avc_has_perm - Linux

Overview

avc_has_perm is a versatile command for inspecting the access vector cache (AVC) and determining whether a specific process has the necessary permissions to perform an action. It’s especially useful for administrators and developers working with SELinux-based systems to troubleshoot security policies and identify potential access issues.

Syntax

avc_has_perm SUBJECT SID CLASS PERMISSION [FLAGS]

Options/Flags

• -c: Print the AVC context in human-readable format.
• -r: Print the raw AVC decision in numerical format.
• -v: Verbose output, providing additional details about the AVC check.
• -p: Print all permissions that the subject has for the given class.
• -P: Print all permissions that are available for the given class.
• -t: Run the check in test mode, which simulates the check without actually granting access.

Examples

Example 1: Check if the httpd process has read access to the /var/www/html directory:

avc_has_perm httpd httpd_t httpd_sys_content_t read

Example 2: Print all permissions available for the httpd_sys_content_t class:

avc_has_perm -P httpd_t httpd_sys_content_t

Example 3: Run the check in test mode and print the raw AVC decision:

avc_has_perm -t -r httpd httpd_t httpd_sys_content_t read

Common Issues

• Ensure that the SELinux policy is loaded and active.
• Verify that the subject and class specified in the command correspond to the security context and object type being checked.
• If the check fails, examine the output for additional information about the denial reason.

Integration

avc_has_perm can be combined with other Linux commands to automate tasks and diagnose access issues. For example, it can be used with awk to extract specific fields from the output or with grep to filter results.

Related Commands

• getsebool: Manage SELinux boolean settings.
• semanage: Configure SELinux policy settings.
• chcon: Change file or directory security context.