Book Image

SELinux System Administration. - Second Edition

Book Image

SELinux System Administration. - Second Edition

Overview of this book

Do you have the crucial job of protecting your private and company systems from malicious attacks and undefined application behavior? Are you looking to secure your Linux systems with improved access controls? Look no further, intrepid administrator! This book will show you how to enhance your system’s secure state across Linux distributions, helping you keep application vulnerabilities at bay. This book covers the core SELinux concepts and shows you how to leverage SELinux to improve the protection measures of a Linux system. You will learn the SELinux fundamentals and all of SELinux’s configuration handles including conditional policies, constraints, policy types, and audit capabilities. These topics are paired with genuine examples of situations and issues you may come across as an administrator. In addition, you will learn how to further harden the virtualization offering of both libvirt (sVirt) and Docker through SELinux. By the end of the book you will know how SELinux works and how you can tune it to meet your needs.
Table of Contents (16 chapters)
SELinux System Administration - Second Edition
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface

Replacing existing policies


When adding custom SELinux policies, all that users can do is to add more allow rules. SELinux does not have a deny rule that can be used to remove currently allowed access rules from the active policy.

If the current policy is too permissive to the administrator's liking, then the administrator will need to update the policy rather than just enhance it. And that implies that the administrator has access to the current SELinux policy rules used.

Replacing existing policies depends on the SELinux user space utilities (the more recent one supports priority-based loading) and the source of the current policy. Let's look at two approaches: one for RHEL and another for Gentoo Linux.

Replacing RHEL policies

To replace an active Red Hat policy, we need to download the source RPM of the SELinux policy package and use the rpmbuild application to extract the files. Once extracted, we update the policy files, rebuild them, and then install them on the system.

First, find out...