hien/udica

This repository contains a tool for generating SELinux security profiles for containers

udica

This repository contains a tool for generating SELinux security profiles for containers. The whole concept is based on "block inheritence" feature inside CIL intermediate language supported by SELinux userspace. The tool creates a policy which combines rules inherited from specified CIL blocks(templates) and rules discovered by inspection of container JSON file, which contains mountpoints and ports definitions.

Final policy could be loaded immediately or moved to another system where it could be loaded via semodule.

State

This tool is still in early phase of development. Any feedback, ideas, pull requests are welcome. We're still adding new features, parameters and policy blocks which could be used.

Proof of concept

Tool was created based on following PoC where process of creating policy is described: https://github.com/fedora-selinux/container-selinux-customization

Installing

Install udica tool with all dependencies

$ sudo dnf install -y podman setools-console git container-selinux
$ git clone https://github.com/containers/udica
$ cd udica && sudo python3 ./setup.py install

Alternatively tou can run udica directly from git:

$ python3 -m udica --help

Another way how to install udica is to use fedora repository:

# dnf install udica -y

Or you can use Python Package Index (Pypi):

# pip install udica

Make sure that SELinux is in Enforcing mode

# setenforce 1
# getenforce
Enforcing

Current situation

Let's start podman container with following parameters:

# podman run -v /home:/home:ro -v /var/spool:/var/spool:rw -p 21:21 -it fedora bash

• Container will bind mount /home with read only perms
• Container will bind mount /var/spool with read/write perms
• Container will publish container's port 21 to the host

Container runs with container_t type and c447,c628 categories.

Access mounted /home is not working:

[root@37a3635afb8f /]# cd /home/
[root@37a3635afb8f home]# ls
ls: cannot open directory '.': Permission denied

Because there is no allow rule for container_t to access /home

# sesearch -A -s container_t -t home_root_t
#

Access mounted /var/spool is not working:

[root@37a3635afb8f home]# cd /var/spool/
[root@37a3635afb8f spool]# ls
ls: cannot open directory '.': Permission denied
[root@37a3635afb8f spool]# touch test
touch: cannot touch 'test': Permission denied

Because there is no allow rule for container_t to access /var/spool

# sesearch -A -s container_t -t var_spool_t -c dir -p read
#

On the other hand, what is completely allowed is network access.

# sesearch -A -s container_t -t port_type -c tcp_socket
allow container_net_domain port_type:tcp_socket { name_bind name_connect recv_msg send_msg };
allow sandbox_net_domain port_type:tcp_socket { name_bind name_connect recv_msg send_msg };

# sesearch -A -s container_t -t port_type -c udp_socket
allow container_net_domain port_type:udp_socket { name_bind recv_msg send_msg };
allow sandbox_net_domain port_type:udp_socket { name_bind recv_msg send_msg };

It would be great to restrict this access and allow container bind just on tcp port 21 or with the same label.

Creating SELinux policy for container

To create policy for container, it's necessary to have running container for which a policy will be generated. Container from previous chapter will be used.

Let's find container id using podman ps command:

# podman ps
CONTAINER ID   IMAGE                             COMMAND   CREATED          STATUS              PORTS   NAMES
37a3635afb8f   docker.io/library/fedora:latest   bash      15 minutes ago   Up 15 minutes ago           heuristic_lewin

Container ID is 37a3635afb8f.

To create policy for it udica tool could be used. Parameter '-j' is for container json file and SELinux policy name for container.

# podman inspect 37a3635afb8f > container.json
# udica -j container.json  my_container

or

# 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

Policy is generated. Let's follow instructions from output:

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

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

Container is now running with 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 fedora bash
system_u:system_r:my_container.process:s0:c270,c963 root 2317 2305  0 13:49 pts/0 00:00:00 bash

Proof that SELinux now allowing access /home and /var/spool mount points:

[root@814ec56079e5 /]# cd /home
[root@814ec56079e5 home]# ls
lvrabec

[root@814ec56079e5 ~]# cd /var/spool/
[root@814ec56079e5 spool]# touch test
[root@814ec56079e5 spool]#

Proof that SELinux allows binding only to tcp/udp 21 port.

[root@5bd8cb2ad911 /]# nc -lvp 21
Ncat: Version 7.60 ( https://nmap.org/ncat )
Ncat: Generating a temporary 1024-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.
Ncat: SHA-1 fingerprint: 6EEC 102E 6666 5F96 CC4F E5FA A1BE 4A5E 6C76 B6DC
Ncat: Listening on :::21
Ncat: Listening on 0.0.0.0:21

[root@5bd8cb2ad911 /]# nc -lvp 80
Ncat: Version 7.60 ( https://nmap.org/ncat )
Ncat: Generating a temporary 1024-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.
Ncat: SHA-1 fingerprint: 6EEC 102E 6666 5F96 CC4F E5FA A1BE 4A5E 6C76 B6DC
Ncat: bind to :::80: Permission denied. QUITTING.

Testing

Udica repository contains units tests for basic functionality of the tool. To run tests follow these commands:

$ cd tests
$ python3 -m unittest

Known issues

• It's not possible to detect capabilities used by container in docker engine, therefore you have to use '-c' to specify capabilities for docker container manually.
• It's not possible to generate custom local policy using "audit2allow -M" tool from AVCs where source context was generated by udica. Issue reported #8