governance/goals/selected/migrate-to-privsep.rst

Migrate from oslo.rootwrap to oslo.privsep

The oslo.rootwrap library is a precursor of oslo.privsep that allows code to run commands under "sudo" if it matches a predefined filter. Beyond the bad performance of calling full commands in order to accomplish simple tasks, oslo.rootwrap also led to bad security; it was difficult to filter commands in a way that would not easily allow privilege escalation.

oslo.privsep offers a superior security model, faster and more secure. Since oslo.privsep was released, the community has encouraged the usage of oslo.privsep and the deprecation of any existing code still using oslo.rootwrap.

Champion

Rodolfo Alonso Hernandez <ralonsoh@redhat.com> (ralonsoh)

Gerrit Topic

To facilitate tracking, commits related to this goal should use the gerrit topic:

privsep-migration

A new Story in https://storyboard.openstack.org/ will be created to track any related patch.

Completion Criteria

#. A migrated project should not import oslo.rootwrap, the rootwrap filters should be deleted and the library should not be required anymore during the project installation.

#. The migration will be considered complete when no project inherits oslo.rootwrap and this import is added to hacking¹.

References

The main reference guide could be found in². This guide provides information about how to create a privsep context, assign privileges and use it as a decorator for a function. As commented in the first section, this context should contain the minimum set of needed capabilities to execute the decorated function. For example:

default = priv_context.PrivContext(
   __name__,
   cfg_section='privsep',
   pypath=__name__ + '.default',
   capabilities=[caps.CAP_SYS_ADMIN,
                 caps.CAP_NET_ADMIN,
                 caps.CAP_DAC_OVERRIDE,
                 caps.CAP_DAC_READ_SEARCH,
                 caps.CAP_SYS_PTRACE],
)

The function “entrypoint”³ of this instance can be used as a decorator for another function:

@privileged.default.entrypoint
def delete_interface(ifname, namespace, **kwargs):
    _run_iproute_link("del", ifname, namespace, **kwargs)

From this same link, there is also a reference to convert from oslo.rootwrap to oslo.privsep. These are some migration examples:

• Nova:⁴
• Neutron:⁵
• os-vif:⁶

Replacing instances of oslo.rootwrap usage requires more than just a drop-in replacement. The oslo.privsep approach is different and will require rethinking the way each privileged operation is conducted in a way that precludes a blind or programmatic substitution. As commented in the OpenStack mailing list⁷, the security idea is based on the principle of least privilege. That means any command executed inside a privsep context⁸ should gain the minimum needed privileges to execute the task and exit. Unfortunately some projects have implemented all privileged commands under a single privsep context, containing all needed capabilities⁹ to execute all those commands. This is an incorrect implementation of oslo.privsep and should be considered during the migration.

Current State / Anticipated Impact

These are the projects still using oslo.rootwrap that should migrate:

• ceilometer
• cinder
• cinderlib
• designate
• freezer
• glance_store
• ironic
• ironic-inspector
• ironic-lib
• kolla
• magnum
• manila
• monasca-agent
• networking-bagpipe
• neutron
• neutron-vpnaas
• os-brick
• sahara
• solum
• tacker
• tripleo-common

Links

---

1. openstack/hacking/src/branch/master/hacking/checks/imports.py↩︎

2. https://docs.openstack.org/oslo.privsep/latest/user/index.html↩︎

3. openstack/oslo.privsep/src/tag/2.1.1/oslo_privsep/priv_context.py#L216↩︎

4. https://review.opendev.org/#/q/project:openstack/nova+branch:master+topic:my-own-personal-alternative-universe↩︎

5. https://review.opendev.org/#/q/status:merged+project:openstack/neutron+branch:master+topic:bug/1492714↩︎

6. https://review.opendev.org/#/c/287725/↩︎

7. http://lists.openstack.org/pipermail/openstack-discuss/2019-March/004358.html↩︎

8. https://docs.openstack.org/oslo.privsep/latest/user/index.html#defining-a-context↩︎

9. http://man7.org/linux/man-pages/man7/capabilities.7.html↩︎