9.2. Creating and using an SELinux policy for a custom container

Procedure

1. Install the udica package:

   # dnf install -y udica

   Alternatively, install the container-tools module, which provides a set of container software packages, including udica:

   # dnf module install -y container-tools

2. Start the ubi8 container that mounts the /home directory with read-only permissions and the /var/spool directory with permissions to read and write. The container exposes the port 21.

   # podman run --env container=podman -v /home:/home:ro -v /var/spool:/var/spool:rw -p 21:21 -it ubi8 bash

   Note that now the container runs with the container_t SELinux type. This type is a generic domain for all containers in the SELinux policy and it might be either too strict or too loose for your scenario.

3. Open a new terminal, and enter the podman ps command to obtain the ID of the container:

   # podman ps
   CONTAINER ID   IMAGE                                   COMMAND   CREATED          STATUS              PORTS   NAMES
   37a3635afb8f   registry.access.redhat.com/ubi8:latest  bash      15 minutes ago   Up 15 minutes ago           heuristic_lewin

4. Create a container JSON file, and use udica for creating a policy module based on the information in the JSON file:

   # podman inspect 37a3635afb8f > container.json
   # udica -j container.json my_container
   Policy my_container with container id 37a3635afb8f created!
   […]

   Alternatively:

   # podman inspect 37a3635afb8f | udica my_container
   Policy my_container with container id 37a3635afb8f created!
   
   Please load these modules using:
   # semodule -i my_container.cil /usr/share/udica/templates/{base_container.cil,net_container.cil,home_container.cil}
   
   Restart the container with: "--security-opt label=type:my_container.process" parameter

5. As suggested by the output of udica in the previous step, load the policy module:

   # semodule -i my_container.cil /usr/share/udica/templates/{base_container.cil,net_container.cil,home_container.cil}

6. Stop the container and start it again with the --security-opt label=type:my_container.process option:

   # podman stop 37a3635afb8f
   # podman run --security-opt label=type:my_container.process -v /home:/home:ro -v /var/spool:/var/spool:rw -p 21:21 -it ubi8 bash

Verification

1. Check that the container runs with the my_container.process type:

   # ps -efZ | grep my_container.process
   unconfined_u:system_r:container_runtime_t:s0-s0:c0.c1023 root 2275 434  1 13:49 pts/1 00:00:00 podman run --security-opt label=type:my_container.process -v /home:/home:ro -v /var/spool:/var/spool:rw -p 21:21 -it ubi8 bash
   system_u:system_r:my_container.process:s0:c270,c963 root 2317 2305  0 13:49 pts/0 00:00:00 bash

2. Verify that SELinux now allows access the /home and /var/spool mount points:

   [root@37a3635afb8f /]# cd /home
   [root@37a3635afb8f home]# ls
   username
   [root@37a3635afb8f ~]# cd /var/spool/
   [root@37a3635afb8f spool]# touch test
   [root@37a3635afb8f spool]#

3. Check that SELinux allows binding only to the port 21:

   [root@37a3635afb8f /]# dnf install nmap-ncat
   [root@37a3635afb8f /]# nc -lvp 21
   …
   Ncat: Listening on :::21
   Ncat: Listening on 0.0.0.0:21
   ^C
   [root@37a3635afb8f /]# nc -lvp 80
   …
   Ncat: bind to :::80: Permission denied. QUITTING.