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

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Date:   Tue, 7 Feb 2017 15:24:51 -0800
From:   Kees Cook <keescook@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 Tue, Feb 7, 2017 at 2:48 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 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.

As in, entirely remote CONFIG_TIMER_STATS?

-Kees

-- 
Kees Cook
Pixel Security