Flatpak Permission Survey
When working through yesterday’s post, half-way through I found the 2020 flatkill.org post and the TheEvilSkeleton response. The response was early 2021 and felt hopeful for the future.
One very different take is they were both focused on popular applications. I
was focused more on productivity applications and those that I could choose
between my distro and Flatpak to get a feel of Flatpak, apples to apples. But
the biggest concern is the statistics about 27 out of 50 popular applications
not having --filesystem=host or --filesystem=home. As I saw yesterday,
there are other ways to break out of the sandbox. I figured I’d take a look
myself, but unfortunately the popular apps today are mostly emulators and
Blink-based, so things look pretty bleak with that set. I think it is a skewed
set due to the Steam Deck, and worse than the majority of packages.
Popular
The following is from the first page of
popular on Flathub, sorted
hopefully by popularity. It is the top 30 items, because the pages hold 30. The
first three columns are straight from Flatpak’s website. “Verified” is whether
the packager has a blue check. “Security” is the sandbox permission badge
color. “Concerning permissions” is my own selection of permissions that are
concerning. I made some arbitrary decisions on what to include, mostly focusing
on sandbox escapes and unfortunate mixes of permissions. In particular, it
includes --device=all but not pulseaudio, as access to all devices might have
more implications than just webcam access.
| Name | Verified | Security | Concerning permissions |
|---|---|---|---|
| Google Chrome | 0 | Red | –device=all –socket=x11 –share=network –talk-name=org.freedesktop.secrets –filesystem=xdg-run/dconf Why so much file access? |
| Firefox | 1 | Red | –device=all –share=network |
| VLC | 0 | Red | –filesystem=host –device=all –socket=x11 –share=network –talk-name=org.freedesktop.secrets |
| Discord | 1 | Red | –device=all –socket=x11 –share=network |
| Dolphin Emulator | 0 | Red | –filesystem=host:ro –device=all –socket=x11 –share=network |
| RPCS3 | 0 | Red | –filesystem=home:ro –device=all –share=network –filesystem=/media |
| PPSSPP | 1 | Red | –device=all –socket=x11 –share=network |
| DuckStation | 1 | Red | –device=all –socket=x11 –share=network |
| Citra | 1 | Red | –filesystem=host:ro –device=all –socket=x11 –share=network |
| Brave Browser | 0 | Red | –device=all –socket=x11 –share=network –talk-name=org.freedesktop.secrets –filesystem=xdg-run/dconf |
| RetroArch | 1 | Red | –filesystem=host –share=network |
| xemu | 0 | Red | –filesystem=host:ro –device=all –share=network |
| melonDS | 1 | Red | –filesystem=home –device=all –socket=x11 –share=network |
| PrimeHack | 1 | Red | –filesystem=host:ro –device=all –socket=x11 –share=network |
| Telegram Desktop | 1 | Red | –device=all –share=network |
| Spotify | 0 | Red | –device=all –share=network |
| Visual Studio Code | 0 | Red | –filesystem=host –device=all –socket=x11 –share=network –socket=ssh-auth –talk-name=org.freedesktop.secrets |
| Steam | 0 | Red | –device=all –socket=x11 –share=network |
| ProtonUp-Qt | 1 | Red | –filesystem=~/.bashrc –device=all –socket=x11 –share=network |
| Microsoft Edge | 0 | Red | –device=all –socket=x11 –share=network –talk-name=org.freedesktop.secrets –filesystem=xdg-run/dconf |
| Flatseal | 1 | Red | –filesystem=xdg-data/flatpak/overrides:create |
| Bottles | 1 | Red | –device=all –socket=x11 –share=network –system-talk-name=org.freedesktop.UDisks2 |
| ScummVM | 1 | Red | –filesystem=home –device=all –socket=x11 –share=network |
| Protontricks | 1 | Red | –device=all –socket=x11 –share=network –system-talk-name=org.freedesktop.UDisks2 |
| Extension Manager | 1 | Yellow | –share=network |
| GIMP | 1 | Red | –filesystem=host –socket=x11 –share=network |
| OBS Studio | 1 | Red | –filesystem=host –device=all –socket=x11 –share=network |
| Heroic Games Launcher | 1 | Red | –device=all –filesystem=mnt/media –filesystem=~/.local/share/applications –socket=x11 –share=network |
| LibreOffice | 1 | Red | –filesystem=host –share=network –filesystem=xdg-run/gvfsd |
| qBittorrent | 1 | Red | –filesystem=host –share=network |
Some comments:
- 2/3 have a verified packager
- The security badge is normally red
- Every top app has
--share=network - Every top app, except for Extension Manager, has
--device=allor--filesystem=host - 2/3 have
--socket=x11
While going through the manifests, I noticed that --talk-name doesn’t show up
in the listed permissions on the Flatpak website. That is very serious, as
--talk-name=org.freedesktop.secrets seems important and access to the systemd
service provides a trivial sandbox escape. I tried to guess which dbus services
are “dangerous”, and some I looked up their definiton to make a judgement.
Strangely, I couldn’t find the definition of org.gnome.Software.
Some permission combinations are a problem without sandbox escape.
As examples, there’s little need to escape from the sandbox with
--filesystem=home:ro --share=network or --talk-name=org.freedesktop.secrets --share=network.
Only a minor concern, but I noticed that --metadata=X-DConf=migrate-path=
isn’t listed on the Flatpak website. This is a very good feature that avoids
sharing write access to all settings. But I’d have to investigate more to see
if just read-only access to settings can be a problem. It won’t contain
secrets, but there’s so many options it makes me wonder.
My programs of interest
These are the programs that I was looking at when making yesterday’s post, with a few additions. They are mostly GNOME/GTK, but with some oddballs mixed in. There are both very old GNOME programs (Videos, a.k.a. Totem) and some more recent remakes (Image Viewer, a.k.a. Loupe). I chose these as an “interesting” set. They are sorted by name.
| Name | Verified | Security | Concerning permissions |
|---|---|---|---|
| Boxes | 1 | Red | –filesystem=host –device=all –share=network –talk-name=org.gnome.Settings –filesystem=xdg-run/dconf |
| Calculator | 1 | Yellow | –share=network |
| Characters | 1 | Green | |
| Connections | 1 | Yellow | –share=network |
| Disk Usage Analyzer | 1 | Red | –filesystem=host –filesystem=xdg-run/gvfs |
| Document Scanner | 0 | Red | –device=all –share=network |
| Document Viewer | 1 | Red | –filesystem=home:ro –filesystem=xdg-run/gvfsd |
| Ear Tag | 1 | Red | –share=network |
| File Roller | 1 | Red | –filesystem=home |
| Flips | 0 | Red | –filesystem=home |
| Foliate | 1 | Red | –share=network |
| gedit | 0 | Red | –filesystem=host –filesystem=xdg-run/gvfsd |
| GHex | 0 | Red | –filesystem=host –filesystem=xdg-run/gvfsd |
| GnuCash | 0 | Red | –filesystem=host –share=network |
| gThumb Image Viewer | 0 | Red | –talk-name=org.freedesktop.secrets –filesystem=xdg-run/gvfs |
| HxC Floppy Emulator | 0 | Red | –socket=x11 |
| Image Viewer | 1 | Red | –filesystem=host –filesystem=xdg-run/gvfs |
| KiCad | 1 | Red | –filesystem=home –socket=x11 –share=network |
| Meld | 0 | Red | –filesystem=host |
| Piper | 0 | Red | –socket=x11 |
| Remmina | 1 | Red | –filesystem=home –device=all –share=network –socket=ssh-auth –talk-name=ca.desrt.dconf –filesystem=xdg-run/gvfsd |
| Rhythmbox | 0 | Red | –share=network –filesystem=xdg-run/gvfsd |
| Videos | 1 | Red | –device=all –share=network –talk-name=org.gnome.OnlineAccounts –filesystem=/run/media –filesystem=xdg-run/gvfs |
Some comments:
- 1/2 have a verified packager
- The security badge is normally red, but greens aren’t entirely mythical
- Four have
--share=networkwithout other relatively problematic permissions - Most that are missing
--share=networkhave a trivial sandbox escape - Foliate is only red only because it has
--filesystem=xdg-run/speech-dispatcher:ro.
With this set of apps, we are in the murky sandbox territory that I was
wrestling with yesterday. A sandbox might help some of these. But the
permission list exposed to users is insufficient for determining if the app is
sandboxed more than in name. It also doesn’t really matter, because with almost
universal red security badges, the user is required ignore it. If
--share=network allows access to the session bus on my distro, then only
Characters is safe, ignoring upgrades adding permissions and assuming I trust
Flatpak after all this.
Flatpak Permissions on Upgrade, Unravelled
Flatpak has been around for a while, but I’ve not cared about it. I got interested in Fedora Silverblue as a ChromeOS replacement so have been trying Flatpak out on Arch.
It has a sandbox, which is nice, but what is the security model of the sandbox? I can see the permissions before installing a package, but what if those permissions change? Is the sandbox there to restrict the impact of a remote-code-execution of a hacked app, or is it there to protect me against the software packager? Glancing through pages wasn’t clear.
The main difference between the options is, “what happens when an app adds new permissions to its manifest?” If Flatpak happily upgrades it, then the sandbox trusts the software packager. But I didn’t find any documentation about how added permissions are handled.
I followed the org.flatpak.Hello example, building the app and adding it to a repository, then installing the app. I then rebuilt the app to see what the ordinary flow looked like:
$ flatpak update
Looking for updates…
ID Branch Op Remote Download
1. org.flatpak.Hello master u tutorial-repo < 601 bytes
Proceed with these changes to the user installation? [Y/n]:
I then appended to org.flatpak.Hello.yml:
finish-args:
- --share=network
I rebuilt the app and then updated:
$ flatpak update
Looking for updates…
New org.flatpak.Hello permissions:
network
ID Branch Op Remote Download
1. org.flatpak.Hello master u tutorial-repo < 647 bytes
Proceed with these changes to the user installation? [Y/n]:
Well, that’s good that it tells me, but it also isn’t the least bit scary and
is easy to miss, especially if there are many updates. I’m also left wondering
what happens with automatic updates. flatpak update --assumeyes is probably a
bad idea (which isn’t mentioned in --help), but --noninteractive looks
promising:
$ flatpak info --show-permissions org.flatpak.Hello
$ flatpak update --noninteractive
Updating app/org.flatpak.Hello/x86_64/master
$ flatpak info --show-permissions org.flatpak.Hello
[Context]
shared=network;
It happily accepts the new permissions without any notification. The output is identical to when permissions stay the same. I had expected it to either error or ignore the update. I’d gladly accept it making an override that denies the new permission, but it doesn’t do that either. I wasn’t really expecting that, because there wasn’t an option to do that interactively.
Now, you could argue “CLI is for advanced usage; use Gnome Software.”
Unfortunately, this hello world example doesn’t show up at all in Gnome
Software, so I couldn’t test. But if I search specifically for gnome software upgrade change permission then I can find Gnome Software issue 943: UX for
Flatpak permission changes on update. It shows Gnome Software is in a
good place, but it doesn’t fill me with confidence about Flatpak overall. If I
had Discover installed and logged into KDE, would I still be okay?
Installs default to system-wide
Using flatpak list I can see apps installed in the “system” Installation.
This is not clear in Gnome Software. Upgrading these apps changes the
permissions for all users, yet I don’t get a “you are about to change your
system” dialog before using elevated privileges. Gnome Software does sorta tell
me if I go to Software Repositories and see “System Installation • 3 apps
installed”.
Apparently it is system-wide because Flathub is configured in
/etc/flatpak/remotes.d/. If the repo is system-wide, then the install is
system-wide. I can accept that logic, but this was done by default by the Arch
flatpak package. The Fedora package
doesn’t include Flathub. Flatpak is aware of this in their setup docs:
Arch vs
Fedora. They encourage the system
installation in their docs, and the flatpak CLI defaults to system
installation.
Easy mistakes with flatpak CLI
I also discovered that flatpak permission-show and flatpak permissions
don’t do what they would appear. They show only some of the permissions; the
extra permissions granted, above those in the app’s manifest. They also
report no warnings/errors if the app name is mispelled. Very easy to be misled.
flatpak override is poor as well, as there does not seem to be a way to list
all overrides; you need to dig into ~/.local/share/flatpak/overrides, which
at least is documented in man flatpak-override.
$ flatpak override --user --unshare=network org.flatpak.Hello
$ flatpak override
error: Permission denied
$ flatpak override --show
$ flatpak override --user
$ flatpak override --user --show
$ flatpak override --show org.flatpak.Hello
$ flatpak override --user --show org.flatpak.Hello
[Context]
shared=!network;
There’s no UIs for those things in Gnome Software. Given how much I’ve heard about the sandbox in Flatpak, I’m disappointed in the cavalier security usability stance.
How can a user accept permissions?
While doing the above I wondered about Flatseal, because it is particularly powerful in a “can attack you” sense. Flatseal lists “No Network Access” in its permissions in Gnome Software, but it also has an entry for “Arbitrary Permissions” with the description “Can acquire arbitrary permissions”. It seems in that case the various green “No $X access” should be removed.
How bad are other cases? If an app has access to “Pictures folder,” it seems
that is probably mostly predictable. But isn’t it trivial to escape the sandbox
with “Session Services” (--socket=session-bus) using systemd-run? How would a
user know that “No Network Access” is meaningless when the service “Can access
D-Bus services on the session bus”?
But also an app might have access to the session bus because of abstract Unix sockets. From the Flatpak Sandbox Permissions Reference:
Giving network access also grants access to all host services listening on abstract Unix sockets (due to how network namespaces work), and these have no permission checks. This unfortunately affects e.g. the X server and the session bus which listens to abstract sockets by default. A secure distribution should disable these and just use regular sockets.
On Arch, lsof -U | grep @ shows dbus-broker and gnome-session available
as abstract sockets.
If an app has write access to the XDG config directory
(--filesystem=xdg-config) it can write configuration for systemd to start a
service on next login. Write access to the home directory can write .bashrc.
Write access to all settings can change which program is executed with my
custom keyboard shortcuts.
Having the sandbox in many of these cases seems useless, because it takes 10 minutes for an attacker to work around it. This isn’t even to the level that “defense in depth” becomes helpful. I think the only benefit of the sandbox for these is when developing an application and incrementally making your application sandbox-ready. But the user should be told there isn’t a sandbox. Even if it is nominally present, it isn’t providing its function.
Gnome Software does give such permissions red and yellow security levels, but the explanations of the permissions undersells their power and then acts like other permissions are still restricted.
Relatively small beans
When opening a file with a Flatpak app in Nautilus and xdg-open, my entire
environment is copied onto the command line and visible through ps. I
understand some OSes allow users to view each other’s environment and that
secrets need to be shared through files or pipes. But this is still surprising.
By poking around with the CLI I noticed that every time I open a file in a portal or with File Roller it adds a new (permanent?) permission for the opening app. But Gnome Software doesn’t have a UI to show me the added permissions. And the permissions are kept even if I uninstall and reinstall the app.
I can clear out all permissions for a specific app using flatpak permission-reset APP_ID or all apps with flatpak permission-reset --all.
Although the permission rows remains, listing each opened file, just with the
app removed. To delete the row I need flatpak permission-remove TABLE ID, but
each row has to be deleted individually.
Takeaways
I started with a very precise concern, didn’t get a clear answer, and now I have additional concerns. Before this investigation I had thought “if an app doesn’t have both network and data access, then that is progress.”
But I don’t think Flatpak is actually communicating the security impact of permissions. And while I now know the full severity of a longer list of risky permissions, what attacks am I not noticing? And do I actually trust Flatpak that a fully-locked-down “all green” app can’t easily escape given so much wasted effort on permissions elsewhere? (I accept that the sandbox can be escaped, but I want to avoid someone knowledgable only needing 10 minutes to break out.)
Fedora (and Silverblue) doesn’t use Flathub by default. That seems like a wise decision. On that system I could use Flatpak without much worry as it is just a different package format for the distro.
Looking through the ~20 apps I’m interested in, all of them show red in Gnome Software except for two yellows: “Calculator” and “Connections,” both of which have network access (Calculator looks up currency exchange rates). Flathub is looking like just another distro but with each user needing to vet most packagers.
Hugo Migration
I converted the site from XSLT to Hugo. If you notice something awry, please let me know. I’m hoping the change makes posting easy enough for me to do it more frequently.
Hugo felt reasonably natural to me. It isn’t that far away in concept from phppen used by the main ersoft.org, except it isn’t using PHP nor MySQL for its backing store. There were some things that needed figuring out, but that was partly because I wanted to match the existing page structure. The only strong oddity was it not having built-in Atom support.
Surprisingly it had trouble computing URLs for attachments to posts. That same
problem was a pain when implementing the XSLT-powered code. I’m happy for
layouts/_markup/, as it allows fixing the problem without shortcode, which
would have made the posts depend on Hugo. Looks like the next Hugo version will
improve the deault and I might be able to remove my custom code.
Youtube Music Playlist Dumping
Via Google Play Music, I have some old Youtube Music playlists. But there does not seem to be a way to export them into a useful form. Takeout lets you export them, but you just get video IDs and a timestamp which is not immediately helpful and for uploaded music prohibitive to make sense of.
Here’s a javascript snippet that can be pasted into the web inspector while viewing a playlist on music.youtube.com, to dump the track metadata. It exports tab-separated values.
// Scroll to bottom of playlist.
// To save results, right click and "Copy Object".
// Double-check the number of results; if entries are missing, you might need to scroll further.
// (Sometimes the number of entries simply doesn't match the playlist's count. May be limited to auto playlists.)
{
const playlistName = document.getElementsByTagName('ytmusic-detail-header-renderer')[0].__data.data.title.runs[0].text;
const playlist = document.getElementsByTagName('ytmusic-playlist-shelf-renderer')[0];
const entries = ["Video Id\tTitle\tArtist\tAlbum"];
function textFromColumnIfPresent(col) {
return col.musicResponsiveListItemFlexColumnRenderer.text.runs ? col.musicResponsiveListItemFlexColumnRenderer.text.runs[0].text : "";
}
for (const item of playlist.__data.data.contents) {
const renderer = item.musicResponsiveListItemRenderer;q
const id = renderer.playlistItemData ? renderer.playlistItemData.videoId : ""; // Track may be unavailable
const title = textFromColumnIfPresent(renderer.flexColumns[0]);
const artist = textFromColumnIfPresent(renderer.flexColumns[1]);
const album = textFromColumnIfPresent(renderer.flexColumns[2]);
entries.push(id + "\t" + title + "\t" + artist + "\t" + album);
}
console.log("Found " + (entries.length-1) + " tracks");
console.log("Playlist: " + playlistName);
console.log(entries.join('\n'));
}
Vector 4 Technical Information
I recently came into possession of the Vector 4 Technical Information (P/N 7200-0001) by Vector Graphic Inc, and it is a gold mine. The Vector 4 User’s Manual and Vector 4 Programmer’s Guide seemed to have been standard issue so my family had multiple copies (one per computer), and they are already digitized by bitsavers. But the Technical Information seems to be much rarer, and seems to be oriented toward maintenance shops. But that means it has very detailed information including jumpers, clock timing, and schematics, with lots of text explaining it all. I’ve found it to be extremely helpful for working on my Vector 4.
I’ve happily digitized my copy. The schematics at the end are ledger-size pages (17" x 11") which made them difficult to scan, and unfortunately I was only able to scan them at 400 dpi. They are usable, but the originals are easier to read.