Re: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature

[Ingo Molnar <mingo@elte.hu>]

* Paul Davis <paul@linuxaudiosystems.com> wrote:

> Just a reminder: setuid root is precisely what we are attempting to
> avoid. 
> 
> >If you have the source code for the programs then they could be modified 
> >to drop the root euid after they've changed policy.  Or even do the 
> 
> This is insufficient, since they need to be able to drop RT scheduling
> and then reacquire it again later.

i believe RT-LSM provides a way to solve this cleanly: you can make your
audio app setguid-audio (note: NOT setuid), and make the audio group
have CAP_SYS_NICE-equivalent privilege via the RT-LSM, and then you
could have a finegrained per-app way of enabling SCHED_FIFO scheduling,
without giving _users_ the blanket permission to SCHED_FIFO. Ok?

this way if jackd (or a client) gets run by _any_ user, all jackd
processes will be part of the audio group and can do SCHED_FIFO - but
users are not automatically trusted with SCHED_FIFO.

you are currently using RT-LSM to enable a user to do SCHED_FIFO, right? 
I think the above mechanism is more secure and more finegrained than
that.

	Ingo