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

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Message-ID: <20250602194914.1011890-1-jonas.gorski@gmail.com>
Date: Mon,  2 Jun 2025 21:49:14 +0200
From: Jonas Gorski <jonas.gorski@...il.com>
To: 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>,
	Paolo Abeni <pabeni@...hat.com>,
	Jonas Gorski <jonas.gorski@...il.com>
Cc: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net] net: dsa: b53: fix untagged traffic sent via cpu tagged with VID 0

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);
 	}
 }
-- 
2.43.0