[pulseaudio-discuss] How to close a session?

[Colin Guthrie]

'Twas brillig, and Haug Bürger at 13/12/10 20:37 did gyre and gimble:
> Colin Guthrie schrieb:
>> 'Twas brillig, and Haug Bürger at 12/12/10 10:59 did gyre and gimble:
>>  
>>> The leatest Ubuntu has a serious security bug caused by pulseaudio. If
>>> you configure pammount to mount a crypted home directory it is not able
>>> to unmount it because pulseaudio has files in use (.pulse/*). You can
>>> not even kill the daemon because it is set to user session.
>>>
>>> So, how can you stop the pulseaudio user session? In the hope that this
>>> releases the files.
>>>
>>> Is it really necessary for the deamon to lock the files that you can not
>>> unmount or is this a bug?
>>>     
>>
>> It's quite deliberate. PA has a timeout that prevents it from closing
>> immediate. This means that if PA autospawns, it will stick around for a
>> little while in case it's needed again (while startup is fairly quick,
>> we do have to probe the hardware so it does take time). This is
>> primarily for console applications rather than X11 however, as under X11
>> a Session Manager module is loaded which keeps PA alive for the duration
>> of the X session.
>>
>> You can make a change in daemon.conf to set exit-idle-time to 0. This
>> should allow PA to exit when the X11 session exits.
>>   
> This doesn't work. Probably because you might have another user session
> with X11 active. This means PA is not closed and gdm can not close the
> session properly.

Do you mean you have two X11 sessions for the same user active? If so I
don't understand why you'd want to unmount your $HOME in this case....
If you do not mean that there are two sessions by the same user active
can you please explain this statement some more as I don't fully
appreciate what your are describing.

> I don't care if PA still runs but why does it lock files in my home
> directory?

Well it uses a socket file to communicate with other processes. This
file is typically stored in $TMPDIR which is often $HOME/tmp. I suspect
it is this socket file that is causing you problems.


> It is not even possible as root to shut down a user session. Gdm can not
> even kill the user session. This makes PA a pain in the a...

Not really sure what you mean here? Root can easily kill any PA process.
Can you describe what you mean in more detail here?

> So, how can you stop the pulseaudio user session?

A user can simply call "pulseaudio -k" will kill their PA session.
However, depending on what other applications are still running, it may
very well be autospawned again.

It would be very trivial to add a option to
src/modules/x11/module-x11-xsmp.c in the kill_cb() that would shut down
the PA daemon on X11 logout, but it is not currently done in order to
ensure that multiple X11 sessions by one user are supported. I guess
some smarts could allow for checking the loaded modules and only exit if
no other x11-xmsp module instances exist.


I'm still not 100% sure why this whole thing is a problem tho'. I'm sure
there is an easy way to kill all processes started by a user - this will
certainly be especially true/easier when systemd handles user sessions:

http://0pointer.de/blog/projects/systemd-update-2.html
"We now safely destroy all user session before going down. This is a
feature long missing on Linux: since user processes were not killed
until the very last moment the unhealthy situation that user code was
running at a time where no other daemon was remaining was a normal part
of shutdown."


-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

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