audit2why

The audit2why command is part of the policycoreutils package in SELinux, designed to provide explanations for why specific access denials occurred according to the SELinux policy. It helps administrators understand the reasons behind denied access and offers guidance on potential solutions. This tool is particularly useful for troubleshooting SELinux denials by translating audit messages into a more understandable format.

Purpose of audit2why

The main purposes of audit2why are to:

• Analyze SELinux audit logs to explain why access was denied.

• Provide human-readable explanations for SELinux denials.

• Suggest potential solutions or adjustments to the SELinux policy.

Key Features and Functionality

1. Explanation of Denials: Translates SELinux audit logs into understandable explanations, detailing the reason behind each denial.

2. Policy Adjustment Suggestions: Offers suggestions on how to modify the SELinux policy to prevent future denials, including changes to policies or Boolean settings.

3. Integration with ausearch: Often used in conjunction with the ausearch command to filter relevant SELinux denial messages from the audit logs.

Usage

To use audit2why, you typically need SELinux audit messages as input. These messages can be obtained from audit logs using tools like ausearch. Here’s how you can use audit2why effectively:

1. Get Denial Messages with ausearch: Use ausearch to search for SELinux denial messages in the audit logs.

2. Pipe Output to audit2why: Pipe the output of ausearch to audit2why for explanations.

Example Commands

Example 1: Basic Usage

ausearch -m avc -ts recent | audit2why

This command searches for recent SELinux denials (-m avc -ts recent) and pipes the results to audit2why.

Example 2: Specific Denial Explanation

ausearch -m avc -c httpd | audit2why

This command filters audit logs for AVC denials related to the httpd process and then pipes the results to audit2why for explanations.

Example 3: Using a Log File

cat /var/log/audit/audit.log | audit2why

This command reads the audit log file and pipes its contents to audit2why.

Example Output

Running audit2why might produce output similar to the following:

type=AVC msg=audit(1623677883.123:567): avc:  denied  { read } for  pid=1234 comm="httpd" name="config" dev="sda1" ino=45678 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:httpd_config_t:s0 tclass=file

Was caused by:
    Missing type enforcement (TE) allow rule.

    You can use audit2allow to generate a loadable module to allow this access.

Explanation of Output

• Audit Message: Shows the original SELinux denial message from the audit log.

• Explanation: Provides a human-readable explanation for the denial, indicating the missing rules or contexts.

• Suggestion: Often includes a suggestion to use audit2allow to create a policy module that permits the denied access.

Benefits

• Troubleshooting: Simplifies the process of understanding SELinux denials, making it easier to troubleshoot access issues.

• Policy Management: Helps administrators make informed decisions about policy adjustments to accommodate legitimate access needs.

• User-Friendly: Converts complex audit log entries into readable explanations, making SELinux more accessible to users.

Security Considerations

• Careful Policy Changes: Use the suggestions from audit2why judiciously. Always review and understand the implications of modifying SELinux policies before applying changes.

• Audit Regularly: Regularly monitor and analyze SELinux audit logs to maintain a secure system configuration.

Conclusion

The audit2why command is a valuable tool for administrators working with SELinux. It helps explain the reasons behind access denials and offers suggestions for resolving these issues. By using audit2why, administrators can effectively troubleshoot and manage SELinux policies, ensuring that legitimate access is permitted while maintaining the security of the system.