95db526867029321275e247fbd986037247ef594
1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) University of Cambridge 1995 - 2012 */
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 #ifndef DISABLE_DNSSEC
205 # ifdef RES_USE_DNSSEC
206 # ifndef RES_USE_EDNS0
207 # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ...
209 if (dns_use_dnssec
>= 0)
211 if (dns_use_edns0
== 0 && dns_use_dnssec
!= 0)
214 debug_printf("CONFLICT: dns_use_edns0 forced false, dns_use_dnssec forced true!\n");
219 resp
->options
|= RES_USE_DNSSEC
;
221 resp
->options
&= ~RES_USE_DNSSEC
;
222 DEBUG(D_resolver
) debug_printf("Coerced resolver DNSSEC support %s.\n",
223 dns_use_dnssec
? "on" : "off");
227 if (dns_use_dnssec
>= 0)
229 debug_printf("Unable to %sset DNSSEC without resolver support.\n",
230 dns_use_dnssec
? "" : "un");
232 #endif /* DISABLE_DNSSEC */
234 os_put_dns_resolver_res(resp
);
239 /*************************************************
240 * Build key name for PTR records *
241 *************************************************/
243 /* This function inverts an IP address and adds the relevant domain, to produce
244 a name that can be used to look up PTR records.
247 string the IP address as a string
248 buffer a suitable buffer, long enough to hold the result
254 dns_build_reverse(uschar
*string
, uschar
*buffer
)
256 uschar
*p
= string
+ Ustrlen(string
);
259 /* Handle IPv4 address */
262 if (Ustrchr(string
, ':') == NULL
)
266 for (i
= 0; i
< 4; i
++)
269 while (ppp
> string
&& ppp
[-1] != '.') ppp
--;
270 Ustrncpy(pp
, ppp
, p
- ppp
);
275 Ustrcpy(pp
, "in-addr.arpa");
278 /* Handle IPv6 address; convert to binary so as to fill out any
279 abbreviation in the textual form. */
286 (void)host_aton(string
, v6
);
288 /* The original specification for IPv6 reverse lookup was to invert each
289 nibble, and look in the ip6.int domain. The domain was subsequently
290 changed to ip6.arpa. */
292 for (i
= 3; i
>= 0; i
--)
295 for (j
= 0; j
< 32; j
+= 4)
297 sprintf(CS pp
, "%x.", (v6
[i
] >> j
) & 15);
301 Ustrcpy(pp
, "ip6.arpa.");
303 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
304 with A6 records. However, it fell out of favour when they did. The
305 alternative was to construct a binary key, and look in ip6.arpa. I tried
306 to make this code do that, but I could not make it work on Solaris 8. The
307 resolver seems to lose the initial backslash somehow. However, now that
308 this style of reverse lookup has been dropped, it doesn't matter. These
309 lines are left here purely for historical interest. */
311 /**************************************************
315 for (i = 0; i < 4; i++)
317 sprintf(pp, "%08X", v6[i]);
320 Ustrcpy(pp, "].ip6.arpa.");
321 **************************************************/
330 /*************************************************
331 * Get next DNS record from answer block *
332 *************************************************/
334 /* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
335 RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
336 scan the additional records, and reset == RESET_NEXT to get the next record.
337 The result is in static storage which must be copied if it is to be preserved.
340 dnsa pointer to dns answer block
341 dnss pointer to dns scan block
342 reset option specifing what portion to scan, as described above
344 Returns: next dns record, or NULL when no more
348 dns_next_rr(dns_answer
*dnsa
, dns_scan
*dnss
, int reset
)
350 HEADER
*h
= (HEADER
*)dnsa
->answer
;
353 /* Reset the saved data when requested to, and skip to the first required RR */
355 if (reset
!= RESET_NEXT
)
357 dnss
->rrcount
= ntohs(h
->qdcount
);
358 dnss
->aptr
= dnsa
->answer
+ sizeof(HEADER
);
360 /* Skip over questions; failure to expand the name just gives up */
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
+ 4; /* skip name & type & class */
370 /* Get the number of answer records. */
372 dnss
->rrcount
= ntohs(h
->ancount
);
374 /* Skip over answers if we want to look at the authority section. Also skip
375 the NS records (i.e. authority section) if wanting to look at the additional
378 if (reset
== RESET_ADDITIONAL
) dnss
->rrcount
+= ntohs(h
->nscount
);
380 if (reset
== RESET_AUTHORITY
|| reset
== RESET_ADDITIONAL
)
382 while (dnss
->rrcount
-- > 0)
384 namelen
= dn_expand(dnsa
->answer
, dnsa
->answer
+ dnsa
->answerlen
,
385 dnss
->aptr
, (DN_EXPAND_ARG4_TYPE
) &(dnss
->srr
.name
), DNS_MAXNAME
);
386 if (namelen
< 0) { dnss
->rrcount
= 0; return NULL
; }
387 dnss
->aptr
+= namelen
+ 8; /* skip name, type, class & TTL */
388 GETSHORT(dnss
->srr
.size
, dnss
->aptr
); /* size of data portion */
389 dnss
->aptr
+= dnss
->srr
.size
; /* skip over it */
391 dnss
->rrcount
= (reset
== RESET_AUTHORITY
)
392 ? ntohs(h
->nscount
) : ntohs(h
->arcount
);
396 /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
397 contains the number of RR records left. */
399 if (dnss
->rrcount
-- <= 0) return NULL
;
401 /* If expanding the RR domain name fails, behave as if no more records
404 namelen
= dn_expand(dnsa
->answer
, dnsa
->answer
+ dnsa
->answerlen
, dnss
->aptr
,
405 (DN_EXPAND_ARG4_TYPE
) &(dnss
->srr
.name
), DNS_MAXNAME
);
406 if (namelen
< 0) { dnss
->rrcount
= 0; return NULL
; }
408 /* Move the pointer past the name and fill in the rest of the data structure
409 from the following bytes. */
411 dnss
->aptr
+= namelen
;
412 GETSHORT(dnss
->srr
.type
, dnss
->aptr
); /* Record type */
413 dnss
->aptr
+= 6; /* Don't want class or TTL */
414 GETSHORT(dnss
->srr
.size
, dnss
->aptr
); /* Size of data portion */
415 dnss
->srr
.data
= dnss
->aptr
; /* The record's data follows */
416 dnss
->aptr
+= dnss
->srr
.size
; /* Advance to next RR */
418 /* Return a pointer to the dns_record structure within the dns_answer. This is
419 for convenience so that the scans can use nice-looking for loops. */
427 /*************************************************
428 * Return whether AD bit set in DNS result *
429 *************************************************/
431 /* We do not perform DNSSEC work ourselves; if the administrator has installed
432 a verifying resolver which sets AD as appropriate, though, we'll use that.
433 (AD = Authentic Data)
435 Argument: pointer to dns answer block
436 Returns: bool indicating presence of AD bit
440 dns_is_secure(dns_answer
*dnsa
)
442 #ifdef DISABLE_DNSSEC
444 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
447 HEADER
*h
= (HEADER
*)dnsa
->answer
;
448 return h
->ad
? TRUE
: FALSE
;
455 /*************************************************
456 * Turn DNS type into text *
457 *************************************************/
459 /* Turn the coded record type into a string for printing. All those that Exim
460 uses should be included here.
462 Argument: record type
463 Returns: pointer to string
471 case T_A
: return US
"A";
472 case T_MX
: return US
"MX";
473 case T_AAAA
: return US
"AAAA";
474 case T_A6
: return US
"A6";
475 case T_TXT
: return US
"TXT";
476 case T_SPF
: return US
"SPF";
477 case T_PTR
: return US
"PTR";
478 case T_SOA
: return US
"SOA";
479 case T_SRV
: return US
"SRV";
480 case T_NS
: return US
"NS";
481 case T_CNAME
: return US
"CNAME";
482 default: return US
"?";
488 /*************************************************
489 * Cache a failed DNS lookup result *
490 *************************************************/
492 /* We cache failed lookup results so as not to experience timeouts many
493 times for the same domain. We need to retain the resolver options because they
494 may change. For successful lookups, we rely on resolver and/or name server
502 Returns: the return code
506 dns_return(uschar
*name
, int type
, int rc
)
508 res_state resp
= os_get_dns_resolver_res();
509 tree_node
*node
= store_get_perm(sizeof(tree_node
) + 290);
510 sprintf(CS node
->name
, "%.255s-%s-%lx", name
, dns_text_type(type
),
513 (void)tree_insertnode(&tree_dns_fails
, node
);
519 /*************************************************
520 * Do basic DNS lookup *
521 *************************************************/
523 /* Call the resolver to look up the given domain name, using the given type,
524 and check the result. The error code TRY_AGAIN is documented as meaning "non-
525 Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set
526 up nameservers that produce this error continually, so there is the option of
527 providing a list of domains for which this is treated as a non-existent
531 dnsa pointer to dns_answer structure
533 type type of DNS record required (T_A, T_MX, etc)
535 Returns: DNS_SUCCEED successful lookup
536 DNS_NOMATCH name not found (NXDOMAIN)
537 or name contains illegal characters (if checking)
538 or name is an IP address (for IP address lookup)
539 DNS_NODATA domain exists, but no data for this type (NODATA)
540 DNS_AGAIN soft failure, try again later
545 dns_basic_lookup(dns_answer
*dnsa
, uschar
*name
, int type
)
551 res_state resp
= os_get_dns_resolver_res();
554 uschar node_name
[290];
556 /* DNS lookup failures of any kind are cached in a tree. This is mainly so that
557 a timeout on one domain doesn't happen time and time again for messages that
558 have many addresses in the same domain. We rely on the resolver and name server
559 caching for successful lookups. */
561 sprintf(CS node_name
, "%.255s-%s-%lx", name
, dns_text_type(type
),
563 previous
= tree_search(tree_dns_fails
, node_name
);
564 if (previous
!= NULL
)
566 DEBUG(D_dns
) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
567 name
, dns_text_type(type
),
568 (previous
->data
.val
== DNS_NOMATCH
)? "DNS_NOMATCH" :
569 (previous
->data
.val
== DNS_NODATA
)? "DNS_NODATA" :
570 (previous
->data
.val
== DNS_AGAIN
)? "DNS_AGAIN" :
571 (previous
->data
.val
== DNS_FAIL
)? "DNS_FAIL" : "??");
572 return previous
->data
.val
;
575 /* If configured, check the hygene of the name passed to lookup. Otherwise,
576 although DNS lookups may give REFUSED at the lower level, some resolvers
577 turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
578 domains cannot be in the DNS. The check is now done by a regular expression;
579 give it space for substring storage to save it having to get its own if the
580 regex has substrings that are used - the default uses a conditional.
582 This test is omitted for PTR records. These occur only in calls from the dnsdb
583 lookup, which constructs the names itself, so they should be OK. Besides,
584 bitstring labels don't conform to normal name syntax. (But the aren't used any
587 For SRV records, we omit the initial _smtp._tcp. components at the start. */
589 #ifndef STAND_ALONE /* Omit this for stand-alone tests */
591 if (check_dns_names_pattern
[0] != 0 && type
!= T_PTR
&& type
!= T_TXT
)
593 uschar
*checkname
= name
;
594 int ovector
[3*(EXPAND_MAXN
+1)];
596 if (regex_check_dns_names
== NULL
)
597 regex_check_dns_names
=
598 regex_must_compile(check_dns_names_pattern
, FALSE
, TRUE
);
600 /* For an SRV lookup, skip over the first two components (the service and
601 protocol names, which both start with an underscore). */
605 while (*checkname
++ != '.');
606 while (*checkname
++ != '.');
609 if (pcre_exec(regex_check_dns_names
, NULL
, CS checkname
, Ustrlen(checkname
),
610 0, PCRE_EOPT
, ovector
, sizeof(ovector
)/sizeof(int)) < 0)
613 debug_printf("DNS name syntax check failed: %s (%s)\n", name
,
614 dns_text_type(type
));
615 host_find_failed_syntax
= TRUE
;
620 #endif /* STAND_ALONE */
622 /* Call the resolver; for an overlong response, res_search() will return the
623 number of bytes the message would need, so we need to check for this case. The
624 effect is to truncate overlong data.
626 On some systems, res_search() will recognize "A-for-A" queries and return
627 the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
628 nameservers are also believed to do this. It is, of course, contrary to the
629 specification of the DNS, so we lock it out. */
635 type
== T_A
|| type
== T_AAAA
) &&
636 string_is_ip_address(name
, NULL
) != 0)
639 /* If we are running in the test harness, instead of calling the normal resolver
640 (res_search), we call fakens_search(), which recognizes certain special
641 domains, and interfaces to a fake nameserver for certain special zones. */
643 if (running_in_test_harness
)
644 dnsa
->answerlen
= fakens_search(name
, type
, dnsa
->answer
, MAXPACKET
);
646 dnsa
->answerlen
= res_search(CS name
, C_IN
, type
, dnsa
->answer
, MAXPACKET
);
648 if (dnsa
->answerlen
> MAXPACKET
)
650 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n",
651 name
, dns_text_type(type
), dnsa
->answerlen
, MAXPACKET
);
652 dnsa
->answerlen
= MAXPACKET
;
655 if (dnsa
->answerlen
< 0) switch (h_errno
)
658 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
659 "returning DNS_NOMATCH\n", name
, dns_text_type(type
));
660 return dns_return(name
, type
, DNS_NOMATCH
);
663 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
664 name
, dns_text_type(type
));
666 /* Cut this out for various test programs */
668 save
= deliver_domain
;
669 deliver_domain
= name
; /* set $domain */
670 rc
= match_isinlist(name
, &dns_again_means_nonexist
, 0, NULL
, NULL
,
671 MCL_DOMAIN
, TRUE
, NULL
);
672 deliver_domain
= save
;
675 DEBUG(D_dns
) debug_printf("returning DNS_AGAIN\n");
676 return dns_return(name
, type
, DNS_AGAIN
);
678 DEBUG(D_dns
) debug_printf("%s is in dns_again_means_nonexist: returning "
679 "DNS_NOMATCH\n", name
);
680 return dns_return(name
, type
, DNS_NOMATCH
);
682 #else /* For stand-alone tests */
683 return dns_return(name
, type
, DNS_AGAIN
);
687 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
688 "returning DNS_FAIL\n", name
, dns_text_type(type
));
689 return dns_return(name
, type
, DNS_FAIL
);
692 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
693 "returning DNS_NODATA\n", name
, dns_text_type(type
));
694 return dns_return(name
, type
, DNS_NODATA
);
697 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
698 "returning DNS_FAIL\n", name
, dns_text_type(type
), h_errno
);
699 return dns_return(name
, type
, DNS_FAIL
);
702 DEBUG(D_dns
) debug_printf("DNS lookup of %s (%s) succeeded\n",
703 name
, dns_text_type(type
));
711 /************************************************
712 * Do a DNS lookup and handle CNAMES *
713 ************************************************/
715 /* Look up the given domain name, using the given type. Follow CNAMEs if
716 necessary, but only so many times. There aren't supposed to be CNAME chains in
717 the DNS, but you are supposed to cope with them if you find them.
719 The assumption is made that if the resolver gives back records of the
720 requested type *and* a CNAME, we don't need to make another call to look up
721 the CNAME. I can't see how it could return only some of the right records. If
722 it's done a CNAME lookup in the past, it will have all of them; if not, it
725 If fully_qualified_name is not NULL, set it to point to the full name
726 returned by the resolver, if this is different to what it is given, unless
727 the returned name starts with "*" as some nameservers seem to be returning
728 wildcards in this form.
731 dnsa pointer to dns_answer structure
732 name domain name to look up
733 type DNS record type (T_A, T_MX, etc)
734 fully_qualified_name if not NULL, return the returned name here if its
735 contents are different (i.e. it must be preset)
737 Returns: DNS_SUCCEED successful lookup
738 DNS_NOMATCH name not found
739 DNS_NODATA no data found
740 DNS_AGAIN soft failure, try again later
745 dns_lookup(dns_answer
*dnsa
, uschar
*name
, int type
, uschar
**fully_qualified_name
)
748 uschar
*orig_name
= name
;
750 /* Loop to follow CNAME chains so far, but no further... */
752 for (i
= 0; i
< 10; i
++)
755 dns_record
*rr
, cname_rr
, type_rr
;
759 /* DNS lookup failures get passed straight back. */
761 if ((rc
= dns_basic_lookup(dnsa
, name
, type
)) != DNS_SUCCEED
) return rc
;
763 /* We should have either records of the required type, or a CNAME record,
764 or both. We need to know whether both exist for getting the fully qualified
765 name, but avoid scanning more than necessary. Note that we must copy the
766 contents of any rr blocks returned by dns_next_rr() as they use the same
767 area in the dnsa block. */
769 cname_rr
.data
= type_rr
.data
= NULL
;
770 for (rr
= dns_next_rr(dnsa
, &dnss
, RESET_ANSWERS
);
772 rr
= dns_next_rr(dnsa
, &dnss
, RESET_NEXT
))
774 if (rr
->type
== type
)
776 if (type_rr
.data
== NULL
) type_rr
= *rr
;
777 if (cname_rr
.data
!= NULL
) break;
779 else if (rr
->type
== T_CNAME
) cname_rr
= *rr
;
782 /* For the first time round this loop, if a CNAME was found, take the fully
783 qualified name from it; otherwise from the first data record, if present. */
785 if (i
== 0 && fully_qualified_name
!= NULL
)
787 if (cname_rr
.data
!= NULL
)
789 if (Ustrcmp(cname_rr
.name
, *fully_qualified_name
) != 0 &&
790 cname_rr
.name
[0] != '*')
791 *fully_qualified_name
= string_copy_dnsdomain(cname_rr
.name
);
793 else if (type_rr
.data
!= NULL
)
795 if (Ustrcmp(type_rr
.name
, *fully_qualified_name
) != 0 &&
796 type_rr
.name
[0] != '*')
797 *fully_qualified_name
= string_copy_dnsdomain(type_rr
.name
);
801 /* If any data records of the correct type were found, we are done. */
803 if (type_rr
.data
!= NULL
) return DNS_SUCCEED
;
805 /* If there are no data records, we need to re-scan the DNS using the
806 domain given in the CNAME record, which should exist (otherwise we should
807 have had a failure from dns_lookup). However code against the possibility of
810 if (cname_rr
.data
== NULL
) return DNS_FAIL
;
811 datalen
= dn_expand(dnsa
->answer
, dnsa
->answer
+ dnsa
->answerlen
,
812 cname_rr
.data
, (DN_EXPAND_ARG4_TYPE
)data
, 256);
813 if (datalen
< 0) return DNS_FAIL
;
816 DEBUG(D_dns
) debug_printf("CNAME found: change to %s\n", name
);
817 } /* Loop back to do another lookup */
819 /*Control reaches here after 10 times round the CNAME loop. Something isn't
822 log_write(0, LOG_MAIN
, "CNAME loop for %s encountered", orig_name
);
831 /************************************************
832 * Do a DNS lookup and handle virtual types *
833 ************************************************/
835 /* This function handles some invented "lookup types" that synthesize feature
836 not available in the basic types. The special types all have negative values.
837 Positive type values are passed straight on to dns_lookup().
840 dnsa pointer to dns_answer structure
841 name domain name to look up
842 type DNS record type (T_A, T_MX, etc or a "special")
843 fully_qualified_name if not NULL, return the returned name here if its
844 contents are different (i.e. it must be preset)
846 Returns: DNS_SUCCEED successful lookup
847 DNS_NOMATCH name not found
848 DNS_NODATA no data found
849 DNS_AGAIN soft failure, try again later
854 dns_special_lookup(dns_answer
*dnsa
, uschar
*name
, int type
,
855 uschar
**fully_qualified_name
)
857 if (type
>= 0) return dns_lookup(dnsa
, name
, type
, fully_qualified_name
);
859 /* The "mx hosts only" type doesn't require any special action here */
861 if (type
== T_MXH
) return dns_lookup(dnsa
, name
, T_MX
, fully_qualified_name
);
863 /* Find nameservers for the domain or the nearest enclosing zone, excluding the
871 int rc
= dns_lookup(dnsa
, d
, T_NS
, fully_qualified_name
);
872 if (rc
!= DNS_NOMATCH
&& rc
!= DNS_NODATA
) return rc
;
873 while (*d
!= 0 && *d
!= '.') d
++;
874 if (*d
++ == 0) break;
879 /* Try to look up the Client SMTP Authorization SRV record for the name. If
880 there isn't one, search from the top downwards for a CSA record in a parent
881 domain, which might be making assertions about subdomains. If we find a record
882 we set fully_qualified_name to whichever lookup succeeded, so that the caller
883 can tell whether to look at the explicit authorization field or the subdomain
888 uschar
*srvname
, *namesuff
, *tld
, *p
;
889 int priority
, weight
, port
;
895 DEBUG(D_dns
) debug_printf("CSA lookup of %s\n", name
);
897 srvname
= string_sprintf("_client._smtp.%s", name
);
898 rc
= dns_lookup(dnsa
, srvname
, T_SRV
, NULL
);
899 if (rc
== DNS_SUCCEED
|| rc
== DNS_AGAIN
)
901 if (rc
== DNS_SUCCEED
) *fully_qualified_name
= name
;
905 /* Search for CSA subdomain assertion SRV records from the top downwards,
906 starting with the 2nd level domain. This order maximizes cache-friendliness.
907 We skip the top level domains to avoid loading their nameservers and because
908 we know they'll never have CSA SRV records. */
910 namesuff
= Ustrrchr(name
, '.');
911 if (namesuff
== NULL
) return DNS_NOMATCH
;
914 limit
= dns_csa_search_limit
;
916 /* Use more appropriate search parameters if we are in the reverse DNS. */
918 if (strcmpic(namesuff
, US
".arpa") == 0)
920 if (namesuff
- 8 > name
&& strcmpic(namesuff
- 8, US
".in-addr.arpa") == 0)
926 else if (namesuff
- 4 > name
&& strcmpic(namesuff
- 4, US
".ip6.arpa") == 0)
935 DEBUG(D_dns
) debug_printf("CSA TLD %s\n", tld
);
937 /* Do not perform the search if the top level or 2nd level domains do not
938 exist. This is quite common, and when it occurs all the search queries would
939 go to the root or TLD name servers, which is not friendly. So we check the
940 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
941 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
942 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
943 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
945 if (rc
== DNS_NOMATCH
)
947 /* This is really gross. The successful return value from res_search() is
948 the packet length, which is stored in dnsa->answerlen. If we get a
949 negative DNS reply then res_search() returns -1, which causes the bounds
950 checks for name decompression to fail when it is treated as a packet
951 length, which in turn causes the authority search to fail. The correct
952 packet length has been lost inside libresolv, so we have to guess a
953 replacement value. (The only way to fix this properly would be to
954 re-implement res_search() and res_query() so that they don't muddle their
955 success and packet length return values.) For added safety we only reset
956 the packet length if the packet header looks plausible. */
958 HEADER
*h
= (HEADER
*)dnsa
->answer
;
959 if (h
->qr
== 1 && h
->opcode
== QUERY
&& h
->tc
== 0
960 && (h
->rcode
== NOERROR
|| h
->rcode
== NXDOMAIN
)
961 && ntohs(h
->qdcount
) == 1 && ntohs(h
->ancount
) == 0
962 && ntohs(h
->nscount
) >= 1)
963 dnsa
->answerlen
= MAXPACKET
;
965 for (rr
= dns_next_rr(dnsa
, &dnss
, RESET_AUTHORITY
);
967 rr
= dns_next_rr(dnsa
, &dnss
, RESET_NEXT
))
968 if (rr
->type
!= T_SOA
) continue;
969 else if (strcmpic(rr
->name
, US
"") == 0 ||
970 strcmpic(rr
->name
, tld
) == 0) return DNS_NOMATCH
;
974 for (i
= 0; i
< limit
; i
++)
978 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
979 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
981 if (namesuff
<= name
) return DNS_NOMATCH
;
984 /* Find the start of the preceding domain name label. */
986 if (--namesuff
<= name
) return DNS_NOMATCH
;
987 while (*namesuff
!= '.');
989 DEBUG(D_dns
) debug_printf("CSA parent search at %s\n", namesuff
+ 1);
991 srvname
= string_sprintf("_client._smtp.%s", namesuff
+ 1);
992 rc
= dns_lookup(dnsa
, srvname
, T_SRV
, NULL
);
993 if (rc
== DNS_AGAIN
) return rc
;
994 if (rc
!= DNS_SUCCEED
) continue;
996 /* Check that the SRV record we have found is worth returning. We don't
997 just return the first one we find, because some lower level SRV record
998 might make stricter assertions than its parent domain. */
1000 for (rr
= dns_next_rr(dnsa
, &dnss
, RESET_ANSWERS
);
1002 rr
= dns_next_rr(dnsa
, &dnss
, RESET_NEXT
))
1004 if (rr
->type
!= T_SRV
) continue;
1006 /* Extract the numerical SRV fields (p is incremented) */
1008 GETSHORT(priority
, p
);
1009 GETSHORT(weight
, p
);
1012 /* Check the CSA version number */
1013 if (priority
!= 1) continue;
1015 /* If it's making an interesting assertion, return this response. */
1018 *fully_qualified_name
= namesuff
+ 1;
1026 /* Control should never reach here */
1033 /* Support for A6 records has been commented out since they were demoted to
1034 experimental status at IETF 51. */
1036 #if HAVE_IPV6 && defined(SUPPORT_A6)
1038 /*************************************************
1039 * Search DNS block for prefix RRs *
1040 *************************************************/
1042 /* Called from dns_complete_a6() to search an additional section or a main
1043 answer section for required prefix records to complete an IPv6 address obtained
1044 from an A6 record. For each prefix record, a recursive call to dns_complete_a6
1045 is made, with a new copy of the address so far.
1048 dnsa the DNS answer block
1049 which RESET_ADDITIONAL or RESET_ANSWERS
1050 name name of prefix record
1051 yptrptr pointer to the pointer that points to where to hang the next
1052 dns_address structure
1053 bits number of bits we have already got
1054 bitvec the bits we have already got
1056 Returns: TRUE if any records were found
1060 dns_find_prefix(dns_answer
*dnsa
, int which
, uschar
*name
, dns_address
1061 ***yptrptr
, int bits
, uschar
*bitvec
)
1067 for (rr
= dns_next_rr(dnsa
, &dnss
, which
);
1069 rr
= dns_next_rr(dnsa
, &dnss
, RESET_NEXT
))
1072 if (rr
->type
!= T_A6
|| strcmpic(rr
->name
, name
) != 0) continue;
1074 memcpy(cbitvec
, bitvec
, sizeof(cbitvec
));
1075 dns_complete_a6(yptrptr
, dnsa
, rr
, bits
, cbitvec
);
1083 /*************************************************
1084 * Follow chains of A6 records *
1085 *************************************************/
1087 /* A6 records may be incomplete, with pointers to other records containing more
1088 bits of the address. There can be a tree structure, leading to a number of
1089 addresses originating from a single initial A6 record.
1092 yptrptr pointer to the pointer that points to where to hang the next
1093 dns_address structure
1094 dnsa the current DNS answer block
1095 rr the RR we have at present
1096 bits number of bits we have already got
1097 bitvec the bits we have already got
1103 dns_complete_a6(dns_address
***yptrptr
, dns_answer
*dnsa
, dns_record
*rr
,
1104 int bits
, uschar
*bitvec
)
1106 static uschar bitmask
[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 };
1107 uschar
*p
= (uschar
*)(rr
->data
);
1108 int prefix_len
, suffix_len
;
1114 /* The prefix length is the first byte. It defines the prefix which is missing
1115 from the data in this record as a number of bits. Zero means this is the end of
1116 a chain. The suffix is the data in this record; only sufficient bytes to hold
1117 it are supplied. There may be zero bytes. We have to ignore trailing bits that
1118 we have already obtained from earlier RRs in the chain. */
1120 prefix_len
= *p
++; /* bits */
1121 suffix_len
= (128 - prefix_len
+ 7)/8; /* bytes */
1123 /* If the prefix in this record is greater than the prefix in the previous
1124 record in the chain, we have to ignore the record (RFC 2874). */
1126 if (prefix_len
> 128 - bits
) return;
1128 /* In this little loop, the number of bits up to and including the current byte
1129 is held in k. If we have none of the bits in this byte, we can just or it into
1130 the current data. If we have all of the bits in this byte, we skip it.
1131 Otherwise, some masking has to be done. */
1133 for (i
= suffix_len
- 1, j
= 15, k
= 8; i
>= 0; i
--)
1135 int required
= k
- bits
;
1136 if (required
>= 8) bitvec
[j
] |= p
[i
];
1137 else if (required
> 0) bitvec
[j
] |= p
[i
] & bitmask
[required
];
1138 j
--; /* I tried putting these in the "for" statement, but gcc muttered */
1139 k
+= 8; /* about computed values not being used. */
1142 /* If the prefix_length is zero, we are at the end of a chain. Build a
1143 dns_address item with the current data, hang it onto the end of the chain,
1144 adjust the hanging pointer, and we are done. */
1146 if (prefix_len
== 0)
1148 dns_address
*new = store_get(sizeof(dns_address
) + 50);
1149 inet_ntop(AF_INET6
, bitvec
, CS
new->address
, 50);
1152 *yptrptr
= &(new->next
);
1156 /* Prefix length is not zero. Reset the number of bits that we have collected
1157 so far, and extract the chain name. */
1159 bits
= 128 - prefix_len
;
1163 while ((i
= *p
++) != 0)
1165 if (chainptr
!= chain
) *chainptr
++ = '.';
1166 memcpy(chainptr
, p
, i
);
1173 /* Now scan the current DNS response record to see if the additional section
1174 contains the records we want. This processing can be cut out for testing
1177 if (dns_find_prefix(dnsa
, RESET_ADDITIONAL
, chainptr
, yptrptr
, bits
, bitvec
))
1180 /* No chain records were found in the current DNS response block. Do a new DNS
1181 lookup to try to find these records. This opens up the possibility of DNS
1182 failures. We ignore them at this point; if all branches of the tree fail, there
1183 will be no addresses at the end. */
1185 if (dns_lookup(&cdnsa
, chainptr
, T_A6
, NULL
) == DNS_SUCCEED
)
1186 (void)dns_find_prefix(&cdnsa
, RESET_ANSWERS
, chainptr
, yptrptr
, bits
, bitvec
);
1188 #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */
1193 /*************************************************
1194 * Get address(es) from DNS record *
1195 *************************************************/
1197 /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when
1198 supported) for an IPv6 address. In the A6 case, there may be several addresses,
1199 generated by following chains. A recursive function does all the hard work. A6
1200 records now look like passing into history, so the code is only included when
1201 explicitly asked for.
1204 dnsa the DNS answer block
1207 Returns: pointer a chain of dns_address items
1211 dns_address_from_rr(dns_answer
*dnsa
, dns_record
*rr
)
1213 dns_address
*yield
= NULL
;
1215 #if HAVE_IPV6 && defined(SUPPORT_A6)
1216 dns_address
**yieldptr
= &yield
;
1219 dnsa
= dnsa
; /* Stop picky compilers warning */
1222 if (rr
->type
== T_A
)
1224 uschar
*p
= (uschar
*)(rr
->data
);
1225 yield
= store_get(sizeof(dns_address
) + 20);
1226 (void)sprintf(CS yield
->address
, "%d.%d.%d.%d", p
[0], p
[1], p
[2], p
[3]);
1233 else if (rr
->type
== T_A6
)
1235 memset(bitvec
, 0, sizeof(bitvec
));
1236 dns_complete_a6(&yieldptr
, dnsa
, rr
, 0, bitvec
);
1238 #endif /* SUPPORT_A6 */
1242 yield
= store_get(sizeof(dns_address
) + 50);
1243 inet_ntop(AF_INET6
, (uschar
*)(rr
->data
), CS yield
->address
, 50);
1246 #endif /* HAVE_IPV6 */