Fix leak of modulus structures in tests

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/include/test/bignum_helpers.h

@@ -61,7 +61,8 @@ int mbedtls_test_read_mpi_core( mbedtls_mpi_uint **pX, size_t *plimbs,
  * the length of the input. In other words, it preserves leading zeros.
  *
  * The limb array is allocated with mbedtls_calloc() and must later be
- * freed with mbedtls_free().
+ * freed with mbedtls_free(). You can do that by calling
+ * mbedtls_test_mpi_mod_modulus_free_with_limbs().
  *
  * \param[in,out] N     A modulus structure. It must be initialized, but
  *                      not set up.
@@ -74,6 +75,13 @@ int mbedtls_test_read_mpi_modulus( mbedtls_mpi_mod_modulus *N,
                                    const char *s,
                                    mbedtls_mpi_mod_rep_selector int_rep );
 
+/** Free a modulus and its limbs.
+ *
+ * \param[in] N         A modulus structure such that there is no other
+ *                      reference to `N->p`.
+ */
+void mbedtls_test_mpi_mod_modulus_free_with_limbs( mbedtls_mpi_mod_modulus *N );
+
 /** Read an MPI from a hexadecimal string.
  *
  * Like mbedtls_mpi_read_string(), but with tighter guarantees around

tests/src/bignum_helpers.c

@@ -102,6 +102,12 @@ int mbedtls_test_read_mpi_modulus( mbedtls_mpi_mod_modulus *N,
     return( ret );
 }
 
+void mbedtls_test_mpi_mod_modulus_free_with_limbs( mbedtls_mpi_mod_modulus *N )
+{
+    mbedtls_free( (mbedtls_mpi_uint*) N->p );
+    mbedtls_mpi_mod_modulus_free( N );
+}
+
 int mbedtls_test_read_mpi( mbedtls_mpi *X, const char *s )
 {
     int negative = 0;

tests/suites/test_suite_bignum_random.function

@@ -208,7 +208,7 @@ void mpi_mod_random_values( int min, char *max_hex )
                     &rnd_mod_raw, sizeof( rnd_mod_raw ) );
 
 exit:
-    mbedtls_mpi_mod_modulus_free( &N );
+    mbedtls_test_mpi_mod_modulus_free_with_limbs( &N );
     mbedtls_free( R_core );
     mbedtls_free( R_mod_raw );
 }