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

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Date:	Mon, 16 Jan 2012 14:26:05 -0500
From:	Colin Walters <walters@...bum.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Casey Schaufler <casey@...aufler-ca.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jamie Lokier <jamie@...reable.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

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.

Incidentally I ended up putting my setuid program here:
http://git.gnome.org/browse/linux-user-chroot/

Now unfortunately, even if we say that a new setuid program is the way
to gain these privileges, you still can't nest it, because all of these
things are predicated on disabling setuid programs.  But it would at
least not fail initially if your process was inside a chroot.






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