CVE-2021-47396

In the Linux kernel, the following vulnerability has been resolved:
mac80211-hwsim: fix late beacon hrtimer handling Thomas explained in
https://lore.kernel.org/r/87mtoeb4hb.ffs@tglx that our handling of the
hrtimer here is wrong: If the timer fires late (e.g. due to vCPU
scheduling, as reported by Dmitry/syzbot) then it tries to actually rearm
the timer at the next deadline, which might be in the past already: 1 2 3 N
N+1 | | | … | | ^ intended to fire here (1) ^ next deadline here (2) ^
actually fired here The next time it fires, it’s later, but will still try
to schedule for the next deadline (now 3), etc. until it catches up with N,
but that might take a long time, causing stalls etc. Now, all of this is
simulation, so we just have to fix it, but note that the behaviour is wrong
even per spec, since there’s no value then in sending all those beacons
unaligned - they should be aligned to the TBTT (1, 2, 3, … in the
picture), and if we’re a bit (or a lot) late, then just resume at that
point. Therefore, change the code to use hrtimer_forward_now() which will
ensure that the next firing of the timer would be at N+1 (in the picture),
i.e. the next interval point after the current time.