Re: [RESEND][PATCH] proc: Fix timerslack_ns CAP_SYS_NICE check when adjusting self

From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: John Stultz <john.stultz@linaro.org>,
	lkml <linux-kernel@vger.kernel.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Oren Laadan <orenl@cellrox.com>,
	Ruchi Kandoi <kandoiruchi@google.com>,
	Rom Lemarchand <romlem@android.com>, Todd Kjos <tkjos@google.com>,
	Colin Cross <ccross@android.com>, Nick Kralevich <nnk@google.com>,
	Dmitry Shmidt <dimitrysh@google.com>,
	Elliott Hughes <enh@google.com>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [RESEND][PATCH] proc: Fix timerslack_ns CAP_SYS_NICE check when adjusting self
Date: Tue, 30 Aug 2016 19:12:19 -0400	[thread overview]
Message-ID: <CAGXu5jJ3zsE2kq+0X+v8qFsGFjzTuZbdVR6Qbfp30Fh4MAxVXg@mail.gmail.com> (raw)
In-Reply-To: <20160830160606.9088798dc1ec62105ae19b78@linux-foundation.org>

On Tue, Aug 30, 2016 at 7:06 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Tue, 30 Aug 2016 18:46:23 -0400 Kees Cook <keescook@chromium.org> wrote:
>
>> On Mon, Aug 22, 2016 at 7:01 PM, John Stultz <john.stultz@linaro.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@chromium.org>
>> > Cc: "Serge E. Hallyn" <serge@hallyn.com>
>> > Cc: Andrew Morton <akpm@linux-foundation.org>
>> > Cc: Thomas Gleixner <tglx@linutronix.de>
>> > CC: Arjan van de Ven <arjan@linux.intel.com>
>> > Cc: Oren Laadan <orenl@cellrox.com>
>> > Cc: Ruchi Kandoi <kandoiruchi@google.com>
>> > Cc: Rom Lemarchand <romlem@android.com>
>> > Cc: Todd Kjos <tkjos@google.com>
>> > Cc: Colin Cross <ccross@android.com>
>> > Cc: Nick Kralevich <nnk@google.com>
>> > Cc: Dmitry Shmidt <dimitrysh@google.com>
>> > Cc: Elliott Hughes <enh@google.com>
>> > Cc: Android Kernel Team <kernel-team@android.com>
>> > Acked-by: Kees Cook <keescook@chromium.org>
>> > Signed-off-by: John Stultz <john.stultz@linaro.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