Scenario: * Multicast frame send from mesh to a BLA backbone (multiple nodes with their bat0 bridged together, with BLA enabled)
Issue: * BLA backbone nodes receive the frame multiple times on bat0, once from mesh->bat0 and once from each backbone_gw from LAN
For unicast, a node will send only to the best backbone gateway according to the TQ. However for multicast we currently cannot determine if multiple destination nodes share the same backbone if they don't share the same backbone with us. So we need to keep sending the unicasts to all backbone gateways and let the backbone gateways decide which one will forward the frame. We can use the CLAIM mechanism to make this decision.
One catch: The batman-adv gateway feature for DHCP packets potentially sends multicast packets in the same batman-adv unicast header as the multicast optimizations code. And we are not allowed to drop those even if we did not claim the source address of the sender, as for such packets there is only this one multicast-in-unicast packet.
How can we distinguish the two cases?
For DHCPv4: Here the broadcast MAC address is used and the multicast optimizations will never send a broadcast frame via batman-adv unicast packets (see the !is_broadcast_ether_addr() check in after the goto-send in batadv_interface_tx().
For DHCPv6: This is even trickier... DHCPv6 potentially uses non-broadcast multicast addresses. However according to RFC8415, section 7.1 it seems that currently multicast is only used from a DHCPv6 client to a DHCPv6 server, but not the other way round.
Working through the gateway feature part in batadv_interface_tx() it can be inferred that a DHCPv6 packet to a DHCP client would have been the only option for a DHCPv6 multicast packet to be sent via unicast through the gateway feature. Ergo, the newly introduced claim check won't wrongly drop a DHCPv6 packet received via the gateway feature either.
Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue --- net/batman-adv/bridge_loop_avoidance.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c index d8c5d317..9603a6d0 100644 --- a/net/batman-adv/bridge_loop_avoidance.c +++ b/net/batman-adv/bridge_loop_avoidance.c @@ -1848,7 +1848,8 @@ bool batadv_bla_rx(struct batadv_priv *bat_priv, struct sk_buff *skb,
if (unlikely(atomic_read(&bat_priv->bla.num_requests))) /* don't allow broadcasts while requests are in flight */ - if (is_multicast_ether_addr(ethhdr->h_dest) && is_bcast) + if (is_multicast_ether_addr(ethhdr->h_dest) && + (!is_broadcast_ether_addr(ethhdr->h_dest) || is_bcast)) goto handled;
ether_addr_copy(search_claim.addr, ethhdr->h_source); @@ -1885,7 +1886,8 @@ bool batadv_bla_rx(struct batadv_priv *bat_priv, struct sk_buff *skb, }
/* if it is a broadcast ... */ - if (is_multicast_ether_addr(ethhdr->h_dest) && is_bcast) { + if (is_multicast_ether_addr(ethhdr->h_dest) && + (!is_broadcast_ether_addr(ethhdr->h_dest) || is_bcast)) { /* ... drop it. the responsible gateway is in charge. * * We need to check is_bcast because with the gateway