CVE-2021-47396

/// Technical description

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 unali

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References