Difference between revisions of "AppArmor"

From ArchWiki
Jump to: navigation, search
(Preventing circumvention of path-based MAC via links: rq)
m (Fix style)
 
(38 intermediate revisions by 17 users not shown)
Line 1: Line 1:
 
[[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{{Out of date}}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 ===
  
== Preventing circumvention of path-based MAC via links ==
+
When compiling the kernel, it needs 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.
+
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}}.
  
See [[Sysctl#Preventing_link_TOCTOU_vulnerabilities]] for details.
+
There also is a stock kernel with AppArmor: {{AUR|linux-apparmor}}{{Broken package link|{{aur-mirror|linux-apparmor}}}}. However, as of May 2015, the kernel is outdated.
  
== 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.
+
The userspace tools and libraries to control AppArmor are supplied by the {{AUR|apparmor}} package.
  
* https://aur.archlinux.org/packages.php?ID=42279
+
The package is a split package which consists of following sub-packages:
 
+
* apparmor (meta 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.
+
* apparmor-libapparmor
Also there is an [https://aur.archlinux.org/packages.php?ID=60269 AUR kernel]
+
* apparmor-utils
which includes apparmor specific patches from Ubuntu's [https://launchpad.net/apparmor launchpad].
+
 
+
=== AUR/apparmor package ===
+
Added lot of features:
+
 
* apparmor-parser
 
* apparmor-parser
* libapparmor
 
* apparmor-utils
 
 
* 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):
+
* 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 ====
+
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 ====
+
To load all AppArmor profiles on startup, the {{AUR|apparmor}} package includes a systemd unit:
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).
+
{{bc|# systemctl enable apparmor}}
  
  # (0) Arch Linux
+
=== Testing ===
  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 40:
 
(Y=enabled, N=disabled, no such file = module not in kernel)
 
(Y=enabled, N=disabled, no such file = module not in kernel)
  
==== Disable ====
+
{{Note|Since AppArmor builds and installs a kernel module it must be rebuilt against the current kernel on each update}}
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 ==
+
== Disabling ==
=== Mounts (/etc/fstab securityfs) ===
+
To disable AppArmor temporarily, you can add {{ic|apparmor=0 security=""}} to the [[kernel parameters|kernel boot parameters]].
https://apparmor.wiki.kernel.org/index.php/Kernel_interfaces
+
  none    /sys/kernel/security securityfs defaults            0      0
+
  
=== Init scripts ===
+
Alternatively run
In the future, we'll implement some {{ic|/etc/rc.d/}} scripts that will enable and load profiles during startup.
+
# systemctl stop apparmor.service
http://aur.pastebin.com/beQ4BjGX
+
to disable it for the current session.
  
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.
+
== Creating new profiles ==
 +
To create new profiles using {{ic|aa-genprof}}, {{ic|auditd.service}} from the package {{Pkg|audit}} must be running.
 +
Be sure to stop the service afterwards (and maybe clear {{ic|/var/log/audit/audit.log}}) because it causes overhead.
  
==== For developers ====
+
== Security considerations ==
 +
=== Preventing circumvention of path-based MAC via links ===
  
From {{ic|/lib/apparmor/rc.apparmor.functions}}
+
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.
  
  # NOTE: rc.apparmor initscripts that source this file need to implement
+
See [[Security#Preventing link TOCTOU vulnerabilities]] for details.
  # the following set of functions:
+
  # aa_action
+
  # aa_log_action_start
+
  # aa_log_action_end
+
  # 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 ==
+
== Tips and tricks ==
=== Users ===
+
=== Get desktop notification on DENIED actions ===
You can currently install userspace tools from [[AUR]].
+
To get a notification on your desktop whenever AppArmor enters a "DENIED" log entry start the notify daemon by
 
+
# aa-notify -p --display $DISPLAY
=== Maintainers ===
+
This daemon must be started at each boot.
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
+
e.g.: Kernel 2.6.36 is compatible with AppArmor 2.5.1
+
  
 
== More Info ==
 
== More Info ==
Line 180: Line 76:
  
 
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 ==
 +
* Official pages
 +
** Kernel: https://apparmor.wiki.kernel.org/ http://wiki.apparmor.net/
 +
** 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
 +
* http://wiki.apparmor.net/index.php/Kernel_interfaces
 +
* http://wiki.apparmor.net/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
 +
* http://wiki.apparmor.net/index.php/Distro_CentOS
 +
* http://bodhizazen.net/aa-profiles/
 +
* https://wiki.ubuntu.com/ApparmorProfileMigration
 +
* [[wikipedia:Linux Security Modules]]
 +
* http://wiki.apparmor.net/index.php/Gittutorial
  
 
== See also ==
 
== See also ==
 
* [[TOMOYO Linux]]
 
* [[TOMOYO Linux]]
 
* [[SELinux]]
 
* [[SELinux]]

Latest revision as of 03:37, 22 December 2015

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

Installation

Kernel

When compiling the kernel, it needs the following options:

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

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

There also is a stock kernel with AppArmor: linux-apparmorAUR[broken link: archived in aur-mirror]. However, as of May 2015, the kernel is outdated.

Userspace Tools

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, the apparmorAUR package includes a systemd unit:

# systemctl enable apparmor

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)

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

Disabling

To disable AppArmor temporarily, you can add apparmor=0 security="" to the kernel boot parameters.

Alternatively run

# systemctl stop apparmor.service

to disable it for the current session.

Creating new profiles

To create new profiles using aa-genprof, auditd.service from the package audit must be running. Be sure to stop the service afterwards (and maybe clear /var/log/audit/audit.log) because it causes overhead.

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 now includes the ability to prevent this vulnerability, without needing the patches distributions like Ubuntu have applied to their kernels as workarounds.

See Security#Preventing link TOCTOU vulnerabilities for details.

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.

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