flatpacks falling flat, packing bugs, snaps snapping resources, both suck [LWN.net]

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 8:53 UTC (Tue) by mbunkus (subscriber, #87248)
In reply to: flatpacks falling flat, packing bugs, snaps snapping resources, both suck by Cyberax
Parent article: Fedora discusses Flatpak priorities

As the author of an application that needs to read files that reference other files which it also needs to read, this approach is rather limited. Think of LibreOffice documents referencing externally stored pictures or, in my case, Blu-ray index/playlist files referencing tens of M2TS and image files. It is a way to sandbox, just not a really comprehensive or good one.

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flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 9:29 UTC (Tue) by intelfx (subscriber, #130118) [Link] (16 responses)

> Think of LibreOffice documents referencing externally stored pictures or, in my case, Blu-ray index/playlist files referencing tens of M2TS and image files. It is a way to sandbox, just not a really comprehensive or good one.

How would you solve this?

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 9:35 UTC (Tue) by mbunkus (subscriber, #87248) [Link] (15 responses)

I don't have a solution. I'm only pointing out a fundamental flaw in one of the advertised central advantages of systems such as Flatpak I've had to deal with as an application developer providing AppImags & Flatpaks. In my case I have to disable the file system sandbox, allowing the application access to the whole host file system (Unix permissions still apply, of course; it only means the sandbox doesn't apply further restrictions).

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 9:40 UTC (Tue) by intelfx (subscriber, #130118) [Link] (14 responses)

Are you sure the flaw is *fundamental*?

If you think that what Flatpak does is "a way to sandbox, just not a really comprehensive or good one", then *what exactly* would be a comprehensive or a good one instead?

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 9:58 UTC (Tue) by mbunkus (subscriber, #87248) [Link] (1 responses)

I haven't thought about how file access might be sandboxed better because I'm not interested in designing such systems. I'm simply observing & reacting to how it affects me as an application developer. To me it seems that the sandboxes targeting the Linux desktop use the "require user interaction for each file accessed" model. This has two problems that I can see right from the start:

1. The "files referencing other files" issue I've already mentioned
2. Making it much harder for cli-only applications as they usually don't use GUI libraries such as Qt, meaning there's no easy way to shove portal-like functionality in there without having to adjust your code — but I may be wrong here; I simply have never seen it (Flatpak is very much tailored towards GUI applications; as a matter of fact you cannot package cli-only applications as Flatpaks properly)

There are two other sandboxing systems out there that I know about tangentially: Android & systemd. I know little about Andoid, but what little I know seems to be a two-part system: an application always has access to its own private piece of land within the file system that no other application has access to, and you can grant it access to the rest of the non-system parts of the file system via Android's permission system. It's not as fine-granular as Flatpak's system but requires much less interaction. It benefits from the fact that Android itself has a rigid design that it can impose on all applications, unlike generic Linux systems where users can store files anywhere, really.

systemd's sandboxing system is quite fine granular as you can set up certain paths to be read-only, others to be read/write, restrict capabilities etc. However, this setup is required before the program is started, meaning the admin has to know in advance which parts of the file system will be accessed in which way. This works fine for well-known daemons; it doesn't work so well for applications dealing with general user data such as LibreOffice or my own applications. In my case users often have stuff in their home, or on mounted network shares, on in places such as /data on different partitions etc. etc.

Again, I have no solutions here. This is a hard problem. Maybe there isn't a good one-model-fits-all solution at all, though I hesitate to say that as I certainly lack the knowledge in the area of sandboxing techniques to make such an assertions.

Maybe I'm just a bit annoyed with statements such as "<sandboxing technique> apps are more secure as they limit what the application can access". Yeah, it's partially true, and I'm probably just an annoying nitpicker.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 10:18 UTC (Tue) by intelfx (subscriber, #130118) [Link]

> I know little about Andoid, but what little I know seems to be a two-part system: an application always has access to its own private piece of land within the file system that no other application has access to <...>

> systemd's sandboxing system is quite fine granular as you can set up certain paths to be read-only, others to be read/write, restrict capabilities etc. However, this setup is required before the program is started

Flatpaks also have their own internal store that they can access freely without any permissions. They also have an option to statically require RO or RW access to specific parts of the host filesystem (like systemd daemons).

> <...> and you can grant it access to the rest of the non-system parts of the file system via Android's permission system

Like you said, in Android's case, this likely only works because *almost all* storage is compartmentalized. So "non-system parts of the file system" is basically "free-form user files". There's no way for an app to abuse this grant to access system files or, importantly, other apps' files.

On Linux, this is not an option — direct filesystem access (even limited to non-system files) is a much broader brush. Except, maybe, if you filter all the dotfiles via some kind of security layer (and even then, you'll eventually get stuck with either false-positives or false-negatives).

Perhaps what's missing is just an ability for an app to request access to the containing directory along the user-picked file, or request access to a precomputed path. Does not sound like a *fundamental* problem to me — has anyone tried asking the XDG guys to add this to the relevant portal spec?

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 9:58 UTC (Tue) by Wol (subscriber, #4433) [Link] (11 responses)

> Are you sure the flaw is *fundamental*?

If by "fundamental" you mean "a real pain in the proverbial for the user", then I think it is. Unless you comprehensively think through all use-case scenarios (which imnsho most developers are cognitively incapable of doing) you are going to have quite a horde of users complaining "my use case is broken".

For example, something I do, for very simple and good reasons, is have a humungous load of hard links all over my system. Less so now, but my wife and I took loads of photos (my camera tells me it can only store 1100 photos on the 100GB of flash cards in it ...) so they were all stored in a central area, owned by root (to prevent accidental damage), and linked everywhere they were required. Niche usage, sure, but most apps don't have a clue about that sort of setup. And there'll be plenty of other niche cases out there ...

Cheers,
Wol

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 10:06 UTC (Tue) by intelfx (subscriber, #130118) [Link] (10 responses)

No, by *fundamental* I mean "essential to how Flatpak operates", "unfixable".

It might be an important problem, but I'm almost certain it's not a fundamental one.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 6:26 UTC (Wed) by andrejp (guest, #47396) [Link] (9 responses)

Actually, it is. Both. See my original message.

It's akin to scratching your ass if your arm itches. It might feel good, but won't actually do anything about the itch. Alas the "Lennarts" of the world insist that "this isn't the itch you're looking for" (waving hand) and would instead provide users with a fat sticker to put over the arm, claiming that that will somehow fix or prevent any and all itches. Which in theory sounds fine until the arm starts to itch anyway. For which Lennarts provide more, bigger and fatter stickers, along with a stick as a "free" bonus (so don't complain, 'coz it's free) so you can scratch your ass more conveniently.

Check the internet. Or at least LWN. Seems like a whole lot of people with itches they can't scratch, 'coz Lennart and his one-fix-for-all stickers.

The solution ofc is to uninstall Lennart, along with packs that fall flat, snaps that mostly snap the system's resources, and systemT (T as in "trash"). Then the itch can be scratched by the user in the proper place. And if you want to feel good too, you can also scratch your ass, even if it doesn't itch. All without Lennart's "free" sticks and stickers.

It's pretty simple actually. A system-wide MAC can do it. It's helpful if a systems integrator ("distro") - and /not/ the 3rd party that provides the app - provides the default MAC sandbox for the app(s), but not strictly required. Then the *user* can add the required permissions/exceptions for *his* use case. All "in the system" (and not "in the app package"). No Lennart required.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 6:42 UTC (Wed) by zdzichu (subscriber, #17118) [Link] (6 responses)

Such an elaborate comment, ruined by hate speech and personal attacks. Don't do it again, please keep the discussion civil.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 9:42 UTC (Wed) by andrejp (guest, #47396) [Link] (5 responses)

If you're seeing "hate speech", you should probably check the dictionary on what that actually means.

That I loathe Lennart's "solutions" that much is obvious. Hardly "hate speech" though, unless you define "hate speech" as "you disagree with my solutions" == "you hate me".

Or perhaps you equate my using "Lennarts of the world" with "hating Lennart"? Well I don't "hate Lennart", but I do use the idiom a bit akin to "Karens of the world". Perhaps it's not "fair" to Lennart, so let me give an example.

Suppose someone was to park a proverbial truck in your living room as a "solution". Would that make you happy? No? What if that someone then told you that the truck solves *his* problem superbly and that if you don't like the truck, that is *your* problem, so *you* should "work around" the truck (ie. "WONTFIX")? No? You'd still protest? Darn. I'm sure though that if the proverbial truck displayed a big red sign in the windshield that said "truck tainted 'coz living room too small", that would definitely make you love the truck. Fo' sure. Or else you're just a "hater" lol. Especially if you suggested in no uncertain terms to remove the fscking truck - that would no doubt be a big, "uncivilized" no-no.

Right?

So perhaps you can understand what I mean by "Lennarts of the world": the types that park proverbial trucks in other peoples' living rooms and expect other people to "work around" the truck while at the same time waving off and labeling any criticisms or objections or suggestions to remove the truck as "hate speech" and "personal attacks". It *is* just a truck, right? And it's not even that big - it didn't even fill the *whole* room, you can still walk around it, and it comes with a built-in kitchen sink too! You've just saved space in the kitchen! And best of all, "it's free"! So why so much "hate"?

Or, perhaps you just disagree with me seeing LP as a "Lennart" per example above.

Well okay, that's perfectly fine. I'm sure a number of other readers would possibly - even probably - agree with my own view. YMMV.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 9:58 UTC (Wed) by andrejp (guest, #47396) [Link] (4 responses)

And just to make this perfectly clear: I don't view *everything* by LP as bad. Some of it is actually pretty good. The bad tho is like the proverbial truck given in the example. And with no means of separating the truck from the bundled kitchen sink while at the same time making the truck a hard dependency of the living room, can you really blame me for wanting to remove the whole effin' truck? Or for not wanting that "someone" to park more trucks in other rooms?

I mean... "GRUB tries to do too much, and most of those things are a mistake, he said."
No, wait, that wasn't my comment. Hm.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 13:07 UTC (Wed) by daroc (editor, #160859) [Link] (3 responses)

Regardless of the precise terms they used, zdzichu is completely correct. We require comments here to be polite, and to avoid personal attacks. Saying that you dislike systemd is perfectly fine. Explaining your technical problems with it is welcome. Being rude about it and personally insulting Lennart isn't.

Please stop this thread of conversion here, and be less vitriolic in your future comments.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 21, 2025 14:52 UTC (Fri) by andrejp (guest, #47396) [Link] (2 responses)

Funny how even after it has been thoroughly explained what this is and what this is not, you still found it in you the need to point out how you agree with the labeling. That is actually far more "rude" than anything I've said - you're lecturing me on how comments should be polite and to avoid personal attacks and that rudeness has no place in the comment section, while at the same time completely ignoring everything I've said and just reapplying the labels, even adding more ("vitriolic").

I don't think you see how rude and personally insulting *that* is.

But then again, it's part of the same reason why Lennart has been getting all that flak: snubbing and hand-waving off anyone that happens to not quite fit into the crowd of cheerleaders, or even outright disagrees with the crap that's being pushed on users.

I understand - you don't like words like ass, shit, crap, fuck and so on and so forth. But gee, see what happens if I first snub and hand-wave you off (like I just did - deliberately, not to offend or incite you, but in order to demonstrate a point), then label you with some juicy and colorful labels ("you're 'hating me'", "your comment is full of 'vitriol'", "I find your comment to be 'personally insulting'"). First you're going to "warn" me "politely" (check). That failing, you're going to use "stronger" words ("hate speech", check). That failing, you're going to propose "uninstalling" this uid, 'coz "he's parking 'trucks' (ass, shit, fuck, crap) into the 'living room' (this comment section)" (pending, probably being considered). That still not having the desired effect (new uid), your next step is probably going to be to suggest "uninstalling" the IP this comment has come from. Then probably "uninstalling" by "legal action". And so on.

In other words, you'll want "the *whole* 'truck' out of your fscking 'living room'".

To which my response to you is, again deliberately, in order to demonstrate the point: "please stop with the hate speech", "please stop personally insulting me" and "be less vitriolic in your future comments".

Stop now

Posted Mar 21, 2025 15:14 UTC (Fri) by jzb (editor, #7867) [Link]

OK. Time to end this thread. To be very clear—the comment section is not the place for people to snipe at one another. It's quite OK to have disagreements on topics, but nobody needs or wants to read two or more commenters just arguing with each other. Stop here.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 21, 2025 15:15 UTC (Fri) by andrejp (guest, #47396) [Link]

In other words, you're saying "your communication is not welcome here" and "please remove the truck from my living room".

I understand. I apologize for the inconvenience.
Hm. No that's the wrong quote.
So long, and thanks for all the fish?
Lol.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 7:01 UTC (Wed) by intelfx (subscriber, #130118) [Link] (1 responses)

I see lots of text here, but unfortunately all of it is starkly content-free. Please try again.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 9:43 UTC (Wed) by andrejp (guest, #47396) [Link]

Which part did you find to be "content-free"? The problem? The "solutions"? Or the solution? I addressed all three.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 18, 2025 21:36 UTC (Tue) by Cyberax (✭ supporter ✭, #52523) [Link] (14 responses)

> Blu-ray index/playlist files referencing tens of M2TS and image files.

Such as the all-important list of the greatest titles stored in `/etc/shadow`. At some point, these kinds of features need to just go away as fundamentally insecure. As a compromise, you might be able to refer to files in the same directory and its subdirectories.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 10:16 UTC (Wed) by farnz (subscriber, #17727) [Link] (13 responses)

Note that the portal API already lets you open a directory, instead of a file - you can ask for the directory representing the root of the Bluray instead of the index file, and you will be granted access to that entire directory and all its subdirectories. This is plenty for a Bluray player, but problematic if you want access to /etc/shadow.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 11:33 UTC (Wed) by andrejp (guest, #47396) [Link] (11 responses)

Probably not entirely on topic, but I'm looking for my pet and I'd like to post a short "wanted" notice on the board.

Her name is Performance. If you find her please return her safely.
Unfortunately I can't offer any financial reward to the finder, but I'll let the finder keep her as compensation.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 12:01 UTC (Wed) by farnz (subscriber, #17727) [Link] (10 responses)

How, exactly, does asking the system to bind mount a directory chosen by the user into the mount namespace your process is using, hurt performance?

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 12:05 UTC (Wed) by Wol (subscriber, #4433) [Link] (1 responses)

> How, exactly, does asking the system to bind mount a directory chosen by the user into the mount namespace your process is using, hurt performance?

An extra layer of indirection can solve all manner of problems, except the problem of too many layers of indirection.

Cheers,
Wol

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 12:09 UTC (Wed) by farnz (subscriber, #17727) [Link]

Except that this isn't a layer of indirection, as implemented in the Linux kernel - it causes the mount point (the user's chosen directory or file) to directly point to the right place in the underlying filesystem structures. You pay a bigger price when the kernel does UID/GID permissions checks on open.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 13:53 UTC (Wed) by andrejp (guest, #47396) [Link] (7 responses)

Oh, so you found her already? Good for you, she's yours to keep :)
This particular kitty though only wants /etc/hostname to play with in the sandbox, root(rw) -> root(r-) (you don't want the kitty to mess the toy up, safe-to-play sandbox right?).
Bind mount /etc?

Linux bind mounts

Posted Mar 19, 2025 13:58 UTC (Wed) by farnz (subscriber, #17727) [Link] (6 responses)

You can bind-mount files as well as directories, under Linux, and have the bind mount reduce permissions as compared to the original pointer to the file. So if you genuinely need read access to /etc/hostname, you can bind-mount that into the sandbox as read only, getting you read access but not write.

That said, if reading /etc/hostname is something your program does often enough for performance of that read to matter, you've got bigger concerns than sandboxing - why are you rereading a value that rarely changes, instead of caching it after first read and invalidating the cache when you get told it's changed?

Linux bind mounts

Posted Mar 19, 2025 14:24 UTC (Wed) by andrejp (guest, #47396) [Link] (1 responses)

> You can bind-mount files as well as directories, under Linux

Really? Well that's new lol. Lemme check.

# cd /tmp
# touch sfile; mkdir sdir
# mount --bind sfile sbox
mount: /tmp/sbox: mount system call failed: Not a directory.
Hm. It does say "Not a dir". Perhaps I'm not doing it right?
# mount --bind sfile sbox/sfile
mount: sbox/sfile: mount point does not exist.
Hm. Perhaps the file must exist before?
# touch sbox/sfile
# mount --bind sfile sbox/sfile
#
Yup. Indeed.
Tnx, I just learned something new :)

Linux bind mounts

Posted Mar 19, 2025 14:40 UTC (Wed) by andrejp (guest, #47396) [Link]

(^^ new for me, it has probably been around for a while)

Linux bind mounts

Posted Mar 19, 2025 14:33 UTC (Wed) by andrejp (guest, #47396) [Link] (3 responses)

> That said, if reading /etc/hostname is something your program does often enough for performance of that read to matter,

No I just made up a trivial test for demonstration purposes. I still wouldn't use a pack/snap for other reasons (have you tried bind mounting a couple of 1000s of files, then ran 'mount' to list them on the host side? that's one of the objections)

But hey, like I said - you find it, you keep it. Though I'm not sure if the kitty would stick around after say 10k bind-mounted files, skittish as she is :)

Linux bind mounts

Posted Mar 19, 2025 14:49 UTC (Wed) by farnz (subscriber, #17727) [Link] (2 responses)

Why would you bind-mount 1,000s of files? That's not something that Flatpak normally does (I have several running at the moment, with open files, and only a few bind-mounted files); when you tell the portal that you're finished with a file, the sandbox automatically unmounts the bind-mounted file so that you no longer have access to it.

The only time you'd ever bind-mount 1,000s of files in a Flatpak world is if you've had the user open thousands of files individually, and then not released them - but again, if this hurts performance, why are you keeping thousands of files open?

Linux bind mounts

Posted Mar 19, 2025 15:49 UTC (Wed) by andrejp (guest, #47396) [Link] (1 responses)

Right. And who would ever need more than 640k lol...

No the point is that there probably is a perf impact once the number goes up, and considering how all these distros seem to like these packs it's not inconceivable that the number does go up. 'mount | wc -l' currently shows *59* on this system - enough that some "work-around" is required if you just want to see the actual disk mounts (read: usefulness). The second point is that bind-mount really isn't the right spot for what MAC does already and (much more) cleanly. The third is that since these app packs are composed by 3rd parties I wouldn't necessarily trust them to do it right, and with potentially not much insight (without digging out source/build files) into how it's actually put together. The fourth I've already pointed out, which is that even if the admin is diligent and updates are applied regularly, the packs might for one reason or another skip updating these dependencies. The fifth I've also pointed out, which is the duplicity of versions of these packs. An old pack might have vulnerable binaries which might conceivably be available as a vector, say by LD_PRELOADing some libs from old/other packs; not that I know of one atm, but still. The sixth is, again, waste of resources by keeping multiple copies; disk is cheap, sure, but I'd prefer not having to constantly up-size partitions. #7 I like a *single* tool on the system to install sw, not mixing apples and oranges; dunno 'bout you but I don't fancy a mixed deb/rpm/snap/flat/whatever system with overlapping namespaces; besides, consider that these packs are a supposed "solution" to the problem of non-unified sw management - devs don't like deb or rpm or don't want to provide both, so they provide a... third... and fourth... and fifth... type, 'coz that's so much "better" and "solves" the problem of too many different pkg managers... right.. so even just listing all the installed software.. umm.. you get the idea. Anyway, #8 taking all of the above in consideration, there are very few salient selling points to these packs; "more secure" certainly isn't one of them - simply unpacking a tgz in /opt/app and providing some standard way of sandboxing ("chroot", except not chroot) would probably be just as good as any app pack out there, if not better, for the simple reason that it'd be standard, inspectable, verifiable and not dependent on the 3rd party to do it right while at the same time keeping various other interfaces clean (mount, df etc)

Linux bind mounts

Posted Mar 19, 2025 16:04 UTC (Wed) by farnz (subscriber, #17727) [Link]

There's no reason why Flatpak couldn't use MAC instead in future - it doesn't, because of the mess that Linux MAC schemes currently are (AppArmor/SELinux/others, some enabled, some force-disabled etc).

And if you genuinely have thousands of user-visible files opened, you need something, somewhere, to track which ones an application currently has access to - otherwise your complaint translates to "I don't like my applications being restricted from sending data they shouldn't have access to out to spy agencies".

Most of your complaints are just about one way to use Flatpaks - Flatpaks can be more secure, thanks to having a standard way of sandboxing and a standard way to transfer the application bundle around, along with isolation between different Flatpaks. And Flatpaks don't have to be "3rd party"; Fedora Flatpaks, for example, are just an automated repackaging of Fedora RPMs with a sandbox policy added to make them a Flatpak.

flatpacks falling flat, packing bugs, snaps snapping resources, both suck

Posted Mar 19, 2025 17:31 UTC (Wed) by Cyberax (✭ supporter ✭, #52523) [Link]

Yep. But there's still a bit of missing functionality, if you open a file as a file, it doesn't allow you access to subdirectories. And I don't think it can be expressed with the current functionality? Although I haven't checked the Portal API in a while.