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Sunday, 10 April 2022

Bubblejail

Bubblewrap based sandboxing for desktop applications.

Language grade: Python Total alerts Python (mypy, flake8)

Bubblejail is a bubblewrap-based alternative to Firejail.

Description

Bubblejail's design is based on observations of Firejail's faults.

One of the biggest issues with Firejail is that you can accidentally run unsandboxed applications and not notice.

Bubblejail, instead of trying to transparently overlay an existing home directory, creates a separate home directory.

Every Instance represents a separate home directory. Typically, every sandboxed application has its own home directory.

Each instance has a services.toml file which defines the configuration of the instance such as system resources that the sandbox should have access to.

Service represents some system resources that the sandbox can be given access to. For example, the Pulse Audio service gives access to the Pulse Audio socket so that the application can use sound.

Profile is a predefined set of services that a particular application uses. Using profiles is entirely optional.

Installation

Packages

Packaging status

AUR git

AUR stable

Manual Installation

If your distro does not have a package you can try to manually install with meson

Requirements

  • Python 3 (>= 3.9) - python interpreter
  • Python XDG - XDG standards for python
  • Python TOML - TOML file support for python
  • Bubblewrap (>= 0.5.0) - sandboxing command line utility
  • XDG D-Bus Proxy - filtering dbus proxy
  • Desktop File Utils - to manipulate default applications
  • Python Qt5 - for GUI
  • Meson - build system
  • m4 - macro generator used during build
  • libseccomp - helper library for seccomp rules

Optional:

  • bash-completion - auto-completions for bash shell
  • fish - auto-completions for fish shell

Using meson to install

  1. Run meson setup build to setup build directory
  2. Switch to build directory cd build
  3. Compile meson compile
  4. Install sudo meson install

If you want to uninstall run ninja uninstall from build directory.

Screenshots

Configuration utility

bubblejailGUI

Quick start

  1. Install bubblejail from AUR git or AUR stable
  2. Install the application you want to sandbox (for example, firefox)
  3. Run GUI. (should be found under name Bubblejail Configuration)
  4. Press 'Create instance' button at the bottom.
  5. Select a profile. (for example, firefox)
  6. Optionally change name
  7. Press 'Create'
  8. The new instance is created along with new desktop entry.

Command-line utility documentation

See man page:

man 1 bubblejail

Usage examples

Create new instance using firefox profile

bubblejail create --profile firefox FirefoxInstance

Run instance

bubblejail run FirefoxInstance

Create a generic instance without a desktop entry

bubblejail create --no-desktop-entry --profile generic Test

Available services

  • common: settings that are not categorized
  • x11: X windowing system. Also includes Xwayland.
  • wayland: Pure wayland windowing system.
  • network: Access to network.
  • pulse_audio: Pulse Audio audio system.
  • home_share: Shared folder relative to home.
    • home_paths: List of path strings to share with sandbox. Required.
  • direct_rendering: Access to GPU.
    • enable_aco: Boolean to enable high performance Vulkan compiler for AMD GPUs.
  • systray: Access to the desktop tray bar.
  • joystick: Access to joysticks and gamepads.
  • root_share: Share access relative to /.
    • paths: List of path strings to share with sandbox. Required.
  • openjdk: Access to Java libraries.
  • notify: Access to desktop notifications.
  • ibus: Multilingual input.

Available profiles

  • firefox
  • firefox_wayland: Firefox on wayland
  • code_oss: open source build of vscode
  • steam
  • lutris
  • chromium
  • transmission-gtk
  • generic: most common services, useful for sandboxing applications without profiles.
from  https://github.com/igo95862/bubblejail
-----

Unprivileged sandboxing tool.

Bubblewrap

Many container runtime tools like systemd-nspawndocker, etc. focus on providing infrastructure for system administrators and orchestration tools (e.g. Kubernetes) to run containers.

These tools are not suitable to give to unprivileged users, because it is trivial to turn such access into a fully privileged root shell on the host.

User namespaces

There is an effort in the Linux kernel called user namespaces which attempts to allow unprivileged users to use container features. While significant progress has been made, there are still concerns about it, and it is not available to unprivileged users in several production distributions such as CentOS/Red Hat Enterprise Linux 7, Debian Jessie, etc.

See for example CVE-2016-3135 which is a local root vulnerability introduced by userns. This March 2016 post has some more discussion.

Bubblewrap could be viewed as setuid implementation of a subset of user namespaces. Emphasis on subset - specifically relevant to the above CVE, bubblewrap does not allow control over iptables.

The original bubblewrap code existed before user namespaces - it inherits code from xdg-app helper which in turn distantly derives from linux-user-chroot.

Security

The maintainers of this tool believe that it does not, even when used in combination with typical software installed on that distribution, allow privilege escalation. It may increase the ability of a logged in user to perform denial of service attacks, however.

In particular, bubblewrap uses PR_SET_NO_NEW_PRIVS to turn off setuid binaries, which is the traditional way to get out of things like chroots.

Users

This program can be shared by all container tools which perform non-root operation, such as:

We would also like to see this be available in Kubernetes/OpenShift clusters. Having the ability for unprivileged users to use container features would make it significantly easier to do interactive debugging scenarios and the like.

Installation

bubblewrap is available in the package repositories of the most Linux distributions and can be installed from there.

If you need to build bubblewrap from source, you can do this with meson or autotools.

meson:

meson _builddir
meson compile -C _builddir
meson install -C _builddir

autotools:

./autogen.sh
make
sudo make install

Usage

bubblewrap works by creating a new, completely empty, mount namespace where the root is on a tmpfs that is invisible from the host, and will be automatically cleaned up when the last process exits. You can then use commandline options to construct the root filesystem and process environment and command to run in the namespace.

There's a larger demo script in the source code, but here's a trimmed down version which runs a new shell reusing the host's /usr.

bwrap --ro-bind /usr /usr --symlink usr/lib64 /lib64 --proc /proc --dev /dev --unshare-pid bash

This is an incomplete example, but useful for purposes of illustration. More often, rather than creating a container using the host's filesystem tree, you want to target a chroot. There, rather than creating the symlink lib64 -> usr/lib64 in the tmpfs, you might have already created it in the target rootfs.

Sandboxing

The goal of bubblewrap is to run an application in a sandbox, where it has restricted access to parts of the operating system or user data such as the home directory.

bubblewrap always creates a new mount namespace, and the user can specify exactly what parts of the filesystem should be visible in the sandbox. Any such directories you specify mounted nodev by default, and can be made readonly.

Additionally you can use these kernel features:

User namespaces (CLONE_NEWUSER): This hides all but the current uid and gid from the sandbox. You can also change what the value of uid/gid should be in the sandbox.

IPC namespaces (CLONE_NEWIPC): The sandbox will get its own copy of all the different forms of IPCs, like SysV shared memory and semaphores.

PID namespaces (CLONE_NEWPID): The sandbox will not see any processes outside the sandbox. Additionally, bubblewrap will run a trivial pid1 inside your container to handle the requirements of reaping children in the sandbox. This avoids what is known now as the Docker pid 1 problem.

Network namespaces (CLONE_NEWNET): The sandbox will not see the network. Instead it will have its own network namespace with only a loopback device.

UTS namespace (CLONE_NEWUTS): The sandbox will have its own hostname.

Seccomp filters: You can pass in seccomp filters that limit which syscalls can be done in the sandbox. For more information, see Seccomp.

Related project comparison: Firejail

Firejail is similar to Flatpak before bubblewrap was split out in that it combines a setuid tool with a lot of desktop-specific sandboxing features. For example, Firejail knows about Pulseaudio, whereas bubblewrap does not.

The bubblewrap authors believe it's much easier to audit a small setuid program, and keep features such as Pulseaudio filtering as an unprivileged process, as now occurs in Flatpak.

Also, @cgwalters thinks trying to whitelist file paths is a bad idea given the myriad ways users have to manipulate paths, and the myriad ways in which system administrators may configure a system. The bubblewrap approach is to only retain a few specific Linux capabilities such as CAP_SYS_ADMIN, but to always access the filesystem as the invoking uid. This entirely closes TOCTTOU attacks and such.

Related project comparison: Sandstorm.io

Sandstorm.io requires unprivileged user namespaces to set up its sandbox, though it could easily be adapted to operate in a setuid mode as well. @cgwalters believes their code is fairly good, but it could still make sense to unify on bubblewrap. However, @kentonv (of Sandstorm) feels that while this makes sense in principle, the switching cost outweighs the practical benefits for now. This decision could be re-evaluated in the future, but it is not being actively pursued today.

Related project comparison: runc/binctr

runC is currently working on supporting rootless containers, without needing setuid or any other privileges during installation of runC (using unprivileged user namespaces rather than setuid), creation, and management of containers. However, the standard mode of using runC is similar to systemd nspawn in that it is tooling intended to be invoked by root.

The bubblewrap authors believe that runc and systemd-nspawn are not designed to be made setuid, and are distant from supporting such a mode. However with rootless containers, runC will be able to fulfill certain usecases that bubblewrap supports (with the added benefit of being a standardised and complete OCI runtime).

binctr is just a wrapper for runC, so inherits all of its design tradeoffs.

What's with the name?!

The name bubblewrap was chosen to convey that this tool runs as the parent of the application (so wraps it in some sense) and creates a protective layer (the sandbox) around it.

from https://github.com/containers/bubblewrap

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