[PATCH 4.5 146/200] lib/mpi: Endianness fix

Greg Kroah-Hartman
2016-05-03T00:50:55Z

From: Michal Marek <mmarek@suse.com>

commit 3ee0cb5fb5eea2110db1b5cb7f67029b7be8a376 upstream.

The limbs are integers in the host endianness, so we can't simply
iterate over the individual bytes. The current code happens to work on
little-endian, because the order of the limbs in the MPI array is the
same as the order of the bytes in each limb, but it breaks on
big-endian.

Fixes: 0f74fbf77d45 ("MPI: Fix mpi_read_buffer")
Signed-off-by: Michal Marek <mmarek@suse.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
lib/mpi/mpicoder.c | 39 +++++++++++++++++++++------------------
1 file changed, 21 insertions(+), 18 deletions(-)

--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -128,6 +128,23 @@ leave:
}
EXPORT_SYMBOL_GPL(mpi_read_from_buffer);

+static int count_lzeros(MPI a)
+{
+ mpi_limb_t alimb;
+ int i, lzeros = 0;
+
+ for (i = a->nlimbs - 1; i >= 0; i--) {
+ alimb = a->d[i];
+ if (alimb == 0) {
+ lzeros += sizeof(mpi_limb_t);
+ } else {
+ lzeros += count_leading_zeros(alimb) / 8;
+ break;
+ }
+ }
+ return lzeros;
+}
+
/**
* mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
*
@@ -148,7 +165,7 @@ int mpi_read_buffer(MPI a, uint8_t *buf,
uint8_t *p;
mpi_limb_t alimb;
unsigned int n = mpi_get_size(a);
- int i, lzeros = 0;
+ int i, lzeros;

if (!buf || !nbytes)
return -EINVAL;
@@ -156,14 +173,7 @@ int mpi_read_buffer(MPI a, uint8_t *buf,
if (sign)
*sign = a->sign;

- p = (void *)&a->d[a->nlimbs] - 1;
-
- for (i = a->nlimbs * sizeof(alimb) - 1; i >= 0; i--, p--) {
- if (!*p)
- lzeros++;
- else
- break;
- }
+ lzeros = count_lzeros(a);

if (buf_len < n - lzeros) {
*nbytes = n - lzeros;
@@ -351,7 +361,7 @@ int mpi_write_to_sgl(MPI a, struct scatt
u8 *p, *p2;
mpi_limb_t alimb, alimb2;
unsigned int n = mpi_get_size(a);
- int i, x, y = 0, lzeros = 0, buf_len;
+ int i, x, y = 0, lzeros, buf_len;

if (!nbytes)
return -EINVAL;
@@ -359,14 +369,7 @@ int mpi_write_to_sgl(MPI a, struct scatt
if (sign)
*sign = a->sign;

- p = (void *)&a->d[a->nlimbs] - 1;
-
- for (i = a->nlimbs * sizeof(alimb) - 1; i >= 0; i--, p--) {
- if (!*p)
- lzeros++;
- else
- break;
- }
+ lzeros = count_lzeros(a);

if (*nbytes < n - lzeros) {
*nbytes = n - lzeros;