[PATCH v1 2/2] Input: sur40 - keep device state alive until the video node is released

[Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>]

sur40_disconnect() frees the sur40_state, which embeds the video_device,
the v4l2_device and the vb2_queue, while a video node may still be open.
Closing that file afterwards touches freed memory:

  BUG: KASAN: slab-use-after-free in vb2_core_queue_release+0x12d/0x150
  Read of size 4 at addr ffff888066fa8aa8 by task v4l_id/28733
   vb2_core_queue_release+0x12d/0x150
   vb2_fop_release+0x16e/0x200
   v4l2_release+0x22c/0x350
   __fput+0x418/0xa50
  Freed by task 16811:
   kfree+0x1c5/0x650
   sur40_disconnect+0xaf/0x140

Give the v4l2_device a release callback that frees the bulk buffer and
the state, and drop the disconnect path's own reference with
v4l2_device_put(). The last closer of the node then does the freeing.
The probe error paths never open the node and keep freeing directly.

Reported-by: syzbot+eb4706daf505f9c4b547@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=eb4706daf505f9c4b547
Fixes: e831cd251fb9 ("[media] add raw video stream support for Samsung SUR40")
Cc: stable@vger.kernel.org
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
---
 drivers/input/touchscreen/sur40.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
index 7020bcf9b81a..efd4fe557cef 100644
--- a/drivers/input/touchscreen/sur40.c
+++ b/drivers/input/touchscreen/sur40.c
@@ -648,6 +648,15 @@ static int sur40_input_setup_events(struct input_dev *input_dev)
 }
 
 /* Check candidate USB interface. */
+/* Runs once the last video node reference is gone. */
+static void sur40_release(struct v4l2_device *v4l2)
+{
+	struct sur40_state *sur40 = container_of(v4l2, struct sur40_state, v4l2);
+
+	kfree(sur40->bulk_in_buffer);
+	kfree(sur40);
+}
+
 static int sur40_probe(struct usb_interface *interface,
 		       const struct usb_device_id *id)
 {
@@ -733,6 +742,7 @@ static int sur40_probe(struct usb_interface *interface,
 			"Unable to register video master device.");
 		goto err_free_buffer;
 	}
+	sur40->v4l2.release = sur40_release;
 
 	/* initialize the lock and subdevice */
 	sur40->queue = sur40_queue;
@@ -831,11 +841,10 @@ static void sur40_disconnect(struct usb_interface *interface)
 	video_unregister_device(&sur40->vdev);
 	v4l2_device_unregister(&sur40->v4l2);
 
-	kfree(sur40->bulk_in_buffer);
-	kfree(sur40);
-
 	usb_set_intfdata(interface, NULL);
 	dev_dbg(&interface->dev, "%s is now disconnected\n", DRIVER_DESC);
+
+	v4l2_device_put(&sur40->v4l2);
 }
 
 /*
-- 
2.43.0