**AppArmor** is a kernel enhancement to confine **programs** to a **limited** set of **resources** with **per-program profiles**. Profiles can **allow****capabilities** like network access, raw socket access, and the permission to read, write, or execute files on matching paths.
It's a Mandatory Access Control or **MAC** that binds **access control** attributes **to programs rather than to users**.\
AppArmor confinement is provided via **profiles loaded into the kernel**, typically on boot.\
AppArmor profiles can be in one of **two modes**:
* **Enforcement**: Profiles loaded in enforcement mode will result in **enforcement of the policy** defined in the profile **as well as reporting** policy violation attempts (either via syslog or auditd).
* **Complain**: Profiles in complain mode **will not enforce policy** but instead **report** policy **violation** attempts.
AppArmor differs from some other MAC systems on Linux: it is **path-based**, it allows mixing of enforcement and complain mode profiles, it uses include files to ease development, and it has a far lower barrier to entry than other popular MAC systems.
### Parts of AppArmor
* **Kernel module**: Does the actual work
* **Policies**: Defines the behaviour and containment
* **Parser**: Loads the policies into kernel
* **Utilities**: Usermode programs to interact with apparmor
### Profiles path
Apparmor profiles are usually saved in _**/etc/apparmor.d/**_\
With `sudo aa-status` you will be able to list the binaries that are restricted by some profile. If you can change the char "/" for a dot of the path of each listed binary and you will obtain the name of the apparmor profile inside the mentioned folder.
For example, a **apparmor** profile for _/usr/bin/man_ will be located in _/etc/apparmor.d/usr.bin.man_
### Commands
```bash
aa-status #check the current status
aa-enforce #set profile to enforce mode (from disable or complain)
aa-complain #set profile to complain mode (from diable or enforcement)
apparmor_parser #to load/reload an altered policy
aa-genprof #generate a new profile
aa-logprof #used to change the policy when the binary/program is changed
aa-mergeprof #used to merge the policies
```
## Creating a profile
* In order to indicate the affected executable, **absolute paths and wildcards** are allowed (for file globbing) for specifying files.
* **ix** (to execute another program with the new program inheriting policy)
* **Px** (execute under another profile, after cleaning the environment)
* **Cx** (execute under a child profile, after cleaning the environment)
* **Ux** (execute unconfined, after cleaning the environment)
* **Variables** can be defined in the profiles and can be manipulated from outside the profile. For example: @{PROC} and @{HOME} (add #include \<tunables/global> to the profile file)
* **Deny rules are supported to override allow rules**.
### aa-genprof
To easily start creating a profile apparmor can help you. It's possible to make **apparmor inspect the actions performed by a binary and then let you decide which actions you want to allow or deny**.\
You just need to run:
```bash
sudo aa-genprof /path/to/binary
```
Then, in a different console perform all the actions that the binary will usually perform:
```bash
/path/to/binary -a dosomething
```
Then, in the first console press "**s**" and then in the recorded actions indicate if you want to ignore, allow, or whatever. When you have finished press "**f**" and the new profile will be created in _/etc/apparmor.d/path.to.binary_
{% hint style="info" %}
Using the arrow keys you can select what you want to allow/deny/whatever
{% endhint %}
### aa-easyprof
You can also create a template of an apparmor profile of a binary with:
```bash
sudo aa-easyprof /path/to/binary
# vim:syntax=apparmor
# AppArmor policy for binary
# ###AUTHOR###
# ###COPYRIGHT###
# ###COMMENT###
#include <tunables/global>
# No template variables specified
"/path/to/binary" {
#include<abstractions/base>
# No abstractions specified
# No policy groups specified
# No read paths specified
# No write paths specified
}
```
{% hint style="info" %}
Note that by default in a created profile nothing is allowed, so everything is denied. You will need to add lines like `/etc/passwd r,` to allow the binary read `/etc/passwd` for example.
{% endhint %}
You can then **enforce** the new profile with
```bash
sudo apparmor_parser -a /etc/apparmor.d/path.to.binary
```
### Modifying a profile from logs
The following tool will read the logs and ask the user if he wants to permit some of the detected forbidden actions:
```bash
sudo aa-logprof
```
{% hint style="info" %}
Using the arrow keys you can select what you want to allow/deny/whatever
{% endhint %}
### Managing a Profile
```bash
#Main profile management commands
apparmor_parser -a /etc/apparmor.d/profile.name #Load a new profile in enforce mode
apparmor_parser -C /etc/apparmor.d/profile.name #Load a new profile in complain mode
By default **Apparmor docker-default profile** is generated from [https://github.com/moby/moby/tree/master/profiles/apparmor](https://github.com/moby/moby/tree/master/profiles/apparmor)
**docker-default profile Summary**:
* **Access** to all **networking**
* **No capability** is defined (However, some capabilities will come from including basic base rules i.e. #include \<abstractions/base> )
* **Writing** to any **/proc** file is **not allowed**
* Other **subdirectories**/**files** of /**proc** and /**sys** are **denied** read/write/lock/link/execute access
* **Mount** is **not allowed**
* **Ptrace** can only be run on a process that is confined by **same apparmor profile**
Once you **run a docker container** you should see the following output:
Note that **apparmor will even block capabilities privileges** granted to the container by default. For example, it will be able to **block permission to write inside /proc even if the SYS\_ADMIN capability is granted** because by default docker apparmor profile denies this access:
Note that you can **add/remove****capabilities** to the docker container (this will be still restricted by protection methods like **AppArmor** and **Seccomp**):
*`--cap-drop=ALL --cap-add=SYS_PTRACE` drop all caps and only give `SYS_PTRACE`
{% hint style="info" %}
Usually, when you **find** that you have a **privileged capability** available **inside** a **docker** container **but** some part of the **exploit isn't working**, this will be because docker **apparmor will be preventing it**.
{% endhint %}
### Example
(Example from [**here**](https://sreeninet.wordpress.com/2016/03/06/docker-security-part-2docker-engine/))
To illustrate AppArmor functionality, I created a new Docker profile “mydocker” with the following line added:
```
deny /etc/* w, # deny write for all files directly in /etc (not in a subdir)
```
To activate the profile, we need to do the following:
```
sudo apparmor_parser -r -W mydocker
```
To list the profiles, we can do the following command. The command below is listing my new AppArmor profile.
```
$ sudo apparmor_status | grep mydocker
mydocker
```
As shown below, we get error when trying to change “/etc/” since AppArmor profile is preventing write access to “/etc”.
**AppArmor is path based**, this means that even if it might be **protecting** files inside a directory like **`/proc`** if you can **configure how the container is going to be run**, you could **mount** the proc directory of the host inside **`/host/proc`** and it **won't be protected by AppArmor anymore**.
In [**this bug**](https://bugs.launchpad.net/apparmor/+bug/1911431) you can see an example of how **even if you are preventing perl to be run with certain resources**, if you just create a a shell script **specifying** in the first line **`#!/usr/bin/perl`** and you **execute the file directly**, you will be able to execute whatever you want. E.g.:
