Gitweb:
https://git.exim.org/exim.git/commitdiff/d8d9f9301c9a31c826635bbdd334bb4be99ea05a
Commit: d8d9f9301c9a31c826635bbdd334bb4be99ea05a
Parent: 7b9822bffe67da2a43a82d12caf5db00a3ed71c2
Author: Jeremy Harris <jgh146exb@???>
AuthorDate: Thu Jun 7 18:08:22 2018 +0100
Committer: Jeremy Harris <jgh146exb@???>
CommitDate: Thu Jun 7 18:08:22 2018 +0100
Follow CNAME chains only one step. Bug 2264
---
doc/doc-docbook/spec.xfpt | 14 ++++++++++++++
doc/doc-txt/ChangeLog | 7 +++++++
doc/doc-txt/OptionLists.txt | 1 +
src/README.UPDATING | 8 ++++++++
src/src/dns.c | 19 +++++++++++++------
src/src/globals.c | 1 +
src/src/globals.h | 1 +
src/src/readconf.c | 1 +
src/src/verify.c | 5 ++---
test/aux-var-src/tls_conf_prefix | 1 +
test/stdout/0572 | 2 ++
test/stdout/0577 | 1 +
12 files changed, 52 insertions(+), 9 deletions(-)
diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index c4b3837..431d456 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -13873,6 +13873,7 @@ listed in more than one group.
.row &%av_scanner%& "specify virus scanner"
.row &%check_rfc2047_length%& "check length of RFC 2047 &""encoded &&&
words""&"
+.row &%dns_cname_loops%& "follow CNAMEs returned by resolver"
.row &%dns_csa_search_limit%& "control CSA parent search depth"
.row &%dns_csa_use_reverse%& "en/disable CSA IP reverse search"
.row &%header_maxsize%& "total size of message header"
@@ -14775,6 +14776,19 @@ This option controls whether or not an IP address, given as a CSA domain, is
reversed and looked up in the reverse DNS, as described in more detail in
section &<<SECTverifyCSA>>&.
+.new
+.option dns_cname_loops main integer 1
+.cindex DNS "CNAME following"
+This option controls the following of CNAME chains, needed if the resolver does
+not do it internally.
+As of 2018 most should, and the default can be left.
+If you have an ancient one, a value of 10 is likely needed.
+
+The default value of one CNAME-follow is needed
+thanks to the observed return for an MX request,
+given no MX presence but a CNAME to an A, of the CNAME.
+.wen
+
.option dns_dnssec_ok main integer -1
.cindex "DNS" "resolver options"
diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 36f2d70..6b36763 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -52,6 +52,13 @@ JH/09 Bug 2274: Fix logging of cmdline args when starting in an unlinked cwd.
JH/10 Fix ARC signing for case when DKIM signing failed. Previously this would
segfault.
+JH/11 Bug 2264: Exim now only follows CNAME chains one step by default. We'd
+ like zero, since the resolver should be doing this for us, But we need one
+ as a CNAME but no MX presence gets the CNAME returned; we need to check
+ that doesn't point to an MX to declare it "no MX returned" rather than
+ "error, loop". A new main option is added so the older capability of
+ following some limited number of chain links is maintained.
+
Exim version 4.91
-----------------
diff --git a/doc/doc-txt/OptionLists.txt b/doc/doc-txt/OptionLists.txt
index dfb0219..91ce182 100644
--- a/doc/doc-txt/OptionLists.txt
+++ b/doc/doc-txt/OptionLists.txt
@@ -182,6 +182,7 @@ dmarc_history_file string unset main
dmarc_tld_file string unset main 4.82 if experimental_dmarc
dns_again_means_nonexist domain list unset main 1.89
dns_check_names_pattern string + main 2.11
+dns_cname_loops integer 0 main 4.92 Set to 9 for older behaviour
dns_csa_search_limit integer 5 main 4.60
dns_csa_use_reverse boolean true main 4.60
dns_dnssec_ok integer -1 main 4.82
diff --git a/src/README.UPDATING b/src/README.UPDATING
index 73b52e4..2438cc9 100644
--- a/src/README.UPDATING
+++ b/src/README.UPDATING
@@ -26,6 +26,14 @@ The rest of this document contains information about changes in 4.xx releases
that might affect a running system.
+Exim version 4.92
+-----------------
+
+ * Exim used to manually follow CNAME chains, to a limited depth. In this
+ day-and-age we expect the resolver to be doing this for us, so the loop
+ is limited to one retry unless the (new) config option dns_cname_loops
+ is changed.
+
Exim version 4.91
-----------------
diff --git a/src/src/dns.c b/src/src/dns.c
index 83de7c2..cb17666 100644
--- a/src/src/dns.c
+++ b/src/src/dns.c
@@ -674,10 +674,10 @@ if ((previous = tree_search(tree_dns_fails, node_name)))
{
DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n",
name, dns_text_type(type),
- (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" :
- (previous->data.val == DNS_NODATA)? "DNS_NODATA" :
- (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" :
- (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??");
+ previous->data.val == DNS_NOMATCH ? "DNS_NOMATCH" :
+ previous->data.val == DNS_NODATA ? "DNS_NODATA" :
+ previous->data.val == DNS_AGAIN ? "DNS_AGAIN" :
+ previous->data.val == DNS_FAIL ? "DNS_FAIL" : "??");
return previous->data.val;
}
@@ -836,6 +836,8 @@ return DNS_SUCCEED;
/* Look up the given domain name, using the given type. Follow CNAMEs if
necessary, but only so many times. There aren't supposed to be CNAME chains in
the DNS, but you are supposed to cope with them if you find them.
+By default, follow one CNAME since a resolver has been seen, faced with
+an MX request and a CNAME (to an A) but no MX present, returning the CNAME.
The assumption is made that if the resolver gives back records of the
requested type *and* a CNAME, we don't need to make another call to look up
@@ -871,9 +873,14 @@ int i;
const uschar *orig_name = name;
BOOL secure_so_far = TRUE;
-/* Loop to follow CNAME chains so far, but no further... */
+/* By default, assume the resolver follows CNAME chains (and returns NODATA for
+an unterminated one). If it also does that for a CNAME loop, fine; if it returns
+a CNAME (maybe the last?) whine about it. However, retain the coding for dumb
+resolvers hiding behind a config variable. Loop to follow CNAME chains so far,
+but no further... The testsuite tests the latter case, mostly assuming that the
+former will work. */
-for (i = 0; i < 10; i++)
+for (i = 0; i <= dns_cname_loops; i++)
{
uschar * data;
dns_record *rr, cname_rr, type_rr;
diff --git a/src/src/globals.c b/src/src/globals.c
index ec94815..138a29e 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -698,6 +698,7 @@ BOOL dmarc_enable_forensic = FALSE;
uschar *dns_again_means_nonexist = NULL;
int dns_csa_search_limit = 5;
BOOL dns_csa_use_reverse = TRUE;
+int dns_cname_loops = 1;
#ifdef SUPPORT_DANE
int dns_dane_ok = -1;
#endif
diff --git a/src/src/globals.h b/src/src/globals.h
index 9c7d8cc..f9be8b8 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -421,6 +421,7 @@ extern BOOL dmarc_enable_forensic; /* Set via ACL control statement. When se
extern uschar *dns_again_means_nonexist; /* Domains that are badly set up */
extern int dns_csa_search_limit; /* How deep to search for CSA SRV records */
extern BOOL dns_csa_use_reverse; /* Check CSA in reverse DNS? (non-standard) */
+extern int dns_cname_loops; /* Follow CNAMEs returned by resolver to this depth */
extern uschar *dns_ipv4_lookup; /* For these domains, don't look for AAAA (or A6) */
#ifdef SUPPORT_DANE
extern int dns_dane_ok; /* Ok to use DANE when checking TLS authenticity */
diff --git a/src/src/readconf.c b/src/src/readconf.c
index 919fbc2..3f307fd 100644
--- a/src/src/readconf.c
+++ b/src/src/readconf.c
@@ -123,6 +123,7 @@ static optionlist optionlist_config[] = {
#endif
{ "dns_again_means_nonexist", opt_stringptr, &dns_again_means_nonexist },
{ "dns_check_names_pattern", opt_stringptr, &check_dns_names_pattern },
+ { "dns_cname_loops", opt_int, &dns_cname_loops },
{ "dns_csa_search_limit", opt_int, &dns_csa_search_limit },
{ "dns_csa_use_reverse", opt_bool, &dns_csa_use_reverse },
{ "dns_dnssec_ok", opt_int, &dns_dnssec_ok },
diff --git a/src/src/verify.c b/src/src/verify.c
index 95876d1..5d0551e 100644
--- a/src/src/verify.c
+++ b/src/src/verify.c
@@ -3411,9 +3411,8 @@ else
/* If the lookup succeeded, cache the RHS address. The code allows for
more than one address - this was for complete generality and the possible
- use of A6 records. However, A6 records have been reduced to experimental
- status (August 2001) and may die out. So they may never get used at all,
- let alone in dnsbl records. However, leave the code here, just in case.
+ use of A6 records. However, A6 records are no longer supported. Leave the code
+ here, just in case.
Quite apart from one A6 RR generating multiple addresses, there are DNS
lists that return more than one A record, so we must handle multiple
diff --git a/test/aux-var-src/tls_conf_prefix b/test/aux-var-src/tls_conf_prefix
index 20b6fe8..e357b99 100644
--- a/test/aux-var-src/tls_conf_prefix
+++ b/test/aux-var-src/tls_conf_prefix
@@ -11,4 +11,5 @@ log_file_path = DIR/spool/log/%slog
gecos_pattern = ""
gecos_name = CALLER_NAME
+dns_cname_loops = 9
chunking_advertise_hosts =
diff --git a/test/stdout/0572 b/test/stdout/0572
index 96ab561..272aa06 100644
--- a/test/stdout/0572
+++ b/test/stdout/0572
@@ -85,6 +85,7 @@ spool_directory = TESTSUITE/spool
log_file_path = TESTSUITE/spool/log/%slog
gecos_pattern = ""
gecos_name = CALLER_NAME
+dns_cname_loops = 9
chunking_advertise_hosts =
# 1 "TESTSUITE/aux-var/std_conf_prefix"
# 5 "TESTSUITE/test-config"
@@ -124,6 +125,7 @@ spool_directory = TESTSUITE/spool
log_file_path = TESTSUITE/spool/log/%slog
gecos_pattern = ""
gecos_name = CALLER_NAME
+dns_cname_loops = 9
chunking_advertise_hosts =
# 1 "TESTSUITE/aux-var/std_conf_prefix"
# 5 "TESTSUITE/test-config"
diff --git a/test/stdout/0577 b/test/stdout/0577
index 893f922..80cf3da 100644
--- a/test/stdout/0577
+++ b/test/stdout/0577
@@ -11,6 +11,7 @@ spool_directory = TESTSUITE/spool
log_file_path = TESTSUITE/spool/log/%slog
gecos_pattern = ""
gecos_name = CALLER_NAME
+dns_cname_loops = 9
chunking_advertise_hosts =
# 1 "TESTSUITE/aux-var/std_conf_prefix"
tls_advertise_hosts =
