[libvirt] [PATCH] storage: fix device detach regression with cgroup ACLs

[Peter Krempa]

On 11/27/12 15:04, Eric Blake wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=876828
>
> Commit 38c4a9cc introduced a regression in hot unplugging of disks
> from qemu, where cgroup device ACLs were no longer being revoked
> (thankfully not a security hole: cgroup ACLs only prevent open()
> of the disk; so reverting the ACL prevents future abuse but doesn't
> stop abuse from an fd that was already opened before the ACL change).
>
> The actual regression is due to a latent bug.  The hot unplug code
> was computing the set of files to do cgroup ACL revocation based
> on the XML passed in by the user, rather than based on the domain's
> details on which disk was being deleted.  As long as the revoke
> path was always recomputing the backing chain, this didn't really
> matter; but now that we want to compute the chain exactly once and
> remember that computation, we need to hang on to the backing chain
> until after the revoke has happened.
>
> * src/qemu/qemu_hotplug.c (qemuDomainDetachPciDiskDevice):
> Transfer backing chain before deletion.
> ---
>
> The patch is deceptively small for how long it took me to figure out
> why we had a regression :)
>
>   src/qemu/qemu_hotplug.c |    2 ++
>   1 files changed, 2 insertions(+), 0 deletions(-)
>

ACK.

Peter