SELinux is a mandatory access control (MAC) system on Linux which adds a fine granular permission system for access to all resources on the system such as files, devices, networks and inter-process communication.
The most important questions are answered briefly in the [FAQ of the SELinux Project](http://selinuxproject.org/page/FAQ). For more details on SELinux and how to actually use and administrate it on your systems have a look at [Red Hat Enterprise Linux 7 - SELinux User's and Administrator's Guide](https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide/index.html). For an simplified (and funny) introduction download the [SELinux Coloring Book](https://github.com/mairin/selinux-coloring-book).
This documentation will use a similar format like the SELinux User's and Administrator's Guide.
Icinga 2 is providing its own SELinux Policy. At the moment it is not upstreamed to the reference policy because it is under development. Target of the development is a policy package for Red Hat Enterprise Linux 7 and its derivates running the targeted policy which confines Icinga2 with all features and all checks executed.
Later the policy will be installed by a seperate package and this section will be removed. Now it describes the installation to support development and testing. It assumes that Icinga 2 is already installed from packages and running on the system.
The policy package will run the daemon in a permissive domain so nothing will be denied also if the system runs in enforcing mode, so please make sure to run the system in this mode.
# sestatus
SELinux status: enabled
SELinuxfs mount: /sys/fs/selinux
SELinux root directory: /etc/selinux
Loaded policy name: targeted
Current mode: enforcing
Mode from config file: enforcing
Policy MLS status: enabled
Policy deny_unknown status: allowed
Max kernel policy version: 28
You can change the configured mode by editing `/etc/selinux/config` and the current mode by executing `setenforce 0`.
As a prerequisite install the `git`, `selinux-policy-devel` and `audit` package. Enable and start the audit daemon afterwards.
After that clone the icinga2 git repository and checkout the feature branch.
# git clone git://git.icinga.org/icinga2.git
# git checkout feature/rpm-selinux-8332
To create and install the policy package run the installation script which also labels the resources. (The script assumes Icinga 2 was started once after system startup, the labeling of the port will only happen once and fail later on.)
Some changes to the systemd scripts are also required to handle file contexts correctly. This is at the moment only included in the feature branch, so it has to be copied manually.
When the SELinux policy package for Icinga 2 is installed, the Icinga 2 daemon (icinga2) runs in its own domain `icinga2_t` and is separated from other confined services.
Files have to be labeled correctly for allowing icinga2 access to it. For example it writes to its own log files labeled `icinga2_log_t`. Also the API port is labeled `icinga_port_t` and the icinga2 is allowed to manage it. Furthermore icinga2 can open high ports and unix sockets to connect to databases and features like graphite. It executes the nagios plugins and transitions to their context if those are labeled for example `nagios_services_plugin_exec_t` or `nagios_system_plugin_exec_t`.
Additional the Apache webserver is allowed to connect to the Command pipe of Icinga 2 to allow web interfaces sending commands to icinga2. This will perhaps change later on while investigating Icinga Web 2 for SELinux!
The command pipe is labeled `icinga2_command_t` and other services can request access to it by using the interface `icinga2_send_commands`.
The nagios plugins use their own contexts and icinga2 will transition to it. This means plugins have to be labeled correctly for their required permissions. The plugins installed from package should have set their permissions by the corresponding policy module and you can restore them using `restorecon -R -v /usr/lib64/nagios/plugins/`. To label your own plugins use `chcon -t type /path/to/plugin`, for the type have a look at table below.
Type | Domain | Use case | Provided by policy package
cat: /var/log/icinga2/icinga2.log: Keine Berechtigung
$ sudo systemctl reload icinga2.service
Failed to get D-Bus connection: No connection to service manager.
Those commands fail because you only switch to root but do not change your SELinux role. Try again but tell sudo also to switch the SELinux role and type.
$ sudo -r icinga2adm_r -t icinga2adm_t id -Z
staff_u:icinga2adm_r:icinga2adm_t:s0-s0:c0.c1023
$ sudo -r icinga2adm_r -t icinga2adm_t vi /etc/icinga2/icinga2.conf
Now try the commands again without providing the role and type and they will work, but if you try to read apache logs or restart apache for example it will still fail.
$ sudo cat /var/log/httpd/error_log
/bin/cat: /var/log/httpd/error_log: Keine Berechtigung
If you experience any problems while running in enforcing mode try to reproduce it in permissive mode. If the problem persists it is not related to SELinux because in permissive mode SELinux will not deny anything.
For now Icinga 2 is running in a permissive domain and adds also some rules for other necessary services so no problems should occure at all. But you can help to enhance the policy by testing Icinga 2 running confined by SELinux.
When filing a bug report please add the following information additionally to the [normal ones](https://www.icinga.org/icinga/faq/):
If access to a file is blocked and you can tell which one please provided the output of `ls -lZ /path/to/file` (and perhaps the directory above).
If asked for full audit.log add `-w /etc/shadow -p w` to `/etc/audit/rules.d/audit.rules`, restart the audit daemon, reproduce the problem and add `/var/log/audit/audit.log` to the bug report. With the added audit rule it will include the path of files access was denied to.
If asked to provide full audit log with dontaudit rules disabled executed `semodule -DB` before reproducing the problem. After that enable the rules again to prevent auditd spamming your logfile by executing `semodule -B`.
