Difference between revisions of "AppArmor"

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[[Category:Security]]
 
[[Category:Security]]
 
[[Category:Kernel]]
 
[[Category:Kernel]]
{{Out of date}}
+
[[ja:AppArmor]]
 +
[[Wikipedia:AppArmor|AppArmor]] is a [[Wikipedia:Mandatory_access_control|Mandatory Access Control]] (MAC) system, implemented upon the [[Wikipedia:Linux_Security_Modules|Linux Security Modules]] (LSM).
  
[[Wikipedia:AppArmor|AppArmor]] is a MAC (Mandatory Access Control) system, implemented upon LSM (Linux Security Modules).
+
== Installation ==
 +
=== Kernel ===
 +
{{Note|The highly disputed user namespace ({{ic|1=CONFIG_USER_NS=Y}}) isn't set in the [[kernel]] configuration, but may bring additional functionality to AppArmor. See {{bug|36969}} for details on user namespaces.}}
  
== Preventing circumvention of path-based MAC via links ==
+
When compiling the kernel, it is required to at least set the following options:
 +
  CONFIG_SECURITY_APPARMOR=y
 +
  CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1
 +
  CONFIG_DEFAULT_SECURITY_APPARMOR=y
 +
  CONFIG_AUDIT=y
  
AppArmor can be circumvented via hardlinks in the standard POSIX security model. However, the kernel now includes the ability to prevent this vulnerability, without needing the patches distributions like Ubuntu have applied to their kernels as workarounds.
+
For those new or altered variables to not get overridden, place them at the bottom of the config file or adjust the previous invocations accordingly.
  
See [[Sysctl#Preventing_link_TOCTOU_vulnerabilities]] for details.
+
Instead of setting {{ic|CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE}} and {{ic|CONFIG_DEFAULT_SECURITY_APPARMOR}}, you can also set [[kernel parameters|kernel boot parameters]]: {{ic|apparmor=1 security=apparmor}}.
  
== Implementation Status ==
+
=== Userspace Tools ===
AppArmor is currently available in the [https://bugs.archlinux.org/task/21406 Arch Linux kernel], but it has to be activated on kernel boot.
+
  
The userspace support requires [[AUR]] packages.
+
{{Note|Since AppArmor builds and installs a kernel module it must be rebuilt against the current kernel on each update}}
  
* https://aur.archlinux.org/packages.php?ID=42279
+
The userspace tools and libraries to control AppArmor are supplied by the {{AUR|apparmor}} package.
  
Not all the packages work out-of-the-box, but it is a work in progress. If you know how to build profiles yourself you shouldn't have too many problems.
+
The package is a split package which consists of following sub-packages:
Also there is an [https://aur.archlinux.org/packages.php?ID=60269 AUR kernel]
+
which includes apparmor specific patches from Ubuntu's [https://launchpad.net/apparmor launchpad].
+
  
=== AUR/apparmor package ===
+
* apparmor (meta package)
Added lot of features:
+
* apparmor-libapparmor
* apparmor-parser
+
* libapparmor
+
 
* apparmor-utils
 
* apparmor-utils
 +
* apparmor-parser
 
* apparmor-profiles
 
* apparmor-profiles
* apparmor-notify
+
* apparmor-pam
* apparmor-lib
+
* apparmor-vim
* apparmor-perl
+
* apparmor-python
+
* apparmor-ruby
+
* apparmor-dbus
+
* apparmor-profile-editor
+
  
But we still miss following features (TODO):
+
To load all AppArmor profiles on startup, [[enable]] {{ic|apparmor.service}}.
* init (rc.d) scripts! http://aur.pastebin.com/beQ4BjGX
+
* chase missing dependencies
+
* test everything
+
* make list of files that should go to backup=() arrays in packages...
+
* changehat modules for PAM(!), Apache and Tomcat (btw those are dependent on libapparmor)
+
* out-of-box-experience know-how
+
** make some package with profiles for all [core] packages enabled by default without need for any further user configuration
+
** etc...
+
* apparmor gnome applet (can't build, deprecated...)
+
  
==== When compared to Ubuntu ====
+
=== Testing ===
we have almost everything that is in following Ubuntu packages:
+
* apparmor
+
* apparmor-profiles
+
* apparmor-utils
+
* apparmor-notify
+
* apparmor-docs
+
* libapparmor1
+
* libapparmor-dev
+
* libapparmor-perl
+
 
+
We do not have
+
* {{ic|/etc/init.d/apparmor}} http://aur.pastebin.com/beQ4BjGX
+
* packages: libapache2-mod-apparmor libpam-apparmor
+
* KNOW-HOW
+
 
+
== Links ==
+
* Official pages
+
** Kernel: https://apparmor.wiki.kernel.org/ http://wiki.apparmor.net/index.php/Main_Page
+
** Userspace: https://launchpad.net/apparmor
+
 
+
* http://www.kernel.org/pub/linux/security/apparmor/AppArmor-2.6/
+
* http://wiki.apparmor.net/index.php/AppArmor_Core_Policy_Reference
+
 
+
* http://ubuntuforums.org/showthread.php?t=1008906 (Tutorial)
+
* https://help.ubuntu.com/community/AppArmor
+
*{{Bug|21406}}
+
* http://stuff.mit.edu/afs/sipb/contrib/linux/Documentation/apparmor.txt
+
* https://apparmor.wiki.kernel.org/index.php/Kernel_interfaces
+
* https://apparmor.wiki.kernel.org/index.php/AppArmor_versions
+
* http://manpages.ubuntu.com/manpages/oneiric/man5/apparmor.d.5.html
+
* http://manpages.ubuntu.com/manpages/oneiric/man8/apparmor_parser.8.html
+
* https://apparmor.wiki.kernel.org/index.php/Distro_CentOS
+
* http://bodhizazen.net/aa-profiles/
+
* https://wiki.ubuntu.com/ApparmorProfileMigration
+
* [[wikipedia:Linux_Security_Modules]]
+
* https://apparmor.wiki.kernel.org/index.php/Gittutorial
+
 
+
== AppArmor Packages ==
+
* Arch's {{Pkg|linux}} package has AppArmor support
+
* aur/[https://aur.archlinux.org/packages.php?ID=42279 apparmor]
+
 
+
== Kernel Configuration ==
+
Here is configuration of ArchLinux kernel which enables AppArmor (just FYI, you do not need to touch it):
+
  CONFIG_SECURITY_APPARMOR=y
+
  CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=0
+
  # CONFIG_DEFAULT_SECURITY_APPARMOR is not set
+
 
+
However, integration of AppArmor into the 2.6.36 kernel is not quite complete. It is missing network mediation and some of the interfaces for introspection. See [https://apparmor.wiki.kernel.org/index.php/Apparmor/upstream_release_notes here] for details. There are compatibility patches that can be applied to every recent kernel to reintroduce these interfaces. The patchset is pretty small and should be applied if you decide to use AppArmor. (Note: the patchset for 2.6.39 works with Kernel 3.0.x)
+
 
+
== GRUB Configuration ==
+
=== GRUB1 ===
+
To test profiles, or enforce the use of AppArmor it must be enabled at boot time. To do this add {{ic|1=apparmor=1 security=apparmor}} to the kernel boot parameters in {{ic|/boot/grub/menu.lst}} so the entry for the Arch Linux kernel looks something like
+
 
+
# (0) Arch Linux
+
title  Arch Linux [/boot/vmlinuz26]
+
root  (hd0,1)
+
kernel /boot/vmlinuz26 root=/dev/sdaX resume=/dev/sdaY ro '''apparmor=1 security=apparmor'''
+
initrd /boot/kernel26.img
+
 
+
Once you are happy with all your profiles, you may wish to force users to boot with AppArmor enabled. To do this add a password entry to the start of {{ic|/boot/grub/menu.lst}}. This will prevent users editing any boot entries or using the GRUB shell (which permits read access to any file on the system such as {{ic|/etc/shadow}}) before booting. You can also password protect any insecure entries in {{ic|/boot/grub/menu.lst}} that you do not want unauthorized users to boot by adding the lock command (or another password) immediately below the title line for that entry. See [[GRUB#Password_protection]] or [http://www.gnu.org/software/grub/manual/legacy/Security.html#Security Security in the GRUB Manual] for more details. If you are going through the trouble of securing GRUB, do not forget to secure your BIOS settings as well or users will be able to boot from their own CDs and USB sticks, gaining root access to the machine.
+
 
+
=== GRUB2 ===
+
 
+
==== Enable ====
+
Note that you can safely enable AppArmor and '''it will not affect the system''' at all until you enable it, load profiles, and set them to enforce mode with userspace tools. So you do not have to be afraid to enable AppArmor for testing purposes until you are enforcing AA profiles from init scripts (on each startup).
+
 
+
  # (0) Arch Linux
+
  menuentry "Arch Linux" {
+
    set root=(hd0,1)
+
    linux /vmlinuz26 root=/dev/sda1 ro '''apparmor=1 security=apparmor'''
+
    initrd /kernel26.img
+
  }
+
  
 
After reboot you can test if AppArmor is really enabled using this command as root:
 
After reboot you can test if AppArmor is really enabled using this command as root:
Line 126: Line 43:
 
(Y=enabled, N=disabled, no such file = module not in kernel)
 
(Y=enabled, N=disabled, no such file = module not in kernel)
  
==== Disable ====
+
== Disabling ==
AppArmor will be disabled by default in Arch Linux, so you will not need to disable it explicitly until you will build your own kernel with AppArmor enabled by default.
+
  # (0) Arch Linux
+
  menuentry "Arch Linux" {
+
    set root=(hd0,1)
+
    linux /vmlinuz26 root=/dev/sda1 ro '''apparmor=0 security=""'''
+
    initrd /kernel26.img
+
  }
+
  
== System Configuration ==
+
To disable AppArmor for the current session, [[stop]] {{ic|apparmor.service}}, or disable it to prevent it from starting at the next boot.
=== Mounts (/etc/fstab securityfs) ===
+
https://apparmor.wiki.kernel.org/index.php/Kernel_interfaces
+
  none    /sys/kernel/security securityfs defaults            0      0
+
  
=== Init scripts ===
+
Alternatively you may choose to disable the kernel modules required by AppArmor by appending {{ic|apparmor=0 security=""}} to the [[kernel parameters|kernel boot parameters]].
In the future, we'll implement some {{ic|/etc/rc.d/}} scripts that will enable and load profiles during startup.
+
http://aur.pastebin.com/beQ4BjGX
+
  
The RC.d file of Slackware might be more interesting than Ubuntu's init.d version http://bazaar.launchpad.net/~apparmor-dev/apparmor/2.8/view/head:/parser/rc.apparmor.slackware. NOTE: when using {{ic|/usr/lib/apparmor/rc.apparmor.functions}} (indirectly used by rc.apparmor.slackware) or the {{ic|aa-status}} program, you NEED a kernel with [http://bazaar.launchpad.net/~apparmor-dev/apparmor/2.8/view/head:/kernel-patches/3.4/0001-UBUNTU-SAUCE-AppArmor-Add-profile-introspection-file.patch 0001-UBUNTU-SAUCE-AppArmor-Add-profile-introspection-file.patch]. This is at least true for AppArmor 2.8, in version 2.9 things will go into mainline and a different interface will be used for introspecting profiles.
+
== Configuration ==
 +
=== Creating new profiles ===
 +
To create new profiles using {{ic|aa-genprof}}, {{ic|auditd.service}} from the package {{Pkg|audit}} must be running. This is because Arch Linux adopted systemd and doesn't do kernel logging to file by default. Apparmor can grab kernel audit logs from the userspace auditd daemon, allowing you to build a profile.
 +
To get kernel audit logs, you'll need to have rules in place to monitor the desired application. Most often a basic rule configured with {{man|8|auditctl|url=http://linux.die.net/man/8/auditctl}} will suffice:
 +
# auditctl -a exit,always -F arch=b64 -S all -F path=/usr/bin/chromium -F key=MonitorChromium
 +
but be sure to read [[Audit framework#Adding rules]] if this is unfamiliar to you.
 +
{{Note|Remember to stop the service afterwards (and maybe clear {{ic|/var/log/audit/audit.log}}) because it may cause overhead depending on your rules.}}
  
==== For developers ====
+
=== Parsing profiles ===
 +
To load, unload, reload, cache and stat profiles use {{ic|apparmor_parser}}. The default action ({{ic|-a}}) is to load a new profile, in order to overwrite an existing profile use the {{ic|-r}} option and to remove a profile use {{ic|-R}}. Each action may also apply to multiple profiles. Refer to {{man|8|apparmor_parser|url=http://man.cx/apparmor_parser(8)}} man page for more information.
  
From {{ic|/lib/apparmor/rc.apparmor.functions}}
+
== Security considerations ==
 +
=== Preventing circumvention of path-based MAC via links ===
  
  # NOTE: rc.apparmor initscripts that source this file need to implement
+
AppArmor can be circumvented via hardlinks in the standard POSIX security model. However, the kernel [https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=800179c9b8a1e796e441674776d11cd4c05d61d7 included] the ability to prevent this vulnerability via the following settings:  
  # the following set of functions:
+
{{hc|/usr/lib/sysctl.d/50-default.conf|2=
  # aa_action
+
...
  # aa_log_action_start
+
fs.protected_hardlinks = 1
  # aa_log_action_end
+
fs.protected_symlinks = 1}}
  # aa_log_success_msg
+
  # aa_log_warning_msg
+
  # aa_log_failure_msg
+
  # aa_log_skipped_msg
+
  # aa_log_daemon_msg
+
  # aa_log_end_msg
+
  
== UserSpace Tools ==
+
Patches distributions like Ubuntu have applied to their kernels as workarounds as not needed anymore.
=== Users ===
+
You can currently install userspace tools from [[AUR]].
+
  
=== Maintainers ===
+
== Tips and tricks ==
You need userspace tools that are compatible with your kernel version. The compatibility list can be found here: https://apparmor.wiki.kernel.org/index.php/AppArmor_versions
+
=== Get desktop notification on DENIED actions ===
e.g.: Kernel 2.6.36 is compatible with AppArmor 2.5.1
+
To get a notification on your desktop whenever AppArmor enters a "DENIED" log entry start the notify daemon by
 +
# aa-notify -p --display $DISPLAY
 +
This daemon must be started at each boot.
 +
 
 +
=== Cache profiles ===
 +
Since AppArmor has to translate the configured profiles into a binary format it may take some time to load them. Besides being bothersome for the user, it may also increases the boot time significantly!
 +
 
 +
To circumvent some of those problems AppArmor can cache profiles in {{ic|/etc/apparmor.d/cache/}}. However this behaviour is disabled by default therefore it must be done manually with {{ic|apparmor_parser}}. In order to write to the cache use {{ic|-W}} (overwrite existing profiles with {{ic|-T}}) and reload the profiles using {{ic|-r}}. Refer to [[#Parsing profiles]] for a brief overview of additional arguments.
  
 
== More Info ==
 
== More Info ==
Line 180: Line 92:
  
 
Every breach of policy triggers a message in the system log, and many distributions also integrate it into DBUS so that you get real-time violation warnings popping up on your desktop.
 
Every breach of policy triggers a message in the system log, and many distributions also integrate it into DBUS so that you get real-time violation warnings popping up on your desktop.
 +
 +
== Links ==
 +
* [http://wiki.apparmor.net/index.php/Main_Page Home Page]
 +
* [http://wiki.apparmor.net/index.php/AppArmor_Core_Policy_Reference AppArmor Core Policy Reference] — Detailed description of available options in a profile
 +
* [http://ubuntuforums.org/showthread.php?t=1008906 Ubuntu Tutorial] — General overview of available utilities and profile creation
 +
* [https://help.ubuntu.com/community/AppArmor Ubuntu Wiki] — Basic command overview
 +
* [http://wiki.apparmor.net/index.php/AppArmor_versions AppArmor Verions] — Version overview and links to the respective release notes
 +
* {{man|5|apparmor.d|url=http://manpages.ubuntu.com/manpages/oneiric/man5/apparmor.d.5.html}} — Structure of the AppArmor configuration directory
 +
* {{man|8|apparmor_parse|url=http://manpages.ubuntu.com/manpages/oneiric/man8/apparmor_parser.8.html}} — The most fundamental AppArmor utility to load, unload, cache and stat profiles
 +
* [http://wiki.apparmor.net/index.php/Kernel_interfaces Kernel Interfaces] — Low level interfaces to the AppArmor kernel module
 +
* [https://wiki.ubuntu.com/ApparmorProfileMigration Apparmor Profile Migration] — Emergence of profiles
 +
* [http://wiki.apparmor.net/index.php/Distro_CentOS Build Instructions for CentOS]
 +
* [[wikipedia:Linux Security Modules]] — Linux kernel module on which basis AppArmor is build upon
 +
* [https://launchpad.net/apparmor Launchpad Project Page]
 +
* [http://wiki.apparmor.net/index.php/Gittutorial Contributing] — Introduction to git mechanics and on how to contribute
 +
* {{Bug|21406}} — Initial discussion about the introduction of AppArmor
  
 
== See also ==
 
== See also ==
 
* [[TOMOYO Linux]]
 
* [[TOMOYO Linux]]
 
* [[SELinux]]
 
* [[SELinux]]

Latest revision as of 00:01, 15 September 2016

AppArmor is a Mandatory Access Control (MAC) system, implemented upon the Linux Security Modules (LSM).

Installation

Kernel

Note: The highly disputed user namespace (CONFIG_USER_NS=Y) isn't set in the kernel configuration, but may bring additional functionality to AppArmor. See FS#36969 for details on user namespaces.

When compiling the kernel, it is required to at least set the following options:

 CONFIG_SECURITY_APPARMOR=y
 CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1
 CONFIG_DEFAULT_SECURITY_APPARMOR=y
 CONFIG_AUDIT=y

For those new or altered variables to not get overridden, place them at the bottom of the config file or adjust the previous invocations accordingly.

Instead of setting CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE and CONFIG_DEFAULT_SECURITY_APPARMOR, you can also set kernel boot parameters: apparmor=1 security=apparmor.

Userspace Tools

Note: Since AppArmor builds and installs a kernel module it must be rebuilt against the current kernel on each update

The userspace tools and libraries to control AppArmor are supplied by the apparmorAUR package.

The package is a split package which consists of following sub-packages:

  • apparmor (meta package)
  • apparmor-libapparmor
  • apparmor-utils
  • apparmor-parser
  • apparmor-profiles
  • apparmor-pam
  • apparmor-vim

To load all AppArmor profiles on startup, enable apparmor.service.

Testing

After reboot you can test if AppArmor is really enabled using this command as root:

 # cat /sys/module/apparmor/parameters/enabled 
 Y

(Y=enabled, N=disabled, no such file = module not in kernel)

Disabling

To disable AppArmor for the current session, stop apparmor.service, or disable it to prevent it from starting at the next boot.

Alternatively you may choose to disable the kernel modules required by AppArmor by appending apparmor=0 security="" to the kernel boot parameters.

Configuration

Creating new profiles

To create new profiles using aa-genprof, auditd.service from the package audit must be running. This is because Arch Linux adopted systemd and doesn't do kernel logging to file by default. Apparmor can grab kernel audit logs from the userspace auditd daemon, allowing you to build a profile. To get kernel audit logs, you'll need to have rules in place to monitor the desired application. Most often a basic rule configured with auditctl(8) will suffice:

# auditctl -a exit,always -F arch=b64 -S all -F path=/usr/bin/chromium -F key=MonitorChromium

but be sure to read Audit framework#Adding rules if this is unfamiliar to you.

Note: Remember to stop the service afterwards (and maybe clear /var/log/audit/audit.log) because it may cause overhead depending on your rules.

Parsing profiles

To load, unload, reload, cache and stat profiles use apparmor_parser. The default action (-a) is to load a new profile, in order to overwrite an existing profile use the -r option and to remove a profile use -R. Each action may also apply to multiple profiles. Refer to apparmor_parser(8) man page for more information.

Security considerations

Preventing circumvention of path-based MAC via links

AppArmor can be circumvented via hardlinks in the standard POSIX security model. However, the kernel included the ability to prevent this vulnerability via the following settings:

/usr/lib/sysctl.d/50-default.conf
...
fs.protected_hardlinks = 1
fs.protected_symlinks = 1

Patches distributions like Ubuntu have applied to their kernels as workarounds as not needed anymore.

Tips and tricks

Get desktop notification on DENIED actions

To get a notification on your desktop whenever AppArmor enters a "DENIED" log entry start the notify daemon by

# aa-notify -p --display $DISPLAY

This daemon must be started at each boot.

Cache profiles

Since AppArmor has to translate the configured profiles into a binary format it may take some time to load them. Besides being bothersome for the user, it may also increases the boot time significantly!

To circumvent some of those problems AppArmor can cache profiles in /etc/apparmor.d/cache/. However this behaviour is disabled by default therefore it must be done manually with apparmor_parser. In order to write to the cache use -W (overwrite existing profiles with -T) and reload the profiles using -r. Refer to #Parsing profiles for a brief overview of additional arguments.

More Info

AppArmor, like most other LSMs, supplements rather than replaces the default Discretionary access control. As such it's impossible to grant a process more privileges than it had in the first place.

Ubuntu, SUSE and a number of other distributions use it by default. RHEL (and it's variants) use SELinux which requires good userspace integration to work properly. People tend to agree that it is also much much harder to configure correctly.

Taking a common example - A new Flash vulnerability: If you were to browse to a malicious website AppArmor can prevent the exploited plugin from accessing anything that may contain private information. In almost all browsers, plugins run out of process which makes isolating them much easier.

AppArmor profiles (usually) get stored in easy to read text files in /etc/apparmor.d

Every breach of policy triggers a message in the system log, and many distributions also integrate it into DBUS so that you get real-time violation warnings popping up on your desktop.

Links

See also