Firejail

Resources

Firejail is a SUID sandboxing program. It reduces the risk of security breaches by restricting the running environment of untrusted applications using, inter alia, Linux namespaces and seccomp-bpf. The software includes security profiles for a large number of applications like Mozilla Firefox, Chromium, VLC, or Transmission.

Installation

USE flags

USE flags for sys-apps/firejail Security sandbox for any type of processes

`X`	Enable X11 sandboxing
`apparmor`	Enable support for custom AppArmor profiles
`chroot`	Enable chrooting to custom directory
`contrib`	Install contrib scripts
`dbusproxy`	Enable DBus proxying to filter access in supporting profiles
`file-transfer`	Enable file transfers between sandboxes and the host system
`globalcfg`	Enable global config file
`network`	Enable networking features
`overlayfs`	Enable overlayfs
`private-home`	Enable private home feature
`suid`	Enable setuid root program, with potential security risks
`test`	Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
`userns`	Enable attaching a new user namespace to a sandbox (--noroot option)
`whitelist`	Enable whitelist

Data provided by the Gentoo Package Database · Last update: 2020-12-02 23:21 More information about USE flags

The x11 USE flag sandbox replaces the regular X11 server with Xpra or Xephyr server. This prevents X11 keyboard loggers and screenshot utilities from accessing the main X11 server but introduces a lot of additional dependencies.

Emerge

root #emerge --ask sys-apps/firejail

Alternatively sys-apps/firejail-lts can be used.

Configuration

Firejail comes with numerous default profiles for many popular applications located in /etc/firejail/. In many cases the default profile configuration is sufficient. In addition to configuring a profile users may wish to set up a shortcut to enable firejail to be run by default for their selected application.

Profiles

The list of preconfigured profiles is available in /etc/firejail/.

If you wish to make customizations for an existing profile simply copy it to your home directory and edit as necessary:

user $cp /etc/firejail/firefox.profile ~/.config/firejail/firefox.profile

To make a profile for an application without a preconfigured profile you can use the default profile as a basis:

user $cp /etc/firejail/default.profile ~/.config/firejail/app-name.profile

Here are some example options you may wish to include in a custom profile:

FILE ~/.config/firejail/app-name.configCustom profile example

whitelist ~/pictures/

whitelist ~/share/
read-only ~/share/

whitelist ~/dev/WebExtensions/
read-only ~/dev/WebExtensions/

whitelist ~/.cache/fish/

blacklist /mnt
blacklist /opt

Using Firejail by default

A symbolic link to /usr/bin/firejail under the name of a program, will start the program in Firejail sandbox. A good place is /usr/local/bin directory. For example to run Firefox with firejail by default:

root #ln -s /usr/bin/firejail /usr/local/bin/firefox

This works for clicking on desktop environment icons, menus etc. Use firejail --tree to verify the program is sandboxed.

user $firejail --tree

23615:larry:firejail /usr/bin/firefox 
  23616:larry:firejail /usr/bin/firefox 
    23618:larry:/usr/bin/firefox

Alternatively you can create the following file instead and make it executable:

FILE /usr/local/bin/firefoxFirejail Desktop Integration

#!/bin/bash
firejail /usr/bin/firefox $@

This method allows command line options to be passed to firejail. Remember to make it executable with chmod +x /usr/local/bin/firefox.

To use Firejail by default for all applications for which it has profiles, run the firecfg tool as root.

root #firecfg

System-wide Configuration

System-wide configuration is set in /etc/firejail/firejail.config. If you have executables in /usr/local/bin corresponding to one of your firejailed applications combined with the private-bin profile option then make sure private-bin-no-local is set to yes

FILE /etc/firejail/firejail.configSystem-wide settings example

# Remove /usr/local directories from private-bin list, default disabled.
private-bin-no-local yes

Kernel

Optionally you can enable user namespaces in the kernel so they can be utilized by firejail:

KERNEL Enabling user namespaces

General setup --->
  Namespaces support --->
    <*>  User namespace

Usage

Usage is simple as:

user $firejail firefox

Private mode can be used as a quick way of hiding all the files in your home directory from sandboxed programs. It is enabled using --private command line option:

user $firejail --private firefox

Additionally, firejail can provide full graphical isolation for X11-based programs like firefox; an in-depth tutorial for doing so may be read here.

Troubleshooting

firemon

firejail comes with a tool firemon which can be used to help with troubleshooting. To use it run firemon as root then in a separate terminal start the application you wish to troubleshoot with firejail application.

not all executables from --private-bin list were found.

Either disable the private-bin option in your application profile or ensure private-bin-no-local yes is set in /etc/firejail/firejail.config.

user namespaces not available in the current kernel.

Make sure user namespaces are set in the kernel. CONFIG_USER_NS=y

External resources