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Date: Sun, 3 Nov 2002 11:56:22 -0500 (EST)
From: Alexander Viro <viro@math.psu.edu>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: Linus Torvalds <torvalds@transmeta.com>,
       Olaf Dietsche <olaf.dietsche#list.linux-kernel@t-online.de>,
       "Theodore Ts'o" <tytso@mit.edu>, Dax Kelson <dax@gurulabs.com>,
       Rusty Russell <rusty@rustcorp.com.au>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, davej@suse.de
Subject: Re: Filesystem Capabilities in 2.6?
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On 3 Nov 2002, Alan Cox wrote:

> On Sun, 2002-11-03 at 14:51, Alexander Viro wrote:
> > No messing with chroot needed - just a way to irrevertibly turn off the
> > ability (for anybody) to do mounts/umounts in a given namespace and ability
> > to clone that namespace.  Then give them ramfs for root and bind whatever
> > you need in there.  No breaking out of that, since there is nothing below
> > their root where they could break out to...
> 
> mkdir foo
> chroot foo
> cd ../../../..
> chroot .

... will give him nothing, since he is not in chroot jail to start with.
He has a namespace of his own with his own root filesystem.  Which has
several empty directories and nothing else - everything else is bound on
these.  He is at his absolute root and can't break out of it - there is
nowhere to break out.  So his /foo will be a subdirectory of root of his
root filesystem.  OK, he chroots there.  His cwd is still at absolute root
and he can follow .. until he's blue in the face - he will stay where he
started.

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