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Message-ID: <20110929172821.GA19601@albatros>
Date: Thu, 29 Sep 2011 21:28:21 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: David Rientjes <rientjes@...gle.com>
Cc: Christoph Lameter <cl@...two.org>, kernel-hardening@...ts.openwall.com,
Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
Kees Cook <kees@...ntu.com>, Dave Hansen <dave@...ux.vnet.ibm.com>,
Valdis.Kletnieks@...edu,
Linus Torvalds <torvalds@...ux-foundation.org>,
Alan Cox <alan@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: restrict access to /proc/meminfo
On Thu, Sep 29, 2011 at 20:18 +0400, Vasiliy Kulikov wrote:
> On Tue, Sep 27, 2011 at 13:33 -0700, David Rientjes wrote:
> > I'd much rather just convert everything to use MB rather than KB so you
> > can't determine things at a page level. I think that gets us much closer
> > to what the patch is intending to restrict. But I also expect some
> > breakage from things that just expect meminfo to be in KB units without
> > parsing what the kernel is exporting.
>
> I'm not convinced with rounding the information to MBs. The attacker
> still may fill slabs with new objects to trigger new slab pages
> allocations. He will be able to see when this MB-granularity barrier is
> overrun thus seeing how many kbs there were before:
>
> old = new - filled_obj_size_sum
>
> As `new' is just increased, it means it is known with KB granularity,
> not MB. By counting used slab objects he learns filled_obj_size_sum.
s/filled_obj_size_sum/old/ of course.
> So, rounding gives us nothing, but obscurity.
>
> Thanks,
--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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