CVE-2021-47396

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux01e59e467ecf976c782eecd4dc99644802cc60e2 < 9bee85de2c8155388c09a2e1530a243ec1c96f05affected
LinuxLinux01e59e467ecf976c782eecd4dc99644802cc60e2 < 2c204cf594df3b9468368dc9d0b24d482d93cda7affected
LinuxLinux01e59e467ecf976c782eecd4dc99644802cc60e2 < ed2adf69e29848d1eb9df99633dde655421c92edaffected
LinuxLinux01e59e467ecf976c782eecd4dc99644802cc60e2 < 313bbd1990b6ddfdaa7da098d0c56b098a833572affected
LinuxLinux3.9affected
LinuxLinux0 < 3.9unaffected
LinuxLinux5.4.151 <= 5.4.*unaffected
LinuxLinux5.10.71 <= 5.10.*unaffected
LinuxLinux5.14.10 <= 5.14.*unaffected
LinuxLinux5.15 <= *unaffected

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References