linux-kernel - Re: [AppArmor 00/44] AppArmor security module overview

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Message-Id: <200706271537.10566.agruen@suse.de>
Date:	Wed, 27 Jun 2007 15:37:10 +0200
From:	Andreas Gruenbacher <agruen@...e.de>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	John Johansen <jjohansen@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [AppArmor 00/44] AppArmor security module overview

On Wednesday 27 June 2007 12:58, Kyle Moffett wrote:
> I seem to recall you could actually end up racing and building a path
> to the file in those directories as "a/d/0/3" or some other path at
> which it never even remotely existed. I'd love to be wrong,

Cheer up, you recall wrong.

> but I can't help but see this problem in any reverse-pathname-generation
> proposal which gets the locking right.

Have a look at how __d_path() is implemented (with the fixes): It takes the 
dcache_lock, and the vfsmount_lock where necessary, and this ensures that the 
pathname can't change under it, neither because of a rename nor unlink nor 
remount. The pathname computed is *exactly* the name the file has at that 
specific point time.

A few more details about how pathnames work are explained in the tech doc at:
http://forge.novell.com/modules/xfcontent/downloads.php/apparmor/LKML_Submission-May_07

Andreas
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