linux-kernel - Re: [PATCH 4/4] Allow unprivileged chroot when safe

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Message-ID: <20120117101447.GF7180@jl-vm1.vm.bytemark.co.uk>
Date:	Tue, 17 Jan 2012 10:14:47 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Colin Walters <walters@...bum.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	oleg@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH 4/4] Allow unprivileged chroot when safe

Colin Walters wrote:
> On Sun, 2012-01-15 at 16:37 -0800, Andy Lutomirski wrote:
> 
> > Because chroot is an easy way to break out of chroot jail, CAP_SYS_ADMIN
> > is still required if the caller is already chrooted.
> 
> This part is pretty gross.  It means it won't work for stuff like
> containers (systemd-nspawn etc.) and furthermore

> I have plans that involve running OS trees inside a chroot, and this
> would obviously not work for that.

Indeed, I do run many of my machines inside a chroot.
The real filesystem has:

    /distro/that
    /distro/newer
    /distro/this

instead of partitions.  I'm chroot'd and fully booted up in
/distro/this, although I can see files in the others and I might run a
few things from them as well.

This isn't "userland chroot", it's the top level of the process tree:
/distro/this/sbin/init.  It would be a shame if it behaved differently
just because "it's a chroot".

-- Jamie
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