Trouble with key rotation in noisy environments [resend]

Avery Pennarun apenwarr at gmail.com
Mon Oct 27 19:55:48 EDT 2014


[Resending since my message was rejected - not subscribed to the list.]

Hi all,

Can anyone else reproduce this?  I'm using ath9k and ath10k APs with
the latest hostapd from HEAD (though we've tried several other
versions without any difference).

Steps:
- Pick a channel in a noisy environment (eg. 2.4 GHz)
- Configure hostapd to rotate keys extremely frequently:
    wep_rekey_period=10
    wpa_group_rekey=10
    wpa_strict_rekey=1
    wpa_gmk_rekey=9
    wpa_ptk_rekey=10
- Connect a client device (tested with Macbook Air and two different
Linux clients)
- On the client, load a tool like http://gfblip.appspot.com/ to
generate and monitor continuous traffic.
- On the AP, watch the hostapd logs to see key rotations as they happen.

Expected:
- Key rotations occur every 10 seconds or so but do not affect the traffic.

Actual:
- Most key rotations go through fine and don't show latency spikes in
the "blip" application linked above.
- Every now and then, something goes wrong with the key rotation and
data stops flowing.  The AP thinks the key rotation has worked, but it
apparently has not.
- After about 10 more seconds (possibly because that is the next key
rotation), hostapd decides the station is broken and disassociates it.
- Immediately afterward, the station reconnects and resumes its
activity, and the cycle repeats.

I would appreciate any hints you all can provide.

Thanks!

Avery


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