fe2536b844
These are subsets of the host keyword, which provide access to operating system files but not to users' personal files. In particular, the experimental support for namespace-based sandboxes in the Steam Runtime[1] uses the graphics stack from the host system, which requires access to the host /usr/libQUAL, /libQUAL (even if the host OS has undergone the /usr merge, the canonical paths of ELF interpreters start with /lib), /etc/ld.so.cache, and for some libraries on Debian-based systems, /etc/alternatives. It will not be possible to do similar things in Flatpak without either allowing full host filesystem access (which exposes personal files, and in any case cannot be done by the Steam app because it is incompatible with --persist=.), or adding the ability to expose /usr and related directories without including the rest of the host filesystem. To the best of my knowledge, host-etc is not necessary for anything; I've mainly provided it for symmetry, since it's the other significant thing that we mount in /run/host and cannot get via --filesystem=/path. Some notes on the security/privacy implications of the new keywords: - Neither new keyword allows anything that was not already allowed by "host". - Neither new keyword can allow anything that was not already allowed to the user outside the sandbox. - "host-os" allows enumeration of the installed packages on the host system, and often their version numbers too. A malicious app could use this to look for exploitable security vulnerabilities on the host system. An app could also use this for fingerprinting, although this is not a regression, because the systemd/D-Bus machine ID, MAC addresses, hostname, kernel boot UUID, DMI product ID and many other unique or relatively unique properties are already available inside the sandbox. - "host-os" allows read access, and possibly write access (if the user has it outside the sandbox, for example members of group 'staff' in older Debian installations), to /usr/local. - "host-etc" allows reading configuration files whose contents might be considered sensitive, such as /etc/passwd. [1] https://steamcommunity.com/app/221410/discussions/0/1638675549018366706/ Signed-off-by: Simon McVittie <smcv@collabora.com>
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux.
See https://flatpak.org/ for more information.
Community discussion happens in #flatpak on Freenode and on the mailing list.
Read documentation for Flatpak, its commandline tools, and for the libflatpak library API.
Contributing
Flatpak welcomes contributions from anyone! Here are some ways you can help:
- Fix one of the issues and submit a PR
- Update flatpak's translations and submit a PR
- Improve flatpak's documentation, hosted at http://docs.flatpak.org and developed over in flatpak-docs
- Find a bug and submit a detailed report including your OS, flatpak version, and the steps to reproduce
- Add your favorite application to Flathub by writing a flatpak-builder manifest and submitting it
- Improve the Flatpak support in your favorite Linux distribution
Hacking
Flatpak uses a traditional autoconf-style build mechanism. To build just do
./autogen.sh
./configure [args]
make
make install
To automatically install dependencies on apt-based distributions you can try
running apt build-dep flatpak and on dnf ones try dnf builddep flatpak.
Dependencies you will need include: autoconf, automake, libtool, bison,
gettext, gtk-doc, gobject-introspection, libcap, libarchive, libxml2, libsoup,
gpgme, polkit, libXau, ostree, json-glib, appstream, libseccomp (or their devel
packages).
Most configure arguments are documented in ./configure --help. However,
there are some options that are a bit more complicated.
Flatpak relies on a project called Bubblewrap for the
low-level sandboxing. By default, an in-tree copy of this is built
(distributed in the tarball or using git submodules in the git
tree). This will build a helper called flatpak-bwrap. If your system
has a recent enough version of Bubblewrap already, you can use
--with-system-bubblewrap to use that instead.
Bubblewrap can run in two modes, either using unprivileged user
namespaces or setuid mode. This requires that the kernel supports this,
which some distributions disable. For instance, Debian and Arch
(linux kernel v4.14.5
or later), support user namespaces with the kernel.unprivileged_userns_clone
sysctl enabled.
If unprivileged user namespaces are not available, then Bubblewrap must be built as setuid root. This is believed to be safe, as it is designed to do this. Any build of Bubblewrap supports both unprivileged and setuid mode, you just need to set the setuid bit for it to change mode.
However, this does complicate the installation a bit. If you pass
--with-priv-mode=setuid to configure (of Flatpak or Bubblewrap) then
make install will try to set the setuid bit. However that means you
have to run make install as root. Alternatively, you can pass
--enable-sudo to configure and it will call sudo when setting the
setuid bit. Alternatively you can enable setuid completely outside of
the installation, which is common for example when packaging Bubblewrap
in a .deb or .rpm.
There are some complications when building Flatpak to a different
prefix than the system-installed version. First of all, the newly
built Flatpak will look for system-installed flatpaks in
$PREFIX/var/lib/flatpak, which will not match existing installations.
You can use --with-system-install-dir=/var/lib/flatpak to make both
installations use the same location.
Secondly, Flatpak ships with a root-privileged PolicyKit helper for
system-wide installation, called flatpak-system-helper. It is D-Bus
activated (on the system bus) and if you install in a non-standard
location it is likely that D-Bus will not find it and PolicyKit
integration will not work. However, if the system installation is
synchronized, you can often use the system installed helper instead—
at least if the two versions are close enough.
This repository
The Flatpak project consists of multiple pieces, and it can be a bit challenging to find your way around at first. Here is a quick intro to the major components of the flatpak repo:
common: contains the library, libflatpak. It also contains various pieces of code that are shared between the library, the client and the services. Non-public code can be recognized by having a-private.hheader file.app: the commandline client. Each command has aflatpak-builtins-source filedata: D-Bus interface definition filessession-helper: The flatpak-session-helper service, which provides various helpers for the sandbox setup at runtimesystem-helper: The flatpak-system-helper service, which runs as root on the system bus and allows non-root users to modify system installationsportal: The Flatpak portal service, which lets sandboxed apps request the creation of new sandboxesdoc: The sources for the documentation, both man pages and library documentationtests: The testsuitebubblewrap: Flatpak's unprivileged sandboxing tool which is developed separately and exists here as a submodulelibglnx: a small utility library for projects that use GLib on Linux, as a submoduledbus-proxy: a filtering proxy for D-Bus connections, as a submoduleicon-validator: A small utility that is used to validate iconsrevokefs: A fuse filesystem that is used to transfer files to the system-helper without copying