media: ddbridge: fix teardown/deregistration order in ddb_input_detach()

Brought to attention by Matthias Schwarzott <zzam@gentoo.org> by fixing
possible use-after-free faults in some demod drivers:

In ddb_input_detach(), the i2c_client is unregistered and removed before
dvb frontends are unregistered and detached. While no use-after-free issue
was observed so far, there is another issue with this:

dvb->attached keeps track of the state of the input/output registration,
and the i2c_client unregistration takes place only if everything was
successful (dvb->attached == 0x31). If for some reason an error occurred
during the frontend setup, that value stays at 0x20. In the following
error handling and cleanup, ddb_input_detach() will skip down to that
state, leaving the i2c_client registered, causing refcount issues.

Fix this by moving the i2c_client deregistration down to case 0x20.

Cc: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/pci/ddbridge/ddbridge-core.c

@@ -1255,11 +1255,6 @@ static void dvb_input_detach(struct ddb_input *input)
 
 	switch (dvb->attached) {
 	case 0x31:
-		client = dvb->i2c_client[0];
-		if (client) {
-			module_put(client->dev.driver->owner);
-			i2c_unregister_device(client);
-		}
 		if (dvb->fe2)
 			dvb_unregister_frontend(dvb->fe2);
 		if (dvb->fe)
@@ -1273,6 +1268,12 @@ static void dvb_input_detach(struct ddb_input *input)
 		dvb->fe = dvb->fe2 = NULL;
 		/* fallthrough */
 	case 0x20:
+		client = dvb->i2c_client[0];
+		if (client) {
+			module_put(client->dev.driver->owner);
+			i2c_unregister_device(client);
+		}
+
 		dvb_net_release(&dvb->dvbnet);
 		/* fallthrough */
 	case 0x12: