library: ssl: remove usage of MBEDTLS_ECP_DP_MAX

MBEDTLS_ECP_DP_MAX is defined in 'ecp.h' which is a tf-psa-crypto private
header. Instead of relying on that value define a new function named
'mbedtls_ssl_get_supported_tls_id_count' which returns the number of
entries in 'tls_id_match_table'.
Rationale: it does not have too much sense to allocate an array for TLS
IDs which is larger than the list of supported TLS IDs in the current
build.

Signed-off-by: Valerio Setti <[email protected]>

library/ssl_misc.h

@@ -1541,6 +1541,15 @@ int mbedtls_ssl_is_tls_id_supported(uint16_t tls_id);
  */
 uint16_t mbedtls_ssl_get_tls_id_from_curve_info(psa_ecc_family_t family, size_t bits);
 
+/**
+ * \brief       Return the number of supported TLS group IDs + 1.
+ *
+ * \return      Number of supported TLS group IDs in \c tls_id_match_table + 1.
+ *              In other words the returned value concides with the array length
+ *              of \c tls_id_match_table.
+ */
+size_t mbedtls_ssl_get_supported_tls_id_count(void);
+
 #if defined(MBEDTLS_DEBUG_C)
 /**
  * \brief Return EC's name for the specified TLS ID.

library/ssl_tls.c

@@ -5871,6 +5871,11 @@ uint16_t mbedtls_ssl_get_tls_id_from_curve_info(psa_ecc_family_t family, size_t
     return 0;
 }
 
+size_t mbedtls_ssl_get_supported_tls_id_count(void)
+{
+    return ARRAY_LENGTH(tls_id_match_table);
+}
+
 #if defined(MBEDTLS_DEBUG_C)
 mbedtls_ssl_iana_tls_group_info_t mbedtls_ssl_iana_tls_group_info[] =
     MBEDTLS_SSL_IANA_TLS_GROUPS_INFO;

library/ssl_tls12_server.c

@@ -202,8 +202,8 @@ static int ssl_parse_supported_groups_ext(mbedtls_ssl_context *ssl,
     /* Don't allow our peer to make us allocate too much memory,
      * and leave room for a final 0 */
     our_size = list_size / 2 + 1;
-    if (our_size > MBEDTLS_ECP_DP_MAX) {
-        our_size = MBEDTLS_ECP_DP_MAX;
+    if (our_size > mbedtls_ssl_get_supported_tls_id_count()) {
+        our_size = mbedtls_ssl_get_supported_tls_id_count();
     }
 
     if ((curves_tls_id = mbedtls_calloc(our_size,