linux-kernel - Re: Chroot bug

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Message-ID: <20070926150238.GA43852@dspnet.fr.eu.org>
Date:	Wed, 26 Sep 2007 17:02:38 +0200
From:	Olivier Galibert <galibert@...ox.com>
To:	David Newall <david@...idnewall.com>
Cc:	Kyle Moffett <mrmacman_g4@....com>, Adrian Bunk <bunk@...nel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Bill Davidsen <davidsen@....com>,
	Philipp Marek <philipp@...ek.priv.at>, 7eggert@....de,
	majkls <majkls@...pere.com>, bunk@...tum.de,
	linux-kernel@...r.kernel.org
Subject: Re: Chroot bug

On Wed, Sep 26, 2007 at 08:43:44PM +0930, David Newall wrote:
> Olivier Galibert wrote:
> >chroot does not allow you to walk out if you're in.
> 
> You're mistaken.  Or more properly, further use of chroot lets you walk 
> out.  This really has been said before, and before, and before.
> 
>    chroot("subtree");   // enter chroot
>    chdir("/");    // now at subtree
>    chroot("/tmp");   // now outside of chroot

Of course.  chroots are not a stack, they're just a point in the
namespace.  You change it, the conditions apply to the new one.

> BSD redefined chroot so that the working directory is set to the new 
> root on subsequent uses of chroot; that's how they solved the bug.

They didn't solve a thing.  fchdir baby.  Unless you want to remove
fchdir.  And mknod.  And mount.  And so many other different syscalls
that I don't even know the list.

  OG.
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