[PATCH net-next v3] net: bridge: locally receive all multicast packets if IFF_ALLMULTI is set
From: Shengyu Qu
Date: Mon Apr 14 2025 - 06:56:33 EST
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@xxxxxxxx>
Closes:https://github.com/openwrt/openwrt/issues/15857#issuecomment-2662851243
Signed-off-by: Shengyu Qu <wiagn233@xxxxxxxxxxx>
---
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