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Full system policy (FSP)

Danger

Full system policy is still under early development:

  • Do not run this outside of a development VM!
  • This is an advanced feature, you should understand what you are doing before use.

You have been warned!!!

Quote

AppArmor is also capable of being used for full system policy where processes are by default not running under the unconfined profile. This might be useful for high security environments or embedded systems.

Source: AppArmor Wiki

Overview

The default mode of apparmor.d is the more advanced confinement configuration we can achieve while being as simple as installing a package and doing some minor configuration on your system. By design, a full system confinement does not work this way. Before enabling you need to consider your use case and security objective.

Particularly:

  • Every system application will be blocked if they do not have a profile.
  • Any non-standard system app need to be explicitly profiled and allowed to run. For instance, if you want to use your own proxy or VPN software, you need to ensure it is correctly profiled and allowed to run in the systemd profile.
  • Desktop environment must be explicitly supported, your UI will not start otherwise. Again, it is a feature.
  • FSP mode will run unknown user application into the default profile. It might be enough for your application. If not you have to make a profile for it.
  • In FSP mode, all sandbox managers must have a profile. Then user sandboxed applications (flatpak, snap, etc) will work as expected.

Installation

This feature is only enabled when the project is built with make full. Early policy load must also be enabled. Once apparmor.d has been installed in FSP mode, it is required to reboot to apply the changes.

In /etc/apparmor/parser.conf ensure you have: 

write-cache
cache-loc /etc/apparmor/earlypolicy/
Optimize=compress-fast

In PKGBUILD, replace make by make full:

-  make
+  make full

Then, build the package with: make pkg

In debian/rules, add the following lines:

override_dh_auto_build:
    make full

Then, build the package with: make dpkg

In debian/rules, add the following lines:

override_dh_auto_build:
    make full

Then, build the package with: make dpkg

In dists/apparmor.d.spec, replace %make_build by %make_build full

-  %make_build
+  %make_build full

Then, build the package with: make rpm

Use the make full command to build instead of make

Structure

The profiles dedicated for full system policies are maintained in the _full group.

Systemd

systemd

This profile aims to confine PID 1. Systemd is (kind of obviously) a highly privileged program. The purpose of this profile is to transition to other less privileged program as soon as possible. On high security environments, it can also be used to strictly limit the list of allowed privileged program.

  • It allows internal systemd access,
  • It allows starting all common root services.

To work as intended, all privileged services started by systemd must have a profile. For a given distribution, the list of these services can be found under: 

/usr/lib/systemd/system-generators/*
/usr/lib/systemd/system-environment-generators/*
/usr/lib/systemd/system/*.service

The main fallback profile (default) is not intended to be used by privileged program or service. Such programs must have a dedicated profile and will fail otherwise. This is a feature, not a bug.

systemd-user

This profile is for systemd --user, it aims to confine userland systemd. It does not require a lot of access and is only intended to handle user services.

  • It allows internal systemd user access,
  • It allows starting all common user services.

To work as intended, userland services started by systemd --user should have a profile. For a given distribution, the list of these services can be found under:

/usr/lib/systemd/user-environment-generators/*
/usr/lib/systemd/user-generators/*
/usr/lib/systemd/user/*.service

Info

To be allowed to run, additional root or user services may need to add extra rules inside the usr/systemd.d or usr/systemd-user.d directory. For example, when installing a new privileged service foo with stacking you may need to add the following to /etc/apparmor.d/usr/systemd.d/foo: 

@{lib}/foo rPx -> systemd//&foo,

Fallback

In addition to the systemd profiles, a full system policy needs to ensure that no programs run in an unconfined state at any time. The fallback profiles consist of a set generic specialized profiles:

  • default is used for any classic user application with a GUI. It has full access to user home directories.
  • bwrap, bwrap-app are used for classic user application that are sandboxed with bwrap.

Warning

The main fallback profile (default) is not intended to be used by privileged program or service. Such programs must have they dedicated profile and would break otherwise.

Additionally, special user access can be setup using PAM rules set such as a random shell interactively opened (as user or as root).