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redhatcveRedhat.comRH:CVE-2021-47396
HistoryMay 22, 2024 - 8:56 a.m.

CVE-2021-47396

2024-05-2208:56:32
redhat.com
access.redhat.com
linux kernel
mac80211-hwsim
vulnerability
cve-2021-47396
fixed
hrtimer
beacon handling
simulation issue
hrtimer_forward_now

6.6 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.5%

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.

6.6 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.5%

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