netdev - Re: [PATCH net] net: dsa: b53: fix untagged traffic sent via cpu tagged with VID 0

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Message-ID: <9092793c-cb9c-4440-b2b6-3e80216a737c@broadcom.com>
Date: Thu, 5 Jun 2025 11:02:29 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Jonas Gorski <jonas.gorski@...il.com>, Andrew Lunn <andrew@...n.ch>,
 Vladimir Oltean <olteanv@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: b53: fix untagged traffic sent via cpu
 tagged with VID 0

On 6/2/25 12:49, Jonas Gorski wrote:
> When Linux sends out untagged traffic from a port, it will enter the CPU
> port without any VLAN tag, even if the port is a member of a vlan
> filtering bridge with a PVID egress untagged VLAN.
> 
> This makes the CPU port's PVID take effect, and the PVID's VLAN
> table entry controls if the packet will be tagged on egress.
> 
> Since commit 45e9d59d3950 ("net: dsa: b53: do not allow to configure
> VLAN 0") we remove bridged ports from VLAN 0 when joining or leaving a
> VLAN aware bridge. But we also clear the untagged bit, causing untagged
> traffic from the controller to become tagged with VID 0 (and priority
> 0).
> 
> Fix this by not touching the untagged map of VLAN 0. Additionally,
> always keep the CPU port as a member, as the untag map is only effective
> as long as there is at least one member, and we would remove it when
> bridging all ports and leaving no standalone ports.
> 
> Since Linux (and the switch) treats VLAN 0 tagged traffic like untagged,
> the actual impact of this is rather low, but this also prevented earlier
> detection of the issue.
> 
> Fixes: 45e9d59d3950 ("net: dsa: b53: do not allow to configure VLAN 0")
> Signed-off-by: Jonas Gorski <jonas.gorski@...il.com>

Reviewed-by: Florian Fainelli <florian.fainelli@...adcom.com>
-- 
Florian