linux-kernel - Re: [kernel-hardening] Re: [RFC PATCH 2/2] mm: restrict access to /proc/slabinfo

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Date:	Mon, 19 Sep 2011 21:58:56 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	kernel-hardening@...ts.openwall.com, Kees Cook <kees@...ntu.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Dan Rosenberg <drosenberg@...curity.com>,
	Theodore Tso <tytso@....edu>, Alan Cox <alan@...ux.intel.com>,
	Jesper Juhl <jj@...osbits.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [kernel-hardening] Re: [RFC PATCH 2/2] mm: restrict access to
 /proc/slabinfo

On Mon, Sep 19, 2011 at 20:51 +0300, Pekka Enberg wrote:
> On Mon, Sep 19, 2011 at 8:35 PM, Vasiliy Kulikov <segoon@...nwall.com> wrote:
> >> Yes, but there's no way for users to know where the allocations came from
> >> if you mix them up with other kmalloc-128 call-sites. That way the number
> >> of private files will stay private to the user, no? Doesn't that give you even
> >> better protection against the infoleak?
> >
> > No, what it gives us is an obscurity, not a protection.  I'm sure it
> > highly depends on the specific situation whether an attacker is able to
> > identify whether the call is from e.g. ecryptfs or from VFS.  Also the
> > correlation between the number in slabinfo and the real private actions
> > still exists.
> 
> How is the attacker able to identify that we kmalloc()'d from ecryptfs or
> VFS based on non-root /proc/slabinfo when the slab allocator itself does
> not have that sort of information if you mix up the allocations?

How can you _guarantee_ that they mix?

> Isn't this
> much stronger protection especially if you combine that with /proc/slabinfo
> restriction?

I don't see any reason to change allocators if we close slabinfo.

Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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