net: marvell: prestera: fix incorrect structure access

In line:
	upper = info->upper_dev;
We access upper_dev field, which is related only for particular events
(e.g. event == NETDEV_CHANGEUPPER). So, this line cause invalid memory
access for another events,
when ptr is not netdev_notifier_changeupper_info.

The KASAN logs are as follows:

[   30.123165] BUG: KASAN: stack-out-of-bounds in prestera_netdev_port_event.constprop.0+0x68/0x538 [prestera]
[   30.133336] Read of size 8 at addr ffff80000cf772b0 by task udevd/778
[   30.139866]
[   30.141398] CPU: 0 PID: 778 Comm: udevd Not tainted 5.16.0-rc3 #6
[   30.147588] Hardware name: DNI AmazonGo1 A7040 board (DT)
[   30.153056] Call trace:
[   30.155547]  dump_backtrace+0x0/0x2c0
[   30.159320]  show_stack+0x18/0x30
[   30.162729]  dump_stack_lvl+0x68/0x84
[   30.166491]  print_address_description.constprop.0+0x74/0x2b8
[   30.172346]  kasan_report+0x1e8/0x250
[   30.176102]  __asan_load8+0x98/0xe0
[   30.179682]  prestera_netdev_port_event.constprop.0+0x68/0x538 [prestera]
[   30.186847]  prestera_netdev_event_handler+0x1b4/0x1c0 [prestera]
[   30.193313]  raw_notifier_call_chain+0x74/0xa0
[   30.197860]  call_netdevice_notifiers_info+0x68/0xc0
[   30.202924]  register_netdevice+0x3cc/0x760
[   30.207190]  register_netdev+0x24/0x50
[   30.211015]  prestera_device_register+0x8a0/0xba0 [prestera]

Fixes: 3d5048cc ("net: marvell: prestera: move netdev topology validation to prestera_main")
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Link: https://lore.kernel.org/r/20211216171714.11341-1-yevhen.orlov@plvision.euSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/prestera/prestera_main.c

@@ -768,23 +768,27 @@ static int prestera_netdev_port_event(struct net_device *lower,
 				      struct net_device *dev,
 				      unsigned long event, void *ptr)
 {
-	struct netdev_notifier_changeupper_info *info = ptr;
+	struct netdev_notifier_info *info = ptr;
+	struct netdev_notifier_changeupper_info *cu_info;
 	struct prestera_port *port = netdev_priv(dev);
 	struct netlink_ext_ack *extack;
 	struct net_device *upper;
 
-	extack = netdev_notifier_info_to_extack(&info->info);
-	upper = info->upper_dev;
+	extack = netdev_notifier_info_to_extack(info);
+	cu_info = container_of(info,
+			       struct netdev_notifier_changeupper_info,
+			       info);
 
 	switch (event) {
 	case NETDEV_PRECHANGEUPPER:
+		upper = cu_info->upper_dev;
 		if (!netif_is_bridge_master(upper) &&
 		    !netif_is_lag_master(upper)) {
 			NL_SET_ERR_MSG_MOD(extack, "Unknown upper device type");
 			return -EINVAL;
 		}
 
-		if (!info->linking)
+		if (!cu_info->linking)
 			break;
 
 		if (netdev_has_any_upper_dev(upper)) {
@@ -793,7 +797,7 @@ static int prestera_netdev_port_event(struct net_device *lower,
 		}
 
 		if (netif_is_lag_master(upper) &&
-		    !prestera_lag_master_check(upper, info->upper_info, extack))
+		    !prestera_lag_master_check(upper, cu_info->upper_info, extack))
 			return -EOPNOTSUPP;
 		if (netif_is_lag_master(upper) && vlan_uses_dev(dev)) {
 			NL_SET_ERR_MSG_MOD(extack,
@@ -809,14 +813,15 @@ static int prestera_netdev_port_event(struct net_device *lower,
 		break;
 
 	case NETDEV_CHANGEUPPER:
+		upper = cu_info->upper_dev;
 		if (netif_is_bridge_master(upper)) {
-			if (info->linking)
+			if (cu_info->linking)
 				return prestera_bridge_port_join(upper, port,
 								 extack);
 			else
 				prestera_bridge_port_leave(upper, port);
 		} else if (netif_is_lag_master(upper)) {
-			if (info->linking)
+			if (cu_info->linking)
 				return prestera_lag_port_add(port, upper);
 			else
 				prestera_lag_port_del(port);