Comment 0 for bug 1739593

Description
===========

At present when swapping encrypted volumes no attempt is made to attach an encryptor to the target volume. This results in the RAW underlying volume being used during the rebase, where decrypted data is copied from the original volume to the target:

https://github.com/openstack/nova/blob/76dfdfc1ad8c0e5376bd997e45f65bec9ff53d12/nova/virt/libvirt/driver.py#L1338-L1372

Any attempt to detach and then reattach this volume from the instance will lead to the volume being reformatted as the os-brick supplied encryptors do not identify the volume as encrypted:

https://github.com/openstack/os-brick/blob/6835b885dc4144fdc6e9863ca59ae54f76938995/os_brick/encryptors/luks.py#L138-L161

Additionally, while unlikely, a malicious user could easily DOS the compute node hosting the instance by writing a corrupt LUKS header to the RAW volume before detaching and reattaching the volume. For example, setting a keyslot iters (used by PBKDF2) to a large value etc (kudos to mdbooth for suggesting this):

https://gitlab.com/cryptsetup/cryptsetup/wikis/LUKS-standard/on-disk-format.pdf

This method of DOS'ing the compute host was previously discussed in the context of bug 1724573 but dismissed as access to the underlying volume was dependent on a host reboot, outside of a users control. This bug differs as a user has full control of the above volume-update/swap_volume flow that provides access to the underlying volume.

Steps to reproduce
==================

- Create two encrypted volumes

$ cinder type-create LUKS
$ cinder encryption-type-create --cipher aes-xts-plain64 \
                                --key_size 256 \
                                --control_location front-end LUKS luks

$ cinder type-create LUKS_NEW
$ cinder encryption-type-create --cipher aes-xts-plain64 \
                                --key_size 256 \
                                --control_location front-end LUKS_NEW luks

$ cinder create --volume-type LUKS 1
$ cinder create --volume-type LUKS_NEW 1

- Spawn an instance, attaching the first volume before swapping to the second:

$ nova boot --image cirros-0.3.5-x86_64-disk --flavor 1 swap_test
$ nova volume-attach $instance $vol-luks
$ nova volume-update $instance $vol-luks $vol-luks-new

- Review the resulting volume attachment on the compute host:

$ virsh domblklist $instance
Target Source
------------------------------------------------
vda /opt/stack/data/nova/instances/3d4c5842-45ab-4660-bf6e-9459f9a2ff8a/disk
vdb /dev/disk/by-id/scsi-36001405ba072cc9f93e444c9433ead1c

$ ll /dev/disk/by-id/scsi-36001405ba072cc9f93e444c9433ead1c
lrwxrwxrwx. 1 root root 9 Dec 21 05:30 /dev/disk/by-id/scsi-36001405ba072cc9f93e444c9433ead1c -> ../../sdd

$ sudo qemu-img info /dev/disk/by-id/scsi-36001405ba072cc9f93e444c9433ead1c
image: /dev/disk/by-id/scsi-36001405ba072cc9f93e444c9433ead1c
file format: raw
virtual size: 1.0G (1073741824 bytes)
disk size: 0

Expected result
===============

The encrypted volumes are rebased with their associated encryptors attached, leading to encrypted data being written to the underlying volumes.

Actual result
=============

Decrypted data from the source volume is written to the underlying target volume. This data will be lost with a subsequent detach / attach cycle. Access to the underlying volume could also be used by a malicious user to DOS the local compute host.

Environment
===========
1. Exact version of OpenStack you are running. See the following
  list for all releases: http://docs.openstack.org/releases/

2. Which hypervisor did you use?
   (For example: Libvirt + KVM, Libvirt + XEN, Hyper-V, PowerKVM, ...)
   What's the version of that?

   Libvirt + KVM

2. Which storage type did you use?
   (For example: Ceph, LVM, GPFS, ...)
   What's the version of that?

   LVM

3. Which networking type did you use?
   (For example: nova-network, Neutron with OpenVSwitch, ...)

   N/A

Logs & Configs
==============

N/A