lib/mpi: kunmap after finishing accessing buffer

Using sg_miter_start and sg_miter_next, the buffer of an SG is kmap'ed
to *buff. The current code calls sg_miter_stop (and thus kunmap) on the
SG entry before the last access of *buff.

The patch moves the sg_miter_stop call after the last access to *buff to
ensure that the memory pointed to by *buff is still mapped.

Fixes: 4816c940 ("lib/mpi: Fix SG miter leak")
Cc: <stable@vger.kernel.org>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/mpi/mpicoder.c

@@ -364,11 +364,11 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 	}
 
 	miter.consumed = lzeros;
-	sg_miter_stop(&miter);
 
 	nbytes -= lzeros;
 	nbits = nbytes * 8;
 	if (nbits > MAX_EXTERN_MPI_BITS) {
+		sg_miter_stop(&miter);
 		pr_info("MPI: mpi too large (%u bits)\n", nbits);
 		return NULL;
 	}
@@ -376,6 +376,8 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 	if (nbytes > 0)
 		nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);
 
+	sg_miter_stop(&miter);
+
 	nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 	val = mpi_alloc(nlimbs);
 	if (!val)