1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2009 */
6 /* See the file NOTICE for conditions of use and distribution. */
8 /* Functions for interfacing with the DNS. */
13 /* Function declaration needed for mutual recursion when A6 records
18 static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *,
24 /*************************************************
26 *************************************************/
28 /* This function is called instead of res_search() when Exim is running in its
29 test harness. It recognizes some special domain names, and uses them to force
30 failure and retry responses (optionally with a delay). Otherwise, it calls an
31 external utility that mocks-up a nameserver, if it can find the utility.
32 If not, it passes its arguments on to res_search(). The fake nameserver may
33 also return a code specifying that the name should be passed on.
35 Background: the original test suite required a real nameserver to carry the
36 test zones, whereas the new test suit has the fake server for portability. This
40 domain the domain name
41 type the DNS record type
42 answerptr where to put the answer
43 size size of the answer area
45 Returns: length of returned data, or -1 on error (h_errno set)
49 fakens_search(uschar *domain, int type, uschar *answerptr, int size)
51 int len = Ustrlen(domain);
52 int asize = size; /* Locally modified */
56 uschar *aptr = answerptr; /* Locally modified */
59 /* Remove terminating dot. */
61 if (domain[len - 1] == '.') len--;
62 Ustrncpy(name, domain, len);
66 /* This code, for forcing TRY_AGAIN and NO_RECOVERY, is here so that it works
67 for the old test suite that uses a real nameserver. When the old test suite is
68 eventually abandoned, this code could be moved into the fakens utility. */
70 if (len >= 14 && Ustrcmp(endname - 14, "test.again.dns") == 0)
72 int delay = Uatoi(name); /* digits at the start of the name */
73 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
74 name, dns_text_type(type));
77 DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay);
84 if (len >= 13 && Ustrcmp(endname - 13, "test.fail.dns") == 0)
86 DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n",
87 name, dns_text_type(type));
88 h_errno = NO_RECOVERY;
92 /* Look for the fakens utility, and if it exists, call it. */
94 (void)string_format(utilname, sizeof(utilname), "%s/../bin/fakens",
97 if (stat(CS utilname, &statbuf) >= 0)
103 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n",
104 name, dns_text_type(type));
107 argv[1] = spool_directory;
109 argv[3] = dns_text_type(type);
112 pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
114 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
119 while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
122 aptr += rc; /* Don't modify the actual arguments, because they */
123 asize -= rc; /* may need to be passed on to res_search(). */
127 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
130 switch(child_close(pid, 0))
133 case 1: h_errno = HOST_NOT_FOUND; return -1;
134 case 2: h_errno = TRY_AGAIN; return -1;
136 case 3: h_errno = NO_RECOVERY; return -1;
137 case 4: h_errno = NO_DATA; return -1;
138 case 5: /* Pass on to res_search() */
139 DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
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
167 dns_init(BOOL qualify_single, BOOL search_parents)
169 res_state resp = os_get_dns_resolver_res();
171 if ((resp->options & RES_INIT) == 0)
173 DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */
174 os_put_dns_resolver_res(resp);
176 DEBUG(D_resolver) resp->options |= RES_DEBUG;
177 os_put_dns_resolver_res(resp);
180 resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
181 resp->options |= (qualify_single? RES_DEFNAMES : 0) |
182 (search_parents? RES_DNSRCH : 0);
183 if (dns_retrans > 0) resp->retrans = dns_retrans;
184 if (dns_retry > 0) resp->retry = dns_retry;
187 if (dns_use_edns0 >= 0)
190 resp->options |= RES_USE_EDNS0;
192 resp->options &= ~RES_USE_EDNS0;
194 debug_printf("Coerced resolver EDNS0 support %s.\n",
195 dns_use_edns0 ? "on" : "off");
198 if (dns_use_edns0 >= 0)
200 debug_printf("Unable to %sset EDNS0 without resolver support.\n",
201 dns_use_edns0 ? "" : "un");
204 os_put_dns_resolver_res(resp);
209 /*************************************************
210 * Build key name for PTR records *
211 *************************************************/
213 /* This function inverts an IP address and adds the relevant domain, to produce
214 a name that can be used to look up PTR records.
217 string the IP address as a string
218 buffer a suitable buffer, long enough to hold the result
224 dns_build_reverse(uschar *string, uschar *buffer)
226 uschar *p = string + Ustrlen(string);
229 /* Handle IPv4 address */
232 if (Ustrchr(string, ':') == NULL)
236 for (i = 0; i < 4; i++)
239 while (ppp > string && ppp[-1] != '.') ppp--;
240 Ustrncpy(pp, ppp, p - ppp);
245 Ustrcpy(pp, "in-addr.arpa");
248 /* Handle IPv6 address; convert to binary so as to fill out any
249 abbreviation in the textual form. */
256 (void)host_aton(string, v6);
258 /* The original specification for IPv6 reverse lookup was to invert each
259 nibble, and look in the ip6.int domain. The domain was subsequently
260 changed to ip6.arpa. */
262 for (i = 3; i >= 0; i--)
265 for (j = 0; j < 32; j += 4)
267 sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
271 Ustrcpy(pp, "ip6.arpa.");
273 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
274 with A6 records. However, it fell out of favour when they did. The
275 alternative was to construct a binary key, and look in ip6.arpa. I tried
276 to make this code do that, but I could not make it work on Solaris 8. The
277 resolver seems to lose the initial backslash somehow. However, now that
278 this style of reverse lookup has been dropped, it doesn't matter. These
279 lines are left here purely for historical interest. */
281 /**************************************************
285 for (i = 0; i < 4; i++)
287 sprintf(pp, "%08X", v6[i]);
290 Ustrcpy(pp, "].ip6.arpa.");
291 **************************************************/
300 /*************************************************
301 * Get next DNS record from answer block *
302 *************************************************/
304 /* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
305 RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
306 scan the additional records, and reset == RESET_NEXT to get the next record.
307 The result is in static storage which must be copied if it is to be preserved.
310 dnsa pointer to dns answer block
311 dnss pointer to dns scan block
312 reset option specifing what portion to scan, as described above
314 Returns: next dns record, or NULL when no more
318 dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset)
320 HEADER *h = (HEADER *)dnsa->answer;
323 /* Reset the saved data when requested to, and skip to the first required RR */
325 if (reset != RESET_NEXT)
327 dnss->rrcount = ntohs(h->qdcount);
328 dnss->aptr = dnsa->answer + sizeof(HEADER);
330 /* Skip over questions; failure to expand the name just gives up */
332 while (dnss->rrcount-- > 0)
334 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
335 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
336 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
337 dnss->aptr += namelen + 4; /* skip name & type & class */
340 /* Get the number of answer records. */
342 dnss->rrcount = ntohs(h->ancount);
344 /* Skip over answers if we want to look at the authority section. Also skip
345 the NS records (i.e. authority section) if wanting to look at the additional
348 if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount);
350 if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
352 while (dnss->rrcount-- > 0)
354 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
355 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
356 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
357 dnss->aptr += namelen + 8; /* skip name, type, class & TTL */
358 GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
359 dnss->aptr += dnss->srr.size; /* skip over it */
361 dnss->rrcount = (reset == RESET_AUTHORITY)
362 ? ntohs(h->nscount) : ntohs(h->arcount);
366 /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
367 contains the number of RR records left. */
369 if (dnss->rrcount-- <= 0) return NULL;
371 /* If expanding the RR domain name fails, behave as if no more records
374 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
375 (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME);
376 if (namelen < 0) { dnss->rrcount = 0; return NULL; }
378 /* Move the pointer past the name and fill in the rest of the data structure
379 from the following bytes. */
381 dnss->aptr += namelen;
382 GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
383 dnss->aptr += 6; /* Don't want class or TTL */
384 GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
385 dnss->srr.data = dnss->aptr; /* The record's data follows */
386 dnss->aptr += dnss->srr.size; /* Advance to next RR */
388 /* Return a pointer to the dns_record structure within the dns_answer. This is
389 for convenience so that the scans can use nice-looking for loops. */
397 /*************************************************
398 * Turn DNS type into text *
399 *************************************************/
401 /* Turn the coded record type into a string for printing. All those that Exim
402 uses should be included here.
404 Argument: record type
405 Returns: pointer to string
413 case T_A: return US"A";
414 case T_MX: return US"MX";
415 case T_AAAA: return US"AAAA";
416 case T_A6: return US"A6";
417 case T_TXT: return US"TXT";
418 case T_PTR: return US"PTR";
419 case T_SOA: return US"SOA";
420 case T_SRV: return US"SRV";
421 case T_NS: return US"NS";
422 case T_CNAME: return US"CNAME";
423 default: return US"?";
429 /*************************************************
430 * Cache a failed DNS lookup result *
431 *************************************************/
433 /* We cache failed lookup results so as not to experience timeouts many
434 times for the same domain. We need to retain the resolver options because they
435 may change. For successful lookups, we rely on resolver and/or name server
443 Returns: the return code
447 dns_return(uschar *name, int type, int rc)
449 res_state resp = os_get_dns_resolver_res();
450 tree_node *node = store_get_perm(sizeof(tree_node) + 290);
451 sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type),
454 (void)tree_insertnode(&tree_dns_fails, node);
460 /*************************************************
461 * Do basic DNS lookup *
462 *************************************************/
464 /* Call the resolver to look up the given domain name, using the given type,
465 and check the result. The error code TRY_AGAIN is documented as meaning "non-
466 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
467 up nameservers that produce this error continually, so there is the option of
468 providing a list of domains for which this is treated as a non-existent
472 dnsa pointer to dns_answer structure
474 type type of DNS record required (T_A, T_MX, etc)
476 Returns: DNS_SUCCEED successful lookup
477 DNS_NOMATCH name not found (NXDOMAIN)
478 or name contains illegal characters (if checking)
479 or name is an IP address (for IP address lookup)
480 DNS_NODATA domain exists, but no data for this type (NODATA)
481 DNS_AGAIN soft failure, try again later
486 dns_basic_lookup(dns_answer *dnsa, uschar *name, int type)
492 res_state resp = os_get_dns_resolver_res();
495 uschar node_name[290];
497 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
498 a timeout on one domain doesn't happen time and time again for messages that
499 have many addresses in the same domain. We rely on the resolver and name server
500 caching for successful lookups. */
502 sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type),
504 previous = tree_search(tree_dns_fails, node_name);
505 if (previous != NULL)
507 DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
508 name, dns_text_type(type),
509 (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
510 (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
511 (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
512 (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
513 return previous->data.val;
516 /* If configured, check the hygene of the name passed to lookup. Otherwise,
517 although DNS lookups may give REFUSED at the lower level, some resolvers
518 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
519 domains cannot be in the DNS. The check is now done by a regular expression;
520 give it space for substring storage to save it having to get its own if the
521 regex has substrings that are used - the default uses a conditional.
523 This test is omitted for PTR records. These occur only in calls from the dnsdb
524 lookup, which constructs the names itself, so they should be OK. Besides,
525 bitstring labels don't conform to normal name syntax. (But the aren't used any
528 For SRV records, we omit the initial _smtp._tcp. components at the start. */
530 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
532 if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
534 uschar *checkname = name;
535 int ovector[3*(EXPAND_MAXN+1)];
537 if (regex_check_dns_names == NULL)
538 regex_check_dns_names =
539 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);
541 /* For an SRV lookup, skip over the first two components (the service and
542 protocol names, which both start with an underscore). */
546 while (*checkname++ != '.');
547 while (*checkname++ != '.');
550 if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname),
551 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0)
554 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
555 dns_text_type(type));
556 host_find_failed_syntax = TRUE;
561 #endif /* STAND_ALONE */
563 /* Call the resolver; for an overlong response, res_search() will return the
564 number of bytes the message would need, so we need to check for this case. The
565 effect is to truncate overlong data.
567 On some systems, res_search() will recognize "A-for-A" queries and return
568 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
569 nameservers are also believed to do this. It is, of course, contrary to the
570 specification of the DNS, so we lock it out. */
576 type == T_A || type == T_AAAA) &&
577 string_is_ip_address(name, NULL) != 0)
580 /* If we are running in the test harness, instead of calling the normal resolver
581 (res_search), we call fakens_search(), which recognizes certain special
582 domains, and interfaces to a fake nameserver for certain special zones. */
584 if (running_in_test_harness)
585 dnsa->answerlen = fakens_search(name, type, dnsa->answer, MAXPACKET);
587 dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET);
589 if (dnsa->answerlen > MAXPACKET)
591 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
592 name, dns_text_type(type), dnsa->answerlen, MAXPACKET);
593 dnsa->answerlen = MAXPACKET;
596 if (dnsa->answerlen < 0) switch (h_errno)
599 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
600 "returning DNS_NOMATCH\n", name, dns_text_type(type));
601 return dns_return(name, type, DNS_NOMATCH);
604 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
605 name, dns_text_type(type));
607 /* Cut this out for various test programs */
609 save = deliver_domain;
610 deliver_domain = name; /* set $domain */
611 rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL,
612 MCL_DOMAIN, TRUE, NULL);
613 deliver_domain = save;
616 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
617 return dns_return(name, type, DNS_AGAIN);
619 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
620 "DNS_NOMATCH\n", name);
621 return dns_return(name, type, DNS_NOMATCH);
623 #else /* For stand-alone tests */
624 return dns_return(name, type, DNS_AGAIN);
628 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
629 "returning DNS_FAIL\n", name, dns_text_type(type));
630 return dns_return(name, type, DNS_FAIL);
633 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
634 "returning DNS_NODATA\n", name, dns_text_type(type));
635 return dns_return(name, type, DNS_NODATA);
638 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
639 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
640 return dns_return(name, type, DNS_FAIL);
643 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
644 name, dns_text_type(type));
652 /************************************************
653 * Do a DNS lookup and handle CNAMES *
654 ************************************************/
656 /* Look up the given domain name, using the given type. Follow CNAMEs if
657 necessary, but only so many times. There aren't supposed to be CNAME chains in
658 the DNS, but you are supposed to cope with them if you find them.
660 The assumption is made that if the resolver gives back records of the
661 requested type *and* a CNAME, we don't need to make another call to look up
662 the CNAME. I can't see how it could return only some of the right records. If
663 it's done a CNAME lookup in the past, it will have all of them; if not, it
666 If fully_qualified_name is not NULL, set it to point to the full name
667 returned by the resolver, if this is different to what it is given, unless
668 the returned name starts with "*" as some nameservers seem to be returning
669 wildcards in this form.
672 dnsa pointer to dns_answer structure
673 name domain name to look up
674 type DNS record type (T_A, T_MX, etc)
675 fully_qualified_name if not NULL, return the returned name here if its
676 contents are different (i.e. it must be preset)
678 Returns: DNS_SUCCEED successful lookup
679 DNS_NOMATCH name not found
680 DNS_NODATA no data found
681 DNS_AGAIN soft failure, try again later
686 dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name)
689 uschar *orig_name = name;
691 /* Loop to follow CNAME chains so far, but no further... */
693 for (i = 0; i < 10; i++)
696 dns_record *rr, cname_rr, type_rr;
700 /* DNS lookup failures get passed straight back. */
702 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc;
704 /* We should have either records of the required type, or a CNAME record,
705 or both. We need to know whether both exist for getting the fully qualified
706 name, but avoid scanning more than necessary. Note that we must copy the
707 contents of any rr blocks returned by dns_next_rr() as they use the same
708 area in the dnsa block. */
710 cname_rr.data = type_rr.data = NULL;
711 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
713 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
715 if (rr->type == type)
717 if (type_rr.data == NULL) type_rr = *rr;
718 if (cname_rr.data != NULL) break;
720 else if (rr->type == T_CNAME) cname_rr = *rr;
723 /* For the first time round this loop, if a CNAME was found, take the fully
724 qualified name from it; otherwise from the first data record, if present. */
726 if (i == 0 && fully_qualified_name != NULL)
728 if (cname_rr.data != NULL)
730 if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 &&
731 cname_rr.name[0] != '*')
732 *fully_qualified_name = string_copy_dnsdomain(cname_rr.name);
734 else if (type_rr.data != NULL)
736 if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 &&
737 type_rr.name[0] != '*')
738 *fully_qualified_name = string_copy_dnsdomain(type_rr.name);
742 /* If any data records of the correct type were found, we are done. */
744 if (type_rr.data != NULL) return DNS_SUCCEED;
746 /* If there are no data records, we need to re-scan the DNS using the
747 domain given in the CNAME record, which should exist (otherwise we should
748 have had a failure from dns_lookup). However code against the possibility of
751 if (cname_rr.data == NULL) return DNS_FAIL;
752 datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
753 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256);
754 if (datalen < 0) return DNS_FAIL;
757 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
758 } /* Loop back to do another lookup */
760 /*Control reaches here after 10 times round the CNAME loop. Something isn't
763 log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
772 /************************************************
773 * Do a DNS lookup and handle virtual types *
774 ************************************************/
776 /* This function handles some invented "lookup types" that synthesize feature
777 not available in the basic types. The special types all have negative values.
778 Positive type values are passed straight on to dns_lookup().
781 dnsa pointer to dns_answer structure
782 name domain name to look up
783 type DNS record type (T_A, T_MX, etc or a "special")
784 fully_qualified_name if not NULL, return the returned name here if its
785 contents are different (i.e. it must be preset)
787 Returns: DNS_SUCCEED successful lookup
788 DNS_NOMATCH name not found
789 DNS_NODATA no data found
790 DNS_AGAIN soft failure, try again later
795 dns_special_lookup(dns_answer *dnsa, uschar *name, int type,
796 uschar **fully_qualified_name)
798 if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name);
800 /* The "mx hosts only" type doesn't require any special action here */
802 if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
804 /* Find nameservers for the domain or the nearest enclosing zone, excluding the
812 int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name);
813 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
814 while (*d != 0 && *d != '.') d++;
815 if (*d++ == 0) break;
820 /* Try to look up the Client SMTP Authorization SRV record for the name. If
821 there isn't one, search from the top downwards for a CSA record in a parent
822 domain, which might be making assertions about subdomains. If we find a record
823 we set fully_qualified_name to whichever lookup succeeded, so that the caller
824 can tell whether to look at the explicit authorization field or the subdomain
829 uschar *srvname, *namesuff, *tld, *p;
830 int priority, weight, port;
836 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
838 srvname = string_sprintf("_client._smtp.%s", name);
839 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
840 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
842 if (rc == DNS_SUCCEED) *fully_qualified_name = name;
846 /* Search for CSA subdomain assertion SRV records from the top downwards,
847 starting with the 2nd level domain. This order maximizes cache-friendliness.
848 We skip the top level domains to avoid loading their nameservers and because
849 we know they'll never have CSA SRV records. */
851 namesuff = Ustrrchr(name, '.');
852 if (namesuff == NULL) return DNS_NOMATCH;
855 limit = dns_csa_search_limit;
857 /* Use more appropriate search parameters if we are in the reverse DNS. */
859 if (strcmpic(namesuff, US".arpa") == 0)
861 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
867 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
876 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
878 /* Do not perform the search if the top level or 2nd level domains do not
879 exist. This is quite common, and when it occurs all the search queries would
880 go to the root or TLD name servers, which is not friendly. So we check the
881 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
882 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
883 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
884 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
886 if (rc == DNS_NOMATCH)
888 /* This is really gross. The successful return value from res_search() is
889 the packet length, which is stored in dnsa->answerlen. If we get a
890 negative DNS reply then res_search() returns -1, which causes the bounds
891 checks for name decompression to fail when it is treated as a packet
892 length, which in turn causes the authority search to fail. The correct
893 packet length has been lost inside libresolv, so we have to guess a
894 replacement value. (The only way to fix this properly would be to
895 re-implement res_search() and res_query() so that they don't muddle their
896 success and packet length return values.) For added safety we only reset
897 the packet length if the packet header looks plausible. */
899 HEADER *h = (HEADER *)dnsa->answer;
900 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
901 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
902 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
903 && ntohs(h->nscount) >= 1)
904 dnsa->answerlen = MAXPACKET;
906 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
908 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
909 if (rr->type != T_SOA) continue;
910 else if (strcmpic(rr->name, US"") == 0 ||
911 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
915 for (i = 0; i < limit; i++)
919 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
920 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
922 if (namesuff <= name) return DNS_NOMATCH;
925 /* Find the start of the preceding domain name label. */
927 if (--namesuff <= name) return DNS_NOMATCH;
928 while (*namesuff != '.');
930 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
932 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
933 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
934 if (rc == DNS_AGAIN) return rc;
935 if (rc != DNS_SUCCEED) continue;
937 /* Check that the SRV record we have found is worth returning. We don't
938 just return the first one we find, because some lower level SRV record
939 might make stricter assertions than its parent domain. */
941 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
943 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
945 if (rr->type != T_SRV) continue;
947 /* Extract the numerical SRV fields (p is incremented) */
949 GETSHORT(priority, p);
953 /* Check the CSA version number */
954 if (priority != 1) continue;
956 /* If it's making an interesting assertion, return this response. */
959 *fully_qualified_name = namesuff + 1;
967 /* Control should never reach here */
974 /* Support for A6 records has been commented out since they were demoted to
975 experimental status at IETF 51. */
977 #if HAVE_IPV6 && defined(SUPPORT_A6)
979 /*************************************************
980 * Search DNS block for prefix RRs *
981 *************************************************/
983 /* Called from dns_complete_a6() to search an additional section or a main
984 answer section for required prefix records to complete an IPv6 address obtained
985 from an A6 record. For each prefix record, a recursive call to dns_complete_a6
986 is made, with a new copy of the address so far.
989 dnsa the DNS answer block
990 which RESET_ADDITIONAL or RESET_ANSWERS
991 name name of prefix record
992 yptrptr pointer to the pointer that points to where to hang the next
993 dns_address structure
994 bits number of bits we have already got
995 bitvec the bits we have already got
997 Returns: TRUE if any records were found
1001 dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address
1002 ***yptrptr, int bits, uschar *bitvec)
1008 for (rr = dns_next_rr(dnsa, &dnss, which);
1010 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
1013 if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue;
1015 memcpy(cbitvec, bitvec, sizeof(cbitvec));
1016 dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec);
1024 /*************************************************
1025 * Follow chains of A6 records *
1026 *************************************************/
1028 /* A6 records may be incomplete, with pointers to other records containing more
1029 bits of the address. There can be a tree structure, leading to a number of
1030 addresses originating from a single initial A6 record.
1033 yptrptr pointer to the pointer that points to where to hang the next
1034 dns_address structure
1035 dnsa the current DNS answer block
1036 rr the RR we have at present
1037 bits number of bits we have already got
1038 bitvec the bits we have already got
1044 dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr,
1045 int bits, uschar *bitvec)
1047 static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 };
1048 uschar *p = (uschar *)(rr->data);
1049 int prefix_len, suffix_len;
1055 /* The prefix length is the first byte. It defines the prefix which is missing
1056 from the data in this record as a number of bits. Zero means this is the end of
1057 a chain. The suffix is the data in this record; only sufficient bytes to hold
1058 it are supplied. There may be zero bytes. We have to ignore trailing bits that
1059 we have already obtained from earlier RRs in the chain. */
1061 prefix_len = *p++; /* bits */
1062 suffix_len = (128 - prefix_len + 7)/8; /* bytes */
1064 /* If the prefix in this record is greater than the prefix in the previous
1065 record in the chain, we have to ignore the record (RFC 2874). */
1067 if (prefix_len > 128 - bits) return;
1069 /* In this little loop, the number of bits up to and including the current byte
1070 is held in k. If we have none of the bits in this byte, we can just or it into
1071 the current data. If we have all of the bits in this byte, we skip it.
1072 Otherwise, some masking has to be done. */
1074 for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--)
1076 int required = k - bits;
1077 if (required >= 8) bitvec[j] |= p[i];
1078 else if (required > 0) bitvec[j] |= p[i] & bitmask[required];
1079 j--; /* I tried putting these in the "for" statement, but gcc muttered */
1080 k += 8; /* about computed values not being used. */
1083 /* If the prefix_length is zero, we are at the end of a chain. Build a
1084 dns_address item with the current data, hang it onto the end of the chain,
1085 adjust the hanging pointer, and we are done. */
1087 if (prefix_len == 0)
1089 dns_address *new = store_get(sizeof(dns_address) + 50);
1090 inet_ntop(AF_INET6, bitvec, CS new->address, 50);
1093 *yptrptr = &(new->next);
1097 /* Prefix length is not zero. Reset the number of bits that we have collected
1098 so far, and extract the chain name. */
1100 bits = 128 - prefix_len;
1104 while ((i = *p++) != 0)
1106 if (chainptr != chain) *chainptr++ = '.';
1107 memcpy(chainptr, p, i);
1114 /* Now scan the current DNS response record to see if the additional section
1115 contains the records we want. This processing can be cut out for testing
1118 if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec))
1121 /* No chain records were found in the current DNS response block. Do a new DNS
1122 lookup to try to find these records. This opens up the possibility of DNS
1123 failures. We ignore them at this point; if all branches of the tree fail, there
1124 will be no addresses at the end. */
1126 if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED)
1127 (void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec);
1129 #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */
1134 /*************************************************
1135 * Get address(es) from DNS record *
1136 *************************************************/
1138 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1139 supported) for an IPv6 address. In the A6 case, there may be several addresses,
1140 generated by following chains. A recursive function does all the hard work. A6
1141 records now look like passing into history, so the code is only included when
1142 explicitly asked for.
1145 dnsa the DNS answer block
1148 Returns: pointer a chain of dns_address items
1152 dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1154 dns_address *yield = NULL;
1156 #if HAVE_IPV6 && defined(SUPPORT_A6)
1157 dns_address **yieldptr = &yield;
1160 dnsa = dnsa; /* Stop picky compilers warning */
1163 if (rr->type == T_A)
1165 uschar *p = (uschar *)(rr->data);
1166 yield = store_get(sizeof(dns_address) + 20);
1167 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1174 else if (rr->type == T_A6)
1176 memset(bitvec, 0, sizeof(bitvec));
1177 dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec);
1179 #endif /* SUPPORT_A6 */
1183 yield = store_get(sizeof(dns_address) + 50);
1184 inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50);
1187 #endif /* HAVE_IPV6 */