• Linus Lüssing's avatar
    batman-adv: mcast: fix duplicate mcast packets in BLA backbone from LAN · 3236d215
    Linus Lüssing authored
    Scenario:
    * Multicast frame send from a BLA backbone (multiple nodes with
      their bat0 bridged together, with BLA enabled)
    
    Issue:
    * BLA backbone nodes receive the frame multiple times on bat0
    
    For multicast frames received via batman-adv broadcast packets the
    originator of the broadcast packet is checked before decapsulating and
    forwarding the frame to bat0 (batadv_bla_is_backbone_gw()->
    batadv_recv_bcast_packet()). If it came from a node which shares the
    same BLA backbone with us then it is not forwarded to bat0 to avoid a
    loop.
    
    When sending a multicast frame in a non-4-address batman-adv unicast
    packet we are currently missing this check - and cannot do so because
    the batman-adv unicast packet has no originator address field.
    
    However, we can simply fix this on the sender side by only sending the
    multicast frame via unicasts to interested nodes which do not share the
    same BLA backbone with us. This also nicely avoids some unnecessary
    transmissions on mesh side.
    
    Note that no infinite loop was observed, probably because of dropping
    via batadv_interface_tx()->batadv_bla_tx(). However the duplicates still
    utterly confuse switches/bridges, ICMPv6 duplicate address detection and
    neighbor discovery and therefore leads to long delays before being able
    to establish TCP connections, for instance. And it also leads to the Linux
    bridge printing messages like:
    "br-lan: received packet on eth1 with own address as source address ..."
    
    Fixes: 2d3f6ccc ("batman-adv: Modified forwarding behaviour for multicast packets")
    Signed-off-by: default avatarLinus Lüssing <linus.luessing@c0d3.blue>
    Signed-off-by: default avatarSven Eckelmann <sven@narfation.org>
    Signed-off-by: default avatarSimon Wunderlich <sw@simonwunderlich.de>
    3236d215
multicast.h 2.87 KB