[libvirt] [PATCH v5 3/3] security_dac: Favour ACLs over chown()

[Eric Blake]

On 03/28/2013 06:21 AM, Daniel P. Berrange wrote:

> We decided on using xattrs, instead of an in-memory record, because we
> want the data to be accessible to multiple libvirtd daemons on different
> hosts. This does not imply we actually need to store the xattrs on the
> files themselves. Perhaps we should have been creating some parallel
> files to record the original ownership, which are permanently root
> owned.
> 
> eg For a file /var/lib/libvirt/images/foo.img add a
> /var/lib/libvirt/images/.libvirt.dac.foo.img file to record the original
> information.
> 
> Or as with the lock manager, just use a single directory like
> /var/lib/libvirt/dac/ and create files in there based on the SHA256SUM
> of the filename, and declare that you must share that directory between
> hosts ?

Out of the box, libvirt is not set up for sharing unless you mount
/var/lib/libvirt/images on shared storage or add your own storage pool
pointing to shared storage.  Since setting up shared storage pools is
already an admin action, I would be okay with also requiring an admin
action to set up a shared directory that tracks ownership information
across a shared pool.  It might also be nice to make it easy to
associate a shared subdirectory for metainformation inside any storage
pool based on top of a shared directory (although that approach doesn't
really scale to other storage pools such as iscsi or LVM where the pool
isn't really exposing a file system to hold a subdirectory).

For that matter, there have already been requests to allow 'virsh
managedsave' dump memory into a storage pool, rather than into /etc,
since saved state can occupy a lot more space than the / partition is
prepared to handle.  Also, we have the question of coming up with a
default name for saved state files in external snapshots.  Both of these
problems would also benefit from the ability to designate where libvirt
should stick metadata associated with a storage pool, but where a
fallback to a default within /var/lib/libvirt are still okay for
out-of-the-box installation on a single machine.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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