Re: [regression] STP on 80211s is broken in 6.4-rc4

From: Bagas Sanjaya <bagasdotme@gmail.com>
To: "Nicolas Escande" <nico.escande@gmail.com>,
	nbd@nbd.name, "Toke Høiland-Jørgensen" <toke@toke.dk>,
	"Kalle Valo" <kvalo@kernel.org>,
	"Johannes Berg" <johannes.berg@intel.com>
Cc: linux-wireless@vger.kernel.org,
	Linux Regressions <regressions@lists.linux.dev>
Subject: Re: [regression] STP on 80211s is broken in 6.4-rc4
Date: Sat, 10 Jun 2023 13:44:03 +0700	[thread overview]
Message-ID: <ZIQbs0wqdRh7c0Kx@debian.me> (raw)
In-Reply-To: <CT5GNZSK28AI.2K6M69OXM9RW5@syracuse>

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On Tue, Jun 06, 2023 at 12:55:57PM +0200, Nicolas Escande wrote:
> Hello Felix,
> 
> As user of the mesh part of mac80211 on multiple products at work let me say
> thank you for all the work you do on wifi, especially on 80211s, and especially
> the recent improvements you made for mesh fast RX/TX & cross vendor AMSDU compat
> 
> We upgraded our kernel from an older (5.15) to a newer 6.4. The problem is STP 
> doesn't work anymore and alas we use it for now (for the better or worse).
> 
> What I gathered so far from my setup:
>  - we use ath9k & ath10k
>  - in my case STP frames are received as regular packet and not as amsdu
>  - the received packets have a wrong length of 44 in tcpdump
>    (instead of 38 with our previous kernel)
>  - llc_fixup_skb() tries to pull some 41 bytes out of a 35 bytes packet
>    this makes llc_rcv() discard the frames & breaks STP
> 
> >From bisecting the culprit seems to be 986e43b19ae9176093da35e0a844e65c8bf9ede7
> (wifi: mac80211: fix receiving A-MSDU frames on mesh interfaces)
> 
> I guess that your changes to handle both ampdu subframes & normal frames in the
> same datapath ends up putting a wrong skb->len for STP (multicast) frames ?
> Honestly I don't understand enough of the 80211 internals & spec to pinpoint the
> exact problem.
> 
> It seems this change was already in the 6.3 kernel so I guess someone should
> have seen it before (but I didn't find anything..) ? Maybe I missed something...
> 
> Anyway I'm happy to provide more info or try anything you throw at me.
> 

Thanks for the regression report. I'm adding it to regzbot:

(Felix: it looks like this regression is introcued by a commit authored by you.
Would you like to take a look on it?)

#regzbot ^introduced: 986e43b19ae917

-- 
An old man doll... just what I always wanted! - Clara

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