SELinux and Mandatory Access Control

SELinux and Mandatory Access Control

Security-Enhanced Linux (SELinux) implements mandatory access control (MAC), adding an additional layer of security beyond traditional DAC. Developed by the NSA and integrated into mainstream Linux distributions, SELinux enforces security policies that even root cannot override. This approach significantly limits damage from compromised processes or malicious users.

SELinux operates through security contexts assigned to every process, file, and system resource. These contexts consist of user, role, type, and optional level components, forming security labels that determine access permissions. Type Enforcement (TE) represents the primary SELinux mechanism, defining which process types can access which file types, regardless of traditional permissions.

Policy development in SELinux requires understanding both the security model and specific application requirements. The reference policy provides a comprehensive starting point, with modules for common applications and services. Administrators can customize policies through boolean settings, local modifications, or custom policy modules. Tools like audit2allow help create policy rules based on observed denials, streamlining policy development.

SELinux modes provide flexibility during implementation and troubleshooting. Enforcing mode actively blocks policy violations, while permissive mode logs violations without blocking access. Disabled mode completely deactivates SELinux. Most production systems should run in enforcing mode, using permissive mode only for policy development and troubleshooting. Proper SELinux implementation significantly enhances system security without impacting legitimate operations.