[PATCH net v5 3/4] ax25: Fix reference count leak issues of net_device

[Duoming Zhou]

The ax25_dev_device_down() exists reference count leak issues of
the object "net_device". When the ax25 device is shutting down.
The ax25_dev_device_down() drops the reference count of net_device
one or zero times depending on if we goto unlock_put or not, which
will cause memory leak.

In order to solve the above issue, decrease the reference count of
net_device after dev->ax25_ptr is set to null.

Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 net/ax25/ax25_dev.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index 66aa381af0e..c6ab9b0f0be 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -121,15 +121,9 @@ void ax25_dev_device_down(struct net_device *dev)
 	list_for_each_entry(s, &ax25_dev_list, list) {
 		if (s == ax25_dev) {
 			list_del(&s->list);
-			goto unlock_put;
+			break;
 		}
 	}
-	dev->ax25_ptr = NULL;
-	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_put(ax25_dev);
-	return;
-
-unlock_put:
 	dev->ax25_ptr = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
 	netdev_put(dev, &ax25_dev->dev_tracker);
-- 
2.17.1