[linux-audio-dev] Linux Security Module for realtime audio

Fernando Pablo Lopez-Lezcano nando at ccrma.Stanford.EDU
Tue Dec 2 13:28:28 EST 2003


> > > attached is what i have done today.... works, but needs to
> > > be checked by someone who can judge about the sideeffects.
> > > 
> > > i am not so sure about them.
> > 
> > Encouraged by your success, I plan to modify this LSM to implement the
> > `kernel/realtime' and `kernel/realtime-group' interfaces we discussed
> > recently.  I'll keep you posted on how that progresses.
> 
> 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.
> 
> although i am not happy with CAP_SYS_RESOURCE ( needed for RTC interrupts > 64Hz )
> which also allows a process to Override quota limits.

This was needed to make mlockall work (on 2.4.x). CAP_IPC_LOCK was not
enough, I don't know why. We tried removing it and memory locking broke.
Is this on 2.6? Maybe it is different. 

Re: the rtc clock, in 2.4 there is a /proc/sys/dev/rtc/max-user-freq
control file that can be used to rise the maximum rtc clock frequency a
normal user can set. 

> 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. 

-- Fernando




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