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Date: Fri, 23 Mar 2012 00:46:27 +0100 (CET)
From: Thomas Gleixner <>
To: Ingo Molnar <>
cc: Kees Cook <>, 
    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 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.

Thoughts ?


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