linux-kernel - Re: [PATCH] futex: do not leak robust list to unprivileged process

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Date:	Fri, 23 Mar 2012 00:46:27 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Kees Cook <keescook@...omium.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Howells <dhowells@...hat.com>,
	kernel-hardening@...ts.openwall.com, spender@...ecurity.net
Subject: Re: [PATCH] futex: do not leak robust list to unprivileged process

On Tue, 20 Mar 2012, Ingo Molnar wrote:
> * Kees Cook <keescook@...omium.org> wrote:
> > On Tue, Mar 20, 2012 at 10:02 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > > I really wonder why we have this syscall at all.
> > 
> > The documentation I found yesterday while looking at this was: 
> > http://linux.die.net/man/2/get_robust_list
> > 
> > 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 ?

	 tglx
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