Subject: Re: [PATCH net] net: bridge: mst: Check vlan state for egress decision

From: Tobias Waldekranz <[email-masked]>
Date: Sat, 06 Jul 2024 00:00:55 +0200

On fre, jul 05, 2024 at 15:00, Elliot Ayrey <[email-masked]> wrote:
> If a port is blocking in the common instance but forwarding in an MST
> instance, traffic egressing the bridge will be dropped because the
> state of the common instance is overriding that of the MST instance.

Can't believe I missed this - thanks!

> Fix this by temporarily forcing the port state to forwarding when in
> MST mode to allow checking the vlan state via br_allowed_egress().
> This is similar to what happens in br_handle_frame_finish() when
> checking ingress traffic, which was introduced in the change below.
>
> Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode")
> Signed-off-by: Elliot Ayrey <[email-masked]>
> ---
>  net/bridge/br_forward.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
> index d97064d460dc..911b37a38a32 100644
> --- a/net/bridge/br_forward.c
> +++ b/net/bridge/br_forward.c
> @@ -22,10 +22,16 @@ static inline int should_deliver(const struct net_bridge_port *p,
>  				 const struct sk_buff *skb)
>  {
>  	struct net_bridge_vlan_group *vg;
> +	u8 state;
> +
> +	if (br_mst_is_enabled(p->br))
> +		state = BR_STATE_FORWARDING;
> +	else
> +		state = p->state;
>  
>  	vg = nbp_vlan_group_rcu(p);
>  	return ((p->flags & BR_HAIRPIN_MODE) || skb->dev != p->dev) &&

I think it might read a bit better if we model it like the hairpin check
above. I.e. (special_mode || regular_condition)

It's not really that the state is forwarding when mst is enabled, we
simply ignore the port-global state in that case.

> -		p->state == BR_STATE_FORWARDING && br_allowed_egress(vg, skb) &&
> +		state == BR_STATE_FORWARDING && br_allowed_egress(vg, skb) &&

so something like:

    ...
    (br_mst_is_enabled(p->br) || p->state == BR_STATE_FORWARDING) &&
    br_allowed_egress(vg, skb) && nbp_switchdev_allowed_egress(p, skb) &&
    ...

>  		nbp_switchdev_allowed_egress(p, skb) &&
>  		!br_skb_isolated(p, skb);
>  }