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Change A=0 (null) handling in mpi_gcd_invmod_odd()

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Signed-off-by: Felix Conway <felix.conway@arm.com>
This commit is contained in:
Felix Conway
2025-08-05 14:35:53 +01:00
parent d9c4c9c441
commit eefdfe99a4
1 changed files with 9 additions and 14 deletions
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23
library/bignum.c
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@@ -1751,9 +1751,9 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
{
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 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
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 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
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 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
cleanup:
mbedtls_mpi_free(&local_g);
mbedtls_mpi_free(&local_a);
mbedtls_free(T);
return ret;
}