Linux Ethernet Bridging - Sep 2015 - [Bridge] [net-next PATCH] net: bridge: fix for bridging 802.1Q without REORDER_HDR

On Fri, 11 Sep 2015 21:22:03 +0200
Phil Sutter <phil at nwl.cc> 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 <phil at nwl.cc>
> ---
>  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.

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 <phil at nwl.cc>
---
 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);
-- 
2.1.2