[PATCH 4/4] Input: sur40 - fix V4L2 video device lifetime

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

sur40_disconnect() synchronously frees the sur40_state structure (kfree(sur40))
while userspace might still hold an open file descriptor to the V4L2 video
device node. When userspace later accesses or closes the lingering file
descriptor, the V4L2 core invokes file operations (such as vb2_fop_release)
that dereference the already freed sur40 memory, resulting in a use-after-free
vulnerability.

Fix this by implementing a V4L2 release callback (sur40_video_release) in
sur40_video_device to clean up V4L2 components and free the sur40 structure
only when the last video file descriptor is closed.

Additionally, update the sur40_probe() error path to call video_unregister_device()
and return inline if input initialization fails after video device registration
succeeded, allowing the V4L2 release callback to manage cleanup.

Also, call v4l2_device_disconnect() in sur40_disconnect() to safely dissociate
the V4L2 device from the parent USB device during unplug.

Reported-by: sashiko-bot@kernel.org
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/touchscreen/sur40.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
index 1ad68131e3a6..2f0efee23d1e 100644
--- a/drivers/input/touchscreen/sur40.c
+++ b/drivers/input/touchscreen/sur40.c
@@ -806,8 +806,10 @@ static int sur40_probe(struct usb_interface *interface,
 	}
 
 	error = sur40_init_input(sur40);
-	if (error)
-		goto err_unreg_video;
+	if (error) {
+		video_unregister_device(&sur40->vdev);
+		return error;
+	}
 
 	/* we can register the device now, as it is ready */
 	usb_set_intfdata(interface, sur40);
@@ -815,8 +817,6 @@ static int sur40_probe(struct usb_interface *interface,
 
 	return 0;
 
-err_unreg_video:
-	video_unregister_device(&sur40->vdev);
 err_free_ctrl:
 	v4l2_ctrl_handler_free(&sur40->hdl);
 err_unreg_v4l2:
@@ -835,13 +835,8 @@ static void sur40_disconnect(struct usb_interface *interface)
 	struct sur40_state *sur40 = usb_get_intfdata(interface);
 
 	input_unregister_device(sur40->input);
-
-	v4l2_ctrl_handler_free(&sur40->hdl);
 	video_unregister_device(&sur40->vdev);
-	v4l2_device_unregister(&sur40->v4l2);
-
-	kfree(sur40->bulk_in_buffer);
-	kfree(sur40);
+	v4l2_device_disconnect(&sur40->v4l2);
 
 	usb_set_intfdata(interface, NULL);
 	dev_dbg(&interface->dev, "%s is now disconnected\n", DRIVER_DESC);
@@ -1176,11 +1171,21 @@ static const struct v4l2_ioctl_ops sur40_video_ioctl_ops = {
 	.vidioc_streamoff	= vb2_ioctl_streamoff,
 };
 
+static void sur40_video_release(struct video_device *vdev)
+{
+	struct sur40_state *sur40 = video_get_drvdata(vdev);
+
+	v4l2_device_unregister(&sur40->v4l2);
+	v4l2_ctrl_handler_free(&sur40->hdl);
+	kfree(sur40->bulk_in_buffer);
+	kfree(sur40);
+}
+
 static const struct video_device sur40_video_device = {
 	.name = DRIVER_LONG,
 	.fops = &sur40_video_fops,
 	.ioctl_ops = &sur40_video_ioctl_ops,
-	.release = video_device_release_empty,
+	.release = sur40_video_release,
 	.device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_TOUCH |
 		       V4L2_CAP_READWRITE | V4L2_CAP_STREAMING,
 };
-- 
2.54.0.1136.gdb2ca164c4-goog