Re: [Qemu-devel] [RFC][BROKEN] rbd: Allow configuration of authentication scheme

[Kevin Wolf]

Am 18.04.2018 um 18:34 hat Daniel P. Berrangé geschrieben:
> On Wed, Apr 18, 2018 at 06:28:23PM +0200, Kevin Wolf wrote:
> > Am 18.04.2018 um 17:06 hat Markus Armbruster geschrieben:
> 
> > >     Note that users can still configure authentication methods with a
> > >     configuration file.  They probably do that anyway if they use Ceph
> > >     outside QEMU as well.
> > 
> > This solution that we originally intended to offer was dismissed by
> > libvirt as unpractical: libvirt allows the user to specify both a config
> > file and a key, and if it wanted to use a config file to pass the key,
> > it would have to create a merged config file and keep it sync with the
> > user config file at all times. Understandable that they want to avoid
> > this.
> 
> Even if the config file does have auth info setup, we can't assume that
> the QEMU VMs are supposed to use the same auth info. In fact to properly
> protect against compromised QEMU, ideally every QEMU would use a completely
> separate RBD user+password, so that compromised QEMU can't then access
> RBD disks belonging to a different user.
> 
> So from libvirt POV we want to pretend the config file does not exist at
> all and explicitly pass everything that is needed via normal per-disk
> setup for blockdev.

>From the rbd driver:

 * The "conf" option specifies a Ceph configuration file to read.  If
 * it is not specified, we will read from the default Ceph locations
 * (e.g., /etc/ceph/ceph.conf).  To avoid reading _any_ configuration
 * file, specify conf=/dev/null.

So what we actually expected libvirt to do is to create a config file
for each rbd image and pass that to qemu. However, libvirt allows the
user to specify their own config file and passes that, and therefore
doesn't want to create its own config file. If the user doesn't specify
a config file, libvirt should probably indeed use /dev/null at least.

Kevin