Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to aggregation after sender reboot

From: Johannes Berg <johannes@sipsolutions.net>
To: "Krzysztof Hałasa" <khalasa@piap.pl>
Cc: "David S. Miller" <davem@davemloft.net>,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to aggregation after sender reboot
Date: Tue, 29 Oct 2019 10:07:30 +0100	[thread overview]
Message-ID: <4725dcbd6297c74bf949671e7ad48eeeb0ceb0d0.camel@sipsolutions.net> (raw)
In-Reply-To: <m37e4orkxr.fsf@t19.piap.pl>

On Tue, 2019-10-29 at 09:54 +0100, Krzysztof Hałasa wrote:

> The problem I can see is that the dialog_tokens are 8-bit, way too small
> to eliminate conflicts.

Well, they're also per station, we could just randomize the start and
then we'd delete the old session and start a new one, on the receiver.

So that would improve robustness somewhat (down to a 1/256 chance to hit
this problem).

> > Really what I think probably happened is that one of your stations lost
> > the connection to the other, and didn't tell it about it in any way - so
> > the other kept all the status alive.
> 
> You must have missed my previous mail - I simply rebooted that station,
> and alternatively rmmoded/modprobed ath9k. But the problem originated in
> a station going out of and back in range, in fact.

I was on vacation, so yeah, quite possible I missed it.

Sounds like we need not just
4b08d1b6a994 ("mac80211: IBSS: send deauth when expiring inactive STAs")

but also send a deauth when we disconnect. Surprising we don't do that,
actually.

> > I suspect to make all this work well we need to not only have the fixes
> > I made recently to actually send and parse deauth frames, but also to
> > even send an auth and reset the state when we receive that, so if we
> > move out of range and even the deauth frame is lost, we can still reset
> > properly.
> 
> That's one thing. The other is a station trying ADDBA for the first time
> after boot (while the local station has seen it before that reboot).

That's the situation though - the local station needs to know that it
has in fact *not* seen the same instance of the station, but that the
station has reset and needs to be removed & re-added.

> I guess we need to identify "new connection" reliably. Otherwise,
> the new connections are treated as old ones and it doesn't work.

Right. But we can implement the (optional) authentication (which you
actually already get when you implement [encrypted] IBSS with wpa_s),
and reset the station state when we get an authentication frame.

johannes