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

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Message-ID: <CALAqxLVb2YNMWR9TQAeFD8pRTmd8tj0TDdmzqw5-8e69kb_c6w@mail.gmail.com>
Date:	Wed, 10 Aug 2016 13:45:35 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Kees Cook <keescook@...omium.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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: [PATCH] proc: Fix timerslack_ns CAP_SYS_NICE check when adjusting self

On Wed, Aug 10, 2016 at 1:01 PM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
> On 8/10/2016 12:03 PM, John Stultz wrote:
>
>> I wasn't entierly sure. I didn't think PR_SET_TIMERSLACK has a
>> security hook, but looking again I now see the top-level
>> security_task_prctl() check, so maybe not skipping it in this case
>> would be good?
>
>
> the easy fix would be to add back the ptrace check.. just either ptrace-able
> OR CAP_SYS_NICE ;)

Well, I worry that just adds more complexity to trying to understand it.
p==current OR CAP_SYS_NICE makes the most sense to me.

> then you can prove you only added new stuff as well, and have all the LSM
> from before

The LSM bits (and how consistent or inconsistent they can be) is
really the part that I have the most concern about, and I'm not sure
what the best approach would be.

thanks
-john