linux-kernel - Re: [patch 4/6] posix-cpu-timers: Restrict clock

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Date:   Mon, 23 Sep 2019 15:39:06 +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 4/6] posix-cpu-timers: Restrict clock_gettime()
 permissions

On Thu, Sep 05, 2019 at 02:03:43PM +0200, Thomas Gleixner wrote:
> Similar to creating timers on a process there is no restriction at all to
> read the Posix CPU clocks of any process in the system. Per thread CPU
> clock access is limited to threads in the same thread group.
> 
> The per process CPU clocks can be used to observe activity of tasks and
> reading them can affect the execution of the process to which they are
> attached as reading can require to lock sighand lock and sum up the fine
> grained accounting for all threads in the process.
> 
> Restrict it by checking ptrace MODE_READ permissions of the reader on the
> target process.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

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