[CVE-2020-27194] Linux kernel: eBPF verifier bug in `or` binary operation tracking function leads to LPE

CVE-2020-27194 is a eBPF verifier bug that allows an unprivileged attacker to create BPF socket filter programs that can read and write Out of Bounds, trough which an arbitrary kernel read write can be achieved.

Simon reported an issue with the current scalar32_min_max_or() implementation.
That is, compared to the other 32 bit subreg tracking functions, the code in
scalar32_min_max_or() stands out that it's using the 64 bit registers instead
of 32 bit ones. This leads to bounds tracking issues, for …