linux-kernel - Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map

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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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