[B.A.T.M.A.N.] [RFC PATCH] batman-adv: mitigate issue when empty vlan is received

Leonardo Mörlein
2018-05-06T19:55:59Z

This patch is not a fix for the issue itself, but a fix for the
other nodes, which are also influenced by the issue.

- Some (affected) nodes send TT announcements for an empty vlan (for
now only seen with vlan_id = 0).
- This behaviour is a bug! Batman-adv nodes must not send TT
announcements for empty vlans.
- The receiving batman-adv can not handle incoming TT announcements
with empty vlans. (The crc check routine batadv_tt_global_check_crc()
fails.)
- As the receiving node thinks, the crc is broken, it does a full
table request then.
- The announcing node sends a TT full table to the receiving node
then, which also contains the empty vlan, so
*batadv_tt_global_check_crc()* fails again on the receiver side.
- This causes a lot of unneeded TT traffic. In Freifunk Hannover we
decreased the amount of from ~20kpp/s to ~4kpp/s on our supernodes.
We have ~800 nodes, which are connected via vpn to one of six
supernodes. Those supernodes are connected with each other in a fully
connected mesh.

Signed-off-by: Leonardo Mörlein <me@irrelefant.net>
---
net/batman-adv/translation-table.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
index 0225616d..d2a843fd 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -2996,8 +2996,21 @@ static bool batadv_tt_global_check_crc(struct batadv_orig_node *orig_node,

vlan = batadv_orig_node_vlan_get(orig_node,
ntohs(tt_vlan_tmp->vid));
- if (!vlan)
- return false;
+ if (!vlan) {
+ /* Due to a bug, some originators send TT
+ * announcements for empty vlans. As the receiving
+ * nodes will ignore those empty vlans (they do not
+ * add a batadv_orig_node_vlan into the transglobal
+ * for the originating node), crc check will fail
+ * here. To circumvent this issue, we skip the
+ * verification for the vlan if the crc is
+ * equal to 0x00000000.
+ */
+ if (tt_vlan_tmp->crc == 0x00000000)
+ continue;
+ else
+ return false;
+ }

crc = vlan->tt.crc;
batadv_orig_node_vlan_put(vlan);
--
2.17.0