Date: Wed, 26 Sep 2007 12:20:28 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: David Newall <david@davidnewall.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>, Bill Davidsen <davidsen@tmr.com>,
       Philipp Marek <philipp@marek.priv.at>, 7eggert@gmx.de,
       majkls <majkls@prepere.com>, bunk@fs.tum.de,
       linux-kernel@vger.kernel.org
Subject: Re: Chroot bug
Message-ID: <20070926122028.5f842d1e@the-village.bc.nu>
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> >>> The dot-dot entry in the root directory is interpreted to mean the 
> >>> root directory itself. Thus, dot-dot cannot be used to access files 
> >>> outside the subtree rooted at the root directory.
> >>>       
> >
> > Which is behaviour chroot preserves properly.
> >   
> And yet it is the dot-dot entry which is used to access files outside 
> the root.

Read it again, and read all the words. Notably "the dot-dot entry *IN*
the root directory". When your current directory is above your root
directory you do not pass through that dot-dot entry.

> Do you believe that when those words were first written, the hidden 
> conflict, namely that it permits dot-dot to access files outside the 
> subtree, was understood?  

Yes. You need to remember the notion of chroot for "security" is a very
new one, and not one that it was designed for. Which as I've said twice
now is why things like vserver and BSD jails have evolved.

Alan
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