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Date: Wed, 28 Mar 2012 11:33:15 -0700
From: Kees Cook <>
To: Thomas Gleixner <>
Cc: Ingo Molnar <>, Serge Hallyn <>, 
	LKML <>, Darren Hart <>, 
	Peter Zijlstra <>, Andrew Morton <>, 
	Jiri Kosina <>, "Eric W. Biederman" <>, 
	David Howells <>,,
Subject: Re: [PATCH] futex: do not leak robust list to unprivileged process

On Thu, Mar 22, 2012 at 4:46 PM, Thomas Gleixner <> wrote:
> On Tue, 20 Mar 2012, Ingo Molnar wrote:
>> * Kees Cook <> wrote:
>> > On Tue, Mar 20, 2012 at 10:02 AM, Thomas Gleixner <> wrote:
>> > > I really wonder why we have this syscall at all.
>> >
>> > The documentation I found yesterday while looking at this was:
>> >
>> >
>> > Which says "The system call is only available for debugging
>> > purposes and is not needed for normal operations. Both system
>> > calls are not available to application programs as functions;
>> > they can be called using the syscall(3) function."
>> >
>> > Dropping the syscall entirely would certainly make it secure.
>> > ;)
>> The thinking was API completeness. In general it's possible for
>> a sufficiently privileged task to figure out all the state of a
>> task. We can query timers, fds - the robust list is such a
>> resource as well. The information leakage was obviously not
>> intended.
> So I think it's safe to take Kees' patch as is. On top of that we
> should add a WARN_ONCE when the syscall is invoked and schedule the
> sucker for removal.

Can someone claim the first patch? It looks like not everyone agrees
about removal, but I'd like to see at least the first one get in. :)


Kees Cook
ChromeOS Security

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