this post was submitted on 23 Mar 2024
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Why would a system update need privileges? What is the privileged action in pulling and applying updates your distro ships?
I mean, that's one of the things that definitely needs permissions, right? You're overwriting system config and executables for all users on your system. Otherwise a malicious actor could just replace firewall configs, or embed malicious code into your executables. If not /bin and /etc what else should need privileges?
On a mutable distro maybe but also no. You need to update your system, always. The updates come from the distro, and you only invoke your privileged package manager to do these changes for you. Its not privileged.
If a malicious actor is able to replace package repos that your package manager uses, for example an infected server in the same network, this would be the only way to inject arbitrary stuff by using
dnf updateorrpm-ostree update.Installing software and updating the already existing is very different.
The short answer is that my distro did not let me do this easily. But that was for good reason.
A system update would require too many privileges that it would be almost indistinguishable from root.
Currently, every user I have is restricted in what files it has access to. A system update user would need access to so many files, including install locations of all binaries, and non-binary installation paths of all current and future programs I install (some package installs modify /var, many modify /etc, and so on).
This user will also have access to all these programs, down to system applications. It can trivially break a permission system I come up with.
It may be possible to restrict system updates to a user, but it would be such a powerful user that its not really worth it.
Does the user have that access? In my case with rpm-ostree they can just execute 2 commands
rpm-ostree refresh-md(get updates) andrpm-ostree update.rpm-ostree rebaseis used for system upgrades afaik, that one needs a password.Only the root user has access to system updates on my system currently.
What does
rpm-ostree updatedo exactly? Does it execute the update? Or is that the rebase command only?No
rpm-ostreedownloads the diffs, applies existing changes (added or removed packages) and builds a new image that gets staged as first boot target. After reboot you are on an updated system.If it builds a new image that replaces the entire system it could be compromised to give full access to the entire system just as easily as sudo, possibly more easily.
No it just pulls the ostree / OCI image from the fedora image registry and applies changes that need sudo privileges to change, remove etc.
Deploying a different image is not allowed.
See this issue for details
The component that is like sudo in this case is polkit. Of course an unprivileged user can be used to run sudo commands as well, limited by the rules in the sudo config file, just as these polkit rules limit what the user can do...as long as there is no security issue in sudo and polkit respectively but the actual work is done by a privileged process that is merely controlled by the commands given by the unprivileged user.
Yes thats the point, the specific actions are a good way to act like a firewall for the access to the privileged process, invoked by anyone.
This is brilliant, as unprivileged users over ssh, or not even logged in, can invoke the updates in that case, making a "grandma pc" that is immutable and autoupdating possible.
See this discussion on how it would eventually be implemented
I see. I have little knowledge, but I bet that the "root privileges" part of this process is the reboot. Upon rebooting, system updates are applied from the new image via some privileged process.
That's pretty neat. Unfortunately I haven't ventured deeply enough into that type of system yet (was it called immutable distro or something?). I use gentoo, which doesn't support this out of the box.
Thanks for showing me something new!
Rebooting does not need root privileges either, on no system. There really is nothing privileged about updating already existing software. Android is completely rootless and updates are automatic, but can be done manually too.
You can read a bit into OSTree, its very cool. But seems to be very complex and somehow they want to switch to OCI images now, idk.
But the way ublue builds their systems is astonishing, elegant, simple, structured and fully automated.
Tell me again how you want to write system files with a non-admin account, and I'm going to show you my friend Lumpy, who will walk all over your machine so fucking fast. Fuck that, Lumpy's a genius. One of his underlings (he manages now) will do it on a lunch break.
Uhm what?