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

[Kees Cook]

On Thu, Jul 14, 2016 at 9:09 AM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> On Thu, Jul 14, 2016 at 5:48 AM, Serge E. Hallyn <serge@xxxxxxxxxx> wrote:
>> Quoting Kees Cook (keescook@xxxxxxxxxxxx):
>>> 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