netdev - [PATCH net v2 08/11] macsec: fix refcnt leak in module exit routine

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Message-Id: <20190907134722.345-1-ap420073@gmail.com>
Date:   Sat,  7 Sep 2019 22:47:22 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     davem@...emloft.net, netdev@...r.kernel.org, j.vosburgh@...il.com,
        vfalico@...il.com, andy@...yhouse.net, jiri@...nulli.us,
        sd@...asysnail.net, roopa@...ulusnetworks.com, saeedm@...lanox.com,
        manishc@...vell.com, rahulv@...vell.com, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, sashal@...nel.org,
        hare@...e.de, varun@...lsio.com, ubraun@...ux.ibm.com,
        kgraul@...ux.ibm.com, jay.vosburgh@...onical.com
Cc:     ap420073@...il.com
Subject: [PATCH net v2 08/11] macsec: fix refcnt leak in module exit routine

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@...il.com>
---

v1 -> v2 : this patch isn't changed

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

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 25a4fc88145d..41ec1ed0d545 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3031,12 +3031,10 @@ static const struct nla_policy macsec_rtnl_policy[IFLA_MACSEC_MAX + 1] = {
 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)
@@ -3291,8 +3289,6 @@ static int macsec_newlink(struct net *net, struct net_device *dev,
 	if (err < 0)
 		return err;
 
-	dev_hold(real_dev);
-
 	macsec->nest_level = dev_get_nest_level(real_dev) + 1;
 
 	err = netdev_upper_dev_link(real_dev, dev, extack);
-- 
2.17.1