Subject: Re: Latency and connection problems with a carl9170-based AP
From: Johannes Berg <johannes@sipsolutions.net>
To: Christian Lamparter <chunkeey@googlemail.com>
Cc: Harshal Chhaya <harshal@gmail.com>, linux-wireless@vger.kernel.org
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	 <201109141932.02929.chunkeey@googlemail.com>
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Date: Wed, 14 Sep 2011 19:59:19 +0200
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On Wed, 2011-09-14 at 19:38 +0200, Johannes Berg wrote:
> On Wed, 2011-09-14 at 19:32 +0200, Christian Lamparter wrote:
> > On Wednesday, September 14, 2011 01:19:59 PM Harshal Chhaya wrote:
> > > Most of the disconnects seem to be caused by beacons that update the
> > > TIM IE but not the overall length. The result is a corrupted RSN IE
> > > (e.g. the IE length says 20 bytes but the IE is only 19 bytes in size)
> > > which causes the clients to disconnect. This problem lasts for only
> > > one beacon (i.e. the next beacon has the right size) but it is enough
> > > to cause the clients to disconnect. Is there a way to fix this?
> > Now that is really interesting. Do you know if the TIM IE is generated
> > properly by ieee80211_beacon_add_tim in net/mac80211/tx.c?
> 
> Hm, looking at that code, is it really correct?
> 
>         tim = pos = (u8 *) skb_put(skb, 6);
>         *pos++ = WLAN_EID_TIM;
>         *pos++ = 4;
> ...
>                 tim[1] = n2 - n1 + 4;
>                 skb_put(skb, n2 - n1);
> 
> 
> shouldn't the latter be skb_put(skb, n2 - n1 - 2)?

Nah, I'm just confused.

johannes