[PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

[PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

[Joseph Huang]

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@garmin.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);
 }
-- 
2.50.1

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

[Nikolay Aleksandrov]

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@garmin.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@blackwall.org>

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

[Ido Schimmel]

On Wed, Jul 16, 2025 at 11:35:50AM -0400, 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@garmin.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 16 Jul 2025 11:35:50 -0400 you 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:
> 
> [...]

Here is the summary with links:
  - [v3,net] net: bridge: Do not offload IGMP/MLD messages
    https://git.kernel.org/netdev/net/c/683dc24da8bf

You are awesome, thank you!
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