Book Image

SELinux System Administration

By : Sven Vermeulen
Book Image

SELinux System Administration

By: Sven Vermeulen

Overview of this book

NSA Security-Enhanced Linux (SELinux) is a set of patches and added utilities to the Linux kernel to incorporate a strong, flexible, mandatory access control architecture into the major subsystems of the kernel. With its fine-grained yet flexible approach, it is no wonder Linux distributions are firing up SELinux as a default security measure. SELinux System Administration covers the majority of SELinux features through a mix of real-life scenarios, descriptions, and examples. Everything an administrator needs to further tune SELinux to suit their needs are present in this book. This book touches on various SELinux topics, guiding you through the configuration of SELinux contexts, definitions, and the assignment of SELinux roles, and finishes up with policy enhancements. All of SELinux's configuration handles, be they conditional policies, constraints, policy types, or audit capabilities, are covered in this book with genuine examples that administrators might come across. By the end, SELinux System Administration will have taught you how to configure your Linux system to be more secure, powered by a formidable mandatory access control.
Table of Contents (13 chapters)

Reading and changing file contexts


Let us immediately start off with an example here: a web server hosting dokuwiki, a popular PHP wiki site that uses files rather than a database as its backend system.

Getting context information

The application is hosted at /var/www/localhost/htdocs/dokuwiki and stores its wiki pages (user content) in subdirectories of the data/ directory. Getting the contexts of files can easily be accomplished using the -Z option to ls. Most utilities that are able to provide feedback on contexts will try to do so using the -Z option, as we saw already with the id and ps utilities. Let's look at the context of the dokuwiki directory itself:

# ls -lZ /var/www/localhost/htdocs
drwxr-xr-x. 1 root root root:object_r:httpd_sys_content_t 45 May  9 20:05 dokuwiki

File and directory contexts are stored on the filesystem as extended attributes when the filesystem supports this. If not, the context of the files is usually defined by the mounted filesystem type or its mount options...