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

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Date:   Tue, 7 Feb 2017 15:34:31 -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 3:24 PM, Kees Cook <keescook@...gle.com> wrote:
> 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?

s/remote/remove/

I'll send a patch...

-Kees

-- 
Kees Cook
Pixel Security