37ad100cfe
This reverts commit ed1d7eacf4 and fixes
the issue in a different way.
With the introduction of peer (LAN/USB) sources of refs comes a problem:
they may have outdated repository metadata (which is stored as
contentless commits on the branch "ostree-metadata"). Currently Flatpak
allows the older metadata to be pulled into the local repo, but this is
undesirable for a few reasons: it hurts the security properties of the
system because for example the GPG keys might have been rotated and you
don't want to go back to using the old ones, and it's undesirable
because the old metadata might have missing or wrong information about
the apps installed on the system.
So this commit makes Flatpak ignore the downgrade and use the newer
metadata for the offline operation. This is not a perfect solution,
because the newer metadata might have information (such as the download
size or needed runtime) that's not accurate for the old versions of the
refs that are available offline. This issue is significantly mitigated
by the fact that FlatpakTransaction operations use commit metadata to
make decisions, rather than depending on the xa.cache.
Another possible solution would be to read the outdated metadata into
the FlatpakRemoteState object without pulling it into the local repo or
using it to update the remote config, but that's not perfect either
because there's no guarantee you'll pull the metadata from the same
source as the refs (perhaps one comes from a USB drive and the other
from a LAN peer). Longer term, we should figure out how to rely less on
the xa.cache (which is stored in ostree-metadata) or otherwise make
architectural changes to solve those issues. For now, I think this fix
will be enough to make USB updates usable and secure.
Fixes https://github.com/flatpak/flatpak/issues/1473
Closes: #1965
Approved by: alexlarsson
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 the flatpak 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
- Update 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
./configure [args]
make
make install
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 installed
flatpaks. 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-installation, called flatpak-system-helper. This is dbus
activated (on the system-bus) and if you install in a non-standard
location it is likely that this will not be found by dbus and
policykit. However, if the system installation is synchronized,
you can often use the system installed helper instead - at least
if the two versions are close in versions.