lib/mpi: checks for zero divisor length

Divisor length should not be 0.
Signed-off-by: NDmitry Kasatkin <dmitry.kasatkin@intel.com>
Reviewed-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NJames Morris <jmorris@namei.org>

lib/mpi/mpi-div.c

@@ -149,6 +149,9 @@ int mpi_tdiv_qr(MPI quot, MPI rem, MPI num, MPI den)
 	mpi_ptr_t marker[5];
 	int markidx = 0;
 
+	if (!dsize)
+		return -EINVAL;
+
 	memset(marker, 0, sizeof(marker));
 
 	/* Ensure space is enough for quotient and remainder.