[PATCH] Fix race conditions in the WPA group-key state machine

Yen-Jung Chang yenjung at gmail.com
Thu May 22 04:04:51 EDT 2008


Hi Jouni,

I run into the same issue with 0.4.8, so I back port the robust mechanism
from 0.5.10 to 0.4.8.

Would you please give me some advice about the attached patch?

Thanks,
YJ.


2008/3/18 Jouni Malinen <j at w1.fi>:

> On Thu, Mar 06, 2008 at 09:18:46AM +0200, Uri Simchoni wrote:
>
> > Working with madwifi driver, we've encountered some rare conditions in
> > which clients can't receive WPA-encrypted multicast packets. This has
> > become a more serious lately since Windows Vista uses broadcast packets
> > for DHCP by default.
> >
> > After digging into it for a while, we realized that the group-key state
> > machine was stuck in the SETKEYS state, meaning that it negotiates a new
> > group key, but doesn't activate the key at the driver. Further
> > investigation showed that the GNoStations variable got negative.
>
> Thanks for reporting this.
>
> > The supplied patch (against 0.4.10, sorry...) fixes these issues, and
> > also remove the reliance on GNoStations, because it looks like a
> > not-very-robust way to determine how many stations need to negotiate
> > group key (although it's based on the standard...)
>
> I replaced the group key update management with a more robust mechanism
> about a month ago (the new version is included in 0.5.10). It uses a bit
> different solution when compared to your patch, but I would expect the
> end result to be quite similar since GNoStations variable was removed
> completely and only the stations that are really active and ready for
> group key update are include in the dynamic count.
>
> I haven't ported the patch to 0.4.x branch yet, but I would prefer to
> use the same solution in all branches to minimize amount of code to
> maintain in the future.
>
> --
> Jouni Malinen                                            PGP id EFC895FA
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