Re: [PATCH net-next v2] net: bridge: locally receive all multicast packets if IFF_ALLMULTI is set

[Ido Schimmel]

On Sat, Apr 12, 2025 at 09:16:13PM +0800, Shengyu Qu wrote:
> If multicast snooping is enabled, multicast packets may not always end up
> on the local bridge interface, if the host is not a member of the multicast
> group. Similar to how IFF_PROMISC allows all packets to be received
> locally, let IFF_ALLMULTI allow all multicast packets to be received.

Would be good to explain in the commit message why this is needed when
you can instead configure the bridge as a router port. Felix provided
useful information on v1:

https://lore.kernel.org/netdev/7932cd23-571e-4646-b5dd-467ec8106695@xxxxxxxx/

> 
> Signed-off-by: Felix Fietkau <nbd@xxxxxxxx>
> Signed-off-by: Shengyu Qu <wiagn233@xxxxxxxxxxx>
> ---
> Since Felix didn't send v2 for this patch, I decided to do it by myself.

Felix provided his SoB on v2? If not, "Reported-by" might be more
appropriate.

> 
> Changes since v1:
>  - Move to net-next
>  - Changed code according to Nikolay's advice
> ---
>  net/bridge/br_input.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index 232133a0fd21..aefcc3614373 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -189,7 +189,8 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>  		if ((mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb)) &&
>  		    br_multicast_querier_exists(brmctx, eth_hdr(skb), mdst)) {
>  			if ((mdst && mdst->host_joined) ||
> -			    br_multicast_is_router(brmctx, skb)) {
> +			    br_multicast_is_router(brmctx, skb) ||
> +				(br->dev->flags & IFF_ALLMULTI)) {

The alignment here is off. Also, you can drop the parenthesis.

>  				local_rcv = true;
>  				DEV_STATS_INC(br->dev, multicast);
>  			}
> -- 
> 2.43.0
>