Forwarded: [PATCH] KASAN: slab-use-after-free Read in v4l2_release (3)

[syzbot <syzbot+34957180b0ed2581edaf@syzkaller.appspotmail.com>]

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Subject: [PATCH] KASAN: slab-use-after-free Read in v4l2_release (3)
Author: jchuang26@m.fudan.edu.cn

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Reported-by: syzbot+34957180b0ed2581edaf@syzkaller.appspotmail.com

diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
index 09d8c5f8d..39166161d 100644
--- a/drivers/input/touchscreen/sur40.c
+++ b/drivers/input/touchscreen/sur40.c
@@ -647,6 +647,25 @@ static int sur40_input_setup_events(struct input_dev *input_dev)
 	return 0;
 }
 
+/*
+ * Release the sur40 state once the last reference to the video device is
+ * gone. The video_device is embedded in sur40, so sur40 must not be freed
+ * while an open file descriptor can still reach it (e.g. from the v4l2 core
+ * release path). sur40_disconnect() only drops the reference taken by
+ * v4l2_device_register(), which frees sur40 right away if nothing is open
+ * or defers it to this callback until the last user closes the device.
+ */
+static void sur40_release(struct v4l2_device *v4l2_dev)
+{
+	struct sur40_state *sur40 =
+		container_of(v4l2_dev, struct sur40_state, v4l2);
+
+	v4l2_ctrl_handler_free(&sur40->hdl);
+	v4l2_device_unregister(&sur40->v4l2);
+	kfree(sur40->bulk_in_buffer);
+	kfree(sur40);
+}
+
 /* Check candidate USB interface. */
 static int sur40_probe(struct usb_interface *interface,
 		       const struct usb_device_id *id)
@@ -726,6 +745,7 @@ static int sur40_probe(struct usb_interface *interface,
 	}
 
 	/* register the video master device */
+	sur40->v4l2.release = sur40_release;
 	snprintf(sur40->v4l2.name, sizeof(sur40->v4l2.name), "%s", DRIVER_LONG);
 	error = v4l2_device_register(sur40->dev, &sur40->v4l2);
 	if (error) {
@@ -827,14 +847,18 @@ static void sur40_disconnect(struct usb_interface *interface)
 
 	input_unregister_device(sur40->input);
 
-	v4l2_ctrl_handler_free(&sur40->hdl);
+	v4l2_device_disconnect(&sur40->v4l2);
 	video_unregister_device(&sur40->vdev);
-	v4l2_device_unregister(&sur40->v4l2);
-
-	kfree(sur40->bulk_in_buffer);
-	kfree(sur40);
 
 	usb_set_intfdata(interface, NULL);
+
+	/*
+	 * Drop the reference taken by v4l2_device_register(). The state is
+	 * only freed from sur40_release() once the last video device user is
+	 * gone, so an open device node cannot use the freed memory.
+	 */
+	v4l2_device_put(&sur40->v4l2);
+
 	dev_dbg(&interface->dev, "%s is now disconnected\n", DRIVER_DESC);
 }