linux-kernel - Re: /proc/timer_list leaks the real pids of the associated processes

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Date:   Tue, 7 Feb 2017 23:48:45 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kees Cook <keescook@...gle.com>
cc:     Xing Gao <xgao01@...il.wm.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Jessica Frazelle <me@...sfraz.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: /proc/timer_list leaks the real pids of the associated
 processes

On Fri, 3 Feb 2017, Kees Cook wrote:

> On Fri, Feb 3, 2017 at 2:29 PM, Xing Gao <xgao01@...il.wm.edu> wrote:
> > Dear Thomas and Kees,
> >
> > I posted a bug report on bugzilla, and John asked me to send it the lkml.
> >
> > Here is the link, https://bugzilla.kernel.org/show_bug.cgi?id=193921
> >
> > Please cc to me when you reply this email.
> >
> > And please check the information below.
> >
> > The pseudo file /proc/timer_list leaks the real pids of the associated
> > processes.
> >
> > The function print_timer(kernel/time/timer_list.c) displays
> > timer->start_pid, which is set inside the function
> > __timer_stats_timer_set_start_info (kernel/time/timer.c). This is the real
> > pid, rather than the pid in the pid namespace. If the user within a
> > container retrieves the content of /proc/timer_list, this file will leak the
> > real pid of the associated process.
> 
> I feel like this has been pointed out before, but I can't find the
> email about it. Regardless, yeah, this looks true:
> 
>         SEQ_printf(m, ", %s/%d", tmp, timer->start_pid);
> 
>  #11: <0000000000000000>, hrtimer_wakeup, S:01, do_nanosleep, cron/2570
> 
> Seems like this should be made namespace aware... (and why is this
> file needed at all? Seems like it should live in debugfs not proc).

I'm fine with that.

The TIMER_STATS stuff should go away completely. If people are interested
in that information they can use the tracer which gives way better
data than that file.

Thanks,

	tglx
.