linux-kernel - Re: sched: Disallow sched_attr::sched

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Date:	Mon, 2 Jun 2014 16:22:04 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	mtk.manpages@...il.com, peterz@...radead.org,
	torvalds@...ux-foundation.org, mingo@...nel.org
Subject: Re: sched: Disallow sched_attr::sched_policy < 0

On Mon, Jun 02, 2014 at 02:13:19AM +0000, Linux Kernel wrote:
 
 >     sched: Disallow sched_attr::sched_policy < 0
 >     
 >     The scheduler uses policy=-1 to preserve the current policy state to
 >     implement sys_sched_setparam(), this got exposed to userspace by
 >     accident through sys_sched_setattr(), cure this.
 >     
 > ---
 >  kernel/sched/core.c |    3 +++
 >  1 files changed, 3 insertions(+), 0 deletions(-)
 > 
 > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
 > index f2205f0..cdefcf7 100644
 > --- a/kernel/sched/core.c
 > +++ b/kernel/sched/core.c
 > @@ -3662,6 +3662,9 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
 >  	if (retval)
 >  		return retval;
 >  
 > +	if (attr.sched_policy < 0)
 > +		return -EINVAL;
 > +
 >  	rcu_read_lock();
 >  	retval = -ESRCH;
 >  	p = find_process_by_pid(pid);
 
Todays coverity run picked up..

3687
>>>     CID 1219934:  Unsigned compared against 0  (NO_EFFECT)
>>>     This less-than-zero comparison of an unsigned value is never true. "attr.sched_policy < 0U".
3688            if (attr.sched_policy < 0)
3689                    return -EINVAL;


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