From bd79638f1c2c8f765e316c30b15dfb3e5d31e1e4 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Witold=20Kr=C4=99cicki?= <wpk@isc.org>

Date: Thu, 3 Jan 2019 14:58:05 +0100

Subject: [PATCH] If possible don't use forwarders when priming the resolver.

If we try to fetch a record from cache and need to look into

hints database we assume that the resolver is not primed and

start dns_resolver_prime(). Priming query is supposed to return

NSes for "." in ANSWER section and glue records for them in

ADDITIONAL section, so that we can fill that info in 'regular'

cache and not use hints db anymore.

However, if we're using a forwarder the priming query goes through

it, and if it's configured to return minimal answers we won't get

the addresses of root servers in ADDITIONAL section. Since the

only records for root servers we have are in hints database we'll

try to prime the resolver with every single query.

This patch adds a DNS_FETCHOPT_NOFORWARD flag which avoids using

forwarders if possible (that is if we have forward-first policy).

Using this flag on priming fetch fixes the problem as we get the

proper glue. With forward-only policy the problem is non-existent,

as we'll never ask for root server addresses because we'll never

have a need to query them.

Also added a test to confirm priming queries are not forwarded.

(cherry picked from commit b49310ac06ac87733dc2867828e61370a84b2a9a)

(cherry picked from commit f8963ad70e222edad0c1e64f855f7fb41fb13c3c)

(cherry picked from commit aa9866c390a21d6984aa75cdb84d7bc77e114c2f)

---

 bin/tests/system/forward/ns4/named.conf.in |  3 ++

 bin/tests/system/forward/ns7/named.conf.in | 28 +++++++++++++++++

 bin/tests/system/forward/ns7/root.db       | 28 +++++++++++++++++

 bin/tests/system/forward/setup.sh          |  1 +

 bin/tests/system/forward/tests.sh          | 12 ++++++++

 lib/dns/include/dns/resolver.h             | 36 ++++++++++++----------

 lib/dns/resolver.c                         | 17 ++++++++--

 7 files changed, 106 insertions(+), 19 deletions(-)

 create mode 100644 bin/tests/system/forward/ns7/named.conf.in

 create mode 100644 bin/tests/system/forward/ns7/root.db

diff --git a/bin/tests/system/forward/ns4/named.conf.in b/bin/tests/system/forward/ns4/named.conf.in

index 480530b0f2..643e1271b5 100644

--- a/bin/tests/system/forward/ns4/named.conf.in

+++ b/bin/tests/system/forward/ns4/named.conf.in

@@ -17,6 +17,9 @@ options {

 	pid-file "named.pid";

 	listen-on { 10.53.0.4; };

 	listen-on-v6 { none; };

+	recursion yes;

+	dnssec-validation yes;

+	minimal-responses yes;

 };

 zone "." {

diff --git a/bin/tests/system/forward/ns7/named.conf.in b/bin/tests/system/forward/ns7/named.conf.in

new file mode 100644

index 0000000000..d9f5e8a9db

--- /dev/null

+++ b/bin/tests/system/forward/ns7/named.conf.in

@@ -0,0 +1,28 @@

+/*

+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")

+ *

+ * This Source Code Form is subject to the terms of the Mozilla Public

+ * License, v. 2.0. If a copy of the MPL was not distributed with this

+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.

+ *

+ * See the COPYRIGHT file distributed with this work for additional

+ * information regarding copyright ownership.

+ */

+

+options {

+	query-source address 10.53.0.7;

+	notify-source 10.53.0.7;

+	transfer-source 10.53.0.7;

+	port @PORT@;

+	pid-file "named.pid";

+	listen-on { 10.53.0.7; };

+	listen-on-v6 { none; };

+	forwarders { 10.53.0.4; };

+	forward first;

+	dnssec-validation yes;

+};

+

+zone "." {

+	type hint;

+	file "root.db";

+};

diff --git a/bin/tests/system/forward/ns7/root.db b/bin/tests/system/forward/ns7/root.db

new file mode 100644

index 0000000000..7346810ba6

--- /dev/null

+++ b/bin/tests/system/forward/ns7/root.db

@@ -0,0 +1,28 @@

+; Copyright (C) Internet Systems Consortium, Inc. ("ISC")

+;

+; This Source Code Form is subject to the terms of the Mozilla Public

+; License, v. 2.0. If a copy of the MPL was not distributed with this

+; file, You can obtain one at http://mozilla.org/MPL/2.0/.

+;

+; See the COPYRIGHT file distributed with this work for additional

+; information regarding copyright ownership.

+

+$TTL 300

+. 			IN SOA	gson.nominum.com. a.root.servers.nil. (

+				2000042100   	; serial

+				600         	; refresh

+				600         	; retry

+				1200    	; expire

+				600       	; minimum

+				)

+.			NS	a.root-servers.nil.

+a.root-servers.nil.	A	10.53.0.1

+

+example1		NS	ns.example1

+ns.example1		A	10.53.0.1

+

+example2		NS	ns.example2

+ns.example2		A	10.53.0.1

+

+example3		NS	ns.example3

+ns.example3		A	10.53.0.1

diff --git a/bin/tests/system/forward/setup.sh b/bin/tests/system/forward/setup.sh

index c63aeb10d2..d64579e590 100644

--- a/bin/tests/system/forward/setup.sh

+++ b/bin/tests/system/forward/setup.sh

@@ -18,3 +18,4 @@ copy_setports ns2/named.conf.in ns2/named.conf

 copy_setports ns3/named.conf.in ns3/named.conf

 copy_setports ns4/named.conf.in ns4/named.conf

 copy_setports ns5/named.conf.in ns5/named.conf

+copy_setports ns7/named.conf.in ns7/named.conf

diff --git a/bin/tests/system/forward/tests.sh b/bin/tests/system/forward/tests.sh

index f23cde1751..8c6496037d 100644

--- a/bin/tests/system/forward/tests.sh

+++ b/bin/tests/system/forward/tests.sh

@@ -131,5 +131,17 @@ $CHECKCONF ula-notinherited.conf | grep "forward first;" >/dev/null && ret=1

 if [ $ret != 0 ]; then echo_i "failed"; fi

 status=`expr $status + $ret`

+echo_i "checking that priming queries are not forwarded"

+ret=0

+$DIG $DIGOPTS +noadd +noauth txt.example1. txt @10.53.0.7 > dig.out.f7 || ret=1

+sent=`sed -n '/sending packet to 10.53.0.1/,/^$/p' ns7/named.run | grep ";.*IN.*NS" | wc -l`

+[ $sent -eq 1 ] || ret=1

+sent=`grep "10.53.0.7#.* (.): query '\./NS/IN' approved" ns4/named.run | wc -l`

+[ $sent -eq 0 ] || ret=1

+sent=`grep "10.53.0.7#.* (.): query '\./NS/IN' approved" ns1/named.run | wc -l`

+[ $sent -eq 1 ] || ret=1

+if [ $ret != 0 ]; then echo_i "failed"; fi

+status=`expr $status + $ret`

+

 echo_i "exit status: $status"

 [ $status -eq 0 ] || exit 1

diff --git a/lib/dns/include/dns/resolver.h b/lib/dns/include/dns/resolver.h

index f2f8714d16..e1a10295f3 100644

--- a/lib/dns/include/dns/resolver.h

+++ b/lib/dns/include/dns/resolver.h

@@ -88,23 +88,25 @@ typedef enum {

 /*

  * Options that modify how a 'fetch' is done.

  */

-#define DNS_FETCHOPT_TCP		0x0001	     /*%< Use TCP. */

-#define DNS_FETCHOPT_UNSHARED		0x0002	     /*%< See below. */

-#define DNS_FETCHOPT_RECURSIVE		0x0004	     /*%< Set RD? */

-#define DNS_FETCHOPT_NOEDNS0		0x0008	     /*%< Do not use EDNS. */

-#define DNS_FETCHOPT_FORWARDONLY	0x0010	     /*%< Only use forwarders. */

-#define DNS_FETCHOPT_NOVALIDATE		0x0020	     /*%< Disable validation. */

-#define DNS_FETCHOPT_EDNS512		0x0040	     /*%< Advertise a 512 byte

-							  UDP buffer. */

-#define DNS_FETCHOPT_WANTNSID		0x0080	     /*%< Request NSID */

-#define DNS_FETCHOPT_PREFETCH		0x0100	     /*%< Do prefetch */

-#define DNS_FETCHOPT_NOCDFLAG		0x0200	     /*%< Don't set CD flag. */

-#define DNS_FETCHOPT_NONTA		0x0400	     /*%< Ignore NTA table. */

-/* RESERVED ECS				0x0000 */

-/* RESERVED ECS				0x1000 */

-/* RESERVED ECS				0x2000 */

-/* RESERVED TCPCLIENT			0x4000 */

-#define DNS_FETCHOPT_NOCACHED		0x8000	     /*%< Force cache update. */

+#define DNS_FETCHOPT_TCP		0x00001	     /*%< Use TCP. */

+#define DNS_FETCHOPT_UNSHARED		0x00002	     /*%< See below. */

+#define DNS_FETCHOPT_RECURSIVE		0x00004	     /*%< Set RD? */

+#define DNS_FETCHOPT_NOEDNS0		0x00008	     /*%< Do not use EDNS. */

+#define DNS_FETCHOPT_FORWARDONLY	0x00010	     /*%< Only use forwarders. */

+#define DNS_FETCHOPT_NOVALIDATE		0x00020	     /*%< Disable validation. */

+#define DNS_FETCHOPT_EDNS512		0x00040	     /*%< Advertise a 512 byte

+					0		  UDP buffer. */

+#define DNS_FETCHOPT_WANTNSID		0x00080	     /*%< Request NSID */

+#define DNS_FETCHOPT_PREFETCH		0x00100	     /*%< Do prefetch */

+#define DNS_FETCHOPT_NOCDFLAG		0x00200	     /*%< Don't set CD flag. */

+#define DNS_FETCHOPT_NONTA		0x00400	     /*%< Ignore NTA table. */

+/* RESERVED ECS				0x00000 */

+/* RESERVED ECS				0x01000 */

+/* RESERVED ECS				0x02000 */

+/* RESERVED TCPCLIENT			0x04000 */

+#define DNS_FETCHOPT_NOCACHED		0x08000	     /*%< Force cache update. */

+#define DNS_FETCHOPT_NOFORWARD		0x80000 /*%< Do not use forwarders

+							if possible. */

 /* Reserved in use by adb.c		0x00400000 */

 #define	DNS_FETCHOPT_EDNSVERSIONSET	0x00800000

diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c

index 301ad52fe2..f701a09be9 100644

--- a/lib/dns/resolver.c

+++ b/lib/dns/resolver.c

@@ -3261,6 +3261,18 @@ fctx_getaddresses(fetchctx_t *fctx, isc_boolean_t badcache) {

 	INSIST(ISC_LIST_EMPTY(fctx->forwaddrs));

 	INSIST(ISC_LIST_EMPTY(fctx->altaddrs));

+	/*

+	 * If we have DNS_FETCHOPT_NOFORWARD set and forwarding policy

+	 * allows us to not forward - skip forwarders and go straight

+	 * to NSes. This is currently used to make sure that priming query

+	 * gets root servers' IP addresses in ADDITIONAL section.

+	 */

+	if ((fctx->options & DNS_FETCHOPT_NOFORWARD) != 0 &&

+	    (fctx->fwdpolicy != dns_fwdpolicy_only))

+	{

+		goto normal_nses;

+	}

+

 	/*

 	 * If this fctx has forwarders, use them; otherwise use any

 	 * selective forwarders specified in the view; otherwise use the

@@ -3346,7 +3358,7 @@ fctx_getaddresses(fetchctx_t *fctx, isc_boolean_t badcache) {

 	/*

 	 * Normal nameservers.

 	 */

-

+ normal_nses:

 	stdoptions = DNS_ADBFIND_WANTEVENT | DNS_ADBFIND_EMPTYEVENT;

 	if (fctx->restarts == 1) {

 		/*

@@ -9194,7 +9206,8 @@ dns_resolver_prime(dns_resolver_t *res) {

 		LOCK(&res->primelock);

 		result = dns_resolver_createfetch(res, dns_rootname,

 						  dns_rdatatype_ns,

-						  NULL, NULL, NULL, 0,

+						  NULL, NULL, NULL,

+						  DNS_FETCHOPT_NOFORWARD,

 						  res->buckets[0].task,

 						  prime_done,

 						  res, rdataset, NULL,

-- 

2.21.1