linux-kernel - Re: [patch 5/6] posix-cpu-timers: Sanitize thread clock permissions

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Date:   Thu, 5 Sep 2019 16:11:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 5/6] posix-cpu-timers: Sanitize thread clock
 permissions

On Thu, 5 Sep 2019, Peter Zijlstra wrote:

> On Thu, Sep 05, 2019 at 02:03:44PM +0200, Thomas Gleixner wrote:
> > The thread clock permissions are restricted to tasks of the same thread
> > group, but that also prevents a ptracer from reading them. This is
> > inconsistent vs. the process restrictions and unnecessary strict.
> > 
> > Relax it to ptrace permissions in the same way as process permissions are
> > handled.
> 
> More of a meta comment on the added permission checking; so where
> clock_getcpuclockid() is allowed to return -EPERM, it doesn't because
> that's in glibc and it has no clue.
> 
> And these patches implement the ptrace checks and result in -EINVAL for
> timer_create() and clock_gettime(), even though it should arguably be
> -EPERM, but we're not allowed to return that here.

Yeah. Maybe we should nevertheless.

Thanks,

	tglx