Notify special task kill using wait* functions

[Valdis Kl=?utf-8?Q?=c4=93?=tnieks]

On Sat, 03 Apr 2021 09:02:26 +0200, John Wood said:

> Currently, the scenario you propose is fully mitigated :). And notifying to
> userspace that all the tasks has been killed by "Brute" not decrease the
> security. It adds the possibility that the supervisor adopts the correct policy.

So how do you figure out how far up the chain you kill processes?

What does a triple or quadruple fork do? How do you ensure that you deliver
the notification to the correct supervisor? (Hint - walking backwards until you
hit a process running as root isn't necessarily the right answer, especially
once you consider containers and systems where gdm runs as non-root
and other weird stuff..)

Bonus points if you deal correctly with abuse of LD_PRELOAD to front-end
a signal handler that catches SIGSEGV, without breaking the semantics
of legitimate signal handlers...
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