How to Config Security-Enhanced Linux (SELinux) Policies

Security-Enhanced Linux (SELinux) is a Linux kernel security module that provides a mechanism for supporting access control security policies, including mandatory access controls (MAC). SELinux is a set of kernel modifications and user-space tools that have been added to various Linux distributions. It was originally developed by NASA.

Table of Contents

  1. Install Packages
  2. Context Types
  3. Create Policies
  4. Apply Policies
  5. Semanage vs Chcon

Install Packages

At first, we need to ensure that we’ve installed semanage. The semanage command is used to change the SELinux context of a file or directory persistently. The policycoreutils-python package contains semanage.

# CentOS 7
sudo yum install -y policycoreutils-python

# CentOS 8
sudo dnf install -y policycoreutils-python-utils

# Ubuntu
sudo apt install -y policycoreutils-python-utils

For troubleshooting SELinux issues, we’re going to install another package. It’s optional to install:

 # CentOS
sudo yum install -y setroubleshoot

# Ubuntu
sudo apt install -y setroubleshoot

Context Types

Run this command to see all context types for Apache:

man httpd_selinux

See existing policies:

semanage fcontext -l

These 4 are common types:

httpd_sys_content_tRead-only directories and files
httpd_sys_rw_content_tReadable & writable directories and files
httpd_log_tAssign to logs directory
httpd_cache_tAssign to caches directory

Create Policies

May applications like WordPress require to assign policies. To assign httpd_sys_content_t context to the /var/www/ directory, child directories and files:

semanage fcontext -a -t httpd_sys_content_t '/var/www/*)?'

To assign httpd_sys_rw_content_t context to the /var/www/ directory, child directories and files:

semanage fcontext -a -t httpd_sys_rw_content_t '/var/www/*)?'

Assign httpd_log_t to logs directories:

semanage fcontext -a -t httpd_log_t '/var/www/*)?'

Assign httpd_cache_t to logs directories:

semanage fcontext -a -t httpd_cache_t '/var/www/*)?'

Apply Policies

We’ve created our policies. Now we need to  apply the context changes by running this command:

sudo restorecon -R -v /var/www/

After changing any context, we need to re-apply the context changes. We can verify our context types:

ls -lZ /var/www/

Semanage vs Chcon

Like semanage, we can change the SElinux context for files using chcon. Chcon temporarily changes the context of files where semanage changes persistently. Here are some examples:

sudo chcon -t httpd_sys_rw_content_t -R /var/www/
sudo chcon -t httpd_log_t -R /var/www/
sudo chcon -t httpd_cache_t -R /var/www/

# Apply on single file
sudo chcon -t httpd_sys_rw_content_t /var/www/

That’s it. Thanks for reading.