My custom selinux policies seem to be ignored by android system

My custom SELinux policies seem to be ignored by Android system

Custom SELinux policies are a powerful tool for enhancing security on Android devices. However, it can be frustrating when your custom policies seem to be ignored by the system. This article will explore common reasons why this might happen and provide steps to troubleshoot and resolve the issue.

Common Causes and Troubleshooting Steps

Policy Loading Order

SELinux policies are loaded in a specific order. Your custom policy might be overridden by default or system-level policies.

• Check policy loading order: Use seinfo -k to list the loaded policies and their order. This will reveal whether your custom policy is being loaded.

  seinfo -k
  

• Modify policy file names: Prioritize your custom policies by renaming them with a prefix like “99_your_policy.te”. This usually ensures that your policy is loaded after the default ones.

Policy Compilation Issues

Incorrectly compiled policies can lead to them being ignored.

• Verify policy syntax: Use the checkpolicy command to validate your policy file for syntax errors.

  checkpolicy your_policy.te
  

• Ensure proper compilation: After making changes, recompile the policy using the sepolicy tool.

  sepolicy -c your_policy.te 
  

System Configuration

SELinux settings on your device might be interfering with your custom policies.

• Check SELinux mode: Use getenforce to check the current SELinux enforcement mode. If it’s not in enforcing mode (e.g., permissive), your policies won’t be applied.

  getenforce
  

• Set SELinux to enforcing: If necessary, use setenforce 1 to enable enforcing mode.

  setenforce 1
  

Policy Content and Rules

The content of your policy and the rules you’ve defined might be causing the issue.

• Verify policy content: Review your custom policy for potential errors, missing rules, or conflicts with existing rules.
• Use auditd: Enable the auditd service to log SELinux denials. This will help identify potential issues and track access attempts.
• Analyze audit logs: Examine audit logs for any denials that might be related to your custom policies.

Device-Specific Considerations

Android devices have varying SELinux configurations.

• Root access: If your device is rooted, you may need to repackage the system image with your custom policy to make it persistent.
• Custom ROMs: Some custom ROMs might have SELinux settings that are difficult to override. Consider this when applying custom policies.

Troubleshooting Table

Remember that SELinux is a complex system. If you’re experiencing persistent problems, it’s helpful to consult relevant documentation, community forums, or seek expert assistance.