How to Configure SELinux Policy Type on AlmaLinux

Security-Enhanced Linux (SELinux) is a mandatory access control (MAC) system built into Linux, including AlmaLinux, designed to enhance the security of your operating system. By enforcing strict rules about how applications and users interact with the system, SELinux significantly reduces the risk of unauthorized access or malicious activity.

Central to SELinux’s functionality is its policy type, which defines how SELinux behaves and enforces its rules. AlmaLinux supports multiple SELinux policy types, each tailored for specific environments and requirements. This blog will guide you through understanding, configuring, and managing SELinux policy types on AlmaLinux.

What Are SELinux Policy Types?

SELinux policy types dictate the scope and manner in which SELinux enforces security rules. These policies can vary in their complexity and strictness, making them suitable for different use cases. AlmaLinux typically supports the following SELinux policy types:

1. Targeted Policy (default)

   • Focuses on a specific set of processes and services.
   • Most commonly used in general-purpose systems.
   • Allows most user applications to run without restrictions.

2. Strict Policy

   • Applies SELinux rules to all processes, enforcing comprehensive system-wide security.
   • More suitable for high-security environments but requires extensive configuration and maintenance.

3. MLS (Multi-Level Security) Policy

   • Designed for systems that require hierarchical classification of data (e.g., military or government).
   • Complex and rarely used outside highly specialized environments.

Checking the Current SELinux Policy Type

Before making changes, verify the active SELinux policy type on your system.

Method 1: Using sestatus

Run the following command to check the current policy type:

sestatus

The output will include:

• SELinux status: Enabled or disabled.
• Loaded policy name: The currently active policy type (e.g., targeted).

Method 2: Checking the Configuration File

The SELinux policy type is defined in the /etc/selinux/config file. To view it, use:

cat /etc/selinux/config

Look for the SELINUXTYPE parameter:

SELINUXTYPE=targeted

Installing SELinux Policies

Not all SELinux policy types may be pre-installed on your AlmaLinux system. If you need to switch to a different policy type, ensure it is available.

Step 1: Check Installed Policies

List installed SELinux policies using the following command:

ls /etc/selinux/

You should see directories like targeted, mls, or strict.

Step 2: Install Additional Policies

If the desired policy type isn’t available, install it using dnf. For example, to install the strict policy:

sudo dnf install selinux-policy-strict

For the MLS policy:

sudo dnf install selinux-policy-mls

Switching SELinux Policy Types

To change the SELinux policy type, follow these steps:

Step 1: Backup the Configuration File

Before making changes, create a backup of the SELinux configuration file:

sudo cp /etc/selinux/config /etc/selinux/config.bak

Step 2: Modify the Configuration File

Edit the SELinux configuration file using a text editor:

sudo nano /etc/selinux/config

Locate the line defining the policy type:

SELINUXTYPE=targeted

Change the value to your desired policy type (e.g., strict or mls).

Example:

SELINUXTYPE=strict

Save and exit the editor.

Step 3: Rebuild the SELinux Policy

Switching policy types requires relabeling the filesystem to align with the new policy. This process updates file security contexts.

To initiate a full relabeling, create an empty file named .autorelabel in the root directory:

sudo touch /.autorelabel

Step 4: Reboot the System

Reboot your system to apply the changes and perform the relabeling:

sudo reboot

The relabeling process may take some time, depending on your filesystem size.

Testing SELinux Policy Changes

Step 1: Verify the Active Policy

After the system reboots, confirm the new policy type is active:

sestatus

The Loaded policy name should reflect your chosen policy (e.g., strict or mls).

Step 2: Test Applications and Services

• Ensure that critical applications and services function as expected.
• Check SELinux logs for policy violations in /var/log/audit/audit.log.

Step 3: Troubleshoot Denials

Use the ausearch and audit2why tools to analyze and address SELinux denials:

sudo ausearch -m avc
sudo ausearch -m avc | audit2why

If necessary, create custom SELinux policies to allow blocked actions.

Common Use Cases for SELinux Policies

1. Targeted Policy (Default)

• Best suited for general-purpose servers and desktops.
• Focuses on securing high-risk services like web servers, databases, and SSH.
• Minimal configuration required.

2. Strict Policy

• Ideal for environments requiring comprehensive security.
• Enforces MAC on all processes and users.
• Requires careful testing and fine-tuning to avoid disruptions.

3. MLS Policy

• Suitable for systems managing classified or sensitive data.
• Enforces hierarchical data access based on security labels.
• Typically used in government, military, or defense applications.

Creating Custom SELinux Policies

If standard SELinux policies are too restrictive or insufficient for your needs, you can create custom policies.

Step 1: Identify Denials

Generate and analyze logs for denied actions:

sudo ausearch -m avc | audit2allow -m custom_policy

Step 2: Create a Custom Policy

Compile the suggested rules into a custom policy module:

sudo ausearch -m avc | audit2allow -M custom_policy

Step 3: Load the Custom Policy

Load the custom policy module:

sudo semodule -i custom_policy.pp

Step 4: Test the Custom Policy

Verify that the custom policy resolves the issue without introducing new problems.

Best Practices for Configuring SELinux Policies

1. Understand Your Requirements
   Choose a policy type that aligns with your system’s security needs.

   • Use targeted for simplicity.
   • Use strict for high-security environments.
   • Use mls for classified systems.

2. Test Before Deployment

   • Test new policy types in a staging environment.
   • Run applications and services in Permissive mode to identify issues before enforcing policies.

3. Monitor Logs Regularly
   Regularly review SELinux logs to detect and address potential violations.

4. Create Granular Policies
   Use tools like audit2allow to create custom policies that cater to specific needs without weakening security.

5. Avoid Disabling SELinux
   Disabling SELinux reduces your system’s security posture. Configure or adjust policies instead.

Troubleshooting Policy Type Configuration

Issue 1: Application Fails to Start

• Check SELinux logs for denial messages:

  sudo ausearch -m avc
  

• Address denials by adjusting contexts or creating custom policies.

Issue 2: Relabeling Takes Too Long

• Relabeling time depends on filesystem size. To minimize downtime, perform relabeling during off-peak hours.

Issue 3: Policy Conflicts

• Ensure only one policy type is installed to avoid conflicts.

Conclusion

Configuring SELinux policy types on AlmaLinux is a powerful way to control how your system enforces security rules. By selecting the right policy type, testing thoroughly, and leveraging tools like audit2allow, you can create a secure, tailored environment that meets your needs.

Whether you’re securing a general-purpose server, implementing strict system-wide controls, or managing sensitive data classifications, SELinux policies provide the flexibility and granularity needed to protect your system effectively.

Need assistance with advanced SELinux configurations or custom policy creation? Let us know, and we’ll guide you to the best practices!