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Message-ID: <20110905203627.GL761@sun>
Date: Tue, 6 Sep 2011 00:36:27 +0400
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Vasiliy Kulikov <segoon@...nwall.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Kirill A. Shutemov" <kirill@...temov.name>,
containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Nathan Lynch <ntl@...ox.com>,
kernel-hardening@...ts.openwall.com,
Oren Laadan <orenl@...columbia.edu>,
Daniel Lezcano <dlezcano@...ibm.com>,
Glauber Costa <glommer@...allels.com>,
James Bottomley <jbottomley@...allels.com>,
Tejun Heo <tj@...nel.org>, Alexey Dobriyan <adobriyan@...il.com>,
Al Viro <viro@...IV.linux.org.uk>,
Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/
directory v6
On Mon, Sep 05, 2011 at 11:49:08PM +0400, Vasiliy Kulikov wrote:
...
>
> Actually, it can be speed up by introducing the same ptrace check. If
> ptrace check fails, then just drop the dentry, otherwise continue to use
> it. Then each revalidate would trigger ptrace check instead of full
> drop-lookup-alloc cycle. If one process actively looks into
> map_files/ or fd/, it will not become significantly slower. However, it
> will trigger 2 capable() fail alerts in ptrace_may_access() instead of
> one :)
Hmm, at least it's better than trashing dcache I think.
>
> But I still see one very nasty issue - one may trigger this ptrace check,
> trigger d_drop() and then look at /proc/slabinfo at "dentry" row. If
> the number has changed, then the interested dentry existed before the
> revalidate call. This infoleak is tricky to fix without any race.
>
> Probably it's time to close /proc/slabinfo infoleak?
>
Actually I miss to see how exactly this infoleak can be used by attacker
or whoever. So, Vasiliy, what the security issue there?
Cyrill
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