25 Background: the original test suite required a real nameserver to carry the
26 test zones, whereas the new test suite has the fake server for portability. This
30 domain the domain name
31 type the DNS record type
32 answerptr where to put the answer
33 size size of the answer area
35 Returns: length of returned data, or -1 on error (h_errno set)
39 fakens_search(const uschar *domain, int type, uschar *answerptr, int size)
41 int len = Ustrlen(domain);
42 int asize = size; /* Locally modified */
46 uschar *aptr = answerptr; /* Locally modified */
49 /* Remove terminating dot. */
51 if (domain[len - 1] == '.') len--;
52 Ustrncpy(name, domain, len);
56 /* Look for the fakens utility, and if it exists, call it. */
58 (void)string_format(utilname, sizeof(utilname), "%s/bin/fakens",
59 config_main_directory);
61 if (stat(CS utilname, &statbuf) >= 0)
67 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", name, dns_text_type(type));
70 argv[1] = config_main_directory;
72 argv[3] = dns_text_type(type);
75 pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
77 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
82 while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
85 aptr += rc; /* Don't modify the actual arguments, because they */
86 asize -= rc; /* may need to be passed on to res_search(). */
89 /* If we ran out of output buffer before exhasting the return,
90 carry on reading and counting it. */
93 while ((rc = read(outfd, name, sizeof(name))) > 0)
97 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
100 switch(child_close(pid, 0))
103 case 1: h_errno = HOST_NOT_FOUND; return -1;
104 case 2: h_errno = TRY_AGAIN; return -1;
106 case 3: h_errno = NO_RECOVERY; return -1;
107 case 4: h_errno = NO_DATA; return -1;
108 case 5: /* Pass on to res_search() */
109 DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
114 DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname);
117 /* fakens utility not found, or it returned "pass on" */
119 DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain);
121 return res_search(CS domain, C_IN, type, answerptr, size);
126 /*************************************************
127 * Initialize and configure resolver *
128 *************************************************/
130 /* Initialize the resolver and the storage for holding DNS answers if this is
131 the first time we have been here, and set the resolver options.
134 qualify_single TRUE to set the RES_DEFNAMES option
135 search_parents TRUE to set the RES_DNSRCH option
136 use_dnssec TRUE to set the RES_USE_DNSSEC option
142 dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec)
144 res_state resp = os_get_dns_resolver_res();
146 if ((resp->options & RES_INIT) == 0)
148 DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */
149 os_put_dns_resolver_res(resp);
151 DEBUG(D_resolver) resp->options |= RES_DEBUG;
152 os_put_dns_resolver_res(resp);
155 resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
156 resp->options |= (qualify_single? RES_DEFNAMES : 0) |
157 (search_parents? RES_DNSRCH : 0);
158 if (dns_retrans > 0) resp->retrans = dns_retrans;
159 if (dns_retry > 0) resp->retry = dns_retry;
162 if (dns_use_edns0 >= 0)
165 resp->options |= RES_USE_EDNS0;
167 resp->options &= ~RES_USE_EDNS0;
169 debug_printf("Coerced resolver EDNS0 support %s.\n",
170 dns_use_edns0 ? "on" : "off");
173 if (dns_use_edns0 >= 0)
175 debug_printf("Unable to %sset EDNS0 without resolver support.\n",
176 dns_use_edns0 ? "" : "un");
179 #ifndef DISABLE_DNSSEC
180 # ifdef RES_USE_DNSSEC
181 # ifndef RES_USE_EDNS0
182 # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ...
185 resp->options |= RES_USE_DNSSEC;
186 if (dns_dnssec_ok >= 0)
188 if (dns_use_edns0 == 0 && dns_dnssec_ok != 0)
191 debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n");
196 resp->options |= RES_USE_DNSSEC;
198 resp->options &= ~RES_USE_DNSSEC;
199 DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n",
200 dns_dnssec_ok ? "on" : "off");
204 if (dns_dnssec_ok >= 0)
206 debug_printf("Unable to %sset DNSSEC without resolver support.\n",
207 dns_dnssec_ok ? "" : "un");
210 debug_printf("Unable to set DNSSEC without resolver support.\n");
212 #endif /* DISABLE_DNSSEC */
214 os_put_dns_resolver_res(resp);
219 /*************************************************
220 * Build key name for PTR records *
221 *************************************************/
223 /* This function inverts an IP address and adds the relevant domain, to produce
224 a name that can be used to look up PTR records.
227 string the IP address as a string
228 buffer a suitable buffer, long enough to hold the result
234 dns_build_reverse(const uschar *string, uschar *buffer)
236 const uschar *p = string + Ustrlen(string);
239 /* Handle IPv4 address */
242 if (Ustrchr(string, ':') == NULL)
246 for (i = 0; i < 4; i++)
248 const uschar *ppp = p;
249 while (ppp > string && ppp[-1] != '.') ppp--;
250 Ustrncpy(pp, ppp, p - ppp);
255 Ustrcpy(pp, "in-addr.arpa");
258 /* Handle IPv6 address; convert to binary so as to fill out any
259 abbreviation in the textual form. */
266 (void)host_aton(string, v6);
268 /* The original specification for IPv6 reverse lookup was to invert each
269 nibble, and look in the ip6.int domain. The domain was subsequently
270 changed to ip6.arpa. */
272 for (i = 3; i >= 0; i--)
275 for (j = 0; j < 32; j += 4)
277 sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
281 Ustrcpy(pp, "ip6.arpa.");
283 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
284 with A6 records. However, it fell out of favour when they did. The
285 alternative was to construct a binary key, and look in ip6.arpa. I tried
286 to make this code do that, but I could not make it work on Solaris 8. The
287 resolver seems to lose the initial backslash somehow. However, now that
288 this style of reverse lookup has been dropped, it doesn't matter. These
289 lines are left here purely for historical interest. */
291 /**************************************************
295 for (i = 0; i < 4; i++)
297 sprintf(pp, "%08X", v6[i]);
300 Ustrcpy(pp, "].ip6.arpa.");
301 **************************************************/
310 /*************************************************
311 * Get next DNS record from answer block *
312 *************************************************/
314 /* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
315 RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
316 scan the additional records, and reset == RESET_NEXT to get the next record.
317 The result is in static storage which must be copied if it is to be preserved.
320 dnsa pointer to dns answer block
321 dnss pointer to dns scan block
322 reset option specifing what portion to scan, as described above
324 Returns: next dns record, or NULL when no more
328 dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset)
330 HEADER *h = (HEADER *)dnsa->answer;
333 /* Reset the saved data when requested to, and skip to the first required RR */
335 if (reset != RESET_NEXT)
337 dnss->rrcount = ntohs(h->qdcount);
338 dnss->aptr = dnsa->answer + sizeof(HEADER);
340 /* Skip over questions; failure to expand the name just gives up */
342 while (dnss->rrcount-- > 0)
344 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
345 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
346 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
347 dnss->aptr += namelen + 4; /* skip name & type & class */
350 /* Get the number of answer records. */
352 dnss->rrcount = ntohs(h->ancount);
354 /* Skip over answers if we want to look at the authority section. Also skip
355 the NS records (i.e. authority section) if wanting to look at the additional
358 if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
360 if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
362 while (dnss->rrcount-- > 0)
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 + 8; /* skip name, type, class & TTL */
368 GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
369 dnss->aptr += dnss->srr.size; /* skip over it */
371 dnss->rrcount = (reset == RESET_AUTHORITY)
372 ? ntohs(h->nscount) : ntohs(h->arcount);
376 /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
377 contains the number of RR records left. */
379 if (dnss->rrcount-- <= 0) return NULL;
381 /* If expanding the RR domain name fails, behave as if no more records
384 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
385 (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
386 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
388 /* Move the pointer past the name and fill in the rest of the data structure
389 from the following bytes. */
391 dnss->aptr += namelen;
392 GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
393 dnss->aptr += 6; /* Don't want class or TTL */
394 GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
395 dnss->srr.data = dnss->aptr; /* The record's data follows */
396 dnss->aptr += dnss->srr.size; /* Advance to next RR */
398 /* Return a pointer to the dns_record structure within the dns_answer. This is
399 for convenience so that the scans can use nice-looking for loops. */
405 /* Extract the AUTHORITY info from the answer. If the
406 * answer isn't authoritive (AA) we do not extract anything.
407 * We've to search for SOA or NS records, since there may be
408 * other records (e.g. NSEC3) too.
411 dns_extract_auth_name(const dns_answer *dnsa) /* FIXME: const dns_answer */
415 HEADER *h = (HEADER *) dnsa->answer;
416 if (!h->nscount || !h->aa) return NULL;
417 for (rr = dns_next_rr((dns_answer*) dnsa, &dnss, RESET_AUTHORITY);
419 rr = dns_next_rr((dns_answer*) dnsa, &dnss, RESET_NEXT))
420 if (rr->type == T_SOA || rr->type == T_NS) return rr->name;
427 /*************************************************
428 * Return whether AD bit set in DNS result *
429 *************************************************/
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, AA = Authoritive Answer)
435 Argument: pointer to dns answer block
436 Returns: bool indicating presence of AD bit
440 dns_is_secure(const dns_answer * dnsa)
442 #ifdef DISABLE_DNSSEC
444 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
447 HEADER *h = (HEADER *) dnsa->answer;
449 if (h->ad) return TRUE;
452 /* If the resolver we ask is authoritive for the domain in question, it
453 * may not set the AD but the AA bit. If we explicitly trust
454 * the resolver for that domain (via a domainlist in dns_trust_aa),
455 * we return TRUE to indicate a secure answer.
457 const uschar *auth_name;
458 const uschar *trusted;
460 if (!h->aa || !dns_trust_aa) return FALSE;
462 trusted = expand_string(dns_trust_aa);
463 auth_name = dns_extract_auth_name(dnsa);
464 if (OK != match_isinlist(auth_name, &trusted, 0, NULL, NULL, MCL_DOMAIN, TRUE, NULL))
468 debug_printf("DNS faked the AD bit (got AA and matched with dns_trust_aa (%s in %s))\n", auth_name, dns_trust_aa);
476 dns_set_insecure(dns_answer * dnsa)
478 HEADER * h = (HEADER *)dnsa->answer;
482 /************************************************
483 * Check whether the AA bit is set *
484 * We need this to warn if we requested AD *
485 * from an authoritive server *
486 ************************************************/
489 dns_is_aa(const dns_answer *dnsa)
491 return ((HEADER*)dnsa->answer)->aa;
496 /*************************************************
497 * Turn DNS type into text *
498 *************************************************/
500 /* Turn the coded record type into a string for printing. All those that Exim
501 uses should be included here.
503 Argument: record type
504 Returns: pointer to string
512 case T_A: return US"A";
513 case T_MX: return US"MX";
514 case T_AAAA: return US"AAAA";
515 case T_A6: return US"A6";
516 case T_TXT: return US"TXT";
517 case T_SPF: return US"SPF";
518 case T_PTR: return US"PTR";
519 case T_SOA: return US"SOA";
520 case T_SRV: return US"SRV";
521 case T_NS: return US"NS";
522 case T_CNAME: return US"CNAME";
523 case T_TLSA: return US"TLSA";
524 default: return US"?";
530 /*************************************************
531 * Cache a failed DNS lookup result *
532 *************************************************/
534 /* We cache failed lookup results so as not to experience timeouts many
535 times for the same domain. We need to retain the resolver options because they
536 may change. For successful lookups, we rely on resolver and/or name server
544 Returns: the return code
548 dns_return(const uschar * name, int type, int rc)
550 res_state resp = os_get_dns_resolver_res();
551 tree_node *node = store_get_perm(sizeof(tree_node) + 290);
552 sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
555 (void)tree_insertnode(&tree_dns_fails, node);
559 /*************************************************
560 * Do basic DNS lookup *
561 *************************************************/
563 /* Call the resolver to look up the given domain name, using the given type,
564 and check the result. The error code TRY_AGAIN is documented as meaning "non-
565 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
566 up nameservers that produce this error continually, so there is the option of
567 providing a list of domains for which this is treated as a non-existent
571 dnsa pointer to dns_answer structure
573 type type of DNS record required (T_A, T_MX, etc)
575 Returns: DNS_SUCCEED successful lookup
576 DNS_NOMATCH name not found (NXDOMAIN)
577 or name contains illegal characters (if checking)
578 or name is an IP address (for IP address lookup)
579 DNS_NODATA domain exists, but no data for this type (NODATA)
580 DNS_AGAIN soft failure, try again later
585 dns_basic_lookup(dns_answer *dnsa, const uschar *name, int type)
589 const uschar *save_domain;
591 res_state resp = os_get_dns_resolver_res();
594 uschar node_name[290];
596 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
597 a timeout on one domain doesn't happen time and time again for messages that
598 have many addresses in the same domain. We rely on the resolver and name server
599 caching for successful lookups. */
601 sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
603 previous = tree_search(tree_dns_fails, node_name);
604 if (previous != NULL)
606 DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
607 name, dns_text_type(type),
608 (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
609 (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
610 (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
611 (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
612 return previous->data.val;
615 #ifdef EXPERIMENTAL_INTERNATIONAL
616 /* Convert all names to a-label form before doing lookup */
619 uschar * errstr = NULL;
620 DEBUG(D_dns) if (string_is_utf8(name))
621 debug_printf("convert utf8 '%s' to alabel for for lookup\n", name);
622 if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr)
625 debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
627 host_find_failed_syntax = TRUE;
634 /* If configured, check the hygene of the name passed to lookup. Otherwise,
635 although DNS lookups may give REFUSED at the lower level, some resolvers
636 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
637 domains cannot be in the DNS. The check is now done by a regular expression;
638 give it space for substring storage to save it having to get its own if the
639 regex has substrings that are used - the default uses a conditional.
641 This test is omitted for PTR records. These occur only in calls from the dnsdb
642 lookup, which constructs the names itself, so they should be OK. Besides,
643 bitstring labels don't conform to normal name syntax. (But the aren't used any
646 For SRV records, we omit the initial _smtp._tcp. components at the start. */
648 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
650 if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
652 const uschar *checkname = name;
653 int ovector[3*(EXPAND_MAXN+1)];
657 /* For an SRV lookup, skip over the first two components (the service and
658 protocol names, which both start with an underscore). */
660 if (type == T_SRV || type == T_TLSA)
662 while (*checkname++ != '.');
663 while (*checkname++ != '.');
666 if (pcre_exec(regex_check_dns_names, NULL, CCS checkname, Ustrlen(checkname),
667 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
670 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
671 dns_text_type(type));
672 host_find_failed_syntax = TRUE;
677 #endif /* STAND_ALONE */
679 /* Call the resolver; for an overlong response, res_search() will return the
680 number of bytes the message would need, so we need to check for this case. The
681 effect is to truncate overlong data.
683 On some systems, res_search() will recognize "A-for-A" queries and return
684 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
685 nameservers are also believed to do this. It is, of course, contrary to the
686 specification of the DNS, so we lock it out. */
688 if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0)
691 /* If we are running in the test harness, instead of calling the normal resolver
692 (res_search), we call fakens_search(), which recognizes certain special
693 domains, and interfaces to a fake nameserver for certain special zones. */
695 dnsa->answerlen = running_in_test_harness
696 ? fakens_search(name, type, dnsa->answer, MAXPACKET)
697 : res_search(CCS name, C_IN, type, dnsa->answer, MAXPACKET);
699 if (dnsa->answerlen > MAXPACKET)
701 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
702 name, dns_text_type(type), dnsa->answerlen, MAXPACKET);
703 dnsa->answerlen = MAXPACKET;
706 if (dnsa->answerlen < 0) switch (h_errno)
709 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
710 "returning DNS_NOMATCH\n", name, dns_text_type(type));
711 return dns_return(name, type, DNS_NOMATCH);
714 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
715 name, dns_text_type(type));
717 /* Cut this out for various test programs */
719 save_domain = deliver_domain;
720 deliver_domain = string_copy(name); /* set $domain */
721 rc = match_isinlist(name, (const uschar **)&dns_again_means_nonexist, 0, NULL, NULL,
722 MCL_DOMAIN, TRUE, NULL);
723 deliver_domain = save_domain;
726 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
727 return dns_return(name, type, DNS_AGAIN);
729 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
730 "DNS_NOMATCH\n", name);
731 return dns_return(name, type, DNS_NOMATCH);
733 #else /* For stand-alone tests */
734 return dns_return(name, type, DNS_AGAIN);
738 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
739 "returning DNS_FAIL\n", name, dns_text_type(type));
740 return dns_return(name, type, DNS_FAIL);
743 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
744 "returning DNS_NODATA\n", name, dns_text_type(type));
745 return dns_return(name, type, DNS_NODATA);
748 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
749 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
750 return dns_return(name, type, DNS_FAIL);
753 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
754 name, dns_text_type(type));
762 /************************************************
763 * Do a DNS lookup and handle CNAMES *
764 ************************************************/
766 /* Look up the given domain name, using the given type. Follow CNAMEs if
767 necessary, but only so many times. There aren't supposed to be CNAME chains in
768 the DNS, but you are supposed to cope with them if you find them.
770 The assumption is made that if the resolver gives back records of the
771 requested type *and* a CNAME, we don't need to make another call to look up
772 the CNAME. I can't see how it could return only some of the right records. If
773 it's done a CNAME lookup in the past, it will have all of them; if not, it
776 If fully_qualified_name is not NULL, set it to point to the full name
777 returned by the resolver, if this is different to what it is given, unless
778 the returned name starts with "*" as some nameservers seem to be returning
779 wildcards in this form. In international mode "different" means "alabel
780 forms are different".
783 dnsa pointer to dns_answer structure
784 name domain name to look up
785 type DNS record type (T_A, T_MX, etc)
786 fully_qualified_name if not NULL, return the returned name here if its
787 contents are different (i.e. it must be preset)
789 Returns: DNS_SUCCEED successful lookup
790 DNS_NOMATCH name not found
791 DNS_NODATA no data found
792 DNS_AGAIN soft failure, try again later
797 dns_lookup(dns_answer *dnsa, const uschar *name, int type,
798 const uschar **fully_qualified_name)
801 const uschar *orig_name = name;
802 BOOL secure_so_far = TRUE;
804 /* Loop to follow CNAME chains so far, but no further... */
806 for (i = 0; i < 10; i++)
809 dns_record *rr, cname_rr, type_rr;
813 /* DNS lookup failures get passed straight back. */
815 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
817 /* We should have either records of the required type, or a CNAME record,
818 or both. We need to know whether both exist for getting the fully qualified
819 name, but avoid scanning more than necessary. Note that we must copy the
820 contents of any rr blocks returned by dns_next_rr() as they use the same
821 area in the dnsa block. */
823 cname_rr.data = type_rr.data = NULL;
824 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
826 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
828 if (rr->type == type)
830 if (type_rr.data == NULL) type_rr = *rr;
831 if (cname_rr.data != NULL) break;
833 else if (rr->type == T_CNAME) cname_rr = *rr;
836 /* For the first time round this loop, if a CNAME was found, take the fully
837 qualified name from it; otherwise from the first data record, if present. */
839 if (i == 0 && fully_qualified_name != NULL)
841 uschar * rr_name = cname_rr.data ? cname_rr.name
842 : type_rr.data ? type_rr.name : NULL;
844 && Ustrcmp(rr_name, *fully_qualified_name) != 0
846 #ifdef EXPERIMENTAL_INTERNATIONAL
847 && ( !string_is_utf8(*fully_qualified_name)
849 string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0
853 *fully_qualified_name = string_copy_dnsdomain(rr_name);
856 /* If any data records of the correct type were found, we are done. */
858 if (type_rr.data != NULL)
860 if (!secure_so_far) /* mark insecure if any element of CNAME chain was */
861 dns_set_insecure(dnsa);
865 /* If there are no data records, we need to re-scan the DNS using the
866 domain given in the CNAME record, which should exist (otherwise we should
867 have had a failure from dns_lookup). However code against the possibility of
870 if (cname_rr.data == NULL) return DNS_FAIL;
871 datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
872 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, sizeof(data));
873 if (datalen < 0) return DNS_FAIL;
876 if (!dns_is_secure(dnsa))
877 secure_so_far = FALSE;
879 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
880 } /* Loop back to do another lookup */
882 /*Control reaches here after 10 times round the CNAME loop. Something isn't
885 log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
894 /************************************************
895 * Do a DNS lookup and handle virtual types *
896 ************************************************/
898 /* This function handles some invented "lookup types" that synthesize features
899 not available in the basic types. The special types all have negative values.
900 Positive type values are passed straight on to dns_lookup().
903 dnsa pointer to dns_answer structure
904 name domain name to look up
905 type DNS record type (T_A, T_MX, etc or a "special")
906 fully_qualified_name if not NULL, return the returned name here if its
907 contents are different (i.e. it must be preset)
909 Returns: DNS_SUCCEED successful lookup
910 DNS_NOMATCH name not found
911 DNS_NODATA no data found
912 DNS_AGAIN soft failure, try again later
917 dns_special_lookup(dns_answer *dnsa, const uschar *name, int type,
918 const uschar **fully_qualified_name)
922 /* The "mx hosts only" type doesn't require any special action here */
924 return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
926 /* Find nameservers for the domain or the nearest enclosing zone, excluding
933 const uschar *d = name;
936 int rc = dns_lookup(dnsa, d, type, fully_qualified_name);
937 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
938 while (*d != 0 && *d != '.') d++;
939 if (*d++ == 0) break;
944 /* Try to look up the Client SMTP Authorization SRV record for the name. If
945 there isn't one, search from the top downwards for a CSA record in a parent
946 domain, which might be making assertions about subdomains. If we find a record
947 we set fully_qualified_name to whichever lookup succeeded, so that the caller
948 can tell whether to look at the explicit authorization field or the subdomain
952 uschar *srvname, *namesuff, *tld, *p;
953 int priority, weight, port;
959 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
961 srvname = string_sprintf("_client._smtp.%s", name);
962 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
963 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
965 if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name);
969 /* Search for CSA subdomain assertion SRV records from the top downwards,
970 starting with the 2nd level domain. This order maximizes cache-friendliness.
971 We skip the top level domains to avoid loading their nameservers and because
972 we know they'll never have CSA SRV records. */
974 namesuff = Ustrrchr(name, '.');
975 if (namesuff == NULL) return DNS_NOMATCH;
978 limit = dns_csa_search_limit;
980 /* Use more appropriate search parameters if we are in the reverse DNS. */
982 if (strcmpic(namesuff, US".arpa") == 0)
983 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
989 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
997 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
999 /* Do not perform the search if the top level or 2nd level domains do not
1000 exist. This is quite common, and when it occurs all the search queries would
1001 go to the root or TLD name servers, which is not friendly. So we check the
1002 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
1003 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
1004 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
1005 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
1007 if (rc == DNS_NOMATCH)
1009 /* This is really gross. The successful return value from res_search() is
1010 the packet length, which is stored in dnsa->answerlen. If we get a
1011 negative DNS reply then res_search() returns -1, which causes the bounds
1012 checks for name decompression to fail when it is treated as a packet
1013 length, which in turn causes the authority search to fail. The correct
1014 packet length has been lost inside libresolv, so we have to guess a
1015 replacement value. (The only way to fix this properly would be to
1016 re-implement res_search() and res_query() so that they don't muddle their
1017 success and packet length return values.) For added safety we only reset
1018 the packet length if the packet header looks plausible. */
1020 HEADER *h = (HEADER *)dnsa->answer;
1021 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
1022 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
1023 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
1024 && ntohs(h->nscount) >= 1)
1025 dnsa->answerlen = MAXPACKET;
1027 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
1029 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
1031 if (rr->type != T_SOA) continue;
1032 else if (strcmpic(rr->name, US"") == 0 ||
1033 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
1037 for (i = 0; i < limit; i++)
1041 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
1042 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
1044 if (namesuff <= name) return DNS_NOMATCH;
1047 /* Find the start of the preceding domain name label. */
1049 if (--namesuff <= name) return DNS_NOMATCH;
1050 while (*namesuff != '.');
1052 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
1054 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
1055 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
1056 if (rc == DNS_AGAIN) return rc;
1057 if (rc != DNS_SUCCEED) continue;
1059 /* Check that the SRV record we have found is worth returning. We don't
1060 just return the first one we find, because some lower level SRV record
1061 might make stricter assertions than its parent domain. */
1063 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
1065 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1067 if (rr->type != T_SRV) continue;
1069 /* Extract the numerical SRV fields (p is incremented) */
1071 GETSHORT(priority, p);
1072 GETSHORT(weight, p); weight = weight; /* compiler quietening */
1075 /* Check the CSA version number */
1076 if (priority != 1) continue;
1078 /* If it's making an interesting assertion, return this response. */
1081 *fully_qualified_name = namesuff + 1;
1091 return dns_lookup(dnsa, name, type, fully_qualified_name);
1094 /* Control should never reach here */
1103 /*************************************************
1104 * Get address(es) from DNS record *
1105 *************************************************/
1107 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1108 supported) for an IPv6 address.
1111 dnsa the DNS answer block
1114 Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun
1118 dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1120 dns_address * yield = NULL;
1121 uschar * dnsa_lim = dnsa->answer + dnsa->answerlen;
1123 if (rr->type == T_A)
1125 uschar *p = US rr->data;
1126 if (p + 4 <= dnsa_lim)
1128 yield = store_get(sizeof(dns_address) + 20);
1129 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1138 if (rr->data + 16 <= dnsa_lim)
1140 yield = store_get(sizeof(dns_address) + 50);
1141 inet_ntop(AF_INET6, US rr->data, CS yield->address, 50);
1145 #endif /* HAVE_IPV6 */
1153 dns_pattern_init(void)
1155 if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names)
1156 regex_check_dns_names =
1157 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);