[pulseaudio-discuss] Access control

[Wim Taymans]

Hi All,

I took another look at the access control patches.

There was a desire from Arun and Tanu to have the access control
checks more integrated
into the core objects instead of just some checks in the native protocol.

I was a bit reluctant to start this because it would involve passing
around a lot of pa_client
objects to many functions in order to do access control. This week, I
put my brain to 0 and
started this anyway, You can find the result in this branch:

(1)  https://cgit.freedesktop.org/~wtay/pulseaudio/log/?h=access-hooks-arg

I then spent some time thinking about using TLS to pass the client
around, more like a context
to evaluate the functions in than an argument of the function. Tanu
then suggested to put the
current_client in the pa_core object where it can be picked up from
anywhere. The trick is then
to set and clear the current_client in the various protocols. The
result can be seen here:

(2) https://cgit.freedesktop.org/~wtay/pulseaudio/log/?h=access-hooks-core

You can still find the old way here:

(3) https://cgit.freedesktop.org/~wtay/pulseaudio/log/?h=access-hooks

I think (1) is quite ugly and requires you to modify many functions
with a new parameter that
is not at all related to what the function does. It does however give
you good control over what
you can check. One example is pa_sink_update_rate() which might
suspend and unsuspend
the source to implement the rate change. It a new client does not have
permission to suspend a
sink, it will not be able to change the rate.

(2) looks quite ok. Setting and clearing the current_client is
straightforward and easily verifiable.
You can also be certain that when you add new checks, you can just get
the client from there
instead of having to change a method. The downside is that if ever a
non-main thread tries to
do some access control, you get random behaviour. using TLS will, of
course fix this.

(3) is probably still the most simple solution but only deals with the
native-protocol. (1) and (2)
now also automatically work for the cli, DBus, esound, http, simple
and native protocol.

What do you think? Which option do you like best?
Wim