linux-kernel - Re: [PATCHv2 1/5] VFS: DazukoFS, stackable-fs, file access control

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Date:	Fri, 13 Feb 2009 21:00:36 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	John Ogness <dazukocode@...ess.net>
cc:	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	malware-list@...ts.printk.net, eparis@...hat.com,
	hch@...radead.org, alan@...rguk.ukuu.org.uk
Subject: Re: [PATCHv2 1/5] VFS: DazukoFS, stackable-fs, file access control


On Friday 2009-02-13 20:31, 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.

You could write an additional mount helper (and putting that into
/sbin/mount.dazukofs) that does all the security checks:

 - that the device is the same as mountpoint
 - that the device belonging to the underlying '/mnt' is not
   mounted anywhere else (in this namespace, at least)
 - exit(1) otherwise

Sure, it may not protect against all the cases Al can come up with,
but it is better than having nothing.
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