Information
Do not share the host's user namespaces with the containers.
Rationale:
User namespaces ensure that a root process inside the container will be mapped to a non-root process outside the container. Sharing the user namespaces of the host with the container thus does not isolate users on the host with users on the containers.
Solution
Do not share user namespaces between host and containers.
For example, do not run a container as below:
docker run --rm -it --userns=host ubuntu bash
Impact:
None
Default Value:
By default, the host user namespace is shared with the containers until user namespace support is enabled.