media: cec-notifier: clear cec_adap in cec_notifier_unregister

[ Upstream commit 14d55116 ]

If cec_notifier_cec_adap_unregister() is called before
cec_unregister_adapter() then everything is OK (and this is the
case today). But if it is the other way around, then
cec_notifier_unregister() is called first, and that doesn't
set n->cec_adap to NULL.

So if e.g. cec_notifier_set_phys_addr() is called after
cec_notifier_unregister() but before cec_unregister_adapter()
then n->cec_adap points to an unregistered and likely deleted
cec adapter. So just set n->cec_adap->notifier and n->cec_adap
to NULL for rubustness.

Eventually cec_notifier_unregister will disappear and this will
be simplified substantially.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/media/cec/cec-notifier.c

@@ -123,6 +123,8 @@ void cec_notifier_unregister(struct cec_notifier *n)
 {
 	mutex_lock(&n->lock);
 	n->callback = NULL;
+	n->cec_adap->notifier = NULL;
+	n->cec_adap = NULL;
 	mutex_unlock(&n->lock);
 	cec_notifier_put(n);
 }