Master the SELinux Policy Categories

SELinux is a security mechanism based on Mandatory Access Control (MAC) that is used to restrict program and user access to system resources. In SELinux, policy types are one of the important concepts used to define and control access rights to objects. This article will introduce the policy types in SELinux and use specific code examples to help readers better understand.

Overview of SELinux policy types

In SELinux, each object (file, process, etc.) has a corresponding type, and policy types are used to define access rules between different types. Policy types are similar to "labels", used to distinguish different objects and determine the relationship between them. Fine-grained access control can be achieved by defining rules that allow or deny access between different policy types.

In SELinux, the common policy types are as follows:

• user_t: used to represent the user type, each user has a corresponding user_t type;
• role_t: used to represent role types, each role has a corresponding role_t type;
• type_t: used to represent object types, such as files, directories, processes, etc.;
• level_t: Used to indicate the security level.

By defining these policy types, you can restrict the access rights of different users or roles to different types of objects, thereby improving the security of the system.

SELinux policy type code example

In order to understand the policy types in SELinux more intuitively, the following is a simple code example. Suppose we want to define a SELinux policy type that restricts a user to only read files in a specific folder.

First, we need to define a type_t type to represent the folder object:

type folder_t;

Then, define a user_t type to represent the user object:

type user_t;

Then, define an allow Rules that allow users of type user_t to only read files in folders of type folder_t:

allow user_t folder_t:file { read };

Finally, load the policy type and make it effective:

semanage boolean -m --on user_folder_readonly

Through the above code example, We defined a policy type that restricts specific users to only read files in specific folders. Through such fine-grained access control, the security of the system can be strengthened to ensure that users can only access their authorized resources.

Summary

Understanding the policy types in SELinux is crucial to system security. By defining and controlling policy types, fine-grained access control can be achieved and the security and stability of the system can be improved. Through the introduction and code examples of this article, I hope readers can have a deeper understanding of the policy types in SELinux and apply them in practice to ensure system security.

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