On Monday, 14 September 2020 03:21:34 CEST Linus Lüssing wrote:
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: 405cc1e5a81e ("batman-adv: Modified forwarding behaviour for multicast packets") Signed-off-by: Linus Lüssing linus.luessing@c0d3.blue
Sorry, but doesn't build cleanly:
make[1]: Leaving directory '/home/build_test/build_env/linux-build/linux-5.6' /home/build_test/build_env/tmp.3Iw5SQ84oz/net/batman-adv/soft-interface.c:367:31: error: undefined identifier 'batadv_mcast_forw_send_orig' /home/build_test/build_env/tmp.3Iw5SQ84oz/net/batman-adv/soft-interface.c: In function ‘batadv_interface_tx’: /home/build_test/build_env/tmp.3Iw5SQ84oz/net/batman-adv/soft-interface.c:367:10: error: implicit declaration of function ‘batadv_mcast_forw_send_orig’; did you mean ‘batadv_mcast_forw_send’? [-Werror=implicit-function-declaration] ret = batadv_mcast_forw_send_orig(bat_priv, skb, vid, ^~~~~~~~~~~~~~~~~~~~~~~~~~~ batadv_mcast_forw_send cc1: some warnings being treated as errors make[3]: *** [scripts/Makefile.build:268: /home/build_test/build_env/tmp.3Iw5SQ84oz/net/batman-adv/soft-interface.o] Error 1 make[2]: *** [scripts/Makefile.build:505: /home/build_test/build_env/tmp.3Iw5SQ84oz/net/batman-adv] Error 2 make[1]: *** [Makefile:1683: /home/build_test/build_env/tmp.3Iw5SQ84oz] Error 2 make: *** [Makefile:74: all] Error 2
It was tried to build with:
/usr/bin/make -C /home/build_test/build_env/linux-build/linux-5.6 M=/home/build_test/build_env/tmp.3Iw5SQ84oz PWD=/home/build_test/build_env/tmp.3Iw5SQ84oz REVISION= CONFIG_BATMAN_ADV=m CONFIG_BATMAN_ADV_DEBUG=y CONFIG_BATMAN_ADV_DEBUGFS=n CONFIG_BATMAN_ADV_BLA=n CONFIG_BATMAN_ADV_DAT=y CONFIG_BATMAN_ADV_NC=y CONFIG_BATMAN_ADV_MCAST=n CONFIG_BATMAN_ADV_SYSFS=n CONFIG_BATMAN_ADV_TRACING=n CONFIG_BATMAN_ADV_BATMAN_V=n INSTALL_MOD_DIR=updates/ modules
Kind regards, Sven