linux-kernel - Re: [PATCH 2/4] pid: Export find_task_by

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Date:   Thu, 17 May 2018 00:39:37 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Kim Phillips <kim.phillips@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Gargi Sharma <gs051095@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Rik van Riel <riel@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Thierry Reding <treding@...dia.com>,
        Todd Kjos <tkjos@...gle.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] pid: Export find_task_by_vpid for use in external modules

Russell King - ARM Linux <linux@...linux.org.uk> writes:

> On Thu, May 10, 2018 at 01:39:18PM -0600, Mathieu Poirier wrote:
>> Hi Russell,
>> 
>> On 10 May 2018 at 02:40, Russell King - ARM Linux <linux@...linux.org.uk> wrote:
>> > This does not leak information from other namespaces because of the
>> > uniqueness of the global PID.  However, what it does leak is the value
>> > of the global PID which is meaningless in the namespace.  So, before
>> > the event stream is delivered to userspace, this value needs to be
>> > re-written to the namespace's PID value.
>> 
>> Unfortunately that can't be done.  The trace stream is compressed and
>> needs to be decompressed using an external library.  I think the only
>> option is to return an error if a user is trying to use this feature
>> from a namespace.
>
> That sounds like a sensible approach, and that should get rid of the
> vpid stuff too.
>
> Eric, would this solve all your concerns?

It does, and I have given my ack to the respin.

I am moderately concerned about using the global pid with hardware.  But
pids are a core abstraction that aren't going anywhere.  As long as
hardware does not impose constraints on pids that software already does
not we should be fine.

Eric