Installing SELinux on Debian 10

Ubuntu has a Mandatory Access Control (MAC) system similar to SELinux, named AppArmor. Both SELinux and AppArmor provide a set of tools to isolate applications from each other to protect the host system from being compromised. AppArmor offers Ubuntu users mandatory access control options, without the perceived difficulty or learning curve that SELinux may have. However, if you are switching to Debian 10, are already familiar with SELinux, and would like to use it to enforce security on your system, you can install it by following the steps in this guide.

Before You Begin

1. Ensure that you have followed the Getting Started and Securing Your Server guides.

   Note

   This guide is written for a non-root user. Commands that require elevated privileges are prefixed with sudo. If you’re not familiar with the sudo command, you can check our Users and Groups guide.

2. Update your system:

   sudo apt update
   

   Note

   The Linode kernel does not support SELinux by default. If your system is running a Linode kernel, you will need to change to an upstream kernel in order to use SELinux. See the How to Change Your Linode’s Kernel for more steps. Once you’re kernel is set to the upstream kernel, continue on with the steps in this guide.

Remove AppArmor

1. Stop AppArmor using systemctl:

   sudo systemctl stop apparmor
   

2. Purge AppArmor from the system.

   Caution

   Do not purge AppArmor if you believe you may reuse it in the future. If you would like to preserve your AppArmor configuration files, use the remove command, instead:

   sudo apt remove apparmor
   

   sudo apt purge apparmor
   

   Note

   If after issuing the `purge command you receive warnings about remaining AppArmor files or directories. You can remove them manually, if desired. This step is not necessary to get a working SELinux installation.

3. Update your system:

   sudo apt update && sudo apt upgrade -yuf
   

4. Reboot your Linode

    sudo reboot
   

Install SELinux

1. Install the SELinux package along with supporting packages to help you manage your installation.

   sudo apt-get install selinux-basics selinux-policy-default auditd
   

2. Activate your SELinux installation:

    sudo selinux-activate
   

   Your output should resemble the following:

   Activating SE Linux
   Generating grub configuration file ...
   Found linux image: /boot/vmlinuz-4.19.0-8-amd64
   Found initrd image: /boot/initrd.img-4.19.0-8-amd64
   done
   SE Linux is activated.  You may need to reboot now.

3. Reboot your Linode for the installation to complete:

    sudo reboot
   

   Note

   After rebooting your system, SELinux should be enabled, but in permissive mode. Permissive mode means any actions that would have been disallowed are allowed, but logged in your system’s audit log located in the /var/log/audit/audit.log file.

4. Log back into your Linode via SSH. Replace 192.0.2.0 with your own Linode’s IP address.

    ssh username@192.0.2.0
   

5. Verify the status of your SELinux installation:

    sudo sestatus
   

   You should see a similar output:

   SELinux status:                 enabled
   SELinuxfs mount:                /sys/fs/selinux
   SELinux root directory:         /etc/selinux
   Loaded policy name:             default
   Current mode:                   permissive
   Mode from config file:          permissive
   Policy MLS status:              enabled
   Policy deny_unknown status:     allowed
   Memory protection checking:     requested (insecure)
   Max kernel policy version:      31

6. To put SELinux into enforcing mode, use the setenforce command. When in enforcing mode, any actions not permitted by your system’s are blocked and the corresponding event is logged in the audit log.

    sudo setenforce 1
   

7. To maintain enforcing mode after reboot, modify the SELinux configuration file in /etc/selinux/config from the default SELINUX=permissive to SELINUX=enforcing:

   File: /etc/selinux/config

   1 2 3 4 5 6 7

   # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=enforcing

   Note

   If you have set SELinux to enforcing mode, ensure that your SSH port has access before logging out of your session.

   sudo semanage port -l | grep 'ssh'
   

   You should see a similar output if TCP is allowed on port 22.

   ssh_port_t                     tcp      22

   If you do not see the this entry, open the port with the following command:

   sudo semanage port -a -t ssh_port_t -p tcp 22
   

Next Steps

After installing SELinux on your system, use our Getting Started with SELinux Guide to learn the basics of SELinux security.