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@nbd.name>
Closes: https://github.com/openwrt/openwrt/issues/15857#issuecomment-2662851243
Signed-off-by: Shengyu Qu <wiagn233@outlook.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/OSZPR01MB8434308370ACAFA90A22980798B32@OSZPR01MB8434.jpnprd01.prod.outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 232133a0fd21c61ac92d00bc8792bbc8802bb391..5f6ac9bf15275da6a4ec69eb44a971b87cb767b7 100644 (file)
--- 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);
                        }