qTox/security/apparmor

Hardening qTox with AppArmor

qTox can be confined with AppArmor on Linux to reduce attack vectors in case remote code execution exploit is being used. Please note that MAC's (of course) does not guarantee perfect security, but it will:

• Deny access to your ~/.bashrc, ~/.ssh/* ~/.config/path/to/your/password/manager/file, etc.
• Deny creating autostart entries (in ~/.config/autostart, etc).
• Deny launching random executables (like sudo, su, etc...).
• And more.

Consider using additional security measures like Firejail to improve security even more.

Please also note that not all distributions have full AppArmor feature set available. For example, Debian (at least up to Debian 10 (buster)) does not have network, DBus mediation available. Also, X Server, shared user configuration files (like ~/.config/QtProject.conf, caches, etc), opening web links via unconfined browsers introduces additional attack vectors, too. So please be cautious even with number of security measures applied.

AppArmor profile attaches only to /usr/bin/qtox and /usr/local/bin/qtox executables by default. See Tuning permissions for custom setups.

Installing profile

Select AppArmor profile from appropriate security/apparmor/X subdirectory depending on what AppArmor version is available for your Linux distribution release:

• 2.13.2
  • Debian 10 (buster) (or newer)
  • openSUSE Tumbleweed
• 2.12.1
  • Debian 9 (stretch) or older
  • Ubuntu 19.04 or older

To enable AppArmor profile on your system, run prepared install script:

sudo security/apparmor/x.y.z/install.sh

Restart qTox if it was already running before enabling AppArmor profile.

Checking if qTox is actually confined

Run aa-status command line utility and check if qTox is listed within X processes are in enforced mode. list:

sudo aa-status
   ...
21 processes are in enforce mode.
   /usr/lib/ipsec/charon (2421)            
   /usr/sbin/cups-browsed (839)
   ...
   /usr/bin/qtox (16315) qtox
   ...

Alternatively, use ps and grep:

ps auxZ | fgrep qtox
qtox (enforce)                  vincas   16315  2.0  1.1 1502292 180220 ?      SLl  12:21   0:38 /usr/bin/qtox

If OK it's marked as (enforce). unconfined means AppArmor profile is not attached to the process, no confinement is being applied.

Troubleshooting

If you believe that some feature is unavailable, or some files you need access to are inaccessible due to enforced AppArmor profile, check system logs for the hints.

On Debian/Ubuntu:

sudo fgrep DENIED /var/log/syslog

On openSUSE, OR if you have auditd daemon installed:

sudo fgrep DENIED /var/log/audit/audit.log

You will see messages like this:

type=AVC msg=audit(1549793273.269:149): apparmor="DENIED" operation="open" profile="qtox" name="/home/vincas/.config/klanguageove
rridesrc" pid=3037 comm="qtox" requested_mask="r" denied_mask="r" fsuid=1000 ouid=1000

This means that read access was denied to the file /home/vincas/.config/klanguageoverridesrc, owned by you (ouid 1000), by AppArmor profile qtox (available in /etc/apparmor.d/usr.bin.qtox).

Please create issue if you detect new AppArmor DENIED messages and you believe that these denials are relevant for other users too. Meanwhile, workaround by adding manual rule. DO NOT modify /etc/apparmor.d/usr.bin.qtox directly! See Tuning permissions for fixing access issues.

Tuning permissions

If you need access to files (for file sharing) other than from your $HOME or mounted media, create/modify /etc/apparmor.d/tunables/usr.bin.qtox.d/local file and append writable path variable:

@{qtox_additional_rw_dirs} += /path/to/some/directory

Alternatively, if you need more custom/advanced rules (not only for file access), create/modify /etc/apparmor.d/local/usr.bin.qtox file.

Rule example for reading only, recursively (note the comma!):

/path/to/directory/** r,

For reading and writing, recursively:

/path/to/directory/** rw,

Restart AppArmor to reload profiles after modifications:

sudo systemctl restart apparmor

If AppArmor restart fails, check syntax errors by invoking AppArmor parser directly:

sudo apparmor_parser -r /etc/apparmor.d/usr.bin.qtox

For custom installations, when qTox executable is not /usr/bin/qtox or /usr/local/bin/qtox:

1. create /etc/apparmor.d/tunables/usr.bin.qtox.d/local, adding @{qtox_prefix} += /path/to/your/custom/install/prefix line.
2. modify /etc/apparmor.d/usr.bin.qtox profile attachement path: profile qtox /{usr{,local}/bin/qtox,path/to/your/qtox_executable} {

Restart AppArmor and check if qTox process under custom path is actually confined.

Other resources

Check Debian, Ubuntu, Upstream AppArmor Wiki pages for more info.