Both, maybe? I mean: whether or not they broke the jailer, we know the jailer is breakable; it wouldn't really even be newsworthy to have an LPE that breaks the Firecracker jailer.
then the breach happens in KVM? Isn’t KVM its own software repo, and firecracker sits on top? How is this firecracker and not a KvM thing
If they have arbitrary code execution in the Linux kernel itself (which it feels like maybe they should?) then the jailer is a nonfactor. But the exploit they write up sure seems like it's just getting code execution in userland from Firecracker itself.
Sure looks like a C hello world kernel debugger.