Subject: Re: [linux-audio-dev] Linux Security Module for realtime audio
From: torbenh_AT_gmx.de
Date: Wed Dec 03 2003 - 12:46:00 EET
On Tue, Dec 02, 2003 at 11:03:29AM -0600, Jack O'Quin wrote:
> torbenh_AT_gmx.de writes:
>
> > the most simple way would be parameters given to the module for the
> > realtime group and user. There are nice macros for module parameters.
> >
> > i believe that adding to the currently overridden function
> >
> > if( bprm->e_gid == realtime_gid ) {
> > bprm->cap_effective = CAP_IPC_LOCK | CAP_SYS_NICE | CAP_SYS_RESORCE
> > bprm->cap_permitted = CAP_IPC_LOCK | CAP_SYS_NICE | CAP_SYS_RESORCE
> > }
> >
> > should work fine.
>
> That's pretty much what I have in mind. I'm still trying to figure
> out how to pass the group id as a parameter somewhere. I wanted to
> use /proc/sys/kernel/realtime-group, but that seems to require
> patching the kernel. It looks like the new sysfs is intended for this
> purpose. I'll investigate.
there are functions to register inodes in proc.
but i dont consider this necessary. Why would i want to change the
realtime gid once the module is loaded ?
modprobe jackcapabilities rtgid=407
seems sufficient to me...
and this requires 2 lines of code... see attachement..
>
> > although i am not happy with CAP_SYS_RESOURCE ( needed for RTC
> > interrupts > 64Hz ) which also allows a process to Override quota
> > limits.
>
> Agreed. This is sometimes needed but not always. Maybe it should be
> a separate module to use as required.
considering the configurability of the max frequency fernando posted,
we need to investigate on mlockall now...
>
> > But because in drivers/char/rtc.c the check is
> > if ( capable( CAP_SYS_RESOURCE ) ) { allow higher freq }
> >
> > it seems like its not possible with the current implementation.
> > but we could however provide a jackrtc module which checks for a
> > new CAP_RTC_INTS.
>
> Can you add a new capability without patching the kernel?
definitely yes...
capable can be overridden in an LSM.
but we can still use the current implementation, because capable( i )
tests if bit i is set in the effective_caps.
the highest capability number is 28.. so we have 3 caps left.
-- torben Hohn http://galan.sourceforge.net -- The graphical Audio language
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