batman-adv: fix TT sync flag inconsistencies

This patch fixes an issue in the translation table code potentially
leading to a TT Request + Response storm. The issue may occur for nodes
involving BLA and an inconsistent configuration of the batman-adv AP
isolation feature. However, since the new multicast optimizations, a
single, malformed packet may lead to a mesh-wide, persistent
Denial-of-Service, too.

The issue occurs because nodes are currently OR-ing the TT sync flags of
all originators announcing a specific MAC address via the
translation table. When an intermediate node now receives a TT Request
and wants to answer this on behalf of the destination node, then this
intermediate node now responds with an altered flag field and broken
CRC. The next OGM of the real destination will lead to a CRC mismatch
and triggering a TT Request and Response again.

Furthermore, the OR-ing is currently never undone as long as at least
one originator announcing the according MAC address remains, leading to
the potential persistency of this issue.

This patch fixes this issue by storing the flags used in the CRC
calculation on a a per TT orig entry basis to be able to respond with
the correct, original flags in an intermediate TT Response for one
thing. And to be able to correctly unset sync flags once all nodes
announcing a sync flag vanish for another.

Fixes: e9c00136a475 ("batman-adv: fix tt_global_entries flags update")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Acked-by: Antonio Quartulli <a@unstable.cc>
[sw: typo in commit message]
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index ea43a6449247..a62795868794 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1260,6 +1260,7 @@ struct batadv_tt_global_entry {
  * struct batadv_tt_orig_list_entry - orig node announcing a non-mesh client
  * @orig_node: pointer to orig node announcing this non-mesh client
  * @ttvn: translation table version number which added the non-mesh client
+ * @flags: per orig entry TT sync flags
  * @list: list node for batadv_tt_global_entry::orig_list
  * @refcount: number of contexts the object is used
  * @rcu: struct used for freeing in an RCU-safe manner
@@ -1267,6 +1268,7 @@ struct batadv_tt_global_entry {
 struct batadv_tt_orig_list_entry {
 	struct batadv_orig_node *orig_node;
 	u8 ttvn;
+	u8 flags;
 	struct hlist_node list;
 	struct kref refcount;
 	struct rcu_head rcu;