In Gentoo, we have been supporting custom policy packages for a while now. Unlike most other distributions, which focus on binary packages, Gentoo has always supported source-based packages as default (although binary packages are supported as well).

A recent commit now also allows CIL files to be used.

Policy ebuilds, how they work

Gentoo provides its own SELinux policy, based on the reference policy, and provides per-module ebuilds (packages). For instance, the SELinux policy for the screen package is provided by the sec-policy/selinux-screen package.

The package itself is pretty straight forward:

# Copyright 1999-2015 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id$
EAPI="5"

IUSE=""
MODS="screen"

inherit selinux-policy-2

DESCRIPTION="SELinux policy for screen"

if [[ $PV == 9999* ]] ; then
        KEYWORDS=""
else
        KEYWORDS="~amd64 ~x86"
fi

The real workhorse lays within a Gentoo eclass, something that can be seen as a library for ebuilds. It allows consolidation of functions and activities so that a large set of ebuilds can be simplified. The more ebuilds are standardized, the more development can be put inside an eclass instead of in the ebuilds. As a result, some ebuilds are extremely simple, and the SELinux policy ebuilds are a good example of this.

The eclass for SELinux policy ebuilds is called selinux-policy-2.eclass and holds a number of functionalities. One of these (the one we focus on right now) is to support custom SELinux policy modules.

Custom SELinux policy ebuilds

Whenever a user has a SELinux policy that is not part of the Gentoo policy repository, then the user might want to provide these policies through packages still. This has the advantage that Portage (or whatever package manager is used) is aware of the policies on the system, and proper dependencies can be built in.

To use a custom policy, the user needs to create an ebuild which informs the eclass not only about the module name (through the MODS variable) but also about the policy files themselves. These files are put in the files/ location of the ebuild, and referred to through the POLICY_FILES variable:

# Copyright 1999-2015 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id$
EAPI="5"

IUSE=""
MODS="oracle"
POLICY_FILES="oracle.te oracle.if oracle.fc"

inherit selinux-policy-2

DESCRIPTION="SELinux policy for screen"

if [[ $PV == 9999* ]] ; then
        KEYWORDS=""
else
        KEYWORDS="~amd64 ~x86"
fi

The eclass generally will try to build the policies, converting them into .pp files. With CIL, this is no longer needed. Instead, what we do is copy the .cil files straight into the location where we place the .pp files.

From that point onwards, managing the .cil files is similar to .pp files. They are loaded with semodule -i and unloaded with semodule -r when needed.

Enabling CIL in our ebuilds is a small improvement (after the heavy workload to support the 2.4 userspace) which allows Gentoo to stay ahead in the SELinux world.


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