Do you know SELinux in Android?

Introduction to SELinux

SELinux (Security-Enhanced Linux) is a security-enhanced Linux operating system that provides a higher level of system security protection through the mandatory access control (MAC) mechanism. Compared with the traditional Linux access control mechanism (DAC), SELinux provides more fine-grained access control and can perform more sophisticated permission control on each process and file.

The core idea of ​​SELinux is policy-based mandatory access control. It uses security policies to define access rules for various objects in the system (such as processes, files, network ports, etc.). Only access behaviors that comply with the policy regulations are allowed. This policy mechanism can prevent the spread of malicious programs and illegal access to system resources.

SELinux policies are implemented through labels. Each object has a unique label, including processes, files, network ports , etc. SELinux uses labels to determine the access rights between objects. Only when the label matches the access rules specified by the policy can the corresponding operation be performed.

The advantage of SELinux is that it can provide a higher level of system security protection. Through fine-grained access control, SELinux can limit the permissions of processes and prevent the spread of malicious programs. At the same time, SELinux can also protect system resources to prevent illegal access and tampering. This makes SELinux an important security enhancement tool and is widely used in systems that require high-level security protection.

In Android, SELinux implements more fine-grained permission management by marking and controlling access to processes and file systems. It can limit application permissions and prevent malicious applications from abusing system resources. Through SELinux, Android can implement application sandboxing, so that each application runs in an independent security environment and cannot access each other's data and resources.

SELinux in Android works by assigning a security context to each process and file system object and defining a series of rules to control access between objects. These rules are based on the security context of the object and determine the operations that the object can perform and the resources it can access.

Using SELinux can improve the security of the Android system and prevent attacks and abuse by malicious applications. However, due to the complexity of SELinux, it may bring some challenges to developers and requires careful configuration and management.

SELinux Mode

1. Enforcing mode: In this mode, SELinux will enforce security policies, deny any operations that violate the policy, and generate corresponding logs. This is the default SELinux mode, which provides the highest level of security protection.
2. Permissive mode: In this mode, SELinux will log operations that violate the policy but will not deny them. This mode is mainly used for debugging and troubleshooting, and can help system administrators understand which operations will violate SELinux policies.
3. Disabled mode: In this mode, SELinux is completely disabled and will not provide any security protection for the system. This mode is mainly used for testing or special needs, but is not recommended for use in production environments.

To change the SELinux mode, you can use the command line tools semanage or setenforce.

In Android, you can set the SELinux mode by following the steps below:

1. First, make sure your device has root permissions.
2. Open a terminal or use the ADB command line to connect to your device.
3. Enter the following command to view the current SELinux mode:

 getenforce

4. If the output result is "Enforcing", it means SELinux is currently in enforcing mode. If the output result is "Permissive", it means SELinux is currently in permissive mode.
5. If you want to set SELinux mode to permissive mode, you can use the following command:

 setenforce 0

6. If you want to set SELinux mode to enforcing mode, you can use the following command:

 setenforce 1

Please note that changing the SELinux mode may affect the security of the device. Please operate with caution. The SELinux mode will return to Enforcing after restarting.

Version evolution

SELinux is used to enhance system security. It was first developed by the National Security Agency (NSA) of the United States and later introduced into the Android system by Google. SELinux in the Android system has undergone the following evolutions:

1. Android 4.3 and earlier versions: In these earlier versions, SELinux is in "permissive" mode by default, which only logs violations but does not block them. This is because in earlier versions, many applications and system services have not been adapted to SELinux policies, and directly enabling "enforcing" mode may cause system instability.
2. Android 4.4 and later: Starting from Android 4.4, SELinux is in "enforcing" mode by default, which means that access control policies are enforced. This means that all applications and system services must comply with SELinux policies, otherwise they will be blocked from accessing sensitive resources.
3. Android 6.0 and later versions: Starting from Android 6.0, Google introduced more fine-grained SELinux policies to further improve system security. These policies include stricter application sandbox restrictions, more precise permission control, etc.

In general, the evolution of SELinux in Android is to improve the security and stability of the system. Through mandatory access control, SELinux can limit the permissions of applications and system services to prevent malicious behavior and attacks. At the same time, with the upgrade of the version, SELinux policies are constantly improved to adapt to the ever-changing security threats.