Using Configuration as a Short-Term Mitigation for OSSA-2023-003
---

### Summary ###
An unauthorized access to a volume could occur when an iSCSI or FC
connection from a host is severed due to a volume being unmapped on
the storage system and the device is later reused for another volume
on the same host.

### Affected Services / Software ###
- cinder: <20.2.1, >=21.0.0 <21.2.1, ==22.0.0
- glance_store: <3.0.1, >=4.0.0 <4.1.1, >=4.2.0 <4.3.1
- nova: <25.1.2, >=26.0.0 <26.1.2, ==27.0.0
- os-brick: <5.2.3, >=6.0.0 <6.1.1, >=6.2.0 <6.2.2

### Discussion ###
It is recommended to apply the fixes provided in OSSA-2023-003
https://security.openstack.org/ossa/OSSA-2023-003.html but updating
an OpenStack deployment may take a long time requiring a proper
maintenance window and may even require a validation process of the
release prior to the deployment, so operators may prefer applying
tactical configuration changes to their cloud to prevent harmful
actions while they go through their standarized process.

In this case the fastest way to prevent an unsafe attach deletion is
twofold:
    1. ensuring that Nova uses a user with a service role to send
    its token on all the requests made to Cinder on behalf of users,
    and
    2. Cinder protects the vulnerable APIs via policy.

### Recommended Actions ###
If the deployment has Glance using Cinder as a backend, in order to
use this alternative short-term mitigation, Glance must be
configured to use a single user having the service role for all its
requests to Cinder. If your deployment is *not* using a single user
(that is, instead of all the image-volumes being stored in a single
project, they are stored in each user's project), then you cannot
use this Short-Term Mitigation strategy, but must instead apply the
full change described in the previous section.

Steps for Mitigation:
A. Ensure the users used by Nova (and Glance, if applicable) have
the service role
      * In Nova, this is the user configured in the [service_user]
        section of nova.conf
      * In Glance, this user will only be defined if you are using
        Cinder as a Glance storage backend. It is defined in the
        [cinder] section of glance.conf
        ** if you do not use Cinder as a backend for Glance, you do
        not need to define a service user for Glance

B. Configure Nova to send the service token
https://docs.openstack.org/cinder/latest/configuration/block-storage/service-token.html
      * Glance does not have the ability to send a service token to
        Cinder; instead, the mitigation-by-policy strategy described
        below relies upon the user configured in glance in the
        [cinder]/cinder_store_user_name option in glance.conf having
        been granted the service role in Keystone

C. Configure the cinder policies as per
https://docs.openstack.org/cinder/latest/configuration/block-storage/policy-config-HOWTO.html
to have the following:

    "is_service":
        "role:service or service_user_id:<nova_service_uuid>"
    "volume:attachment_delete":
        "rule:xena_system_admin_or_project_member and rule:is_service"
    "volume_extension:volume_actions:terminate_connection":
        "rule:xena_system_admin_or_project_member and rule:is_service"
    "volume_extension:volume_actions:detach":
        "rule:xena_system_admin_or_project_member and rule:is_service"
    "volume_extension:volume_admin_actions:force_detach":
        "!"

    Notes:
          - The operator should replace "<nova_service_uuid>" with
            the actual UUID of the user configured in the
            [service_user] section of nova.conf
          - If the role name in Keystone to identify a service is
            not "service"' then the operator should also replace
            "role:service" accordingly and also make appropriate
            adjustment to the
            [keystone_authtoken]/service_token_roles setting in your
            cinder configuration file.
          - It may not be obvious why there are four policy targets
            defined. It's because the Block Storage API v3 provides
            four different API calls by which an attachment-delete
            may be accomplished:
            ** DELETE /v3/attachments/{attachment_id}
               (introduced in microversion 3.27, the preferred way to do this)
            ** POST /v3/volumes/{volume_id}
               with 'os-detach' action in the request body
            ** POST /v3/volumes/{volume_id}
               with 'os-terminate_connection' action in the request body
            ** POST /v3/volumes/{volume_id}
               with 'os-force_detach' action in the request body

Limitations:
The drawback to this configuration-only approach is that while it
protects against the intentional case described earlier, it does not
protect against the accidental case. Additionally, it is not
fine-grained enough to distinguish acceptable end-user Block Storage
API attachment-delete requests from unsafe ones (the Cinder code
change is required for that). For these reasons, we emphasize that
this is only a short-term mitigation, and we recommend that the full
fix be applied as soon as possible in your deployment.

Warning:
Note that if you deploy this short-term mitigation, you should roll
back the policy changes after the full fix is applied, or end users
will continue to be unable to make acceptable attachment-delete
requests.

### Credits ###
Jan Wasilewski, Atman
Gorka Eguileor, Red Hat

### Contacts / References ###
Authors:
- Brian Rosmaita, Red Hat
- Dan Smith, Red Hat
- Gorka Eguileor, Red Hat
- Jeremy Stanley, OpenInfra Foundation
- Nick Tait, Red Hat
This OSSN: https://wiki.openstack.org/wiki/OSSN/OSSN-0092#Discussion
Original Launchpad bug: https://launchpad.net/bugs/2004555
Mailing List : [security-sig] tag on openstack-discuss@lists.openstack.org
OpenStack Security Project : https://launchpad.net/~openstack-ossg
CVE: CVE-2023-2088