rtnetlink: fix a memory leak when ->newlink fails

It is possible that ->newlink() fails before registering
the device, in this case we should just free it, it's
safe to call free_netdev().

Fixes: commit 0e0eee24 (net: correct error path in rtnl_newlink())
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NCong Wang <cwang@twopensource.com>
Signed-off-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -2019,11 +2019,15 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh)
 		if (ops->newlink) {
 			err = ops->newlink(net, dev, tb, data);
 			/* Drivers should call free_netdev() in ->destructor
-			 * and unregister it on failure so that device could be
-			 * finally freed in rtnl_unlock.
+			 * and unregister it on failure after registration
+			 * so that device could be finally freed in rtnl_unlock.
 			 */
-			if (err < 0)
+			if (err < 0) {
+				/* If device is not registered at all, free it now */
+				if (dev->reg_state == NETREG_UNINITIALIZED)
+					free_netdev(dev);
 				goto out;
+			}
 		} else {
 			err = register_netdevice(dev);
 			if (err < 0) {