eavesdrop in dbus policy

Aubert Malek (MM) malek.aubert at external.magnetimarelli.com
Fri Mar 27 01:20:32 PDT 2015

Ok. I give up. We will try something else. Just two last questions:
If we can't allow any process send anything on system dbus why by running our monitor as root can we see all the messages on dbus?
What is different with Become Monitor? I mean, this method will be used by a root user too. How does this way avoid security vulnerability?

-----Message d'origine-----
De : Simon McVittie [mailto:simon.mcvittie at collabora.co.uk]
Envoyé : mercredi 25 mars 2015 13:02
À : Aubert Malek (MM); dbus at lists.freedesktop.org
Objet : Re: eavesdrop in dbus policy

On 25/03/15 09:33, Aubert Malek (MM) wrote:
>>> <policy user="logging"><allow eavesdrop="true"/> means the
>>> (dbus-monitor that was run by) the "logging" user may receive any
>>> message from anywhere, even if it is considered to be eavesdropping
>>> (the message is not a broadcast and is intended for someone else).
> Isn't that what we want? We need to make monitor application see
> everything on DBus.

It is *necessary* for what you want, but it is not *sufficient*.

Like I already said, there are two separate sets of rules: "A may send to B" and "B may receive from A". You have added a rule to the second set. You are still not going to get all the messages without adding a rule to the first set, and there is currently no way to express the rule you would want to add.

If it was possible to make this work nicely, I wouldn't have spent time and effort on adding BecomeMonitor.

> Why do I get all the messages, with this policy, on session Dbus and
> not on system Dbus. What is blocking on system Dbus?

The "may send" rules are blocking it. On the session bus, any process may send anything; on the system bus, this is not true.

> Sorry for insisting but we have 1.6.8 version of Dbus (so, no Become
> Monitor solution especially that we need to avoid more CPU load
> consumption) and I need to find a way to make it work.

Then it is not possible to do what you want, except by backporting the BecomeMonitor feature from 1.9.


Simon McVittie
Collabora Ltd. <http://www.collabora.com/>


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