net/sched: cbs: Fix error path of cbs_module_init

mainline inclusion
from mainline-v5.2-rc7
commit 45d5cb13
category: bugfix
bugzilla: 16960
CVE: NA

-------------------------------------

If register_qdisc fails, we should unregister
netdevice notifier.
Reported-by: NHulk Robot <hulkci@huawei.com>
Fixes: e0a7683d ("net/sched: cbs: fix port_rate miscalculation")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: Nguodeqing <geffrey.guo@huawei.com>
Reviewed-by: NWenan Mao <maowenan@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

net/sched/sch_cbs.c

@@ -553,12 +553,17 @@ static struct notifier_block cbs_device_notifier = {
 
 static int __init cbs_module_init(void)
 {
-	int err = register_netdevice_notifier(&cbs_device_notifier);
+	int err;
 
+	err = register_netdevice_notifier(&cbs_device_notifier);
 	if (err)
 		return err;
 
-	return register_qdisc(&cbs_qdisc_ops);
+	err = register_qdisc(&cbs_qdisc_ops);
+	if (err)
+		unregister_netdevice_notifier(&cbs_device_notifier);
+
+	return err;
 }
 
 static void __exit cbs_module_exit(void)