batman-adv: mcast: don't send link-local multicast to mcast routers

The addition of routable multicast TX handling introduced a
bug/regression for packets with a link-local multicast destination:
These packets would be sent to all batman-adv nodes with a multicast
router and to all batman-adv nodes with an old version without multicast
router detection.

This even disregards the batman-adv multicast fanout setting, which can
potentially lead to an unwanted, high number of unicast transmissions or
even congestion.

Fixing this by avoiding to send link-local multicast packets to nodes in
the multicast router list.

Fixes: 11d458c1 ("batman-adv: mcast: apply optimizations for routable packets, too")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/multicast.c

@@ -1339,6 +1339,7 @@ batadv_mcast_forw_rtr_node_get(struct batadv_priv *bat_priv,
  * @bat_priv: the bat priv with all the soft interface information
  * @skb: The multicast packet to check
  * @orig: an originator to be set to forward the skb to
+ * @is_routable: stores whether the destination is routable
  *
  * Return: the forwarding mode as enum batadv_forw_mode and in case of
  * BATADV_FORW_SINGLE set the orig to the single originator the skb
@@ -1346,17 +1347,16 @@ batadv_mcast_forw_rtr_node_get(struct batadv_priv *bat_priv,
  */
 enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       struct batadv_orig_node **orig)
+		       struct batadv_orig_node **orig, int *is_routable)
 {
 	int ret, tt_count, ip_count, unsnoop_count, total_count;
 	bool is_unsnoopable = false;
 	unsigned int mcast_fanout;
 	struct ethhdr *ethhdr;
-	int is_routable = 0;
 	int rtr_count = 0;
 
 	ret = batadv_mcast_forw_mode_check(bat_priv, skb, &is_unsnoopable,
-					   &is_routable);
+					   is_routable);
 	if (ret == -ENOMEM)
 		return BATADV_FORW_NONE;
 	else if (ret < 0)
@@ -1369,7 +1369,7 @@ batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
 	ip_count = batadv_mcast_forw_want_all_ip_count(bat_priv, ethhdr);
 	unsnoop_count = !is_unsnoopable ? 0 :
 			atomic_read(&bat_priv->mcast.num_want_all_unsnoopables);
-	rtr_count = batadv_mcast_forw_rtr_count(bat_priv, is_routable);
+	rtr_count = batadv_mcast_forw_rtr_count(bat_priv, *is_routable);
 
 	total_count = tt_count + ip_count + unsnoop_count + rtr_count;
 
@@ -1689,6 +1689,7 @@ batadv_mcast_forw_want_rtr(struct batadv_priv *bat_priv,
  * @bat_priv: the bat priv with all the soft interface information
  * @skb: the multicast packet to transmit
  * @vid: the vlan identifier
+ * @is_routable: stores whether the destination is routable
  *
  * Sends copies of a frame with multicast destination to any node that signaled
  * interest in it, that is either via the translation table or the according
@@ -1701,7 +1702,7 @@ batadv_mcast_forw_want_rtr(struct batadv_priv *bat_priv,
  * is neither IPv4 nor IPv6. NET_XMIT_SUCCESS otherwise.
  */
 int batadv_mcast_forw_send(struct batadv_priv *bat_priv, struct sk_buff *skb,
-			   unsigned short vid)
+			   unsigned short vid, int is_routable)
 {
 	int ret;
 
@@ -1717,12 +1718,16 @@ int batadv_mcast_forw_send(struct batadv_priv *bat_priv, struct sk_buff *skb,
 		return ret;
 	}
 
+	if (!is_routable)
+		goto skip_mc_router;
+
 	ret = batadv_mcast_forw_want_rtr(bat_priv, skb, vid);
 	if (ret != NET_XMIT_SUCCESS) {
 		kfree_skb(skb);
 		return ret;
 	}
 
+skip_mc_router:
 	consume_skb(skb);
 	return ret;
 }

net/batman-adv/multicast.h

@@ -43,7 +43,8 @@ enum batadv_forw_mode {
 
 enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       struct batadv_orig_node **mcast_single_orig);
+		       struct batadv_orig_node **mcast_single_orig,
+		       int *is_routable);
 
 int batadv_mcast_forw_send_orig(struct batadv_priv *bat_priv,
 				struct sk_buff *skb,
@@ -51,7 +52,7 @@ int batadv_mcast_forw_send_orig(struct batadv_priv *bat_priv,
 				struct batadv_orig_node *orig_node);
 
 int batadv_mcast_forw_send(struct batadv_priv *bat_priv, struct sk_buff *skb,
-			   unsigned short vid);
+			   unsigned short vid, int is_routable);
 
 void batadv_mcast_init(struct batadv_priv *bat_priv);
 
@@ -68,7 +69,8 @@ void batadv_mcast_purge_orig(struct batadv_orig_node *orig_node);
 
 static inline enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       struct batadv_orig_node **mcast_single_orig)
+		       struct batadv_orig_node **mcast_single_orig,
+		       int *is_routable)
 {
 	return BATADV_FORW_ALL;
 }
@@ -85,7 +87,7 @@ batadv_mcast_forw_send_orig(struct batadv_priv *bat_priv,
 
 static inline int
 batadv_mcast_forw_send(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       unsigned short vid)
+		       unsigned short vid, int is_routable)
 {
 	kfree_skb(skb);
 	return NET_XMIT_DROP;

net/batman-adv/soft-interface.c

@@ -198,6 +198,7 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 	int gw_mode;
 	enum batadv_forw_mode forw_mode = BATADV_FORW_SINGLE;
 	struct batadv_orig_node *mcast_single_orig = NULL;
+	int mcast_is_routable = 0;
 	int network_offset = ETH_HLEN;
 	__be16 proto;
 
@@ -300,7 +301,8 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 send:
 		if (do_bcast && !is_broadcast_ether_addr(ethhdr->h_dest)) {
 			forw_mode = batadv_mcast_forw_mode(bat_priv, skb,
-							   &mcast_single_orig);
+							   &mcast_single_orig,
+							   &mcast_is_routable);
 			if (forw_mode == BATADV_FORW_NONE)
 				goto dropped;
 
@@ -359,7 +361,8 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 			ret = batadv_mcast_forw_send_orig(bat_priv, skb, vid,
 							  mcast_single_orig);
 		} else if (forw_mode == BATADV_FORW_SOME) {
-			ret = batadv_mcast_forw_send(bat_priv, skb, vid);
+			ret = batadv_mcast_forw_send(bat_priv, skb, vid,
+						     mcast_is_routable);
 		} else {
 			if (batadv_dat_snoop_outgoing_arp_request(bat_priv,
 								  skb))