SELinux Infrastructure SOP

SELinux is a fundamental part of our Operating System but still has a large learning curve and remains quite intimidating to both developers and system administrators. Fedora's Infrastructure continues to evolve over time, and tends to be full of custom software that needs to be locked down. The goal of this SOP is to illustrate how to track down and fix SELinux policy related issues within Fedora's Infrastructure.

Fully deploying SELinux is still an ongoing task, and can be tracked in fedora-infrastructure ticket #230.

Contact Information

Owner: Fedora Infrastructure Team

Contact: #fedora-admin, sysadmin-main, sysadmin-web groups

Purpose: To ensure that we are able to fully wield the power of SELinux within our infrastructure.

Step One: Realizing you have a problem

At the moment, we have no easy way to detect SELinux violations across all of our infrastructure. Once the audit/prelude/prewikka IDS stack is fully deployed, this will no longer be an issue, as all violations will be sent as alerts to the prelude-manager.

Step Two: Tracking down the violation

Generate SELinux policy allow rules from logs of denied operations. This is useful for getting a quick overview of what has been getting denied on the local machine.

# audit2allow -la

You can obtain more detailed audit messages by using ausearch to get the most recent violations

# ausearch -m avc -ts recent

Step Three: Fixing the violation

Below are examples of using our current puppet configuration to make SELinux deployment changes. These constructs are currently home-brewed, and do not exist in upstream Puppet. For these functions to work, you must ensure that the host or servergroup is configured with 'include selinux', which will enable SELinux in permissive mode. Once a host is properly configured, this can be changed to 'include selinux-enforcing' to enable SELinux Enforcing mode.

Allowing ports

    semanage_port { '8081-8089': type => 'http_port_t', proto => 'tcp' }

Toggling an SELinux boolean

SELinux booleans, which can be viewed by running semanage boolean -l, can easily be configured using the following syntax within your puppet configuration.

    selinux_bool { 'httpd_can_network_connect_db': bool => 'on' }

Setting custom context

Our infrastructure contains many custom applications, which may utilize non-standard file locations. These issues can lead to trouble with SELinux, but they can easily be resolved by setting custom file context.

    semanage_fcontext { '/var/tmp/l10n-data(/.*)?':
        type => 'httpd_sys_content_t'
    }

Deploying custom policy modules

• Put your te file in configs/system/selinux/modules in puppet.
• Compile your custom policy

    # make -f /usr/share/selinux/devel/Makefile

• Commit the te and pp files to puppet
• Add the module to the appropriate manifest.

    semodule { 'fedora':
    }