In this lesson, you will learn how to protect your Mandatory Access Control (MAC) policy files by placing them on encrypted storage, preventing unauthorized offline modification of your security posture.
The Weak Link: Offline Policy Manipulation
While AppArmor profiles are highly effective at restricting what running processes can do, they are typically stored as plain-text files on the root partition (usually in /etc/apparmor.d/). If an attacker gains physical access to the machine or boots into a live environment, they can mount your drive, edit those profiles to remove restrictive rules, and reboot the system with a weakened security policy. To prevent this, we must ensure the storage medium hosting these policies is encrypted.
Implementing Policy-Backed Encryption
The most common approach for "Policy Encrypted Storage" is to isolate sensitive policy files on a dedicated partition or volume encrypted with dm-crypt and LUKS. By moving your policy directory to a protected mount point, you ensure that the security definitions are only accessible to the kernel once the filesystem has been unlocked.
For example, if you move your profiles to a directory managed by an encrypted partition:
# Encrypt the partition meant for policies
cryptsetup luksFormat /dev/sdb1
# Mount the encrypted volume to your policy directory
mount /dev/mapper/policy_storage /etc/apparmor.d/
By ensuring that /etc/apparmor.d/ is a mount point for an encrypted drive, the OS cannot load the policies until the passphrase is provided. If an attacker bypasses the bootloader, they cannot read or write to these profiles, rendering their offline attempts to "loosen" your security model ineffective.
Architectural Considerations
When implementing this, remember that your initramfs must be configured to prompt for the decryption key during the boot sequence. This integrates your MAC strategy with the hardening concepts discussed in previous lessons regarding Securing Initramfs and Early Boot. If the policy storage is not decrypted early, the system might default to an unconfined or insecure state, so ensure your boot orchestration is tightly coupled with your key management system.
Key Takeaway: Moving your security profiles to an encrypted partition prevents attackers from circumventing your MAC policies through offline file modification.