linux-kernel - Re: [PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

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Message-ID: <1757a42e-573c-41ab-b2c4-b8e1f2c8f46b@blackwall.org>
Date: Wed, 16 Jul 2025 18:42:46 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Joseph Huang <Joseph.Huang@...min.com>, netdev@...r.kernel.org
Cc: Joseph Huang <joseph.huang.2024@...il.com>,
 Ido Schimmel <idosch@...dia.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Vladimir Oltean <vladimir.oltean@....com>,
 Florian Fainelli <f.fainelli@...il.com>,
 Tobias Waldekranz <tobias@...dekranz.com>, bridge@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

On 7/16/25 18:35, Joseph Huang wrote:
> Do not offload IGMP/MLD messages as it could lead to IGMP/MLD Reports
> being unintentionally flooded to Hosts. Instead, let the bridge decide
> where to send these IGMP/MLD messages.
> 
> Consider the case where the local host is sending out reports in response
> to a remote querier like the following:
> 
>        mcast-listener-process (IP_ADD_MEMBERSHIP)
>           \
>           br0
>          /   \
>       swp1   swp2
>         |     |
>   QUERIER     SOME-OTHER-HOST
> 
> In the above setup, br0 will want to br_forward() reports for
> mcast-listener-process's group(s) via swp1 to QUERIER; but since the
> source hwdom is 0, the report is eligible for tx offloading, and is
> flooded by hardware to both swp1 and swp2, reaching SOME-OTHER-HOST as
> well. (Example and illustration provided by Tobias.)
> 
> Fixes: 472111920f1c ("net: bridge: switchdev: allow the TX data plane forwarding to be offloaded")
> Signed-off-by: Joseph Huang <Joseph.Huang@...min.com>
> ---
> v1: https://lore.kernel.org/netdev/20250701193639.836027-1-Joseph.Huang@garmin.com/
> v2: https://lore.kernel.org/netdev/20250714150101.1168368-1-Joseph.Huang@garmin.com/
>     Updated commit message.
> v3: Return early if it's an IGMP/MLD packet.
> ---
>  net/bridge/br_switchdev.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
> index 95d7355a0407..9a910cf0256e 100644
> --- a/net/bridge/br_switchdev.c
> +++ b/net/bridge/br_switchdev.c
> @@ -17,6 +17,9 @@ static bool nbp_switchdev_can_offload_tx_fwd(const struct net_bridge_port *p,
>  	if (!static_branch_unlikely(&br_switchdev_tx_fwd_offload))
>  		return false;
>  
> +	if (br_multicast_igmp_type(skb))
> +		return false;
> +
>  	return (p->flags & BR_TX_FWD_OFFLOAD) &&
>  	       (p->hwdom != BR_INPUT_SKB_CB(skb)->src_hwdom);
>  }

LGTM,
Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>