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

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Message-ID: <CAFLxGvz4yKJfWyRqh5wnG-05m9P3oxcrvVZLH-Yap8dFz-0ctg@mail.gmail.com>
Date:	Tue, 3 Jun 2014 10:15:44 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: sched: Disallow sched_attr::sched_policy < 0

On Tue, Jun 3, 2014 at 10:08 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jun 02, 2014 at 04:22:04PM -0400, Dave Jones wrote:
>> 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;
>>
>
> Once upon a time GCC also did warns like that, but my compiler is silent
> :-(
>
> Yes, that needs fixing..

I sent already a patch for that...

-- 
Thanks,
//richard
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