Re: [PATCH net] net: bridge: clear bridge's private skb space on xmit

[David Ahern <dsahern@gmail.com>]

On 7/31/20 10:26 AM, Nikolay Aleksandrov wrote:
> We need to clear all of the bridge private skb variables as they can be
> stale due to the packet being recirculated through the stack and then
> transmitted through the bridge device. Similar memset is already done on
> bridge's input. We've seen cases where proxyarp_replied was 1 on routed
> multicast packets transmitted through the bridge to ports with neigh
> suppress which were getting dropped. Same thing can in theory happen with
> the port isolation bit as well.
> 
> Fixes: 821f1b21cabb ("bridge: add new BR_NEIGH_SUPPRESS port flag to suppress arp and nd flood")
> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
> ---
>  net/bridge/br_device.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index 8c7b78f8bc23..9a2fb4aa1a10 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -36,6 +36,8 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
>  	const unsigned char *dest;
>  	u16 vid = 0;
>  
> +	memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
> +
>  	rcu_read_lock();
>  	nf_ops = rcu_dereference(nf_br_ops);
>  	if (nf_ops && nf_ops->br_dev_xmit_hook(skb)) {
> 

What's the performance hit of doing this on every packet?

Can you just set a flag that tells the code to reset on recirculation?
Seems like br_input_skb_cb has space for that.