linux-kernel - Re: [PATCH] sched: core: remove access_ok() before copy_to

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Date:   Wed, 17 Aug 2022 21:34:03 +0800
From:   tuo cao <91tuocao@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: core: remove access_ok() before copy_to_user()

I just think usize has limited in caller of sched_attr_copy_to_user()
: SCHED_ATTR_SIZE_VER0 < usize < PAGE_SIZE. Maybe user provided
garbage input and cause (usize + uattr) > TASK_SIZE,  but if (ksize +
uattr) < TASK_SIZE, user can also get the struct sched_attr correctly
by copy_to_user() only and there are no side effects.
So, should we really limit user get the struct sched_attr in this
situation? Thanks.

Peter Zijlstra <peterz@...radead.org> 于2022年8月16日周二 17:18写道：
>
> On Mon, Aug 15, 2022 at 10:21:37PM +0800, Tuo Cao wrote:
> > If usize > ksize, usize may be not valid and if(!access_ok()) will return
> > -EFAULT. But ksize may be valid, copy_to_user() should be executed.And
> > also, copy_to_user() will calls access_ok() to test whether a block of
> > memory is a valid user space address.
>
> I don't follow, why do you want this to continue if the user provided
> garbage input?