Re: [PATCH v2] btrfs: validate device maj:min during open

On Fri, Mar 08, 2024 at 08:15:07AM +0530, Anand Jain wrote:

@@ -692,6 +692,16 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices, device->bdev = bdev_handle->bdev; clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);

• if (device->devt != device->bdev->bd_dev) {

• btrfs_warn(NULL,
  

• 	   "device %s maj:min changed from %d:%d to %d:%d",
  

• 	   device->name->str, MAJOR(device->devt),
  

• 	   MINOR(device->devt), MAJOR(device->bdev->bd_dev),
  

• 	   MINOR(device->bdev->bd_dev));
  

• device->devt = device->bdev->bd_dev;
  

• }

Just above this calls btrfs_get_bdev_and_sb, which calls bdev_open_by_path. bdev_open_by_path bdev_open_by_path calls lookup_bdev to translate the path to a dev_t and then calls bdev_open_by_dev on the dev_t, which stored the passes in dev_t in bdev->bd_dev. I see absolutely no way how this check could ever trigger.