Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface

From	Kees Cook <keescook@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface
Date	2016-07-14 19:50 +0200
Message-ID	<rUSVP-4ga-3@gated-at.bofh.it> (permalink)
References	(1 earlier) <r2YMW-7mJ-21@gated-at.bofh.it> <rUC4F-1yk-11@gated-at.bofh.it> <rUFFf-43M-11@gated-at.bofh.it> <rUOfw-1kh-15@gated-at.bofh.it> <rURn4-3qz-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Jul 14, 2016 at 9:09 AM, John Stultz <john.stultz@linaro.org> wrote:
> On Thu, Jul 14, 2016 at 5:48 AM, Serge E. Hallyn <serge@hallyn.com> wrote:
>> Quoting Kees Cook (keescook@chromium.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

Thread

Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz <john.stultz@linaro.org> - 2016-07-14 01:50 +0200
  Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Kees Cook <keescook@chromium.org> - 2016-07-14 05:40 +0200
    Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Arjan van de Ven <arjan@linux.intel.com> - 2016-07-14 07:30 +0200
    Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface "Serge E. Hallyn" <serge@hallyn.com> - 2016-07-14 14:50 +0200
      Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Arjan van de Ven <arjan@linux.intel.com> - 2016-07-14 15:50 +0200
        Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz <john.stultz@linaro.org> - 2016-07-14 18:10 +0200
      Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface John Stultz <john.stultz@linaro.org> - 2016-07-14 18:10 +0200
        Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Kees Cook <keescook@chromium.org> - 2016-07-14 19:50 +0200
          Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Arjan van de Ven <arjan@linux.intel.com> - 2016-07-14 19:50 +0200
          Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface "Serge E. Hallyn" <serge@hallyn.com> - 2016-07-14 19:50 +0200
            Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface Kees Cook <keescook@chromium.org> - 2016-07-14 20:00 +0200
              Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface "Serge E. Hallyn" <serge@hallyn.com> - 2016-07-14 22:30 +0200

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