batman-adv: don't add loop detect macs to TT

The bridge loop avoidance (BLA) feature of batman-adv sends packets to
probe for Mesh/LAN packet loops. Those packets are not sent by real
clients and should therefore not be added to the translation table (TT).
Signed-off-by: Simon Wunderlich <simon.wunderlich@open-mesh.com>

net/batman-adv/bridge_loop_avoidance.h

@@ -20,6 +20,8 @@
 
 #include "main.h"
 
+#include <linux/compiler.h>
+#include <linux/stddef.h>
 #include <linux/types.h>
 
 struct net_device;
@@ -27,6 +29,22 @@ struct netlink_callback;
 struct seq_file;
 struct sk_buff;
 
+/**
+ * batadv_bla_is_loopdetect_mac - check if the mac address is from a loop detect
+ *  frame sent by bridge loop avoidance
+ * @mac: mac address to check
+ *
+ * Return: true if the it looks like a loop detect frame
+ * (mac starts with BA:BE), false otherwise
+ */
+static inline bool batadv_bla_is_loopdetect_mac(const uint8_t *mac)
+{
+	if (mac[0] == 0xba && mac[1] == 0xbe)
+		return true;
+
+	return false;
+}
+
 #ifdef CONFIG_BATMAN_ADV_BLA
 bool batadv_bla_rx(struct batadv_priv *bat_priv, struct sk_buff *skb,
 		   unsigned short vid, bool is_bcast);

net/batman-adv/soft-interface.c

@@ -258,7 +258,8 @@ static int batadv_interface_tx(struct sk_buff *skb,
 	ethhdr = eth_hdr(skb);
 
 	/* Register the client MAC in the transtable */
-	if (!is_multicast_ether_addr(ethhdr->h_source)) {
+	if (!is_multicast_ether_addr(ethhdr->h_source) &&
+	    !batadv_bla_is_loopdetect_mac(ethhdr->h_source)) {
 		client_added = batadv_tt_local_add(soft_iface, ethhdr->h_source,
 						   vid, skb->skb_iif,
 						   skb->mark);