Difference between revisions of "AppArmor"

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[[Category:Security]]
 
[[Category:Security]]
 
[[Category:Kernel]]
 
[[Category:Kernel]]
{{Out of date}}
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[[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
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.
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  CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=1
 
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  CONFIG_DEFAULT_SECURITY_APPARMOR=y
See [[Sysctl#Preventing_link_TOCTOU_vulnerabilities]] for details.
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  CONFIG_AUDIT=y
  
== Implementation Status ==
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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}}.
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.
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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 However, as of May 2015, the kernel is outdated.
  
* https://aur.archlinux.org/packages.php?ID=42279
+
=== Userspace Tools ===
  
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 userspace tools and libraries to control AppArmor are supplied by the {{AUR|apparmor}} package.
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 ===
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The package is a split package which consists of following sub-packages:
Added lot of features:
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* apparmor (meta package)
 +
* apparmor-libapparmor
 +
* apparmor-utils
 
* apparmor-parser
 
* apparmor-parser
* libapparmor
 
* apparmor-utils
 
 
* apparmor-profiles
 
* apparmor-profiles
* apparmor-notify
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* apparmor-pam
* apparmor-lib
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* apparmor-vim
* apparmor-perl
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* apparmor-python
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* apparmor-ruby
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* apparmor-dbus
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* apparmor-profile-editor
+
  
But we still miss following features (TODO):
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To load all AppArmor profiles on startup, the {{AUR|apparmor}} package includes a systemd unit:
* init (rc.d) scripts! http://aur.pastebin.com/beQ4BjGX
+
{{bc|# systemctl enable apparmor}}
* chase missing dependencies
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* test everything
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* make list of files that should go to backup=() arrays in packages...
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* changehat modules for PAM(!), Apache and Tomcat (btw those are dependent on libapparmor)
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* out-of-box-experience know-how
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** make some package with profiles for all [core] packages enabled by default without need for any further user configuration
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** etc...
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* apparmor gnome applet (can't build, deprecated...)
+
  
== Links ==
+
=== Testing ===
* Official pages
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** 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/
+
After reboot you can test if AppArmor is really enabled using this command as root:
* http://wiki.apparmor.net/index.php/AppArmor_Core_Policy_Reference
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  # cat /sys/module/apparmor/parameters/enabled
 +
  Y
 +
(Y=enabled, N=disabled, no such file = module not in kernel)
  
* http://ubuntuforums.org/showthread.php?t=1008906 (Tutorial)
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{{Note|Since AppArmor builds and installs a kernel module it must be rebuilt against the current kernel on each update}}
* https://help.ubuntu.com/community/AppArmor
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*{{Bug|21406}}
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* http://stuff.mit.edu/afs/sipb/contrib/linux/Documentation/apparmor.txt
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* http://wiki.apparmor.net/index.php/Kernel_interfaces
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* http://wiki.apparmor.net/index.php/AppArmor_versions
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* http://manpages.ubuntu.com/manpages/oneiric/man5/apparmor.d.5.html
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* http://manpages.ubuntu.com/manpages/oneiric/man8/apparmor_parser.8.html
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* http://wiki.apparmor.net/index.php/Distro_CentOS
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* http://bodhizazen.net/aa-profiles/
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* https://wiki.ubuntu.com/ApparmorProfileMigration
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* [[wikipedia:Linux_Security_Modules]]
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* http://wiki.apparmor.net/index.php/Gittutorial
+
  
== AppArmor Packages ==
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== Disabling ==
* Arch's {{Pkg|linux}} package has AppArmor support
+
To disable AppArmor temporarily, you can add {{ic|apparmor=0 security=""}} to the [[kernel parameters|kernel boot parameters]].
* aur/[https://aur.archlinux.org/packages.php?ID=42279 apparmor]
+
  
== Kernel Configuration ==
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Alternatively run
Here is configuration of ArchLinux kernel which enables AppArmor (just FYI, you do not need to touch it):
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# systemctl stop apparmor.service
  CONFIG_SECURITY_APPARMOR=y
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to disable it for the current session.
  CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE=0
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  # 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)
+
== 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 create rules. See this section: [[Audit framework#Adding rules]].
  
== Bootloader Configuration ==
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Be sure to stop the service afterwards (and maybe clear {{ic|/var/log/audit/audit.log}}) because it causes overhead.
=== Enable ===
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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 parameters|kernel boot parameters]].  
+
  
After reboot you can test if AppArmor is really enabled using this command as root:
+
== Security considerations ==
  # cat /sys/module/apparmor/parameters/enabled
+
=== Preventing circumvention of path-based MAC via links ===
  Y
+
(Y=enabled, N=disabled, no such file = module not in kernel)
+
  
==== Disable ====
+
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:
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. If so, Add {{ic|1=apparmor=0 security=""}} to [[kernel parameters|kernel boot parameters]].
+
{{hc|/usr/lib/sysctl.d/50-default.conf|2=
 +
...
 +
fs.protected_hardlinks = 1
 +
fs.protected_symlinks = 1}}
  
== System Configuration ==
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Patches distributions like Ubuntu have applied to their kernels as workarounds as not needed anymore.
=== Mounts (/etc/fstab securityfs) ===
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http://wiki.apparmor.net/index.php/Kernel_interfaces
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  none    /sys/kernel/security securityfs defaults            0      0
+
  
== UserSpace Tools ==
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== Tips and tricks ==
=== Users ===
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=== Get desktop notification on DENIED actions ===
You can currently install userspace tools from [[AUR]].
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To get a notification on your desktop whenever AppArmor enters a "DENIED" log entry start the notify daemon by
 
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# aa-notify -p --display $DISPLAY
=== Maintainers ===
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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: http://wiki.apparmor.net/index.php/AppArmor_versions
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e.g.: Kernel 2.6.36 is compatible with AppArmor 2.5.1
+
  
 
== More Info ==
 
== More Info ==
Line 116: Line 82:
  
 
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 09:42, 14 August 2016

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. 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 create rules. See this section: Audit framework#Adding rules.

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 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.

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