Change A=0 (null) handling in mpi_gcd_invmod_odd()
Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/library/bignum.c b/library/bignum.c
index e141cda..53ff95e 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1751,9 +1751,9 @@
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_mpi local_g;
- mbedtls_mpi local_a;
mbedtls_mpi_uint *T = NULL;
const size_t T_factor = I != NULL ? 5 : 4;
+ const mbedtls_mpi_uint zero = 0;
/* Check requirements on A and N */
if (mbedtls_mpi_cmp_int(A, 0) < 0 ||
@@ -1768,16 +1768,6 @@
return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
}
- mbedtls_mpi_init(&local_a);
- /* If A is 0 (null), then A->p will be null, which is an issue when A->p is
- * passed to mbedtls_mpi_core_gcd_modinv_odd below, so set A to 0 (1 limb)
- * in this case. */
- if (A->n == 0 && A->p == NULL) {
- mbedtls_mpi_read_string(&local_a, 16, "00");
- } else {
- mbedtls_mpi_copy(&local_a, A);
- }
-
mbedtls_mpi_init(&local_g);
if (G == NULL) {
@@ -1797,9 +1787,15 @@
goto cleanup;
}
+ /* We have to handle G and I carefully as they could be aliased
+ * to A or N. */
mbedtls_mpi_uint *Ip = I != NULL ? I->p : NULL;
- size_t An = local_a.n <= N->n ? local_a.n : N->n;
- mbedtls_mpi_core_gcd_modinv_odd(G->p, Ip, local_a.p, An, N->p, N->n, T);
+ /* If A is 0 (null), then A->p would be null, which would be an issue if
+ * A->p was passed to mbedtls_mpi_core_gcd_modinv_odd below. */
+ const mbedtls_mpi_uint *Ap = A->p != NULL ? A->p : &zero;
+ size_t An = A->p == NULL ? 0 : A->n;
+ An = A->n <= N->n ? A->n : N->n;
+ mbedtls_mpi_core_gcd_modinv_odd(G->p, Ip, Ap, An, N->p, N->n, T);
if (G->n > N->n) {
memset(G->p + N->n, 0, ciL * (G->n - N->n));
@@ -1810,7 +1806,6 @@
cleanup:
mbedtls_mpi_free(&local_g);
- mbedtls_mpi_free(&local_a);
mbedtls_free(T);
return ret;
}