Applies to SUSE Linux Enterprise Server 12 SP5

21 Getting Started #

Prepare a successful deployment of AppArmor on your system by carefully considering the following items:

Determine the applications to profile. Read more on this in Section 21.3, “Choosing Applications to Profile”.
Build the needed profiles as roughly outlined in Section 21.4, “Building and Modifying Profiles”. Check the results and adjust the profiles when necessary.
Update your profiles whenever your environment changes or you need to react to security events logged by the reporting tool of AppArmor. Refer to Section 21.5, “Updating Your Profiles”.

21.1 Installing AppArmor #

AppArmor is installed and running on any installation of SUSE® Linux Enterprise Server by default, regardless of what patterns are installed. The packages listed below are needed for a fully-functional instance of AppArmor:

apparmor-docs
apparmor-parser
apparmor-profiles
apparmor-utils
audit
libapparmor1
perl-libapparmor
yast2-apparmor

Tip

If AppArmor is not installed on your system, install the pattern apparmor for a complete AppArmor installation. Either use the YaST Software Management module for installation, or use Zypper on the command line:

zypper in -t pattern apparmor

21.2 Enabling and Disabling AppArmor #

AppArmor is configured to run by default on any fresh installation of SUSE Linux Enterprise Server. There are two ways of toggling the status of AppArmor:

Using YaST Services Manager: Disable or enable AppArmor by removing or adding its boot script to the sequence of scripts executed on system boot. Status changes are applied on reboot.
Using AppArmor Configuration Window: Toggle the status of AppArmor in a running system by switching it off or on using the YaST AppArmor Control Panel. Changes made here are applied instantaneously. The Control Panel triggers a stop or start event for AppArmor and removes or adds its boot script in the system's boot sequence.

To disable AppArmor permanently (by removing it from the sequence of scripts executed on system boot) proceed as follows:

Start YaST.
Select System › Services Manager.
Mark apparmor by clicking its row in the list of services, then click Enable/Disable in the lower part of the window. Check that Enabled changed to Disabled in the apparmor row.
Confirm with OK.

AppArmor will not be initialized on reboot, and stays inactive until you re-enable it. Re-enabling a service using the YaST Services Manager tool is similar to disabling it.

Toggle the status of AppArmor in a running system by using the AppArmor Configuration window. These changes take effect when you apply them and survive a reboot of the system. To toggle the status of AppArmor, proceed as follows:

Start YaST, select AppArmor Configuration, and click Settings in the main window.
Enable AppArmor by checking Enable AppArmor or disable AppArmor by deselecting it.
Click Done in the AppArmor Configuration window.

21.3 Choosing Applications to Profile #

You only need to protect the programs that are exposed to attacks in your particular setup, so only use profiles for those applications you actually run. Use the following list to determine the most likely candidates:

Network Agents

Web Applications

Cron Jobs

To find out which processes are currently running with open network ports and might need a profile to confine them, run aa-unconfined as root.

Example 21.1: Output of aa-unconfined #

19848 /usr/sbin/cupsd not confined
19887 /usr/sbin/sshd not confined
19947 /usr/lib/postfix/master not confined
1328 /usr/sbin/ntpd confined by '/usr/sbin/ntpd (enforce)'

Each of the processes in the above example labeled not confined might need a custom profile to confine it. Those labeled confined by are already protected by AppArmor.

Tip: For More Information

For more information about choosing the right applications to profile, refer to Section 22.2, “Determining Programs to Immunize”.

21.4 Building and Modifying Profiles #

AppArmor on SUSE Linux Enterprise Server ships with a preconfigured set of profiles for the most important applications. In addition, you can use AppArmor to create your own profiles for any application you want.

There are two ways of managing profiles. One is to use the graphical front-end provided by the YaST AppArmor modules and the other is to use the command line tools provided by the AppArmor suite itself. The main difference is that YaST supports only basic functionality for AppArmor profiles, while the command line tools let you update/tune the profiles in a more fine-grained way.

For each application, perform the following steps to create a profile:

As root, let AppArmor create a rough outline of the application's profile by running aa-genprof PROGRAM_NAME.
or
Outline the basic profile by running YaST › Security and Users › AppArmor Configuration › Manually Add Profile and specifying the complete path to the application you want to profile.
A new basic profile is outlined and put into learning mode, which means that it logs any activity of the program you are executing, but does not yet restrict it.
Run the full range of the application's actions to let AppArmor get a very specific picture of its activities.
Let AppArmor analyze the log files generated in Step 2 by typing S in aa-genprof.
AppArmor scans the logs it recorded during the application's run and asks you to set the access rights for each event that was logged. Either set them for each file or use globbing.
Depending on the complexity of your application, it might be necessary to repeat Step 2 and Step 3. Confine the application, exercise it under the confined conditions, and process any new log events. To properly confine the full range of an application's capabilities, you might be required to repeat this procedure often.
When you finish aa-genprof, your profile is set to enforce mode. The profile is applied and AppArmor restricts the application according to it.
If you started aa-genprof on an application that had an existing profile that was in complain mode, this profile remains in learning mode upon exit of this learning cycle. For more information about changing the mode of a profile, refer to Section 26.7.3.2, “aa-complain—Entering Complain or Learning Mode” and Section 26.7.3.6, “aa-enforce—Entering Enforce Mode”.

Test your profile settings by performing every task you need with the application you confined. Normally, the confined program runs smoothly and you do not notice AppArmor activities. However, if you notice certain misbehavior with your application, check the system logs and see if AppArmor is too tightly confining your application. Depending on the log mechanism used on your system, there are several places to look for AppArmor log entries:

/var/log/audit/audit.log

The command journalctl | grep -i apparmor

The command dmesg -T

To adjust the profile, analyze the log messages relating to this application again as described in Section 26.7.3.9, “aa-logprof—Scanning the System Log”. Determine the access rights or restrictions when prompted.

Tip: For More Information

For more information about profile building and modification, refer to Chapter 23, Profile Components and Syntax, Chapter 25, Building and Managing Profiles with YaST, and Chapter 26, Building Profiles from the Command Line.

21.5 Updating Your Profiles #

Software and system configurations change over time. As a result, your profile setup for AppArmor might need some fine-tuning from time to time. AppArmor checks your system log for policy violations or other AppArmor events and lets you adjust your profile set accordingly. Any application behavior that is outside of any profile definition can be addressed by aa-logprof. For more information, see Section 26.7.3.9, “aa-logprof—Scanning the System Log”.