linux-kernel - Re: [patch 3/6] posix-cpu-timers: Restrict timer

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Date:   Sat, 21 Sep 2019 02:44:46 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 3/6] posix-cpu-timers: Restrict timer_create() permissions

On Thu, Sep 05, 2019 at 02:03:42PM +0200, Thomas Gleixner wrote:
> Right now there is no restriction at all to attach a Posix CPU timer to any
> process in the system. Per thread CPU timers are limited to be created by
> threads in the same thread group.
> 
> Timers can be used to observe activity of tasks and also impose overhead on
> the process to which they are attached because that process needs to do the
> fine grained CPU time accounting.
> 
> Limit the ability to attach timers to a process by checking whether the
> task which is creating the timer has permissions to attach ptrace on the
> target process.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Makes sense. I hope no serious user currently rely on that lack of
restriction. Let's just apply and wait for complains if any.

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>