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
In-Reply-To: <201109141932.02929.chunkeey@googlemail.com> (sfid-20110914_193219_215086_8DB3821B)
References: <CAJ8GFOgNRAr7LvnO8f0Y8uvkQdwhz7uUXRQ6BXomjO05RiiYjg@mail.gmail.com>
	 <201109141932.02929.chunkeey@googlemail.com>
	 (sfid-20110914_193219_215086_8DB3821B)
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Date: Wed, 14 Sep 2011 19:38:35 +0200
Message-ID: <1316021915.4663.0.camel@jlt3.sipsolutions.net> (sfid-20110914_193848_416896_BA7DA3F8)
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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)?

But that'd be the other way around I guess...

johannes