AppArmor

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AppArmor Icon

Introduction[edit]

According to debian.org: [1]

AppArmor is a Mandatory Access Control framework. When enabled, AppArmor confines programs according to a set of rules that specify what files a given program can access. This proactive approach helps protect the system against both known and unknown vulnerabilities.

Whonix ™ developer madaidan has noted: [2]

Mandatory access control (MAC) systems give fine-grained control over what programs can access. This means that your browser won't have access to your entire home directory or similarly. The most used MAC systems are SELinux and AppArmor. SELinux is a lot more secure than AppArmor as it is more fine-grained. For example, it's inode-based rather than path-based, allows enforcing significantly stronger restrictions, can filter kernel ioctls and much more. Unfortunately, this comes at the cost of being much more difficult to use and harder to learn so AppArmor may be preferred by some.

AppArmor provides a number of advantages: [3]

  • It protects the operating system and applications from external or internal threats, including zero-day attacks.
  • "Good behavior" is enforced and it mitigates exploits via unknown application flaws.
  • AppArmor security policies define the system resources that individual applications can access, and with what privileges. For instance:
    • Network access.
    • Raw socket access.
    • Read, write or execute file permissions on specific paths.

Some AppArmor profiles for some default installed applications such as Tor, sdwdate and kloak are enforced by default. To see which, run.

sudo aa-status

More AppArmor profiles are available for testers.

Installation[edit]

Testers only! Testers only!

It is recommended to use the Whonix ™ AppArmor profiles which are available for various programs that run in both Whonix-Gateway ™ and Whonix-Workstation ™, such as Tor, Tor Browser, Thunderbird and more. The profiles are easy to apply and provide a considerable security benefit.

Qubes Users Note[edit]

Qubes-Whonix ™ Note Qubes-Whonix ™ users require some extra steps to set up AppArmor. Non-Qubes-Whonix ™ users can skip this section. [4] [5]

If you are interested, click on Expand on the right.

AppArmor is enabled by default. No extra steps required.

Install all AppArmor Profiles[edit]

Installation[edit]

The easiest method is to install all available AppArmor profiles. This can result in a few profiles being enforced for software that is not installed, but this will not have any adverse impacts.

At time of writing it is not required to change Whonix ™ APT repository.

Note written on 29 June 2022: In a future Whonix ™ version 16.0.5.4 (unreleased at time of writing), the following packages will be installed by default. (forum discussion)

Install package(s) apparmor-profiles apparmor-profiles-extra apparmor-profiles-kicksecure.

A. Update the package lists and upgrade the system.

sudo apt update && sudo apt full-upgrade

B. Install the apparmor-profiles apparmor-profiles-extra apparmor-profiles-kicksecure package(s).

Using apt command line parameter --no-install-recommends is in most cases optional.

sudo apt install --no-install-recommends apparmor-profiles apparmor-profiles-extra apparmor-profiles-kicksecure

C. Done.

The procedure of installing package(s) apparmor-profiles apparmor-profiles-extra apparmor-profiles-kicksecure is complete.

Enabling[edit]

Some profiles in the apparmor-profiles and apparmor-profiles-extra packages are not enforced by default because the Debian maintainers do not believe they are mature enough. [6]

apparmor-profiles provides various experimental AppArmor profiles. Do not expect these profiles to work out-of-the-box.

These profiles are not mature enough to be shipped in enforce mode by default on Debian. They are shipped in complain mode so that users can test them, choose which are desired, and help improve them upstream if needed.

Some even more experimental profiles are included in folder /usr/share/apparmor/extra-profiles.

1. Check which profiles are in complain mode (not actually providing protection) and which are in enforce mode (providing actual protection).

Run.

sudo aa-status

2. Locate the profile to enable.

To enable a profile which is currently in complain mode, locate it in folder /etc/apparmor.d.

ls /etc/apparmor.d

3. Enable the profile.

After locating the relevant profile, enable it. For example.

(The following example is already enforced by default if installed as per above.)

sudo aa-enforce /etc/apparmor.d/home.tor-browser.firefox

It might be inadvisable or unsuitable to enable all available AppArmor profiles.

4. Inspect other available AppArmor profiles.

The /usr/share/apparmor/extra-profiles folder has additional AppArmor profiles.

ls /usr/share/apparmor/extra-profiles

5. Copy relevant AppArmor profiles.

Testers only!

  • Option A) If any of these applications are in use, copy the profile over to folder /etc/apparmor.d. Example:
    sudo cp /usr/share/apparmor/extra-profiles/bin.netstat /etc/apparmor.d
  • Option B) Copy all profiles.
    sudo cp /usr/share/apparmor/extra-profiles/* /etc/apparmor.d

6. View all avaialble AppArmor profiles in the /etc/apparmor.d folder.

Optional.

ls -la /etc/apparmor.d/*

Alternatively also any other tool such as a graphical file manager could be used.

7. Enable the additional profile(s).

  • Option A) Enable a profile. Example:
    sudo aa-enforce /etc/apparmor.d/bin.netstat
  • Option B) Enable all profiles.
    sudo aa-enforce /etc/apparmor.d/*

Install Select AppArmor Profiles[edit]

Click on Expand on the right side.

Update your package lists.

sudo apt update

apparmor-profiles

sudo apt install apparmor-profiles

apparmor-profiles-extra

sudo apt install apparmor-profiles-extra

Profile for Tor Browser. Useful in Whonix-Workstation ™. [7]

sudo apt install apparmor-profile-torbrowser

Profile for the HexChat client. Useful in Whonix-Workstation ™. (Soon to be renamed apparmor-profile-hexchat.)

sudo apt install apparmor-profile-xchat

Profile for the Mozilla Thunderbird E-Mail client. Useful in Whonix-Workstation ™. (Soon to be renamed apparmor-profile-thunderbird.)

sudo apt install apparmor-profile-thunderbird

Profile Unloading[edit]

The name of the specific profile to unload must be known in advance; refer to the list above.

1. If it is necessary to disable an AppArmor profile, first list those which are available.

ls /etc/apparmor.d/

Or.

sudo aa-status

2. Once a profile is loaded in the kernel, it can be easily removed.

sudo aa-disable /etc/apparmor.d/profile-name

This command expects the profile file to exist, so if it has been manually deleted or removed via apt purge, it can only be unloaded by rebooting.

3. Done.

The process of disabling the AppArmor profile has been completed.

4. Verification.

Optional. To confirm, use the aa-status command.

sudo aa-status

Common Operations[edit]

Maintain Tor Browser Functionality[edit]

Tor Browser upgrades frequently break the Whonix ™ AppArmor profile used to contain it. Even when AppArmor-related fixes are confirmed in forums.whonix.org, most often updated, fixed packages are immediately made available to Whonix ™ stable or even the developer version.

If Tor Browser is non-functional with the available AppArmor profile, follow these steps to rectify the problem.

1. Open a terminal in Whonix-Workstation ™ (whonix-ws-16).

whonix-ws-16 → Xfce Terminal

2. List the available AppArmor profiles.

ls /etc/apparmor.d/

3. Edit the Tor Browser AppArmor profile.

Note: change the name of the file to match whatever version is installed on the system.

sudoedit /etc/apparmor.d/home.tor-browser.firefox

4. Navigate to the Whonix ™ Github resource for AppArmor.

The latest git commits can be found here.

Select Code → etc/apparmor.d → home.tor-browser.firefox

Select the Raw button on the right-hand side. [8]

Info It is recommended to check the profile does not contain any unexpected content. For greater security, utilize a different viewer and/or retrieve the profile using git and perform git commit gpg verification.

Cut and paste the profile text into the old Tor Browser profile which is open in nano. Save and exit.

5. Enforce the new Tor Browser profile.

In the command below, change the name of the file to match whatever version is installed on the system.

In Whonix-Workstation ™ (whonix-ws-16), run.

sudo aa-enforce /etc/apparmor.d/home.tor-browser.firefox

6. Shutdown Whonix-Workstation ™ (whonix-ws-16).

7. Restart Whonix-Workstation ™ (anon-whonix).

Launch Tor Browser. If everything has been applied correctly, Tor Browser will have full functionality. If the following AppArmor warning appears, it can be safely ignored. 

Profile: /etc/apparmor.d/home.tor-browser.firefox Operation: open Name: /dev/ Denied: r Logfile: /var/log/kern.log For more information, please see: https://wiki.ubuntu.com/DebuggingApparmor

8. Manually check AppArmor is correctly running and enforced.

In a terminal, run.

sudo aa-status

The output should show the Tor Browser profile is loaded and in enforce mode.

Manually Updating Other Whonix ™ AppArmor Profiles[edit]

The same method can be used to resolve other AppArmor problems impacting full functionality of applications in Whonix ™. For instance, the systemcheck AppArmor profile previously caused continuous "denied" messages in Qubes-Whonix ™. [9] Correcting this issue was quite simple: [10]

  1. Navigate to the raw, updated systemcheck profile.
  2. Replace the existing content in /etc/apparmor.d/usr.bin.systemcheck with the updated github content, in both Templates whonix-gw-16 and whonix-ws-16.
  3. Shut down both Templates and any running instances of sys-whonix and anon-whonix.
  4. Restart sys-whonix and anon-whonix.

AppArmor Notifications[edit]

apparmor-info[edit]

apparmor-info is a helper utility to simplify viewing AppArmor logs. It parses AppArmor logs, hides unnecessary information [11] and removes duplicates.

sudo apparmor-info --boot | grep DENIED

apparmor-notify[edit]

apparmor-notify is not installed by default. [12] By installing it, desktop notifications would appear concerning AppArmor denied messages, which are stored in file /var/log/kern.log.

To install:

Install package(s) apparmor-notify.

A. Update the package lists and upgrade the system.

sudo apt update && sudo apt full-upgrade

B. Install the apparmor-notify package(s).

Using apt command line parameter --no-install-recommends is in most cases optional.

sudo apt install --no-install-recommends apparmor-notify

C. Done.

The procedure of installing package(s) apparmor-notify is complete.

If apparmor-notify is manually installed, then on occasion an application may be functional but AppArmor "denied" messages constantly appear. Rather than updating the relevant AppArmor profile(s), it is possible to disable notifications instead.

In the offending Whonix ™ (App)VM, launch Xfce Terminal and run.

sudo killall aa-notify

To revert this change, reboot the VM.

Manual Notifications Inspection[edit]

Use of apparmor-info is simpler.

1. Manually inspect relevant logs.

Open file /var/log/kern.log in an editor with administrative (root) write permissions.

This box uses sudoedit for better security. This is an example and other tools can also achieve the same goal. If this example does not work for you or if you are not using Whonix ™, please refer to this link.

sudoedit /var/log/kern.log

2. Show denied AppArmor messages of any age.

Run.

sudo cat /var/log/kern.log | grep DENIED

3. Optional: Keep watching the file as it is appended.

This is useful for reproducing AppArmor denied messages and testing amended profiles.

sudo tail -f /var/log/kern.log | grep --line-buffered DENIED

More Profiles[edit]

It is possible to utilize profiles by other vendors, but this is unsupported by Whonix ™ developers. As a reminder, it is not necessary to install AppArmor profiles for any applications that are unlikely to be used (such as dovecot). Additional options include:

  1. Debian has packages that can be easily installed via the APT package manager.
  2. Ubuntu also provides profiles. It is not easy to download these as a package to be installed in Debian. Further, the profiles may or may not differ from (or complement) profiles listed earlier.
  3. Advanced users can attempt to create additional, strict AppArmor profiles by executing: [2]

aa-genprof $path_to_program

Then open the program and use it as normal. AppArmor detects which files need to be accessed and adds them to the profile if you choose. This is insufficient for high quality profiles though; refer to the AppArmor documentation for further details.

Fix Profiles[edit]

1. Put folder /etc/apparmor.d under git version control.

Git is a useful tool to record which files in a folder changed in what way.

Git setup for folder /etc/apparmor.d.

Install package(s) git auditd.

A. Update the package lists and upgrade the system.

sudo apt update && sudo apt full-upgrade

B. Install the git auditd package(s).

Using apt command line parameter --no-install-recommends is in most cases optional.

sudo apt install --no-install-recommends git auditd

C. Done.

The procedure of installing package(s) git auditd is complete.

Change directory to folder /etc/apparmor.d.

cd /etc/apparmor.d

Initialize git in that folder.

sudo git init

Git needs an e-mail address. That e-mail address doesn't need to actually exist. That e-mail address would appear in git commit change logs if that git repository was ever pushed to any remote. If only used locally, the default you@example.com could be kept. Otherwise, the user may change you@example.com to any e-mail address of their choice.

sudo git config user.email "you@example.com"

Git needs an name. That name address doesn't need to actually exist. That name would appear in git commit change logs if that git repository was ever pushed to any remote. If only used locally, the default Your Name could be kept. Otherwise, the user may change Your Name to any name of their choice.

sudo git config user.name "Your Name"

Add all files in that folder to git.

sudo git add -A

Commit all files to git. [13]

sudo git commit -a -m .

2. Open your application/s which caused the Denied/Allowed messages.

3. Use aa-logprof to correct them. [14]

sudo aa-logprof

This is an example for fixing the AppArmor profile for Tor Browser.

Sample printout: 

Reading log entries from /var/log/audit/audit.log.
Updating AppArmor profiles in /etc/apparmor.d.
Enforce-mode changes:

Profile:  /**/*-browser/Browser/firefox
Path:     /sys/bus/pci/devices/
New Mode: r
Severity: 4

 [1 - #include <abstractions/totem>]
  2 - /sys/bus/pci/devices/ r, 
(A)llow / [(D)eny] / (I)gnore / (G)lob / Glob with (E)xtension / (N)ew / Audi(t) / Abo(r)t / (F)inish

Answer with A

Sample printout: 

Adding #include <abstractions/totem> to profile.
Deleted 19 previous matching profile entries.

Profile:  /**/*-browser/Browser/firefox
Path:     /proc/1342/cgroup
New Mode: owner r
Severity: 6

 [1 - owner /proc/*/cgroup r,]
  2 - owner /proc/1342/cgroup r, 
(A)llow / [(D)eny] / (I)gnore / (G)lob / Glob with (E)xtension / (N)ew / Audi(t) / (O)wner permissions off / Abo(r)t / (F)inish

Answer with A

Sample printout: 

Adding owner /proc/*/cgroup r, to profile.

= Changed Local Profiles =

The following local profiles were changed. Would you like to save them?

 [1 - /**/*-browser/Browser/firefox]
(S)ave Changes / Save Selec(t)ed Profile / [(V)iew Changes] / View Changes b/w (C)lean profiles / Abo(r)t

Answer with S

Sample printout: 

Writing updated profile for /**/*-browser/Browser/firefox.

Done.

4. Re-run any applications that had any AppArmor issues

5. Repeat step 2 and 3 until there are no new AppArmor denied or allowed messages.

It should give you similar output if there is nothing left to resolve: 

Reading log entries from /var/log/audit/audit.log.
Updating AppArmor profiles in /etc/apparmor.d.
Enforce-mode changes:

6. See which files were modified by aa-logprof.

From the same folder.

git status

git will show which files have been modified.

Sample printout: 

On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   home.tor-browser.firefox

no changes added to commit (use "git add" and/or "git commit -a")

7. Open the modified file(s) with a text editor.

sudoedit /etc/apparmor.d/home.tor-browser.firefox

8. Submit fixes to developers.

Ideally to github:

Support[edit]

Development[edit]

Footnotes[edit]

This box Expand All is mostly useful for wiki editors. Users can safely ignore it.

  1. ↑ https://wiki.debian.org/AppArmor
  2. ↑ 2.0 2.1 https://madaidans-insecurities.github.io/guides/linux-hardening.html#mac
  3. ↑ http://wiki.apparmor.net/index.php/Main_Page
  4. ↑ Non-Qubes-Whonix ™ means all Whonix ™ platforms except Qubes-Whonix ™. This includes Whonix ™ KVM, Whonix ™ VirtualBox and Whonix ™ Physical Isolation.
  5. ↑ Advanced users attempting to enable SE Linux instead would utilize the following parameters in this section:
    selinux=1 security=selinux
  6. ↑ https://packages.debian.org/bullseye/apparmor-profiles
  7. ↑ Tor Browser is installed by tb-updater; the latter is a default Whonix ™ application.
  8. ↑ Otherwise essential profile formatting might break or unwanted content (such as line numbers) might be copied inadvertently, leading to a non-functional profile.
  9. ↑ In Whonix ™ 13.
  10. ↑ This issue was fixed in the Whonix ™ 14 release.
  11. ↑

    Jul 18 13:50:28 host kernel: [ 117.212029] audit: type=1400 audit(1626616228.947:23):
  12. ↑ https://forums.whonix.org/t/whonix-14-debian-stretch-apparmor-related-changes/3563
  13. ↑ Commits all files to git with commit message . for simplicity. Commit message could also be something else such as {{{sudo_maybe}}} git commit -a -m "initial commit".
  14. ↑ https://gitlab.com/apparmor/apparmor/-/issues/200#note_685907209
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