linux-kernel - Re: [PATCH v2] futex: mark get_robust

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Date:	Fri, 3 Aug 2012 15:35:38 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...otime.net>,
	Darren Hart <dvhart@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	David Howells <dhowells@...hat.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	spender@...ecurity.net
Subject: Re: [PATCH v2] futex: mark get_robust_list as deprecated

On Fri, Aug 03, 2012 at 01:30:31PM +0200, richard -rw- weinberger wrote:
> On Fri, Aug 3, 2012 at 1:27 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> > On Fri, Aug 03, 2012 at 01:19:24PM +0200, richard -rw- weinberger wrote:
> >> >>
> >> >> CRIU folks, how do you deal with futex robust lists?
> >> >
> >> > Well, I believe we were over-optimistic in claiming that we don't need this
> >> > syscall (to be fair I think we simply yet not faced the problem Eric points).
> >> > So we need some way to fetch this address and set it back. If get_robust_list
> >> > get deprecated maybe we could print it out in /proc/pid/stat or something?
> >>
> >> Kees, you said get_robust_list() can be used to bypass ASLR.
> >> How? What makes it worse than /proc/pid/maps?
> >>
> >> If the robust list address itself is bad, removing get_robust_list()
> >> and putting the information into /proc is useless.
> >
> > Look, the /proc entry might check for some CAP and do not allow
> > a regular user to fetch this address.
> 
> We could also add another check to get_robust_list().
> It does already ptrace_may_access().

Yes, and I'm definitely not against that ;) The problem is that this
syscall was marked as deprecated and if people want to drop it we
need to find a way to provide this address back in a sake of c/r.

If c/r is the only _one_ who needs this facility than providing the
address via /proc might be worth thing to do (since I can wrap
it with CONFIG_CHECKPOINT_RESTORE and a regular kernel won't see
this snippet at all).

	Cyrill
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