Include(Debugging/Header)

Introduction

AppArmor is used by Ubuntu to protect the system from misbehaving or compromised applications. When looking at or creating bug reports, it is important to distinguish between bugs in the application and bugs in the apparmor profile for the application.

How to file

When filing a bug report regarding an apparmor profile, you need three things:

1. The package containing the profile. Bugs should be filed against this package. Profiles are found in /etc/apparmor.d/ and you can find what package the profile belongs to with 'dpkg -S'. For example, to find out which package provides /etc/apparmor.d/usr.sbin.cupsd, use:

   $ dpkg -S /etc/apparmor.d/usr.sbin.cupsd

2. The 'audit' entries from /var/log/kern.log, and any files in /var/log/apparmor.
3. The steps needs to trigger the bug in the profile

Note: please remember that it is generally not a bug in the profile if a non-default configuration is being used by the application. One example might be having mysql store its databases in /home/mysql instead of /var/lib/mysql. In these cases, the profile should just be changed by the admin.

Debugging procedure

To debug an apparmor profile, look in /var/log/kern.log for 'audit' entries. An example will look something like:

Feb  4 14:30:33 example-client kernel: [   73.459739] audit(1202153433.710:6): operation="file_mmap" request_mask="mrw::" denied_mask="m::" name="/var/lib/ldap/__db.005" pid=5375 profile="/usr/sbin/slapd" namespace="default"

The important things to look for are:

1. 'audit(...):' -- this tells you it is an apparmor generated log entry
2. 'profile="/usr/sbin/slapd"' -- this tells you what profile generated this message. Profiles are located in /etc/apparmor.d, and when looking for the profile, substitute '.' for the '/' from the log entry. For example, the above entry's apparmor profile is located in /etc/apparmor.d/usr.sbin.slapd

IMPORTANT: If you do not have any 'audit' entries in /var/log/kern.log at the time the application had a problem, then this is not an apparmor bug. Please see DebuggingProcedures for more information on filing a bug.

When debugging, it may also be useful to put apparmor into 'complain' mode. This will allow your application to function normally while apparmor reports accesses that are not in the profile. To enable 'complain' mode, use:

sudo aa-complain /path/to/bin

where '/path/to/bin' is the absolute path to the binary, as reported in the 'profile=...' portion of the 'audit' entry. Eg:

sudo aa-complain /usr/sbin/slapd

To re-enable enforcing mode, use 'aa-enforce' instead:

sudo aa-enforce /path/to/bin

To disable a profile:

sudo touch /etc/apparmor.d/disable/path.to.bin
sudo /etc/init.d/apparmor reload

Fixing profile bugs

Fixing apparmor profiles bugs is usually straightforward. Enable 'complain' mode (see above), then exercise your application. You can then either use 'aa-logprof' to walk you through the process of updating the profile, or simply edit the profile directly. Once the profile is updated, reload the the profile with:

cat /etc/apparmor.d/<profile file> | sudo apparmor_parser -r
sudo /etc/init.d/apparmor reload

After the profile is working as desired, you can attach it to the bug report, stating that you have a working profile. For more on editing and creating profiles, see the community [https://help.ubuntu.com/community/AppArmor AppArmor] documentation.

How to Triage

Help with triaging bugs for apparmor profiles is very welcome. To find out what exactly is the problem, we always need the 'audit' in /var/log/kern.log and if they exist, the log files in /var/log/apparmor/*. Most of the time these provide enough information to know what went wrong. If these are missing, it is recommended to ask for them with a phrase like:

Thanks for taking the time to report this bug and helping to make Ubuntu better. Could you please add '/var/log/kern.log' and the log files in '/var/log/apparmor/*' as attachments to your bug report? Thanks in advance.

If the log shows that the problem is not apparmor related (eg, there are no 'audit' entries in kern.log), then please reassign the bug to the package with the bug.

How to Forward

Forwarding of apparmor profile bugs upstream is not necessary as these profiles are Ubuntu-specific.

Known bugs

Description of known bug reports that may receive duplicates and how to recognise them. This information should be obtained by looking for bugs tagged as 'metabug'.

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CategoryBugSquad CategoryDebugging