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

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Date:	Tue, 20 Mar 2012 18:02:49 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Serge Hallyn <serge.hallyn@...onical.com>
cc:	Kees Cook <keescook@...omium.org>, 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,
	mingo@...nel.org
Subject: Re: [PATCH] futex: do not leak robust list to unprivileged process

On Tue, 20 Mar 2012, Serge Hallyn wrote:

> Quoting Kees Cook (keescook@...omium.org):
> > It was possible to extract the robust list head address from a setuid
> > process if it had used set_robust_list(), allowing an ASLR info leak. This
> > changes the permission checks to be the same as those used for similar
> > info that comes out of /proc.
> > 
> > Running a setuid program that uses robust futexes would have had:
> >   cred->euid != pcred->euid
> >   cred->euid == pcred->uid
> > so the old permissions check would allow it. I'm not aware of any setuid
> > programs that use robust futexes, so this is just a preventative measure.
> > 
> > (This patch is based on changes from grsecurity.)
> > 
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> I like the change.  Much cleaner.  I'm not 100% sure though that
> there are no legitimate cases of robust futexes use which would now
> be forbidden.  (Explicitly cc:ing Ingo)

get_robust_list is not necessary for robust futexes. There is no
reference to get_robust_list in glibc.

I really wonder why we have this syscall at all.

Thanks,

	tglx
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