1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2014 */
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 /* This code, for forcing TRY_AGAIN and NO_RECOVERY, is here so that it works
57 for the old test suite that uses a real nameserver. When the old test suite is
58 eventually abandoned, this code could be moved into the fakens utility. */
60 if (len >= 14 && Ustrcmp(endname - 14, "test.again.dns") == 0)
62 int delay = Uatoi(name); /* digits at the start of the name */
63 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
64 name, dns_text_type(type));
67 DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay);
74 if (len >= 13 && Ustrcmp(endname - 13, "test.fail.dns") == 0)
76 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
77 name, dns_text_type(type));
78 h_errno = NO_RECOVERY;
82 /* Look for the fakens utility, and if it exists, call it. */
84 (void)string_format(utilname, sizeof(utilname), "%s/bin/fakens",
85 config_main_directory);
87 if (stat(CS utilname, &statbuf) >= 0)
93 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", name, dns_text_type(type));
96 argv[1] = config_main_directory;
98 argv[3] = dns_text_type(type);
101 pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
103 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
108 while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
111 aptr += rc; /* Don't modify the actual arguments, because they */
112 asize -= rc; /* may need to be passed on to res_search(). */
115 /* If we ran out of output buffer before exhasting the return,
116 carry on reading and counting it. */
119 while ((rc = read(outfd, name, sizeof(name))) > 0)
123 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
126 switch(child_close(pid, 0))
129 case 1: h_errno = HOST_NOT_FOUND; return -1;
130 case 2: h_errno = TRY_AGAIN; return -1;
132 case 3: h_errno = NO_RECOVERY; return -1;
133 case 4: h_errno = NO_DATA; return -1;
134 case 5: /* Pass on to res_search() */
135 DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
140 DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname);
143 /* fakens utility not found, or it returned "pass on" */
145 DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain);
147 return res_search(CS domain, C_IN, type, answerptr, size);
152 /*************************************************
153 * Initialize and configure resolver *
154 *************************************************/
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.
160 qualify_single TRUE to set the RES_DEFNAMES option
161 search_parents TRUE to set the RES_DNSRCH option
162 use_dnssec TRUE to set the RES_USE_DNSSEC option
168 dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec)
170 res_state resp = os_get_dns_resolver_res();
172 if ((resp->options & RES_INIT) == 0)
174 DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */
175 os_put_dns_resolver_res(resp);
177 DEBUG(D_resolver) resp->options |= RES_DEBUG;
178 os_put_dns_resolver_res(resp);
181 resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
182 resp->options |= (qualify_single? RES_DEFNAMES : 0) |
183 (search_parents? RES_DNSRCH : 0);
184 if (dns_retrans > 0) resp->retrans = dns_retrans;
185 if (dns_retry > 0) resp->retry = dns_retry;
188 if (dns_use_edns0 >= 0)
191 resp->options |= RES_USE_EDNS0;
193 resp->options &= ~RES_USE_EDNS0;
195 debug_printf("Coerced resolver EDNS0 support %s.\n",
196 dns_use_edns0 ? "on" : "off");
199 if (dns_use_edns0 >= 0)
201 debug_printf("Unable to %sset EDNS0 without resolver support.\n",
202 dns_use_edns0 ? "" : "un");
205 #ifndef DISABLE_DNSSEC
206 # ifdef RES_USE_DNSSEC
207 # ifndef RES_USE_EDNS0
208 # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ...
211 resp->options |= RES_USE_DNSSEC;
212 if (dns_dnssec_ok >= 0)
214 if (dns_use_edns0 == 0 && dns_dnssec_ok != 0)
217 debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n");
222 resp->options |= RES_USE_DNSSEC;
224 resp->options &= ~RES_USE_DNSSEC;
225 DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n",
226 dns_dnssec_ok ? "on" : "off");
230 if (dns_dnssec_ok >= 0)
232 debug_printf("Unable to %sset DNSSEC without resolver support.\n",
233 dns_dnssec_ok ? "" : "un");
236 debug_printf("Unable to set DNSSEC without resolver support.\n");
238 #endif /* DISABLE_DNSSEC */
240 os_put_dns_resolver_res(resp);
245 /*************************************************
246 * Build key name for PTR records *
247 *************************************************/
249 /* This function inverts an IP address and adds the relevant domain, to produce
250 a name that can be used to look up PTR records.
253 string the IP address as a string
254 buffer a suitable buffer, long enough to hold the result
260 dns_build_reverse(const uschar *string, uschar *buffer)
262 const uschar *p = string + Ustrlen(string);
265 /* Handle IPv4 address */
268 if (Ustrchr(string, ':') == NULL)
272 for (i = 0; i < 4; i++)
274 const uschar *ppp = p;
275 while (ppp > string && ppp[-1] != '.') ppp--;
276 Ustrncpy(pp, ppp, p - ppp);
281 Ustrcpy(pp, "in-addr.arpa");
284 /* Handle IPv6 address; convert to binary so as to fill out any
285 abbreviation in the textual form. */
292 (void)host_aton(string, v6);
294 /* The original specification for IPv6 reverse lookup was to invert each
295 nibble, and look in the ip6.int domain. The domain was subsequently
296 changed to ip6.arpa. */
298 for (i = 3; i >= 0; i--)
301 for (j = 0; j < 32; j += 4)
303 sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
307 Ustrcpy(pp, "ip6.arpa.");
309 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
310 with A6 records. However, it fell out of favour when they did. The
311 alternative was to construct a binary key, and look in ip6.arpa. I tried
312 to make this code do that, but I could not make it work on Solaris 8. The
313 resolver seems to lose the initial backslash somehow. However, now that
314 this style of reverse lookup has been dropped, it doesn't matter. These
315 lines are left here purely for historical interest. */
317 /**************************************************
321 for (i = 0; i < 4; i++)
323 sprintf(pp, "%08X", v6[i]);
326 Ustrcpy(pp, "].ip6.arpa.");
327 **************************************************/
336 /*************************************************
337 * Get next DNS record from answer block *
338 *************************************************/
340 /* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
341 RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
342 scan the additional records, and reset == RESET_NEXT to get the next record.
343 The result is in static storage which must be copied if it is to be preserved.
346 dnsa pointer to dns answer block
347 dnss pointer to dns scan block
348 reset option specifing what portion to scan, as described above
350 Returns: next dns record, or NULL when no more
354 dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset)
356 HEADER *h = (HEADER *)dnsa->answer;
359 /* Reset the saved data when requested to, and skip to the first required RR */
361 if (reset != RESET_NEXT)
363 dnss->rrcount = ntohs(h->qdcount);
364 dnss->aptr = dnsa->answer + sizeof(HEADER);
366 /* Skip over questions; failure to expand the name just gives up */
368 while (dnss->rrcount-- > 0)
370 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
371 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
372 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
373 dnss->aptr += namelen + 4; /* skip name & type & class */
376 /* Get the number of answer records. */
378 dnss->rrcount = ntohs(h->ancount);
380 /* Skip over answers if we want to look at the authority section. Also skip
381 the NS records (i.e. authority section) if wanting to look at the additional
384 if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
386 if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
388 while (dnss->rrcount-- > 0)
390 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
391 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
392 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
393 dnss->aptr += namelen + 8; /* skip name, type, class & TTL */
394 GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
395 dnss->aptr += dnss->srr.size; /* skip over it */
397 dnss->rrcount = (reset == RESET_AUTHORITY)
398 ? ntohs(h->nscount) : ntohs(h->arcount);
402 /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
403 contains the number of RR records left. */
405 if (dnss->rrcount-- <= 0) return NULL;
407 /* If expanding the RR domain name fails, behave as if no more records
410 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
411 (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
412 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
414 /* Move the pointer past the name and fill in the rest of the data structure
415 from the following bytes. */
417 dnss->aptr += namelen;
418 GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
419 dnss->aptr += 6; /* Don't want class or TTL */
420 GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
421 dnss->srr.data = dnss->aptr; /* The record's data follows */
422 dnss->aptr += dnss->srr.size; /* Advance to next RR */
424 /* Return a pointer to the dns_record structure within the dns_answer. This is
425 for convenience so that the scans can use nice-looking for loops. */
433 /*************************************************
434 * Return whether AD bit set in DNS result *
435 *************************************************/
437 /* We do not perform DNSSEC work ourselves; if the administrator has installed
438 a verifying resolver which sets AD as appropriate, though, we'll use that.
439 (AD = Authentic Data)
441 Argument: pointer to dns answer block
442 Returns: bool indicating presence of AD bit
446 dns_is_secure(const dns_answer * dnsa)
448 #ifdef DISABLE_DNSSEC
450 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
453 HEADER *h = (HEADER *)dnsa->answer;
454 return h->ad ? TRUE : FALSE;
459 dns_set_insecure(dns_answer * dnsa)
461 HEADER * h = (HEADER *)dnsa->answer;
465 /************************************************
466 * Check whether the AA bit is set *
467 * We need this to warn if we requested AD *
468 * from a authoritive server *
469 ************************************************/
472 dns_is_aa(const dns_answer *dnsa)
474 return ((HEADER*)dnsa->answer)->aa;
479 /*************************************************
480 * Turn DNS type into text *
481 *************************************************/
483 /* Turn the coded record type into a string for printing. All those that Exim
484 uses should be included here.
486 Argument: record type
487 Returns: pointer to string
495 case T_A: return US"A";
496 case T_MX: return US"MX";
497 case T_AAAA: return US"AAAA";
498 case T_A6: return US"A6";
499 case T_TXT: return US"TXT";
500 case T_SPF: return US"SPF";
501 case T_PTR: return US"PTR";
502 case T_SOA: return US"SOA";
503 case T_SRV: return US"SRV";
504 case T_NS: return US"NS";
505 case T_CNAME: return US"CNAME";
506 case T_TLSA: return US"TLSA";
507 default: return US"?";
513 /*************************************************
514 * Cache a failed DNS lookup result *
515 *************************************************/
517 /* We cache failed lookup results so as not to experience timeouts many
518 times for the same domain. We need to retain the resolver options because they
519 may change. For successful lookups, we rely on resolver and/or name server
527 Returns: the return code
531 dns_return(const uschar * name, int type, int rc)
533 res_state resp = os_get_dns_resolver_res();
534 tree_node *node = store_get_perm(sizeof(tree_node) + 290);
535 sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
538 (void)tree_insertnode(&tree_dns_fails, node);
544 /*************************************************
545 * Do basic DNS lookup *
546 *************************************************/
548 /* Call the resolver to look up the given domain name, using the given type,
549 and check the result. The error code TRY_AGAIN is documented as meaning "non-
550 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
551 up nameservers that produce this error continually, so there is the option of
552 providing a list of domains for which this is treated as a non-existent
556 dnsa pointer to dns_answer structure
558 type type of DNS record required (T_A, T_MX, etc)
560 Returns: DNS_SUCCEED successful lookup
561 DNS_NOMATCH name not found (NXDOMAIN)
562 or name contains illegal characters (if checking)
563 or name is an IP address (for IP address lookup)
564 DNS_NODATA domain exists, but no data for this type (NODATA)
565 DNS_AGAIN soft failure, try again later
570 dns_basic_lookup(dns_answer *dnsa, const uschar *name, int type)
574 const uschar *save_domain;
576 res_state resp = os_get_dns_resolver_res();
579 uschar node_name[290];
581 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
582 a timeout on one domain doesn't happen time and time again for messages that
583 have many addresses in the same domain. We rely on the resolver and name server
584 caching for successful lookups. */
586 sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
588 previous = tree_search(tree_dns_fails, node_name);
589 if (previous != NULL)
591 DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
592 name, dns_text_type(type),
593 (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
594 (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
595 (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
596 (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
597 return previous->data.val;
600 #ifdef EXPERIMENTAL_INTERNATIONAL
601 /* Convert all names to a-label form before doing lookup */
604 uschar * errstr = NULL;
605 DEBUG(D_dns) if (string_is_utf8(name))
606 debug_printf("convert utf8 '%s' to alabel for for lookup\n", name);
607 if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr)
610 debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
612 host_find_failed_syntax = TRUE;
619 /* If configured, check the hygene of the name passed to lookup. Otherwise,
620 although DNS lookups may give REFUSED at the lower level, some resolvers
621 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
622 domains cannot be in the DNS. The check is now done by a regular expression;
623 give it space for substring storage to save it having to get its own if the
624 regex has substrings that are used - the default uses a conditional.
626 This test is omitted for PTR records. These occur only in calls from the dnsdb
627 lookup, which constructs the names itself, so they should be OK. Besides,
628 bitstring labels don't conform to normal name syntax. (But the aren't used any
631 For SRV records, we omit the initial _smtp._tcp. components at the start. */
633 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
635 if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
637 const uschar *checkname = name;
638 int ovector[3*(EXPAND_MAXN+1)];
642 /* For an SRV lookup, skip over the first two components (the service and
643 protocol names, which both start with an underscore). */
645 if (type == T_SRV || type == T_TLSA)
647 while (*checkname++ != '.');
648 while (*checkname++ != '.');
651 if (pcre_exec(regex_check_dns_names, NULL, CCS checkname, Ustrlen(checkname),
652 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
655 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
656 dns_text_type(type));
657 host_find_failed_syntax = TRUE;
662 #endif /* STAND_ALONE */
664 /* Call the resolver; for an overlong response, res_search() will return the
665 number of bytes the message would need, so we need to check for this case. The
666 effect is to truncate overlong data.
668 On some systems, res_search() will recognize "A-for-A" queries and return
669 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
670 nameservers are also believed to do this. It is, of course, contrary to the
671 specification of the DNS, so we lock it out. */
673 if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0)
676 /* If we are running in the test harness, instead of calling the normal resolver
677 (res_search), we call fakens_search(), which recognizes certain special
678 domains, and interfaces to a fake nameserver for certain special zones. */
680 dnsa->answerlen = running_in_test_harness
681 ? fakens_search(name, type, dnsa->answer, MAXPACKET)
682 : res_search(CCS name, C_IN, type, dnsa->answer, MAXPACKET);
684 if (dnsa->answerlen > MAXPACKET)
686 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
687 name, dns_text_type(type), dnsa->answerlen, MAXPACKET);
688 dnsa->answerlen = MAXPACKET;
691 if (dnsa->answerlen < 0) switch (h_errno)
694 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
695 "returning DNS_NOMATCH\n", name, dns_text_type(type));
696 return dns_return(name, type, DNS_NOMATCH);
699 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
700 name, dns_text_type(type));
702 /* Cut this out for various test programs */
704 save_domain = deliver_domain;
705 deliver_domain = string_copy(name); /* set $domain */
706 rc = match_isinlist(name, (const uschar **)&dns_again_means_nonexist, 0, NULL, NULL,
707 MCL_DOMAIN, TRUE, NULL);
708 deliver_domain = save_domain;
711 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
712 return dns_return(name, type, DNS_AGAIN);
714 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
715 "DNS_NOMATCH\n", name);
716 return dns_return(name, type, DNS_NOMATCH);
718 #else /* For stand-alone tests */
719 return dns_return(name, type, DNS_AGAIN);
723 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
724 "returning DNS_FAIL\n", name, dns_text_type(type));
725 return dns_return(name, type, DNS_FAIL);
728 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
729 "returning DNS_NODATA\n", name, dns_text_type(type));
730 return dns_return(name, type, DNS_NODATA);
733 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
734 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
735 return dns_return(name, type, DNS_FAIL);
738 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
739 name, dns_text_type(type));
747 /************************************************
748 * Do a DNS lookup and handle CNAMES *
749 ************************************************/
751 /* Look up the given domain name, using the given type. Follow CNAMEs if
752 necessary, but only so many times. There aren't supposed to be CNAME chains in
753 the DNS, but you are supposed to cope with them if you find them.
755 The assumption is made that if the resolver gives back records of the
756 requested type *and* a CNAME, we don't need to make another call to look up
757 the CNAME. I can't see how it could return only some of the right records. If
758 it's done a CNAME lookup in the past, it will have all of them; if not, it
761 If fully_qualified_name is not NULL, set it to point to the full name
762 returned by the resolver, if this is different to what it is given, unless
763 the returned name starts with "*" as some nameservers seem to be returning
764 wildcards in this form. In international mode "different" means "alabel
765 forms are different".
768 dnsa pointer to dns_answer structure
769 name domain name to look up
770 type DNS record type (T_A, T_MX, etc)
771 fully_qualified_name if not NULL, return the returned name here if its
772 contents are different (i.e. it must be preset)
774 Returns: DNS_SUCCEED successful lookup
775 DNS_NOMATCH name not found
776 DNS_NODATA no data found
777 DNS_AGAIN soft failure, try again later
782 dns_lookup(dns_answer *dnsa, const uschar *name, int type,
783 const uschar **fully_qualified_name)
786 const uschar *orig_name = name;
787 BOOL secure_so_far = TRUE;
789 /* Loop to follow CNAME chains so far, but no further... */
791 for (i = 0; i < 10; i++)
794 dns_record *rr, cname_rr, type_rr;
798 /* DNS lookup failures get passed straight back. */
800 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
802 /* We should have either records of the required type, or a CNAME record,
803 or both. We need to know whether both exist for getting the fully qualified
804 name, but avoid scanning more than necessary. Note that we must copy the
805 contents of any rr blocks returned by dns_next_rr() as they use the same
806 area in the dnsa block. */
808 cname_rr.data = type_rr.data = NULL;
809 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
811 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
813 if (rr->type == type)
815 if (type_rr.data == NULL) type_rr = *rr;
816 if (cname_rr.data != NULL) break;
818 else if (rr->type == T_CNAME) cname_rr = *rr;
821 /* For the first time round this loop, if a CNAME was found, take the fully
822 qualified name from it; otherwise from the first data record, if present. */
824 if (i == 0 && fully_qualified_name != NULL)
826 uschar * rr_name = cname_rr.data ? cname_rr.name
827 : type_rr.data ? type_rr.name : NULL;
829 && Ustrcmp(rr_name, *fully_qualified_name) != 0
831 #ifdef EXPERIMENTAL_INTERNATIONAL
832 && ( !string_is_utf8(*fully_qualified_name)
834 string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0
838 *fully_qualified_name = string_copy_dnsdomain(rr_name);
841 /* If any data records of the correct type were found, we are done. */
843 if (type_rr.data != NULL)
845 if (!secure_so_far) /* mark insecure if any element of CNAME chain was */
846 dns_set_insecure(dnsa);
850 /* If there are no data records, we need to re-scan the DNS using the
851 domain given in the CNAME record, which should exist (otherwise we should
852 have had a failure from dns_lookup). However code against the possibility of
855 if (cname_rr.data == NULL) return DNS_FAIL;
856 datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
857 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, sizeof(data));
858 if (datalen < 0) return DNS_FAIL;
861 if (!dns_is_secure(dnsa))
862 secure_so_far = FALSE;
864 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
865 } /* Loop back to do another lookup */
867 /*Control reaches here after 10 times round the CNAME loop. Something isn't
870 log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
879 /************************************************
880 * Do a DNS lookup and handle virtual types *
881 ************************************************/
883 /* This function handles some invented "lookup types" that synthesize feature
884 not available in the basic types. The special types all have negative values.
885 Positive type values are passed straight on to dns_lookup().
888 dnsa pointer to dns_answer structure
889 name domain name to look up
890 type DNS record type (T_A, T_MX, etc or a "special")
891 fully_qualified_name if not NULL, return the returned name here if its
892 contents are different (i.e. it must be preset)
894 Returns: DNS_SUCCEED successful lookup
895 DNS_NOMATCH name not found
896 DNS_NODATA no data found
897 DNS_AGAIN soft failure, try again later
902 dns_special_lookup(dns_answer *dnsa, const uschar *name, int type,
903 const uschar **fully_qualified_name)
907 /* The "mx hosts only" type doesn't require any special action here */
909 return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
911 /* Find nameservers for the domain or the nearest enclosing zone, excluding
918 const uschar *d = name;
921 int rc = dns_lookup(dnsa, d, type, fully_qualified_name);
922 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
923 while (*d != 0 && *d != '.') d++;
924 if (*d++ == 0) break;
929 /* Try to look up the Client SMTP Authorization SRV record for the name. If
930 there isn't one, search from the top downwards for a CSA record in a parent
931 domain, which might be making assertions about subdomains. If we find a record
932 we set fully_qualified_name to whichever lookup succeeded, so that the caller
933 can tell whether to look at the explicit authorization field or the subdomain
937 uschar *srvname, *namesuff, *tld, *p;
938 int priority, weight, port;
944 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
946 srvname = string_sprintf("_client._smtp.%s", name);
947 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
948 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
950 if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name);
954 /* Search for CSA subdomain assertion SRV records from the top downwards,
955 starting with the 2nd level domain. This order maximizes cache-friendliness.
956 We skip the top level domains to avoid loading their nameservers and because
957 we know they'll never have CSA SRV records. */
959 namesuff = Ustrrchr(name, '.');
960 if (namesuff == NULL) return DNS_NOMATCH;
963 limit = dns_csa_search_limit;
965 /* Use more appropriate search parameters if we are in the reverse DNS. */
967 if (strcmpic(namesuff, US".arpa") == 0)
968 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
974 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
982 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
984 /* Do not perform the search if the top level or 2nd level domains do not
985 exist. This is quite common, and when it occurs all the search queries would
986 go to the root or TLD name servers, which is not friendly. So we check the
987 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
988 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
989 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
990 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
992 if (rc == DNS_NOMATCH)
994 /* This is really gross. The successful return value from res_search() is
995 the packet length, which is stored in dnsa->answerlen. If we get a
996 negative DNS reply then res_search() returns -1, which causes the bounds
997 checks for name decompression to fail when it is treated as a packet
998 length, which in turn causes the authority search to fail. The correct
999 packet length has been lost inside libresolv, so we have to guess a
1000 replacement value. (The only way to fix this properly would be to
1001 re-implement res_search() and res_query() so that they don't muddle their
1002 success and packet length return values.) For added safety we only reset
1003 the packet length if the packet header looks plausible. */
1005 HEADER *h = (HEADER *)dnsa->answer;
1006 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
1007 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
1008 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
1009 && ntohs(h->nscount) >= 1)
1010 dnsa->answerlen = MAXPACKET;
1012 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
1014 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
1016 if (rr->type != T_SOA) continue;
1017 else if (strcmpic(rr->name, US"") == 0 ||
1018 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
1022 for (i = 0; i < limit; i++)
1026 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
1027 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
1029 if (namesuff <= name) return DNS_NOMATCH;
1032 /* Find the start of the preceding domain name label. */
1034 if (--namesuff <= name) return DNS_NOMATCH;
1035 while (*namesuff != '.');
1037 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
1039 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
1040 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
1041 if (rc == DNS_AGAIN) return rc;
1042 if (rc != DNS_SUCCEED) continue;
1044 /* Check that the SRV record we have found is worth returning. We don't
1045 just return the first one we find, because some lower level SRV record
1046 might make stricter assertions than its parent domain. */
1048 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
1050 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1052 if (rr->type != T_SRV) continue;
1054 /* Extract the numerical SRV fields (p is incremented) */
1056 GETSHORT(priority, p);
1057 GETSHORT(weight, p); weight = weight; /* compiler quietening */
1060 /* Check the CSA version number */
1061 if (priority != 1) continue;
1063 /* If it's making an interesting assertion, return this response. */
1066 *fully_qualified_name = namesuff + 1;
1076 return dns_lookup(dnsa, name, type, fully_qualified_name);
1079 /* Control should never reach here */
1088 /*************************************************
1089 * Get address(es) from DNS record *
1090 *************************************************/
1092 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1093 supported) for an IPv6 address.
1096 dnsa the DNS answer block
1099 Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun
1103 dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1105 dns_address * yield = NULL;
1106 uschar * dnsa_lim = dnsa->answer + dnsa->answerlen;
1108 if (rr->type == T_A)
1110 uschar *p = US rr->data;
1111 if (p + 4 <= dnsa_lim)
1113 yield = store_get(sizeof(dns_address) + 20);
1114 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1123 if (rr->data + 16 <= dnsa_lim)
1125 yield = store_get(sizeof(dns_address) + 50);
1126 inet_ntop(AF_INET6, US rr->data, CS yield->address, 50);
1130 #endif /* HAVE_IPV6 */
1138 dns_pattern_init(void)
1140 if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names)
1141 regex_check_dns_names =
1142 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);