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

[Simon Horman <horms@kernel.org>]

On Tue, Nov 11, 2025 at 09:29:59AM +0000, Ovidiu Panait wrote:
> 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 <ovidiu.panait.rb@renesas.com>

Reviewed-by: Simon Horman <horms@kernel.org>