Improper arithmetics when calculting the address of the extended ref could
lead to an out of bounds memory read and kernel panic.
Signed-off-by: NQuentin Casasnovas <quentin.casasnovas@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.cz>
cc: stable@vger.kernel.org # v3.7+
Signed-off-by: NChris Mason <clm@fb.com>