batman-adv: fix counter for multicast supporting nodes

commit e8829f00 upstream.

A miscounting of nodes having multicast optimizations enabled can lead
to multicast packet loss in the following scenario:

If the first OGM a node receives from another one has no multicast
optimizations support (no multicast tvlv) then we are missing to
increase the counter. This potentially leads to the wrong assumption
that we could safely use multicast optimizations.

Fixings this by increasing the counter if the initial OGM has the
multicast TVLV unset, too.

Introduced by 60432d75
("batman-adv: Announce new capability via multicast TVLV")
Reported-by: Tobias Hachmer <tobias@hachmer.de>
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/batman-adv/multicast.c

@@ -686,11 +686,13 @@ static void batadv_mcast_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
 		if (orig_initialized)
 			atomic_dec(&bat_priv->mcast.num_disabled);
 		orig->capabilities |= BATADV_ORIG_CAPA_HAS_MCAST;
-	/* If mcast support is being switched off increase the disabled
-	 * mcast node counter.
+	/* If mcast support is being switched off or if this is an initial
+	 * OGM without mcast support then increase the disabled mcast
+	 * node counter.
 	 */
 	} else if (!orig_mcast_enabled &&
-		   orig->capabilities & BATADV_ORIG_CAPA_HAS_MCAST) {
+		   (orig->capabilities & BATADV_ORIG_CAPA_HAS_MCAST ||
+		    !orig_initialized)) {
 		atomic_inc(&bat_priv->mcast.num_disabled);
 		orig->capabilities &= ~BATADV_ORIG_CAPA_HAS_MCAST;
 	}