D-Bus Policy needs checking

[Scott James Remnant (Canonical)]

yum builds one or more binary packages that contain D-Bus system
bus services. The following were detected:

  universe/admin/yum etc/dbus-1/system.d/yum-updatesd.conf

The D-Bus policy needs checking!

It was discovered that the default policy of the D-Bus system bus was
not as was expected, due to a quirk of the language. In fact, whereas
the default policy was supposed to have been that messages would not be
allowed by default, the default was in fact that messages _were_
allowed!

CVE-2008-4311 was issued, and a new release of D-Bus was updated to
correct the default policy to be deny-by-default.

    http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-4311

It was quickly discovered that the policy files shipped by most services
no longer worked, and that many were (inadvertently, perhaps) relying on
the misconfiguration of the daemon.

A new version of D-Bus has been uploaded to jaunty co correct this.

Please read the following carefully to assist with updating the
configuration.

The default policy of the D-Bus system bus is:

 - Name ownership is DENIED by default.

 - Method calls are DENIED by default.

 - Replies to method calls, including errors, are PERMITTED by default.

 - Signals are PERMITTED by default.

Therefore each service MUST, in its policy configuration:

 - Permit an appropriate user to own the name it wishes to claim:

        <policy user="example">
            <allow own="com.ubuntu.Example" />
        </policy>

 - Allow method calls to be made on objects it exports, for particular
   users. This may be done in a number of different ways.

   You may simply allow all method calls to your claimed name:

        <policy context="default">
            <allow send_destination="com.ubuntu.example" />
        </policy>

   You may allow method calls to particular interfaces you export,
   especially useful if you have privileged and non-privileged
   interfaces:

        <policy context="default">
            <allow send_destination="com.ubuntu.example"
                   send_interface="com.ubuntu.Example" />
        </policy>

        <policy user="root">
            <allow send_destination="com.ubuntu.example"
                   send_interface="com.ubuntu.Example.System" />
        </policy>

    *IMPORTANT* you MUST include send_destination on ALL allow or deny
    tags. Omitting it is a SERIOUS bug!

                <!-- !! SERIOUS BUG !! -->
                <allow send_interface="x.y.z" />

        This allows any service to receive method calls of the given
        interface, not just your own service!

        It also implicitly allows any service to receive method calls
        with no interface specified, in case they match this interface!

        Using the above means you are potentially allowing exploiting of
        a different service. DO NOT DO IT!

                <!-- !! SERIOUS BUG !! -->
                <deny send_interface="x.y.z" />

        This denies all services from receiving method calls of the
        given interface, not just your own service! It also implicitly
        denies all services from receiving method calls with no
        interface specified. DO NOT DO IT!

 - You must allow standard interfaces as well, such as Introspection and
   Properties:

        <policy context="default">
            <allow send_destination="com.ubuntu.example"
                   send_interface="org.freedesktop.DBus.Introspectable" />
            <allow send_destination="com.ubuntu.example"
                   send_interface="org.freedesktop.DBus.Properties" />
        </policy>

 - You should not normally allow receipt of any messages sent from your
   interface, this is also the default.

   (ie. remove any lines of the form <allow receive_*>)

 - You do not normally need to deny any messages, this is the default.

   (ie. remove any lines of the form <deny...>)

You should fully test the service with the new D-Bus after updating the
policy, you'll need to restart the bus daemon for that (it's probably
easier to reboot).

If messages are being denied, it will be logged in /var/log/auth.log as
follows:

Dec 19 14:17:53 space-ghost dbus: Rejected send message, 1 matched
rules; type="method_return", sender=":1.26" (uid=0 pid=2966
comm="/usr/libexec/nm-dispatcher.action ") interface="(unset)"
member="(unset)" error name="(unset)" requested
_reply=0 destination=":1.18" (uid=0 pid=2806 comm="NetworkManager
--pid-file=/var/run/NetworkManager/"))

Be aware that a denied message may still happen if you have other
invalid policy installed (such as those which don't qualify allow/deny
rules with the destination!). Take the opportunity to fix all you see.

[Thomas Goirand (thomas-goirand)]

Hi,

I'm the package maintainer in Debian.

yum-updatesd init.d is desactivated by default in the package. I don't think that this report is relevant.

Thomas

[Loïc Minier (lool)]

I'm not sure why it's relevant that the init script is disabled by default if it's shipped in the binary package. Either the security hole should be plugged, or the functionality removed entirely.

[Thomas Goirand (thomas-goirand)]

Hi,

As per upstream:

http://lists.baseurl.org/pipermail/yum-devel/2010-April/006955.html

yes, yum-updatesd feature should be totally killed from packaging. I have already sent a bug against the Debian BTS (as a whishlist item, because the default setup has the init script disabled by default so it's not a so bad issue), and I'll upload a fix asap.

Thanks a lot for raising this issue and caring about the yum package in Ubuntu (and as a consequence in Debian),

Thomas

PS: I intend to upload an update of yum before Squeeze. Anyone interested in testing would be appreciated, as we just use yum to do CentOS bootstraping in chroots and don't do much more intensive testings.

[Mike Miller (mtmiller)]

All remnants of yum-updatesd have been removed from 3.4.3-1ubuntu1 now in raring.