SELinux in Android: Security Guide

SELinux, short for Security-Enhanced Linux, is a security mechanism based on the Linux kernel that employs Mandatory Access Control (MAC) policies to restrict process privileges.

In Android, SELinux is utilized to provide an additional layer of security to shield the system from the impact of malicious apps and attacks. Its main functions include:

1. Mandatory Access Control: SELinux restricts applications’ access to system resources (such as files, devices, and networks) by defining access policies and rules. For example, it can restrict an application to only access specific directories or files while preventing access to other sensitive information.
2. Process isolation: SELinux can separate different applications, services, and system components to restrict their interactions, preventing malicious apps from gaining system permissions by attacking other processes or services.
3. Vulnerability restrictions: SELinux can limit application permissions to minimize the potential impact of vulnerabilities on the system. Even if an application has vulnerabilities, attackers cannot gain additional system privileges.

In the Android system, SELinux is by default in Enforcing mode, restricting all applications. Developers can use SELinux policy files (sepolicy) to define and modify access control rules, and adjust application permissions. However, modifying SELinux policy should be done with great caution to avoid compromising the security and stability of the system.