Book Image

SELinux System Administration, Third Edition - Third Edition

By : Sven Vermeulen
Book Image

SELinux System Administration, Third Edition - Third Edition

By: Sven Vermeulen

Overview of this book

Linux is a dominant player in many organizations and in the cloud. Securing the Linux environment is extremely important for any organization, and Security-Enhanced Linux (SELinux) acts as an additional layer to Linux system security. SELinux System Administration covers basic SELinux concepts and shows you how to enhance Linux system protection measures. You will get to grips with SELinux and understand how it is integrated. As you progress, you’ll get hands-on experience of tuning and configuring SELinux and integrating it into day-to-day administration tasks such as user management, network management, and application maintenance. Platforms such as Kubernetes, system services like systemd, and virtualization solutions like libvirt and Xen, all of which offer SELinux-specific controls, will be explained effectively so that you understand how to apply and configure SELinux within these applications. If applications do not exert the expected behavior, you’ll learn how to fine-tune policies to securely host these applications. In case no policies exist, the book will guide you through developing custom policies on your own. By the end of this Linux book, you’ll be able to harden any Linux system using SELinux to suit your needs and fine-tune existing policies and develop custom ones to protect any app and service running on your Linux systems.
Table of Contents (22 chapters)
1
Section 1: Using SELinux
8
Section 2: SELinux-Aware Platforms
14
Section 3: Policy Management

SELinux file context expressions

When we think that the context of a file is wrong, we need to correct the context. SELinux offers several methods to do so, and some distributions even add in more. We can use tools such as chcon, restorecon (together with semanage), setfiles, rlpkg (Gentoo), and fixfiles. Of course, we could also use the setfattr command, but that would be the least user-friendly approach for setting contexts.

Let's see how we can set context expressions in a more manageable way.

Using context expressions

In the SELinux policy, a list of regular expressions is kept that informs the SELinux utilities and libraries what the context of a file (or other filesystem resource) should be. Though this expression list is not enforced on the system directly, administrators and SELinux utilities use it to see whether a context is correct, and to reset contexts to what they are supposed to be. You can find the list itself in /etc/selinux/targeted/contexts/files in...