From 2bce1ebed17da54c65042ec2b962e3234bad5b47 Mon Sep 17 00:00:00 2001
From: Taehee Yoo <ap420073@gmail.com>
Date: Mon, 21 Oct 2019 18:47:55 +0000
Subject: [PATCH] macsec: fix refcnt leak in module exit routine
Git-commit: 2bce1ebed17da54c65042ec2b962e3234bad5b47
Patch-mainline: v5.4-rc6
References: bsc#1051510

When a macsec interface is created, it increases a refcnt to a lower
device(real device). when macsec interface is deleted, the refcnt is
decreased in macsec_free_netdev(), which is ->priv_destructor() of
macsec interface.

The problem scenario is this.
When nested macsec interfaces are exiting, the exit routine of the
macsec module makes refcnt leaks.

Test commands:
    ip link add dummy0 type dummy
    ip link add macsec0 link dummy0 type macsec
    ip link add macsec1 link macsec0 type macsec
    modprobe -rv macsec

[  208.629433] unregister_netdevice: waiting for macsec0 to become free. Usage count = 1

Steps of exit routine of macsec module are below.
1. Calls ->dellink() in __rtnl_link_unregister().
2. Checks refcnt and wait refcnt to be 0 if refcnt is not 0 in
netdev_run_todo().
3. Calls ->priv_destruvtor() in netdev_run_todo().

Step2 checks refcnt, but step3 decreases refcnt.
So, step2 waits forever.

This patch makes the macsec module do not hold a refcnt of the lower
device because it already holds a refcnt of the lower device with
netdev_upper_dev_link().

Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/net/macsec.c |    4 ----
 1 file changed, 4 deletions(-)

--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -2988,12 +2988,10 @@ static const struct nla_policy macsec_rt
 static void macsec_free_netdev(struct net_device *dev)
 {
 	struct macsec_dev *macsec = macsec_priv(dev);
-	struct net_device *real_dev = macsec->real_dev;
 
 	free_percpu(macsec->stats);
 	free_percpu(macsec->secy.tx_sc.stats);
 
-	dev_put(real_dev);
 }
 
 static void macsec_setup(struct net_device *dev)
@@ -3234,8 +3232,6 @@ static int macsec_newlink(struct net *ne
 	if (err < 0)
 		return err;
 
-	dev_hold(real_dev);
-
 	macsec->nest_level = dev_get_nest_level(real_dev) + 1;
 	netdev_lockdep_set_classes(dev);
 	lockdep_set_class_and_subclass(&dev->addr_list_lock,