linux-kernel - Re: [patch 2/6] posix-cpu-timers: Fix permission check regression

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Message-ID: <alpine.DEB.2.21.1909052054200.1902@nanos.tec.linutronix.de>
Date:   Thu, 5 Sep 2019 20:55:22 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
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 2/6] posix-cpu-timers: Fix permission check regression

On Thu, 5 Sep 2019, Frederic Weisbecker wrote:
> On Thu, Sep 05, 2019 at 02:03:41PM +0200, Thomas Gleixner wrote:
> > +	if (gettime) {
> > +		/*
> > +		 * For clock_gettime() the task does not need to be the
> > +		 * actual group leader. tsk->sighand gives access to the
> > +		 * group's clock.
> > +		 */
> 
> I'm a bit confused with the explanation. Why is it fine to do so with clock
> and not with timer? tsk->sighand gives access to the group's timer as
> well.

Timer stores the target task and that's the group leader for process wide
while clock read is just momentary. Lemme rephrase that.

Thanks,

	tglx