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

[Peter Williams <pwil3058@bigpond.net.au>]

Jack O'Quin wrote:
> Peter Williams <pwil3058@bigpond.net.au> writes:
> 
> 
>>>>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
> 
> 
>>Paul Davis wrote:
>>
>>>This is insufficient, since they need to be able to drop RT
>>>scheduling and then reacquire it again later.
> 
> 
>>I believe that there are mechanisms that allow this.  The setuid man
>>page states that a process with non root real uid but setuid as root
>>can use the seteuid call to use the _POSIX_SAVED_IDS mechanism to
>>drop and regain root privileges as required.
> 
> 
> Which every system cracker knows.  Any attack on such a program is
> going to re-acquire root privileges and take over the system.
> 
> Temporarily dropping privileges gains no security whatsoever.  It is
> nothing more than a coding convenience.

Yes, to help avoid accidentally misusing the privileges.

> The program remains *inside*
> the system security perimeter.

Which is why you have to be careful in writing setuid programs.

Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce