pnfs/blocklayout: Fix device leaks on parse failure

In the Linux kernel, the following vulnerability has been resolved: pnfs/blocklayout: Fix device leaks on parse failure bl_parse_concat() and bl_parse_stripe() allocate a child device array and then parse each child in turn. If parsing a child fails, the failed child is not counted in nr_children and the parent may be left with a children array that bl_free_device() will not release when nr_children is zero. Release the failed child and the already parsed children before returning the error. Also make bl_free_device() release the child array whenever the children pointer is set, so that partially initialised concat or stripe devices are cleaned up correctly. bl_parse_scsi() can also fail after assigning d->bdev_file and dropping the file reference. Clear the pointer after fput() so that an outer cleanup path does not put it again.