media: dvb-core: Fix ignored return value in dvb_register_frontend()

In dvb_register_frontend(), dvb_register_device() is possible to fail
but its return value is ignored.

It will cause use-after-free when module is removed, because in
dvb_unregister_frontend() it tries to unregister a not registered
device.

BUG: KASAN: use-after-free in dvb_remove_device+0x18b/0x1f0 [dvb_core]
Read of size 4 at addr ffff88800dff4824 by task rmmod/428
CPU: 3 PID: 428 Comm: rmmod
Call Trace:
 <TASK>
 ...
 dvb_remove_device+0x18b/0x1f0 [dvb_core]
 dvb_unregister_frontend+0x7b/0x130 [dvb_core]
 vidtv_bridge_remove+0x6e/0x160 [dvb_vidtv_bridge]
 ...

Fix this by catching return value of dvb_register_device().
However the fe->refcount can't be put to zero immediately, because
there are still modules calling dvb_frontend_detach() when
dvb_register_frontend() fails.

Link: https://lore.kernel.org/linux-media/20221108033005.169095-1-chenzhongjin@huawei.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/dvb-core/dvb_frontend.c

@@ -3007,6 +3007,7 @@ int dvb_register_frontend(struct dvb_adapter *dvb,
 		.name = fe->ops.info.name,
 #endif
 	};
+	int ret;
 
 	dev_dbg(dvb->device, "%s:\n", __func__);
 
@@ -3040,8 +3041,13 @@ int dvb_register_frontend(struct dvb_adapter *dvb,
 		 "DVB: registering adapter %i frontend %i (%s)...\n",
 		 fe->dvb->num, fe->id, fe->ops.info.name);
 
-	dvb_register_device(fe->dvb, &fepriv->dvbdev, &dvbdev_template,
+	ret = dvb_register_device(fe->dvb, &fepriv->dvbdev, &dvbdev_template,
 			    fe, DVB_DEVICE_FRONTEND, 0);
+	if (ret) {
+		dvb_frontend_put(fe);
+		mutex_unlock(&frontend_mutex);
+		return ret;
+	}
 
 	/*
 	 * Initialize the cache to the proper values according with the