Creating SELinux policies
by Uday R. Sawant, William Leemans, Jonathan Hobson, Oliver Pelz
Linux: Powerful Server Administration
- Linux: Powerful Server Administration
- Table of Contents
- Linux: Powerful Server Administration
- Linux: Powerful Server Administration
- Credits
- Preface
- 1. Module 1
- 1. Managing Users and Groups
- 2. Networking
- Introduction
- Connecting to a network with a static IP
- Installing the DHCP server
- Installing the DNS server
- Hiding behind the proxy with squid
- Being on time with NTP
- Discussing load balancing with HAProxy
- Tuning the TCP stack
- Troubleshooting network connectivity
- Securing remote access with OpenVPN
- Securing a network with uncomplicated firewall
- Securing against brute force attacks
- Discussing Ubuntu security best practices
- 3. Working with Web Servers
- Introduction
- Installing and configuring the Apache web server
- Serving dynamic contents with PHP
- Hosting multiple websites with a virtual domain
- Securing web traffic with HTTPS
- Installing Nginx with PHP_FPM
- Setting Nginx as a reverse proxy
- Load balancing with Nginx
- Setting HTTPs on Nginx
- Benchmarking and performance tuning of Apache
- Securing the web server
- Troubleshooting the web server
- 4. Working with Mail Servers
- 5. Handling Databases
- Introduction
- Installing relational databases with MySQL
- Storing and retrieving data with MySQL
- Importing and exporting bulk data
- Adding users and assigning access rights
- Installing web access for MySQL
- Setting backups
- Optimizing MySQL performance – queries
- Optimizing MySQL performance – configuration
- Creating MySQL replicas for scaling and high availability
- Troubleshooting MySQL
- Installing MongoDB
- Storing and retrieving data with MongoDB
- 6. Network Storage
- 7. Cloud Computing
- 8. Working with Containers
- Introduction
- Installing LXD, the Linux container daemon
- Deploying your first container with LXD
- Managing LXD containers
- Managing LXD containers – advanced options
- Setting resource limits on LXD containers
- Networking with LXD
- Installing Docker
- Starting and managing Docker containers
- Creating images with a Dockerfile
- Understanding Docker volumes
- Deploying WordPress using a Docker network
- Monitoring Docker containers
- Securing Docker containers
- 9. Streaming with Ampache
- 10. Communication Server with XMPP
- 11. Git Hosting
- Introduction
- Installing Git
- Creating a local repository with Git CLI
- Storing file revisions with Git commit
- Synchronizing the repository with a remote server
- Receiving updates with Git pull
- Creating repository clones
- Installing GitLab, your own Git hosting
- Adding users to the GitLab server
- Creating a repository with GitLab
- Automating common tasks with Git hooks
- 12. Collaboration Tools
- 13. Performance Monitoring
- 14. Centralized Authentication Service
- 2. Module 2
- 1. Installing CentOS
- Introduction
- Downloading CentOS and confirming the checksum on Windows or OS X
- Creating USB installation media on Windows or OS X
- Performing an installation of CentOS using the graphical installer
- Running a netinstall over HTTP
- Installing CentOS 7 using a kickstart file
- Getting started and customising the boot loader
- Troubleshooting the system in rescue mode
- Updating the installation and enhancing the minimal install with additional administration and development tools
- 2. Configuring the System
- Introduction
- Navigating text files with less
- Introduction to Vim
- Speaking the right language
- Synchronizing the system clock with NTP and the chrony suite
- Setting your hostname and resolving the network
- Building a static network connection
- Becoming a superuser
- Customizing your system banners and messages
- Priming the kernel
- 3. Managing the System
- Introduction
- Knowing and managing your background services
- Troubleshooting background services
- Tracking system resources with journald
- Configuring journald to make it persistent
- Managing users and their groups
- Scheduling tasks with cron
- Synchronizing files and doing more with rsync
- Maintaining backups and taking snapshots
- Monitoring important server infrastructure
- Taking control with GIT and Subversion
- 4. Managing Packages with YUM
- 5. Administering the Filesystem
- 6. Providing Security
- 7. Building a Network
- 8. Working with FTP
- 9. Working with Domains
- 10. Working with Databases
- 11. Providing Mail Services
- 12. Providing Web Services
- 13. Operating System-Level Virtualization
- 14. Working with SELinux
- 15. Monitoring IT Infrastructure
- 1. Installing CentOS
- 3. Module 3
- 1. Working with KVM Guests
- 2. Deploying RHEL "En Masse"
- 3. Configuring Your Network
- 4. Configuring Your New System
- 5. Using SELinux
- 6. Orchestrating with Ansible
- 7. Puppet Configuration Management
- 8. Yum and Repositories
- 9. Securing RHEL 7
- 10. Monitoring and Performance Tuning
- Bibliography
- Index
In some cases, you'll need to create a new SELinux policy—for instance, when installing a piece of software from source. Although I do not recommend installing software from source on enterprise systems, this is sometimes your only option for company-developed software.
It is then time to create your own SELinux policy.
We'll use the denied entries in the audit.log log file to build our SELinux policy with audit2allow.
In this recipe, we'll use the same example as in the previous recipe: the SELinux context of /var/www/html/index.html that is changed to system_u:object_r:user_home_t:s0. Perform the following steps:
- First, create a human readable policy for verification via the following command:
~# egrep 'avc.*denied' /var/log/audit/audit.log |audit2allow -m example_policy module example_policy 1.0; require { type httpd_t; type user_home_t; class file { read open }; } #============= httpd_t ============== #!!!! This avc can be allowed using the boolean 'httpd_read_user_content' allow httpd_t user_home_t:file { read open }; ~#
- When this policy is validated, you can create a compiled SELinux policy file, as follows:
egrep 'avc.*denied' /var/log/audit/audit.log |audit2allow -M example_policy ******************** IMPORTANT *********************** To make this policy package active, execute: semodule -i example_policy.pp ~#
When you generate a module package, two files are created: a type enforcement file (.te) and a policy package file (.pp) file. The te file is the human readable policy as generated using audit2allow -m.
The pp file is the SELinux policy module package, which will later be used to enable the new policy.
If you believe you have discovered a bug in an existing SELinux policy, you'll need to produce a type enforcing and policy package file to report with Red Hat Bugzilla.
It's important to make sure that you only parse the correct AVC denial entries with audit2allow as it may result in more access than required. It's a good idea to pipe the AVC denial entries to a temporary file and remove what is not needed before you parse the file with audit2allow.
If the policy you generate in this way is not exactly what you need, you can always edit the generated te policy file, and when you're done, compile a new policy file using the te policy file. You can do this as follows:
- Build a binary policy module out of the policy file through this command:
~# checkmodule -M -m -o example_policy.mod example_policy.te checkmodule: loading policy configuration from example_policy.te checkmodule: policy configuration loaded checkmodule: writing binary representation (version 17) to example_policy.mod ~#
- Create the SELinux policy module package by executing the following:
~# semodule_package -o example_policy.pp -m example_policy.mod ~#
Take a look at the man page for audit2allow(1) for more options on creating a policy
To report bugs, go to https://bugzilla.redhat.com/.
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