[ath9k-devel] GTK/PTK problem - key.c magic-bitshift

[Antonio Quartulli <antonio@open-mesh.com>]

Hello list,

I am debugging a strange problem which symptom is that the PTK of some station
is messed up right after hostapd has configured a new GTK. This happens both in
WPA2 only and WPA/WPA2 mixed mode. I have no real clue of what is going on and
so, after having given a look at the hostapd code, I am now checking the driver
(Ath9k).

While digging I found a piece of code in key.c which I can't understand.
Here is the snippet:

111                 macLo = get_unaligned_le32(mac);
112                 macHi = get_unaligned_le16(mac + 4);
113                 macLo >>= 1;
114                 macLo |= (macHi & 1) << 31;
115                 macHi >>= 1;

At drivers/net/wireless/ath/key.c:113 there is a right-bitshift operation
executed on macLo. Since macLo is a 4byte variable containing 4 out of 6
bytes of the MAC address passed as argument, it looks to me like the bitshift
is throwing away one bit that we will never recover.

I don't want to claim that this is necessarily connected to the problem I am
experiencing, but I'd like to get a better understanding of this part in order
to continue my research.

However the driver I am using is not the latest one, so if somebody knows
whether this GTK/PTK problem is known and fixed I would be glad if you could
tell me :-)


Thanks a lot for your time.

Regards,


-- 
Antonio Quartulli
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