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. */
407 /*************************************************
408 * Return whether AD bit set in DNS result *
409 *************************************************/
411 /* We do not perform DNSSEC work ourselves; if the administrator has installed
412 a verifying resolver which sets AD as appropriate, though, we'll use that.
413 (AD = Authentic Data)
415 Argument: pointer to dns answer block
416 Returns: bool indicating presence of AD bit
420 dns_is_secure(const dns_answer * dnsa)
422 #ifdef DISABLE_DNSSEC
424 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
427 HEADER *h = (HEADER *)dnsa->answer;
428 return h->ad ? TRUE : FALSE;
433 dns_set_insecure(dns_answer * dnsa)
435 HEADER * h = (HEADER *)dnsa->answer;
439 /************************************************
440 * Check whether the AA bit is set *
441 * We need this to warn if we requested AD *
442 * from a authoritive server *
443 ************************************************/
446 dns_is_aa(const dns_answer *dnsa)
448 return ((HEADER*)dnsa->answer)->aa;
453 /*************************************************
454 * Turn DNS type into text *
455 *************************************************/
457 /* Turn the coded record type into a string for printing. All those that Exim
458 uses should be included here.
460 Argument: record type
461 Returns: pointer to string
469 case T_A: return US"A";
470 case T_MX: return US"MX";
471 case T_AAAA: return US"AAAA";
472 case T_A6: return US"A6";
473 case T_TXT: return US"TXT";
474 case T_SPF: return US"SPF";
475 case T_PTR: return US"PTR";
476 case T_SOA: return US"SOA";
477 case T_SRV: return US"SRV";
478 case T_NS: return US"NS";
479 case T_CNAME: return US"CNAME";
480 case T_TLSA: return US"TLSA";
481 default: return US"?";
487 /*************************************************
488 * Cache a failed DNS lookup result *
489 *************************************************/
491 /* We cache failed lookup results so as not to experience timeouts many
492 times for the same domain. We need to retain the resolver options because they
493 may change. For successful lookups, we rely on resolver and/or name server
501 Returns: the return code
505 dns_return(const uschar * name, int type, int rc)
507 res_state resp = os_get_dns_resolver_res();
508 tree_node *node = store_get_perm(sizeof(tree_node) + 290);
509 sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
512 (void)tree_insertnode(&tree_dns_fails, node);
518 /*************************************************
519 * Do basic DNS lookup *
520 *************************************************/
522 /* Call the resolver to look up the given domain name, using the given type,
523 and check the result. The error code TRY_AGAIN is documented as meaning "non-
524 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
525 up nameservers that produce this error continually, so there is the option of
526 providing a list of domains for which this is treated as a non-existent
530 dnsa pointer to dns_answer structure
532 type type of DNS record required (T_A, T_MX, etc)
534 Returns: DNS_SUCCEED successful lookup
535 DNS_NOMATCH name not found (NXDOMAIN)
536 or name contains illegal characters (if checking)
537 or name is an IP address (for IP address lookup)
538 DNS_NODATA domain exists, but no data for this type (NODATA)
539 DNS_AGAIN soft failure, try again later
544 dns_basic_lookup(dns_answer *dnsa, const uschar *name, int type)
548 const uschar *save_domain;
550 res_state resp = os_get_dns_resolver_res();
553 uschar node_name[290];
555 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
556 a timeout on one domain doesn't happen time and time again for messages that
557 have many addresses in the same domain. We rely on the resolver and name server
558 caching for successful lookups. */
560 sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
562 previous = tree_search(tree_dns_fails, node_name);
563 if (previous != NULL)
565 DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
566 name, dns_text_type(type),
567 (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
568 (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
569 (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
570 (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
571 return previous->data.val;
574 #ifdef EXPERIMENTAL_INTERNATIONAL
575 /* Convert all names to a-label form before doing lookup */
578 uschar * errstr = NULL;
579 DEBUG(D_dns) if (string_is_utf8(name))
580 debug_printf("convert utf8 '%s' to alabel for for lookup\n", name);
581 if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr)
584 debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
586 host_find_failed_syntax = TRUE;
593 /* If configured, check the hygene of the name passed to lookup. Otherwise,
594 although DNS lookups may give REFUSED at the lower level, some resolvers
595 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
596 domains cannot be in the DNS. The check is now done by a regular expression;
597 give it space for substring storage to save it having to get its own if the
598 regex has substrings that are used - the default uses a conditional.
600 This test is omitted for PTR records. These occur only in calls from the dnsdb
601 lookup, which constructs the names itself, so they should be OK. Besides,
602 bitstring labels don't conform to normal name syntax. (But the aren't used any
605 For SRV records, we omit the initial _smtp._tcp. components at the start. */
607 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
609 if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
611 const uschar *checkname = name;
612 int ovector[3*(EXPAND_MAXN+1)];
616 /* For an SRV lookup, skip over the first two components (the service and
617 protocol names, which both start with an underscore). */
619 if (type == T_SRV || type == T_TLSA)
621 while (*checkname++ != '.');
622 while (*checkname++ != '.');
625 if (pcre_exec(regex_check_dns_names, NULL, CCS checkname, Ustrlen(checkname),
626 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
629 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
630 dns_text_type(type));
631 host_find_failed_syntax = TRUE;
636 #endif /* STAND_ALONE */
638 /* Call the resolver; for an overlong response, res_search() will return the
639 number of bytes the message would need, so we need to check for this case. The
640 effect is to truncate overlong data.
642 On some systems, res_search() will recognize "A-for-A" queries and return
643 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
644 nameservers are also believed to do this. It is, of course, contrary to the
645 specification of the DNS, so we lock it out. */
647 if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0)
650 /* If we are running in the test harness, instead of calling the normal resolver
651 (res_search), we call fakens_search(), which recognizes certain special
652 domains, and interfaces to a fake nameserver for certain special zones. */
654 dnsa->answerlen = running_in_test_harness
655 ? fakens_search(name, type, dnsa->answer, MAXPACKET)
656 : res_search(CCS name, C_IN, type, dnsa->answer, MAXPACKET);
658 if (dnsa->answerlen > MAXPACKET)
660 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
661 name, dns_text_type(type), dnsa->answerlen, MAXPACKET);
662 dnsa->answerlen = MAXPACKET;
665 if (dnsa->answerlen < 0) switch (h_errno)
668 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
669 "returning DNS_NOMATCH\n", name, dns_text_type(type));
670 return dns_return(name, type, DNS_NOMATCH);
673 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
674 name, dns_text_type(type));
676 /* Cut this out for various test programs */
678 save_domain = deliver_domain;
679 deliver_domain = string_copy(name); /* set $domain */
680 rc = match_isinlist(name, (const uschar **)&dns_again_means_nonexist, 0, NULL, NULL,
681 MCL_DOMAIN, TRUE, NULL);
682 deliver_domain = save_domain;
685 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
686 return dns_return(name, type, DNS_AGAIN);
688 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
689 "DNS_NOMATCH\n", name);
690 return dns_return(name, type, DNS_NOMATCH);
692 #else /* For stand-alone tests */
693 return dns_return(name, type, DNS_AGAIN);
697 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
698 "returning DNS_FAIL\n", name, dns_text_type(type));
699 return dns_return(name, type, DNS_FAIL);
702 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
703 "returning DNS_NODATA\n", name, dns_text_type(type));
704 return dns_return(name, type, DNS_NODATA);
707 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
708 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
709 return dns_return(name, type, DNS_FAIL);
712 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
713 name, dns_text_type(type));
721 /************************************************
722 * Do a DNS lookup and handle CNAMES *
723 ************************************************/
725 /* Look up the given domain name, using the given type. Follow CNAMEs if
726 necessary, but only so many times. There aren't supposed to be CNAME chains in
727 the DNS, but you are supposed to cope with them if you find them.
729 The assumption is made that if the resolver gives back records of the
730 requested type *and* a CNAME, we don't need to make another call to look up
731 the CNAME. I can't see how it could return only some of the right records. If
732 it's done a CNAME lookup in the past, it will have all of them; if not, it
735 If fully_qualified_name is not NULL, set it to point to the full name
736 returned by the resolver, if this is different to what it is given, unless
737 the returned name starts with "*" as some nameservers seem to be returning
738 wildcards in this form. In international mode "different" means "alabel
739 forms are different".
742 dnsa pointer to dns_answer structure
743 name domain name to look up
744 type DNS record type (T_A, T_MX, etc)
745 fully_qualified_name if not NULL, return the returned name here if its
746 contents are different (i.e. it must be preset)
748 Returns: DNS_SUCCEED successful lookup
749 DNS_NOMATCH name not found
750 DNS_NODATA no data found
751 DNS_AGAIN soft failure, try again later
756 dns_lookup(dns_answer *dnsa, const uschar *name, int type,
757 const uschar **fully_qualified_name)
760 const uschar *orig_name = name;
761 BOOL secure_so_far = TRUE;
763 /* Loop to follow CNAME chains so far, but no further... */
765 for (i = 0; i < 10; i++)
768 dns_record *rr, cname_rr, type_rr;
772 /* DNS lookup failures get passed straight back. */
774 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
776 /* We should have either records of the required type, or a CNAME record,
777 or both. We need to know whether both exist for getting the fully qualified
778 name, but avoid scanning more than necessary. Note that we must copy the
779 contents of any rr blocks returned by dns_next_rr() as they use the same
780 area in the dnsa block. */
782 cname_rr.data = type_rr.data = NULL;
783 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
785 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
787 if (rr->type == type)
789 if (type_rr.data == NULL) type_rr = *rr;
790 if (cname_rr.data != NULL) break;
792 else if (rr->type == T_CNAME) cname_rr = *rr;
795 /* For the first time round this loop, if a CNAME was found, take the fully
796 qualified name from it; otherwise from the first data record, if present. */
798 if (i == 0 && fully_qualified_name != NULL)
800 uschar * rr_name = cname_rr.data ? cname_rr.name
801 : type_rr.data ? type_rr.name : NULL;
803 && Ustrcmp(rr_name, *fully_qualified_name) != 0
805 #ifdef EXPERIMENTAL_INTERNATIONAL
806 && ( !string_is_utf8(*fully_qualified_name)
808 string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0
812 *fully_qualified_name = string_copy_dnsdomain(rr_name);
815 /* If any data records of the correct type were found, we are done. */
817 if (type_rr.data != NULL)
819 if (!secure_so_far) /* mark insecure if any element of CNAME chain was */
820 dns_set_insecure(dnsa);
824 /* If there are no data records, we need to re-scan the DNS using the
825 domain given in the CNAME record, which should exist (otherwise we should
826 have had a failure from dns_lookup). However code against the possibility of
829 if (cname_rr.data == NULL) return DNS_FAIL;
830 datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
831 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, sizeof(data));
832 if (datalen < 0) return DNS_FAIL;
835 if (!dns_is_secure(dnsa))
836 secure_so_far = FALSE;
838 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
839 } /* Loop back to do another lookup */
841 /*Control reaches here after 10 times round the CNAME loop. Something isn't
844 log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
853 /************************************************
854 * Do a DNS lookup and handle virtual types *
855 ************************************************/
857 /* This function handles some invented "lookup types" that synthesize feature
858 not available in the basic types. The special types all have negative values.
859 Positive type values are passed straight on to dns_lookup().
862 dnsa pointer to dns_answer structure
863 name domain name to look up
864 type DNS record type (T_A, T_MX, etc or a "special")
865 fully_qualified_name if not NULL, return the returned name here if its
866 contents are different (i.e. it must be preset)
868 Returns: DNS_SUCCEED successful lookup
869 DNS_NOMATCH name not found
870 DNS_NODATA no data found
871 DNS_AGAIN soft failure, try again later
876 dns_special_lookup(dns_answer *dnsa, const uschar *name, int type,
877 const uschar **fully_qualified_name)
881 /* The "mx hosts only" type doesn't require any special action here */
883 return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
885 /* Find nameservers for the domain or the nearest enclosing zone, excluding
892 const uschar *d = name;
895 int rc = dns_lookup(dnsa, d, type, fully_qualified_name);
896 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
897 while (*d != 0 && *d != '.') d++;
898 if (*d++ == 0) break;
903 /* Try to look up the Client SMTP Authorization SRV record for the name. If
904 there isn't one, search from the top downwards for a CSA record in a parent
905 domain, which might be making assertions about subdomains. If we find a record
906 we set fully_qualified_name to whichever lookup succeeded, so that the caller
907 can tell whether to look at the explicit authorization field or the subdomain
911 uschar *srvname, *namesuff, *tld, *p;
912 int priority, weight, port;
918 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
920 srvname = string_sprintf("_client._smtp.%s", name);
921 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
922 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
924 if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name);
928 /* Search for CSA subdomain assertion SRV records from the top downwards,
929 starting with the 2nd level domain. This order maximizes cache-friendliness.
930 We skip the top level domains to avoid loading their nameservers and because
931 we know they'll never have CSA SRV records. */
933 namesuff = Ustrrchr(name, '.');
934 if (namesuff == NULL) return DNS_NOMATCH;
937 limit = dns_csa_search_limit;
939 /* Use more appropriate search parameters if we are in the reverse DNS. */
941 if (strcmpic(namesuff, US".arpa") == 0)
942 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
948 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
956 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
958 /* Do not perform the search if the top level or 2nd level domains do not
959 exist. This is quite common, and when it occurs all the search queries would
960 go to the root or TLD name servers, which is not friendly. So we check the
961 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
962 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
963 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
964 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
966 if (rc == DNS_NOMATCH)
968 /* This is really gross. The successful return value from res_search() is
969 the packet length, which is stored in dnsa->answerlen. If we get a
970 negative DNS reply then res_search() returns -1, which causes the bounds
971 checks for name decompression to fail when it is treated as a packet
972 length, which in turn causes the authority search to fail. The correct
973 packet length has been lost inside libresolv, so we have to guess a
974 replacement value. (The only way to fix this properly would be to
975 re-implement res_search() and res_query() so that they don't muddle their
976 success and packet length return values.) For added safety we only reset
977 the packet length if the packet header looks plausible. */
979 HEADER *h = (HEADER *)dnsa->answer;
980 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
981 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
982 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
983 && ntohs(h->nscount) >= 1)
984 dnsa->answerlen = MAXPACKET;
986 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
988 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
990 if (rr->type != T_SOA) continue;
991 else if (strcmpic(rr->name, US"") == 0 ||
992 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
996 for (i = 0; i < limit; i++)
1000 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
1001 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
1003 if (namesuff <= name) return DNS_NOMATCH;
1006 /* Find the start of the preceding domain name label. */
1008 if (--namesuff <= name) return DNS_NOMATCH;
1009 while (*namesuff != '.');
1011 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
1013 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
1014 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
1015 if (rc == DNS_AGAIN) return rc;
1016 if (rc != DNS_SUCCEED) continue;
1018 /* Check that the SRV record we have found is worth returning. We don't
1019 just return the first one we find, because some lower level SRV record
1020 might make stricter assertions than its parent domain. */
1022 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
1024 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1026 if (rr->type != T_SRV) continue;
1028 /* Extract the numerical SRV fields (p is incremented) */
1030 GETSHORT(priority, p);
1031 GETSHORT(weight, p); weight = weight; /* compiler quietening */
1034 /* Check the CSA version number */
1035 if (priority != 1) continue;
1037 /* If it's making an interesting assertion, return this response. */
1040 *fully_qualified_name = namesuff + 1;
1050 return dns_lookup(dnsa, name, type, fully_qualified_name);
1053 /* Control should never reach here */
1062 /*************************************************
1063 * Get address(es) from DNS record *
1064 *************************************************/
1066 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1067 supported) for an IPv6 address.
1070 dnsa the DNS answer block
1073 Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun
1077 dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1079 dns_address * yield = NULL;
1080 uschar * dnsa_lim = dnsa->answer + dnsa->answerlen;
1082 if (rr->type == T_A)
1084 uschar *p = US rr->data;
1085 if (p + 4 <= dnsa_lim)
1087 yield = store_get(sizeof(dns_address) + 20);
1088 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1097 if (rr->data + 16 <= dnsa_lim)
1099 yield = store_get(sizeof(dns_address) + 50);
1100 inet_ntop(AF_INET6, US rr->data, CS yield->address, 50);
1104 #endif /* HAVE_IPV6 */
1112 dns_pattern_init(void)
1114 if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names)
1115 regex_check_dns_names =
1116 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);