• 👉 Overview
• 👀 What ?
• 🧐 Why ?
• ⛏️ How ?
• ⏳ When ?
• ⚙️ Technical Explanations
• 🖇️ References

👉 Overview

👀 What ?

SELinux, or Security-Enhanced Linux, is a security module that provides a means to enforce access control security policies. When combined with containers, it offers additional layers of security to your containerized applications.

🧐 Why ?

The relevance of SELinux in containers is essential because it provides a robust framework for managing access control policies. It helps in mitigating or preventing the impact of security breaches by restricting the capabilities of a compromised container. This is crucial, especially in today's age where cyber threats are evolving at an alarming rate.

⛏️ How ?

To leverage the benefits of SELinux in containers, you first need to understand the SELinux policy and labeling system. You can implement SELinux by enabling it in your Linux distribution, and then assigning the appropriate SELinux context to your containers. This context defines the set of rules that control the actions that the container can perform. Make sure to test the policies in a non-production environment before applying them to your production systems.

⏳ When ?

The usage of SELinux in containers started becoming mainstream with the rise of container technologies like Docker and Kubernetes around the mid-2010s. While SELinux itself was introduced by the National Security Agency (NSA) in the early 2000s, its applicability to containers has gained prominence recently due to the widespread adoption of containerization.

⚙️ Technical Explanations

SELinux, or Security-Enhanced Linux, is a security module that aids in the enforcement of access control security policies. It operates on the principle of 'least privilege', which means it only provides the minimum privileges required for a process or system object to function. This approach significantly limits the potential damage that could occur if a process is compromised.

In the context of containerized applications, SELinux provides an added layer of security. It assigns a unique SELinux context to each container. This context is then inherited by all the processes running inside that container. The context consists of a set of rules that control what actions these processes can perform. This setup effectively isolates each container from the rest of the system, adding an additional layer of security.

For example, a process inside a container is unable to read or write to files outside its context unless explicitly permitted by the access control policy. This restriction prevents a compromised container from affecting the host system or other containers, thereby mitigating the potential impact of a security breach.

To use SELinux effectively with containers, it’s essential to understand the SELinux policy and labeling system. These policies can be implemented by enabling SELinux in your Linux distribution and then assigning the appropriate SELinux context to your containers. It's always recommended to test these policies in a non-production environment before deploying them in a production system.

The use of SELinux with containers has gained prominence with the rise of container technologies, such as Docker and Kubernetes, around the mid-2010s. While SELinux itself was introduced by the National Security Agency (NSA) in the early 2000s, its application to containers has become increasingly important due to the widespread adoption of containerization in modern software development and deployment practices.

A real-world example of using SELinux with containers could be deploying a web server within a Docker container.

1. Enable SELinux in your Linux distribution: This is typically done by modifying the /etc/selinux/config file and setting SELINUX=enforcing.

sudo nano /etc/selinux/config

Change SELINUX to enforcing and save the file. Then, reboot your system.

2. Create a Docker container: In this case, we'll create a Docker container running an Apache web server.

docker run -d --name myApacheServer httpd:latest

This command runs a Docker container in detached mode, names it "myApacheServer", and uses the latest version of the Apache image.

3. Set the SELinux context: By default, Docker applies a specific SELinux context to the containers it creates. You can check the context by running:

docker inspect --format '{{ .ProcessLabel }}' myApacheServer

This command will return the SELinux context of the running container.

4. Apply SELinux policies: You can apply a custom policy to your container by creating a policy file. Here's an example of a basic policy file:

module httpd_custom 1.0;

require {
    type httpd_t;
    class dir { getattr search open read };
    class file { getattr open read };
}

#============= httpd_t ==============
allow httpd_t self:dir { getattr search open read };
allow httpd_t self:file { getattr open read };

This policy allows the httpd_t (apache server) process to read and open files and directories. You can load this policy using the semodule command:

semodule -i httpd_custom.pp

5. Testing: After applying the policy, you should test your container in a non-production environment to ensure everything works as expected.

In this scenario, SELinux provides an additional layer of security by enforcing access controls. If a process inside the container is compromised, the damage it can cause is limited to its own context, protecting the rest of the system and other containers.

🖇️ References