[PATCH net] lapb: fixed leak of control-blocks.

[Jeremy Sowden <jeremy@azazel.net>]

lapb_register calls lapb_create_cb, which initializes the control-
block's ref-count to one, and __lapb_insert_cb, which increments it when
adding the new block to the list of blocks.

lapb_unregister calls __lapb_remove_cb, which decrements the ref-count
when removing control-block from the list of blocks, and calls lapb_put
itself to decrement the ref-count before returning.

However, lapb_unregister also calls __lapb_devtostruct to look up the
right control-block for the given net_device, and __lapb_devtostruct
also bumps the ref-count, which means that when lapb_unregister returns
the ref-count is still 1 and the control-block is leaked.

Call lapb_put after __lapb_devtostruct to fix leak.

Reported-by: syzbot+afb980676c836b4a0afa@syzkaller.appspotmail.com
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
---
 net/lapb/lapb_iface.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/lapb/lapb_iface.c b/net/lapb/lapb_iface.c
index 600d754a1700..3c03f6512c5f 100644
--- a/net/lapb/lapb_iface.c
+++ b/net/lapb/lapb_iface.c
@@ -176,6 +176,7 @@ int lapb_unregister(struct net_device *dev)
 	lapb = __lapb_devtostruct(dev);
 	if (!lapb)
 		goto out;
+	lapb_put(lapb);
 
 	lapb_stop_t1timer(lapb);
 	lapb_stop_t2timer(lapb);
-- 
2.20.1