linux-kernel - Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGXu5jLtwanTYJeFSw1GjPTfd=k1LXv0bkCP3y0A57_xjj92yQ@mail.gmail.com>
Date:	Thu, 14 Jul 2016 10:45:36 -0700
From:	Kees Cook <keescook@...omium.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Oren Laadan <orenl@...lrox.com>,
	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Android Kernel Team <kernel-team@...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>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface

On Thu, Jul 14, 2016 at 9:09 AM, John Stultz <john.stultz@...aro.org> wrote:
> On Thu, Jul 14, 2016 at 5:48 AM, Serge E. Hallyn <serge@...lyn.com> wrote:
>> Quoting Kees Cook (keescook@...omium.org):
>>> I think the original CAP_SYS_NICE should be fine. A malicious
>>> CAP_SYS_NICE process can do plenty of insane things, I don't feel like
>>> the timer slack adds to any realistic risks.
>>
>> Can someone give a detailed explanation of what you could do with
>> the new timerslack feature and compare it to what you can do with
>> sys_nice?
>
> Looking at the man page for CAP_SYS_NICE, it looks like such a task
> can set a task as SCHED_FIFO, so they could fork some spinning
> processes and set them all SCHED_FIFO 99, in effect delaying all other
> tasks for an infinite amount of time.
>
> So one might argue setting large timerslack vlaues isn't that
> different risk wise?

Right -- you can hose a system with CAP_SYS_NICE already; I don't
think timerslack realistically changes that.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security