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

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Message-ID: <efeeaa50-cf61-4b4f-a2f0-bf15a1dfbaf3@redhat.com>
Date: Thu, 5 Jun 2025 10:54:39 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jonas Gorski <jonas.gorski@...il.com>,
 Florian Fainelli <florian.fainelli@...adcom.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>
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 9:49 PM, 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>
> ---
> My favourite kind of fix, just deleting code :-)
> 
>  drivers/net/dsa/b53/b53_common.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
> index 132683ed3abe..6eac09a267d0 100644
> --- a/drivers/net/dsa/b53/b53_common.c
> +++ b/drivers/net/dsa/b53/b53_common.c
> @@ -2051,9 +2051,6 @@ int b53_br_join(struct dsa_switch *ds, int port, struct dsa_bridge bridge,
>  
>  		b53_get_vlan_entry(dev, pvid, vl);
>  		vl->members &= ~BIT(port);
> -		if (vl->members == BIT(cpu_port))
> -			vl->members &= ~BIT(cpu_port);
> -		vl->untag = vl->members;
>  		b53_set_vlan_entry(dev, pvid, vl);
>  	}
>  
> @@ -2132,8 +2129,7 @@ void b53_br_leave(struct dsa_switch *ds, int port, struct dsa_bridge bridge)
>  		}
>  
>  		b53_get_vlan_entry(dev, pvid, vl);
> -		vl->members |= BIT(port) | BIT(cpu_port);
> -		vl->untag |= BIT(port) | BIT(cpu_port);
> +		vl->members |= BIT(port);
>  		b53_set_vlan_entry(dev, pvid, vl);
>  	}
>  }

Makes sense to, but it could use an explicit ack from Florian...

/P