linux-kernel - Re: [lxc-devel] [RFC PATCH 11/11] loop: Allow priveleged operations for root in the namespace which owns a device

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Message-ID: <20140526154536.GA31721@ubuntu-mba51>
Date:	Mon, 26 May 2014 17:45:36 +0200
From:	Seth Forshee <seth.forshee@...onical.com>
To:	LXC development mailing-list <lxc-devel@...ts.linuxcontainers.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Marian Marinov <mm@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [lxc-devel] [RFC PATCH 11/11] loop: Allow priveleged operations
 for root in the namespace which owns a device

On Mon, May 26, 2014 at 11:32:05AM -0400, Michael H. Warfield wrote:
> On Mon, 2014-05-26 at 11:16 +0200, Seth Forshee wrote:
> > On Fri, May 23, 2014 at 08:48:25AM +0300, Marian Marinov wrote:
> > > -----BEGIN PGP SIGNED MESSAGE-----
> > > Hash: SHA1
> > > 
> > > One question about this patch.
> > > 
> > > Why don't you use the devices cgroup check if the root user in that namespace is allowed to use this device?
> > > 
> > > This way you can be sure that the root in that namespace can not access devices to which the host system did not gave
> > > him access to.
> 
> > That might be possible, but I don't want to require something on the
> > host to whitelist the device for the container. Then loop would need to
> > automatically add the device to devices.allow, which doesn't seem
> > desirable to me. But I'm not entirely opposed to the idea if others
> > think this is a better way to go.
> 
> I don't see any safe way to avoid it.  The host has to be in control of
> what devices can and can not be accessed by the container.

Hmm, for testing I've been giving access to 7:* block devices since my
containers can't mknod and only see device nodes for loop devices they
have access to, but maybe I'm not being sufficiently paranoid.

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