Commit 08cc83cc7f ("net: dsa: add support for BRIDGE_MROUTER
attribute") added an option for users to turn off multicast flooding
towards the CPU if they turn off the IGMP querier on a bridge which
already has enslaved ports (echo 0 > /sys/class/net/br0/bridge/multicast_router).
And commit a8b659e7ff ("net: dsa: act as passthrough for bridge port flags")
simply papered over that issue, because it moved the decision to flood
the CPU with multicast (or not) from the DSA core down to individual drivers,
instead of taking a more radical position then.
The truth is that disabling multicast flooding to the CPU is simply
something we are not prepared to do now, if at all. Some reasons:
- ICMP6 neighbor solicitation messages are unregistered multicast
packets as far as the bridge is concerned. So if we stop flooding
multicast, the outside world cannot ping the bridge device's IPv6
link-local address.
- There might be foreign interfaces bridged with our DSA switch ports
(sending a packet towards the host does not necessarily equal
termination, but maybe software forwarding). So if there is no one
interested in that multicast traffic in the local network stack, that
doesn't mean nobody is.
- PTP over L4 (IPv4, IPv6) is multicast, but is unregistered as far as
the bridge is concerned. This should reach the CPU port.
- The switch driver might not do FDB partitioning. And since we don't
even bother to do more fine-grained flood disabling (such as "disable
flooding _from_port_N_ towards the CPU port" as opposed to "disable
flooding _from_any_port_ towards the CPU port"), this breaks standalone
ports, or even multiple bridges where one has an IGMP querier and one
doesn't.
Reverting the logic makes all of the above work.
Fixes: a8b659e7ff ("net: dsa: act as passthrough for bridge port flags")
Fixes: 08cc83cc7f ("net: dsa: add support for BRIDGE_MROUTER attribute")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
c73c57081b