This email was just sent to the Ubuntu developer list about a change to D-Bus security in 9.04 -- do I need to create a D-Bus .conf file for Wine, or will the default policy suffice for us?
Thanks, Scott Ritchie
Scott James Remnant wrote:
If your package contains a D-Bus system bus service, you need to pay attention!
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-2008-4311It 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.
We've audited the system bus services shipped in Ubuntu, and are confident that there is no security exploit. Those services exporting privileged methods either have sufficient "deny" rules, or use PolicyKit for authorisation.
For this reason, and due to the large potential for regressions, we've opted not to release a security update for previous Ubuntu versions. We may still do so if we discover a potential for exploit.
However this is a bug, and I've uploaded a new version of D-Bus to jaunty that corrects it. I've filed bugs on all packages that appear to ship a D-Bus system bus service (those with /etc/dbus-1/system.d/*.conf files), but I may have missed some. I'd appreciate your help tracking down any I've missed, and updating all of the packages.
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.
Scott