[PATCH net-next 1/2] net: stmmac: Fix VLAN 0 deletion in vlan_del_hw_rx_fltr()

When the "rx-vlan-filter" feature is enabled on a network device, the 8021q
module automatically adds a VLAN 0 hardware filter when the device is
brought administratively up.

For stmmac, this causes vlan_add_hw_rx_fltr() to create a new entry for
VID 0 in the mac_device_info->vlan_filter array, in the following format:

    VLAN_TAG_DATA_ETV | VLAN_TAG_DATA_VEN | vid

Here, VLAN_TAG_DATA_VEN indicates that the hardware filter is enabled for
that VID.

However, on the delete path, vlan_del_hw_rx_fltr() searches the vlan_filter
array by VID only, without verifying whether a VLAN entry is enabled. As a
result, when the 8021q module attempts to remove VLAN 0, the function may
mistakenly match a zero-initialized slot rather than the actual VLAN 0
entry, causing incorrect deletions and leaving stale entries in the
hardware table.

Fix this by verifying that the VLAN entry's enable bit (VLAN_TAG_DATA_VEN)
is set before matching and deleting by VID. This ensures only active VLAN
entries are removed and avoids leaving stale entries in the VLAN filter
table, particularly for VLAN ID 0.

Fixes: ed64639bc1e08 ("net: stmmac: Add support for VLAN Rx filtering")
Signed-off-by: Ovidiu Panait <redacted>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_vlan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_vlan.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_vlan.c
index 0b6f6228ae35..fd97879a8740 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_vlan.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_vlan.c

@@ -122,7 +122,8 @@ static int vlan_del_hw_rx_fltr(struct net_device *dev,
 
 	/* Extended Rx VLAN Filter Enable */
 	for (i = 0; i < hw->num_vlan; i++) {
-		if ((hw->vlan_filter[i] & VLAN_TAG_DATA_VID) == vid) {
+		if ((hw->vlan_filter[i] & VLAN_TAG_DATA_VEN) &&
+		    ((hw->vlan_filter[i] & VLAN_TAG_DATA_VID) == vid)) {
 			ret = vlan_write_filter(dev, hw, i, 0);
 
 			if (!ret)

-- 
2.51.0