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

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Message-ID: <CAGXu5jKRGmfhS48gpuur7P1cbnoBPdnNe3qPbok52TKQD8Sy9w@mail.gmail.com>
Date:	Wed, 28 Mar 2012 11:33:15 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...nel.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 Thu, Mar 22, 2012 at 4:46 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 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.

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

-- 
Kees Cook
ChromeOS Security
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