netdev - [PATCH net v4 08/12] macsec: fix refcnt leak in module exit routine

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Message-Id: <20190928164843.31800-9-ap420073@gmail.com>
Date:   Sat, 28 Sep 2019 16:48:39 +0000
From:   Taehee Yoo <ap420073@...il.com>
To:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, jakub.kicinski@...ronome.com,
        johannes@...solutions.net, 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, stephen@...workplumber.org,
        sashal@...nel.org, hare@...e.de, varun@...lsio.com,
        ubraun@...ux.ibm.com, kgraul@...ux.ibm.com,
        jay.vosburgh@...onical.com, schuffelen@...gle.com, bjorn@...k.no
Cc:     ap420073@...il.com
Subject: [PATCH net v4 08/12] 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 -> v4 :
 - This patch is not changed

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

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index c4a41b90c846..28972da4a0b3 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3032,12 +3032,10 @@ 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)
@@ -3292,8 +3290,6 @@ 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