net: lapbether: fix issue of dev reference count leakage in lapbeth_device_event()

[ Upstream commit 531705a765 ]

When following tests are performed, it will cause dev reference counting
leakage.
a)ip link add bond2 type bond mode balance-rr
b)ip link set bond2 up
c)ifenslave -f bond2 rose1
d)ip link del bond2

When new bond device is created, the default type of the bond device is
ether. And the bond device is up, lapbeth_device_event() receives the
message and creates a new lapbeth device. In this case, the reference
count value of dev is hold once. But after "ifenslave -f bond2 rose1"
command is executed, the type of the bond device is changed to rose. When
the bond device is unregistered, lapbeth_device_event() will not put the
dev reference count.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/wan/lapbether.c

@@ -446,7 +446,7 @@ static int lapbeth_device_event(struct notifier_block *this,
 	if (dev_net(dev) != &init_net)
 		return NOTIFY_DONE;
 
-	if (!dev_is_ethdev(dev))
+	if (!dev_is_ethdev(dev) && !lapbeth_get_x25_dev(dev))
 		return NOTIFY_DONE;
 
 	switch (event) {