linux-kernel - Re: RT scheduling and a way to make a process hang, unkillable

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Message-Id: <1234697096.4713.24.camel@laptop>
Date:	Sun, 15 Feb 2009 12:24:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Corey Hickey <bugfood-ml@...ooh.org>
Cc:	linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Subject: Re: RT scheduling and a way to make a process hang, unkillable

On Sat, 2009-02-14 at 16:51 -0800, Corey Hickey wrote:
> Hello,
> 
> I've encountered a bit of a problem in recent kernels that include
> "Group scheduling for SCHED_RR/FIFO": it is possible for a process run
> by root to hang itself and become unkillable--even by a 'kill -9'.
> 
> The following kernel options must be set:
> CONFIG_GROUP_SCHED=y
> CONFIG_RT_GROUP_SCHED=y
> CONFIG_USER_SCHED=y
> 
> The procedure is for a program to:
> 1. run as root
> 2. set SCHED_FIFO
> 3. change UID to a user with no realtime CPU share allocated

Hmm, setuid() should fail in that situation.

/me goes peek at code.

Can't find any code to make that happen, Dhaval didn't we fix that at
one point?

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