FreeBSD implements and manages mandatory access controls (MAC) using the TrustedBSD MAC Framework. The framework provides a flexible and extensible architecture for enhancing system security by enforcing various security policies. Here is an overview of how FreeBSD implements and manages MAC:
Framework Overview
The TrustedBSD MAC Framework is a security extension for FreeBSD that allows for the implementation of various MAC policies. This framework provides hooks at critical points in the operating system to enforce access control decisions made by different MAC modules.
MAC Policies
MAC policies are modules that define specific rules for access control. FreeBSD includes several built-in MAC policies, and administrators can enable or disable these policies as needed. Some common policies include:
mac_biba: Implements the Biba integrity model.
mac_mls: Implements the Multi-Level Security (MLS) model.
mac_portacl: Controls access to binding to privileged ports.
mac_partition: Restricts inter-process communication and file access within partitions.
Kernel Hooks
The MAC Framework provides a set of hooks in the kernel at various points where security decisions need to be made. These hooks allow MAC policies to inspect and modify the behavior of system calls, file operations, inter-process communication, and network activity.
Policy Enforcement
When a policy is loaded into the system, it registers callbacks for the various hooks provided by the MAC Framework. These callbacks contain the logic for enforcing the policy's rules. For example, a MAC policy can inspect the credentials of a process attempting to open a file and decide whether to allow or deny the operation based on the policy's rules.
Configuration and Management
Loading and Unloading Policies: Policies can be loaded and unloaded at runtime using the `kldload` and `kldunload` commands.
Configuration Files: Policies can be configured through `/etc/rc.conf` and specific configuration files for individual policies, often found in `/etc/mac.conf` or other policy-specific files.
sysctl Interface: The `sysctl` interface allows administrators to tune various aspects of the MAC Framework and individual policies at runtime. This includes enabling or disabling specific policies and adjusting their parameters.
Policy Labels
MAC policies can assign labels to objects (e.g., files, processes) that are used in making access control decisions. These labels store metadata that policies use to enforce rules. For example, a label might indicate the sensitivity level of a file under the MLS policy.
Integration with Base System
The MAC Framework is integrated into the FreeBSD base system, meaning it is available out-of-the-box and can be configured and used without needing additional third-party software. This integration ensures that the MAC Framework is consistently maintained and updated along with the rest of the operating system.
Security Auditing
FreeBSD's audit framework can be used alongside the MAC Framework to log security-relevant events. This auditing capability helps administrators monitor the effectiveness of MAC policies and investigate potential security incidents.
Example Commands
Enable a MAC Policy:
kldload mac_biba
Disable a MAC Policy:
kldunload mac_biba
View MAC Framework Settings:
sysctl security.mac
Configure a Policy:
Add to `/etc/rc.conf`:
mac_biba_load="YES"
By leveraging the MAC Framework, FreeBSD provides a robust and flexible mechanism for implementing mandatory access controls, allowing administrators to enforce stringent security policies tailored to their specific requirements.
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