Staging: batman-adv: Don't write in not allocated packet_buff

Each net_device in a system will automatically managed as a possible
batman_if and holds different informations like a buffer with a prepared
originator messages. To reduce the memory usage, the packet_buff will
only be allocated when the interface is really added/enabled for
batman-adv.

The function to update the hw address information inside the packet_buff
just assumes that the packet_buff is always initialised and thus the
kernel will just oops when we try to change the hw address of a not
already fully enabled interface.

We must always check if the packet_buff is allocated before we try to
change information inside of it.
Reported-by: Tim Glaremin <Tim.Glaremin@web.de>
Reported-by: Kazuki Shimada <zukky@bb.banban.jp>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/batman-adv/hard-interface.c

@@ -129,6 +129,9 @@ static bool hardif_is_iface_up(struct batman_if *batman_if)
 
 static void update_mac_addresses(struct batman_if *batman_if)
 {
+	if (!batman_if || !batman_if->packet_buff)
+		return;
+
 	addr_to_string(batman_if->addr_str, batman_if->net_dev->dev_addr);
 
 	memcpy(((struct batman_packet *)(batman_if->packet_buff))->orig,
@@ -334,6 +337,7 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev)
 	batman_if->if_num = -1;
 	batman_if->net_dev = net_dev;
 	batman_if->if_status = IF_NOT_IN_USE;
+	batman_if->packet_buff = NULL;
 	INIT_LIST_HEAD(&batman_if->list);
 
 	check_known_mac_addr(batman_if->net_dev->dev_addr);