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

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Message-ID: <20110906172952.GA28055@albatros>
Date:	Tue, 6 Sep 2011 21:29:52 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	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>,
	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

Hi Tejun,

On Wed, Sep 07, 2011 at 01:51 +0900, Tejun Heo wrote:
> On Tue, Sep 06, 2011 at 02:15:18PM +0400, Vasiliy Kulikov wrote:
> >   c) If dentry is lazily dropped on each access attempt (or each illegal
> >      access) then PID2 can:
> > 
> >      i) read dentry line of /proc/slabinfo
> >      ii) call link(2) against /proc/PID/fd, which invalidates the
> >          specific dentry
> >      iii) re-read dentry line of /proc/slabinfo.  If it has decreased by
> >          one, the dentry existed before (ii).
> 
> If we really worry about this, probably the right thing to do is
> hiding slabinfo from mortal UIDs instead of worrying about what
> exactly are freed or not from each user.

I agree with you.  I don't think that showing system-global debug
information to all users by default is the right thing.  But some people
doesn't agree with this point of view:

http://thread.gmane.org/gmane.linux.kernel/1108378

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