Worth noting that nothing about Flatpak necessitates that distro maintainers can't compile their own Flatpak apps the same way they currently do. Debian can still compile Firefox from source and patch out trackers and update dependencies, even if at the end of the day it bundles the changes back into another Flatpak app.
In fact, the lack of interdependence between apps makes this considerably easier, because a Debian upstream that sits in the middle and custom-compiles it's "official" software can release security updates immediately for critical apps with critical security flaws -- without waiting to make sure that the security fixes don't break some other app.
Flatpak does not require you to have a separate upstream for every app, or to get your updates straight from the developer. Debian can still be a middleperson and they can still do all of the same moderation/customization/legal analysis.
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Very importantly, on security, Flatpak is a paradigm shift away from the existing model of needing complete trust for the entire app:
> Security: you are trusting random developers on the Internet to handle security of all the dependencies in a flatpack, forever. Most do not provide security updates at all.
A big part of this is that you don't trust random developers with Flatpak, or even your own distro maintainers. Most applications do not need the level of access they have by default. The end goal of Flatpak (it is debatable whether it is achieving this, but the goal at least) is to significantly shrink the attack surface of your app.
If your calculator app doesn't have file access, or network access, or process forking, or any of these things because the runtime blocks them (and honestly, why on earth would it ever need those things), then it is a lot less dangerous for your dependencies to go out of date. A calculator should not need to worry about updating its dependencies, because it should not have access to anything that could be abused.
Now, that's an extreme example. Many apps will not be in the position of needing no privileges, but many of them will still be able to have their attack surfaces shrunk. Firefox for example really shouldn't have that much access to my filesystem. Apps should not (in general) share parts of the filesystem except in user-defined contexts. Many of them don't need Internet access at all.
Flatpak makes it easier for dependencies to go out of date, but it also (ideally) drastically reduces the number of potential security flaws you can have in the first place, and drastically reduces the ability of apps to exfiltrate data from other apps (again, this is the ideal, see X11 vulnerabilities + Wayland for how much of an ongoing process fixing Linux security is).
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I would question a few things:
- Is the reduction in attack surface big enough to balance out the extra attention users/devs need to pay to updating dependencies?
- How many security vulnerabilities are due to dependency issues vs data exfiltration from the home folder, or from other apps that they have no need to access? Linux security is kind of a disaster in this area, how many vulnerabilities would we fix immediately just by sandboxing filesystem access so /home wasn't a free for all?
- Is this actually blocking maintainers from releasing security patches or making it harder for them to do so? I would argue no, I think the maintainers can do the exact same things they're doing today, and that their job may be even easier when they don't need to hold up an entire house of cards with every release.
- Is it better to trust Debian to try and patch out every tracker/telemetry, or is there an improvement to having apps that don't require Internet access just be flat-out unable to call home or send telemetry in the first place? I don't think this blocks maintainers from doing their jobs, and it means I just don't have to worry about trackers at all in my calculator app, even if I download it from a 3rd-party source.
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The weak point here is other Linux vulnerabilities (gotta get off X11!), UX (an eternally hard problem to solve), and Flatpak immaturity/mistakes (I don't like that manifests are still a thing, portals are still being built, I think permissions could be better). But the fundamental concept here isn't bad. People rely on shared libraries/runtimes for a lot of things that they don't need shared runtimes to get.
And I can't stress enough: distros can still moderate and compile custom versions of Flatpak apps.