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Fix gcd_invmod_odd wrapper when A is 0 (null)

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Signed-off-by: Felix Conway <felix.conway@arm.com>
This commit is contained in:
Felix Conway
2025-08-04 17:00:10 +01:00
parent fae58c4a0c
commit f4df43b6c4
1 changed files with 14 additions and 2 deletions
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16
library/bignum.c
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@@ -1751,6 +1751,7 @@ 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;
@@ -1767,6 +1768,16 @@ 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) {
@@ -1787,8 +1798,8 @@ int mbedtls_mpi_gcd_modinv_odd(mbedtls_mpi *G,
}
mbedtls_mpi_uint *Ip = I != NULL ? I->p : NULL;
size_t An = A->n <= N->n ? A->n : N->n;
mbedtls_mpi_core_gcd_modinv_odd(G->p, Ip, A->p, An, N->p, N->n, T);
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 (G->n > N->n) {
memset(G->p + N->n, 0, ciL * (G->n - N->n));
@@ -1799,6 +1810,7 @@ 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;
}