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Date: Fri, 13 Feb 2009 19:48:12 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: John Ogness <dazukocode@ogness.net>
Cc: Jan Engelhardt <jengelh@medozas.de>, linux-kernel@vger.kernel.org,
       malware-list@lists.printk.net, eparis@redhat.com, hch@infradead.org,
       alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCHv2 1/5] VFS: DazukoFS, stackable-fs, file access control
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References: <8663jrgwo4.fsf@johno.fn.ogness.net> <861vufgwlt.fsf@johno.fn.ogness.net> <alpine.LSU.2.00.0902121618500.5658@fbirervta.pbzchgretzou.qr> <86y6wagmmg.fsf@johno.fn.ogness.net>
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On Fri, Feb 13, 2009 at 08:31:03PM +0100, John Ogness wrote:

> If we want to forbid users from being able to do this, I think it
> would be simpler just to fail the mount if it is _not_ specified for
> direct stacking. This forces users to use a syntax that makes it very
> clear what they are doing.
> 
> Since mounting to a different directory could cause problems, I think
> it will be good to forbid it. I will make this change for the next
> patch series.

And just how are you going to do that?  Note that underlying directory
may be visible in many places to start with...