batman-adv: Only put orig_node_vlan list reference when removed

BugLink: https://bugs.launchpad.net/bugs/1868629

commit 3db15209 upstream.

The batadv_orig_node_vlan reference counter in batadv_tt_global_size_mod
can only be reduced when the list entry was actually removed. Otherwise the
reference counter may reach zero when batadv_tt_global_size_mod is called
from two different contexts for the same orig_node_vlan but only one
context is actually removing the entry from the list.

The release function for this orig_node_vlan is not called inside the
vlan_list_lock spinlock protected region because the function
batadv_tt_global_size_mod still holds a orig_node_vlan reference for the
object pointer on the stack. Thus the actual release function (when
required) will be called only at the end of the function.

Fixes: 7ea7b4a1 ("batman-adv: make the TT CRC logic VLAN specific")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/batman-adv/translation-table.c

@@ -303,10 +303,12 @@ static void batadv_tt_global_size_mod(struct batadv_orig_node *orig_node,
 
 	if (atomic_add_return(v, &vlan->tt.num_entries) == 0) {
 		spin_lock_bh(&orig_node->vlan_list_lock);
+		if (!hlist_unhashed(&vlan->list)) {
 			hlist_del_init_rcu(&vlan->list);
-		spin_unlock_bh(&orig_node->vlan_list_lock);
 			batadv_orig_node_vlan_free_ref(vlan);
 		}
+		spin_unlock_bh(&orig_node->vlan_list_lock);
+	}
 
 	batadv_orig_node_vlan_free_ref(vlan);
 }