linux-kernel - Re: [RESEND][PATCH] proc: Fix timerslack_ns CAP_SYS

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Message-ID: <CAGXu5jJ3zsE2kq+0X+v8qFsGFjzTuZbdVR6Qbfp30Fh4MAxVXg@mail.gmail.com>
Date:   Tue, 30 Aug 2016 19:12:19 -0400
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Oren Laadan <orenl@...lrox.com>,
        Ruchi Kandoi <kandoiruchi@...gle.com>,
        Rom Lemarchand <romlem@...roid.com>,
        Todd Kjos <tkjos@...gle.com>, Colin Cross <ccross@...roid.com>,
        Nick Kralevich <nnk@...gle.com>,
        Dmitry Shmidt <dimitrysh@...gle.com>,
        Elliott Hughes <enh@...gle.com>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RESEND][PATCH] proc: Fix timerslack_ns CAP_SYS_NICE check when
 adjusting self

On Tue, Aug 30, 2016 at 7:06 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 30 Aug 2016 18:46:23 -0400 Kees Cook <keescook@...omium.org> wrote:
>
>> On Mon, Aug 22, 2016 at 7:01 PM, John Stultz <john.stultz@...aro.org> wrote:
>> > In changing from checking ptrace_may_access(p, PTRACE_MODE_ATTACH_FSCREDS)
>> > to capable(CAP_SYS_NICE), I missed that ptrace_my_access succeeds
>> > when p == current, but the CAP_SYS_NICE doesn't.
>> >
>> > Thus while the previous commit was intended to loosen the needed
>> > privledges to modify a processes timerslack, it needlessly restricted
>> > a task modifying its own timerslack via the proc/<tid>/timerslack_ns
>> > (which is permitted also via the PR_SET_TIMERSLACK method).
>> >
>> > This patch corrects this by checking if p == current before checking
>> > the CAP_SYS_NICE value.
>> >
>> > This patch applies on top of my two previous patches currently in -mm
>> >
>> > Cc: Kees Cook <keescook@...omium.org>
>> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
>> > Cc: Andrew Morton <akpm@...ux-foundation.org>
>> > Cc: Thomas Gleixner <tglx@...utronix.de>
>> > CC: Arjan van de Ven <arjan@...ux.intel.com>
>> > Cc: Oren Laadan <orenl@...lrox.com>
>> > Cc: Ruchi Kandoi <kandoiruchi@...gle.com>
>> > Cc: Rom Lemarchand <romlem@...roid.com>
>> > Cc: Todd Kjos <tkjos@...gle.com>
>> > Cc: Colin Cross <ccross@...roid.com>
>> > Cc: Nick Kralevich <nnk@...gle.com>
>> > Cc: Dmitry Shmidt <dimitrysh@...gle.com>
>> > Cc: Elliott Hughes <enh@...gle.com>
>> > Cc: Android Kernel Team <kernel-team@...roid.com>
>> > Acked-by: Kees Cook <keescook@...omium.org>
>> > Signed-off-by: John Stultz <john.stultz@...aro.org>
>>
>> Andrew, can you take this for v4.8?
>
> Well, it fixes
> proc-relax-proc-tid-timerslack_ns-capability-requirements.patch,
> somewhat.  And it textually depends on that.
>
> Do we want all of
>
> proc-relax-proc-tid-timerslack_ns-capability-requirements.patch
> proc-add-lsm-hook-checks-to-proc-tid-timerslack_ns.patch
> proc-fix-timerslack_ns-cap_sys_nice-check-when-adjusting-self.patch
>
> in 4.8?  If so, why?

Oh, my misunderstanding. I thought those already landed in 4.8. If
not, nevermind on the "rush". :) Thanks for picking it up!

-Kees

-- 
Kees Cook
Nexus Security