batman-adv: Fix invalid stack access in batadv_dat_select_candidates

commit b7fe3d4f upstream.

batadv_dat_select_candidates provides an u32 to batadv_hash_dat but it
needs a batadv_dat_entry with at least ip and vid filled in.

Fixes: 3e26722bc9f2 ("batman-adv: make the Distributed ARP Table vlan aware")
Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
Acked-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/batman-adv/distributed-arp-table.c

@@ -534,6 +534,7 @@ batadv_dat_select_candidates(struct batadv_priv *bat_priv, __be32 ip_dst)
 	int select;
 	batadv_dat_addr_t last_max = BATADV_DAT_ADDR_MAX, ip_key;
 	struct batadv_dat_candidate *res;
+	struct batadv_dat_entry dat;
 
 	if (!bat_priv->orig_hash)
 		return NULL;
@@ -542,7 +543,9 @@ batadv_dat_select_candidates(struct batadv_priv *bat_priv, __be32 ip_dst)
 	if (!res)
 		return NULL;
 
-	ip_key = (batadv_dat_addr_t)batadv_hash_dat(&ip_dst,
+	dat.ip = ip_dst;
+	dat.vid = 0;
+	ip_key = (batadv_dat_addr_t)batadv_hash_dat(&dat,
 						    BATADV_DAT_ADDR_MAX);
 
 	batadv_dbg(BATADV_DBG_DAT, bat_priv,