linux-kernel - [PATCH net-next v3] net: bridge: locally receive all multicast packets if IFF

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Message-ID:
 <OSZPR01MB8434308370ACAFA90A22980798B32@OSZPR01MB8434.jpnprd01.prod.outlook.com>
Date: Mon, 14 Apr 2025 18:56:01 +0800
From: Shengyu Qu <wiagn233@...look.com>
To: razor@...ckwall.org,
	idosch@...dia.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	bridge@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Shengyu Qu <wiagn233@...look.com>,
	Felix Fietkau <nbd@....name>
Subject: [PATCH net-next v3] net: bridge: locally receive all multicast packets if IFF_ALLMULTI is set

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.

OpenWrt uses a user space daemon for DHCPv6/RA/NDP handling, and in relay
mode it sets the ALLMULTI flag in order to receive all relevant queries on
the network.

This works for normal network interfaces and non-snooping bridges, but not
snooping bridges (unless multicast routing is enabled).

Reported-by: Felix Fietkau <nbd@....name>
Closes:https://github.com/openwrt/openwrt/issues/15857#issuecomment-2662851243
Signed-off-by: Shengyu Qu <wiagn233@...look.com>
---
Changes since v1:
 - Move to net-next
 - Changed code according to Nikolay's advice

Changes since v2:
 - Fix alignment
 - Remove redundant parenthesis
 - Add more infomation in commit message
---
 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..5f6ac9bf1527 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) {
 				local_rcv = true;
 				DEV_STATS_INC(br->dev, multicast);
 			}
-- 
2.43.0