From 366178eb52c78bef4bfefb9005af46d47fb0a9a9 Mon Sep 17 00:00:00 2001

Message-Id: <366178eb52c78bef4bfefb9005af46d47fb0a9a9.1391615407.git.jdenemar@redhat.com>

From: Laine Stump <laine@laine.org>

Date: Wed, 5 Feb 2014 03:09:10 -0700

Subject: [PATCH] network: only prevent forwarding of DNS requests for

 unqualified names

https://bugzilla.redhat.com/show_bug.cgi?id=1061099

In commit f386825 we began adding the options

  --domain-needed

  --local=/$mydomain/

to all dnsmasq commandlines with the stated reason of preventing

forwarding of DNS queries for names that weren't fully qualified

domain names ("FQDN", i.e. a name that included some "."s and a domain

name). This was later changed to

  domain-needed

  local=/$mydomain/

when we moved the options from the dnsmasq commandline to a conf file.

The original patch on the list, and discussion about it, is here:

  https://www.redhat.com/archives/libvir-list/2012-August/msg01594.html

When a domain name isn't specified (mydomain == ""), the addition of

"domain-needed local=//" will prevent forwarding of domain-less

requests to the virtualization host's DNS resolver, but if a domain

*is* specified, the addition of "local=/domain/" will prevent

forwarding of any requests for *qualified* names within that domain

that aren't resolvable by libvirt's dnsmasq itself.

An example of the problems this causes - let's say a network is

defined with:

   <domain name='example.com'/>

   <dhcp>

      ..

      <host mac='52:54:00:11:22:33' ip='1.2.3.4' name='myguest'/>

   </dhcp>

This results in "local=/example.com/" being added to the dnsmasq options.

If a guest requests "myguest" or "myguest.example.com", that will be

resolved by dnsmasq. If the guest asks for "www.example.com", dnsmasq

will not know the answer, but instead of forwarding it to the host, it

will return NOT FOUND to the guest. In most cases that isn't the

behavior an admin is looking for.

A later patch (commit 4f595ba) attempted to remedy this by adding a

"forwardPlainNames" attribute to the <dns> element. The idea was that

if forwardPlainNames='yes' (default is 'no'), we would allow

unresolved names to be forwarded. However, that patch was botched, in

that it only removed the "domain-needed" option when

forwardPlainNames='yes', and left the "local=/mydomain/".

Really we should have been just including the option "--domain-needed

--local=//" (note the lack of domain name) regardless of the

configured domain of the network, so that requests for names without a

domain would be treated as "local to dnsmasq" and not forwarded, but

all others (including those in the network's configured domain) would

be forwarded. We also shouldn't include *either* of those options if

forwardPlainNames='yes'. This patch makes those corrections.

This patch doesn't remedy the fact that default behavior was changed

by the addition of this feature. That will be handled in a subsequent

patch.

(cherry picked from commit f69a6b987d616cf2679ec551a8b905b6a2aace6d)

Conflicts:

 src/network/bridge_driver.c - <forwarder> was added upstream

 tests/networkxml2confdata/nat-network-dns-forwarders.conf - this

   test was added upstream

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

---

 src/network/bridge_driver.c                          | 16 ++++++----------

 tests/networkxml2confdata/dhcp6-network.conf         |  4 ++--

 tests/networkxml2confdata/nat-network-dns-hosts.conf |  4 ++--

 tests/networkxml2confdata/netboot-network.conf       |  4 ++--

 tests/networkxml2confdata/netboot-proxy-network.conf |  4 ++--

 5 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c

index 57c88ae..678ab6d 100644

--- a/src/network/bridge_driver.c

+++ b/src/network/bridge_driver.c

@@ -698,9 +698,6 @@ networkDnsmasqConfContents(virNetworkObjPtr network,

                       "strict-order\n",

                       network->def->name);

-    if (!network->def->dns.forwardPlainNames)

-        virBufferAddLit(&configbuf, "domain-needed\n");

-

     if (network->def->domain) {

         virBufferAsprintf(&configbuf,

                           "domain=%s\n"

@@ -708,14 +705,13 @@ networkDnsmasqConfContents(virNetworkObjPtr network,

                           network->def->domain);

     }

-    if (network->def->domain || !network->def->dns.forwardPlainNames) {

-        /* need to specify local even if no domain specified, unless

-         * the config says we should forward "plain" names (i.e. not

-         * fully qualified, no '.' characters)

+    if (!network->def->dns.forwardPlainNames) {

+        virBufferAddLit(&configbuf, "domain-needed\n");

+        /* need to specify local=// whether or not a domain is

+         * specified, unless the config says we should forward "plain"

+         * names (i.e. not fully qualified, no '.' characters)

          */

-        virBufferAsprintf(&configbuf,

-                          "local=/%s/\n",

-                          network->def->domain ? network->def->domain : "");

+        virBufferAddLit(&configbuf, "local=//\n");

     }

     if (pidfile)

diff --git a/tests/networkxml2confdata/dhcp6-network.conf b/tests/networkxml2confdata/dhcp6-network.conf

index 5fde07f..92ea2a4 100644

--- a/tests/networkxml2confdata/dhcp6-network.conf

+++ b/tests/networkxml2confdata/dhcp6-network.conf

@@ -5,10 +5,10 @@

 ##

 ## dnsmasq conf file created by libvirt

 strict-order

-domain-needed

 domain=mynet

 expand-hosts

-local=/mynet/

+domain-needed

+local=//

 except-interface=lo

 bind-dynamic

 interface=virbr0

diff --git a/tests/networkxml2confdata/nat-network-dns-hosts.conf b/tests/networkxml2confdata/nat-network-dns-hosts.conf

index 2577882..021316f 100644

--- a/tests/networkxml2confdata/nat-network-dns-hosts.conf

+++ b/tests/networkxml2confdata/nat-network-dns-hosts.conf

@@ -5,10 +5,10 @@

 ##

 ## dnsmasq conf file created by libvirt

 strict-order

-domain-needed

 domain=example.com

 expand-hosts

-local=/example.com/

+domain-needed

+local=//

 except-interface=lo

 bind-dynamic

 interface=virbr0

diff --git a/tests/networkxml2confdata/netboot-network.conf b/tests/networkxml2confdata/netboot-network.conf

index b6f3c23..ce33176 100644

--- a/tests/networkxml2confdata/netboot-network.conf

+++ b/tests/networkxml2confdata/netboot-network.conf

@@ -5,10 +5,10 @@

 ##

 ## dnsmasq conf file created by libvirt

 strict-order

-domain-needed

 domain=example.com

 expand-hosts

-local=/example.com/

+domain-needed

+local=//

 except-interface=lo

 bind-interfaces

 listen-address=192.168.122.1

diff --git a/tests/networkxml2confdata/netboot-proxy-network.conf b/tests/networkxml2confdata/netboot-proxy-network.conf

index 1e969fa..f4d3880 100644

--- a/tests/networkxml2confdata/netboot-proxy-network.conf

+++ b/tests/networkxml2confdata/netboot-proxy-network.conf

@@ -5,10 +5,10 @@

 ##

 ## dnsmasq conf file created by libvirt

 strict-order

-domain-needed

 domain=example.com

 expand-hosts

-local=/example.com/

+domain-needed

+local=//

 except-interface=lo

 bind-interfaces

 listen-address=192.168.122.1

-- 

1.8.5.3