Typically none, but the security of someone else's system is not defined by the security of my system. For some users, they might have CUPS running because they have a printer configured, SSH so that people can connect to help them (or so they can push files to the machine over the network), perhaps they're doing some web development and have Apache running. There are any number of daemons that could be running on a laptop with legitimate access to the rest of the network.
> Any adversary with 0days for those would certainly have linux kernel exploits too.
I wouldn't say that's a given, first off, and second off, they may not have a Linux kernel exploit, and even if they do, why should they burn a Linux 0day when they can simply just listen using this open hole?
Runs as root.
>SSH so that people can connect to help them
Runs as root.
>perhaps they're doing some web development and have Apache running
I think you're fundamentally screwed if your adversary is willing to use apache 0days on you.
>There are any number of daemons that could be running on a laptop with legitimate access to the rest of the network
In practice this is a very rare scenario, the severity of this fuckup by Huawei should be viewed in that light. It's not ideal, but this is hardly a big deal.
>why should they burn a Linux 0day
Those are a dime in a dozen, and using an exploit very rarely means burning it.
And even if the adversary didn't have a linux 0day to use on you, you'd almost certainly still be screwed sooner or later as they'd now have persistent local access to your system. Odds are that you'd never notice a cronjob running as debian-tor, pinging the attackers c&c once a day.
It really is game over once someone gets arbitrary code execution on your system, unless you maintain an extraordinary security posture which would preclude installing sketchy huawei drivers anyway.
This means that any daemon with a remote code execution exploit (even if running as its own, compartmentalized user) can now be chained with this to get complete access to your X11 session.