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Re: [libvirt] [PATCH v0.10.2-maint] network: prevent dnsmasq from listening on localhost



On 12/13/12 10:00, Laine Stump wrote:
(I'm sending this v0.10.2-maint "backport" of the upstream patch to
the list because the code in question was completely replaced, so it
required a new patch rather than a backport. The backport for
0.9.11-maint is nearly identical to this, so I won't be sending that
one)

This patch resolves the problem reported in:

    https://bugzilla.redhat.com/show_bug.cgi?id=886663

The source of the problem was the fix for CVE 2011-3411:

    https://bugzilla.redhat.com/show_bug.cgi?id=833033

which was originally committed upstream in commit
753ff83a50263d6975f88d6605d4b5ddfcc97560. That commit improperly
removed the "--except-interface lo" from dnsmasq commandlines when
--bind-dynamic was used (based on comments in the latter bug).

It turns out that the problem reported in the CVE could be eliminated
without removing "--except-interface lo", and removing it actually
caused each instance of dnsmasq to listen on localhost on port 53,
which created a new problem:

If another instance of dnsmasq using "--bind-interfaces" (instead of
"--bind-dynamic") had already been started (or if another instance
started later used "--bind-dynamic"), this wouldn't have any immediately
visible ill effects, but if you tried to start another dnsmasq
instance using "--bind-interfaces" *after* starting any libvirt
networks, the new dnsmasq would fail to start, because there was
already another process listening on port 53.

This patch changes the network driver to *always* add
"--except-interface lo" to dnsmasq conf files, regardless of whether we use
bind-dynamic or bind-interfaces. This way no libvirt dnsmasq instances
are listening on localhost (and the CVE is still fixed).

The actual code change is miniscule, but must be propogated through all
of the test files as well.

(This is *not* a cherry-pick of the upstream commit, because
subsequent to the CVE fix, another patch changed the network driver to
put dnsmasq options in a conf file rather than directly on the dnsmasq
commandline, but preserved the same options.)
---
  src/network/bridge_driver.c                                       | 8 ++++----
  tests/networkxml2argvdata/isolated-network.argv                   | 2 +-
  tests/networkxml2argvdata/nat-network-dns-hosts.argv              | 2 +-
  tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv | 2 +-
  tests/networkxml2argvdata/nat-network-dns-srv-record.argv         | 2 +-
  tests/networkxml2argvdata/nat-network-dns-txt-record.argv         | 2 +-
  tests/networkxml2argvdata/nat-network.argv                        | 2 +-
  tests/networkxml2argvdata/netboot-network.argv                    | 2 +-
  tests/networkxml2argvdata/netboot-proxy-network.argv              | 2 +-
  tests/networkxml2argvdata/routed-network.argv                     | 2 +-
  10 files changed, 13 insertions(+), 13 deletions(-)


ACK to this "backport" too :). I didn't do a compile test of this patch but the changes seem reasonable and according to the manpage.

Peter


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