mir/bind
2
0
Fork 0
mirror of https://gitlab.isc.org/isc-projects/bind9 synced 2025-08-31 14:35:26 +00:00
Code Issues Releases Wiki Activity

If possible don't use forwarders when priming the resolver.

Browse Source 
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.
This commit is contained in:
Witold Kręcicki
2019-01-03 14:58:05 +01:00
committed by Evan Hunt
parent a97a63ad51
commit b49310ac06
8 changed files with 96 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
CHANGES
View File

@@ -1,3 +1,9 @@
5139. [bug] If possible, don't use forwarders when priming.
This ensures we can get root server IP addresses
from priming query response glue, which may not
be present if the forwarding server is returning
minimal responses. [GL #752]
5138. [bug] Under some circumstances named could hit an assertion
failure when doing qname minimization when using
forwarders. [GL #797]

1
bin/tests/system/forward/ns4/named.conf.in
View File

@@ -19,6 +19,7 @@ options {
listen-on-v6 { none; };
recursion yes;
dnssec-validation yes;
minimal-responses yes;
};
zone "." {

28
bin/tests/system/forward/ns7/named.conf.in Normal file
View File

@@ -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";
};

28
bin/tests/system/forward/ns7/root.db Normal file
View File

@@ -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

1
bin/tests/system/forward/setup.sh
View File

@@ -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

12
bin/tests/system/forward/tests.sh
View File

@@ -147,5 +147,17 @@ if [ $sent -ne 1 ]; then ret=1; fi
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

2
lib/dns/include/dns/resolver.h
View File

@@ -118,6 +118,8 @@ typedef enum {
when doing qname
minimization on
ip6.arpa. */
#define DNS_FETCHOPT_NOFORWARD 0x00080000 /*%< Do not use forwarders
if possible. */
/* Reserved in use by adb.c 0x00400000 */
#define DNS_FETCHOPT_EDNSVERSIONSET 0x00800000

25
lib/dns/resolver.c
View File

@@ -3510,6 +3510,18 @@ fctx_getaddresses(fetchctx_t *fctx, bool 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
@@ -3595,7 +3607,7 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
/*
* Normal nameservers.
*/
normal_nses:
stdoptions = DNS_ADBFIND_WANTEVENT | DNS_ADBFIND_EMPTYEVENT;
if (fctx->restarts == 1) {
/*
@@ -10202,12 +10214,11 @@ dns_resolver_prime(dns_resolver_t *res) {
LOCK(&res->primelock);
result = dns_resolver_createfetch(res, dns_rootname,
dns_rdatatype_ns,
NULL, NULL, NULL, NULL, 0, 0,
0, NULL,
res->buckets[0].task,
prime_done,
res, rdataset, NULL,
&res->primefetch);
NULL, NULL, NULL, NULL, 0,
DNS_FETCHOPT_NOFORWARD, 0,
NULL, res->buckets[0].task,
prime_done, res, rdataset,
NULL, &res->primefetch);
UNLOCK(&res->primelock);
if (result != ISC_R_SUCCESS) {
isc_mem_put(res->mctx, rdataset, sizeof(*rdataset));