media: v4l2-core: fix use-after-free error

Fixing use-after-free within __v4l2_ctrl_handler_setup().
Memory is being freed with kfree(new_ref) for duplicate
control reference entry but ctrl->cluster pointer is still
referring to freed duplicate entry resulting in error on
access. Change done to update cluster pointer only when new
control reference is added.

 ==================================================================
 BUG: KASAN: use-after-free in __v4l2_ctrl_handler_setup+0x388/0x428
 Read of size 8 at addr ffffffc324e78618 by task systemd-udevd/312

 Allocated by task 312:

 Freed by task 312:

 The buggy address belongs to the object at ffffffc324e78600
  which belongs to the cache kmalloc-64 of size 64
 The buggy address is located 24 bytes inside of
  64-byte region [ffffffc324e78600, ffffffc324e78640)
 The buggy address belongs to the page:
 page:ffffffbf0c939e00 count:1 mapcount:0 mapping:
					(null) index:0xffffffc324e78f80
 flags: 0x4000000000000100(slab)
 raw: 4000000000000100 0000000000000000 ffffffc324e78f80 000000018020001a
 raw: 0000000000000000 0000000100000001 ffffffc37040fb80 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffffffc324e78500: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
  ffffffc324e78580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 >ffffffc324e78600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                             ^
  ffffffc324e78680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
  ffffffc324e78700: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
 ==================================================================

Suggested-by: Hans Verkuil <[email protected]>
Signed-off-by: Sumit Gupta <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

Author: sumitg

drivers/media/v4l2-core/v4l2-ctrls.c

@@ -2180,15 +2180,6 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
 	if (size_extra_req)
 		new_ref->p_req.p = &new_ref[1];
 
-	if (ctrl->handler == hdl) {
-		/* By default each control starts in a cluster of its own.
-		   new_ref->ctrl is basically a cluster array with one
-		   element, so that's perfect to use as the cluster pointer.
-		   But only do this for the handler that owns the control. */
-		ctrl->cluster = &new_ref->ctrl;
-		ctrl->ncontrols = 1;
-	}
-
 	INIT_LIST_HEAD(&new_ref->node);
 
 	mutex_lock(hdl->lock);
@@ -2221,6 +2212,15 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
 	hdl->buckets[bucket] = new_ref;
 	if (ctrl_ref)
 		*ctrl_ref = new_ref;
+	if (ctrl->handler == hdl) {
+		/* By default each control starts in a cluster of its own.
+		 * new_ref->ctrl is basically a cluster array with one
+		 * element, so that's perfect to use as the cluster pointer.
+		 * But only do this for the handler that owns the control.
+		 */
+		ctrl->cluster = &new_ref->ctrl;
+		ctrl->ncontrols = 1;
+	}
 
 unlock:
 	mutex_unlock(hdl->lock);