Subject: Re: [net-next PATCH] net: bridge: fix for bridging 802.1Q without REORDER_HDR

From: Stephen Hemminger <[email-masked]>
Date: Fri, 11 Sep 2015 12:24:45 -0700

On Fri, 11 Sep 2015 21:22:03 +0200
Phil Sutter <[email-masked]> wrote:

> When forwarding packets from an 802.1Q interface with REORDER_HDR set to
> zero, the VLAN header previously inserted by vlan_do_receive() needs to
> be stripped from the packet and the mac_header adjustment undone,
> otherwise a tagged frame with first four bytes missing will be
> transmitted.
> 
> Signed-off-by: Phil Sutter <[email-masked]>
> ---
>  net/bridge/br_input.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index f921a5d..e4e3fc7 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -288,6 +288,16 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
>  	}
>  
>  forward:
> +	if (is_vlan_dev(skb->dev) &&
> +	    !(vlan_dev_priv(skb->dev)->flags & VLAN_FLAG_REORDER_HDR)) {
> +		unsigned int offset = skb->data - skb_mac_header(skb);
> +
> +		skb_push(skb, offset);
> +		memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
> +		skb->mac_header += VLAN_HLEN;
> +		skb_pull(skb, offset);
> +		skb_reset_mac_len(skb);
> +	}
>  	switch (p->state) {
>  	case BR_STATE_FORWARDING:
>  		rhook = rcu_dereference(br_should_route_hook);

Thanks for finding this. Is this a new thing or has it always been there?

Sorry, this looks so special case it doesn't seem like a good idea.
Something is broken in VLAN handling if this is required.