netdev - Re: [PATCH] net: bridge: set skb->protocol for 802.1Q VLAN packets

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Message-ID: <190cbaa8-1223-4e64-a583-daf9dfe608f5@blackwall.org>
Date: Fri, 28 Mar 2025 00:45:25 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: inuc@...com, bridge@...ts.linux.dev
Cc: netdev@...r.kernel.org, roopa@...dia.com
Subject: Re: [PATCH] net: bridge: set skb->protocol for 802.1Q VLAN packets

On 3/26/25 20:11, inuc@...com wrote:
> From: Liu Jie <inuc@...com>
> 
> When bridging locally originated VLAN-tagged packets, we must ensure
> skb->protocol is properly set to ETH_P_8021Q. Currently, if this field
> remains unset, br_allowed_ingress() may incorrectly drop valid VLAN
> packets during the bridge transmission path.
> 
> Fix this by explicitly checking eth_hdr(skb)->h_proto for VLAN tags when
> handling locally generated packets.
> 
> Signed-off-by: Liu Jie <inuc@...com>
> ---
>   net/bridge/br_device.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index 0ab4613aa..9094ba7e4 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -63,6 +63,9 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
>   	skb_reset_mac_header(skb);
>   	skb_pull(skb, ETH_HLEN);
>   
> +	if (eth_hdr(skb)->h_proto == htons(ETH_P_8021Q))
> +		skb->protocol = htons(ETH_P_8021Q);
> +
>   	if (!br_allowed_ingress(br, br_vlan_group_rcu(br), skb, &vid,
>   				&state, &vlan))
>   		goto out;

Why do you think the protocol is incorrect? Did you see a problem with
some particular setup?