Introduce specific error for ver/cfg mismatch on deserialization

This commit introduces a new SSL error code

  `MBEDTLS_ERR_SSL_VERSION_MISMATCH`

which can be used to indicate operation failure due to a
mismatch of version or configuration.

It is put to use in the implementation of `mbedtls_ssl_session_load()`
to signal the attempt to de-serialize a session which has been serialized
in a build of Mbed TLS using a different version or configuration.

include/mbedtls/error.h

@@ -100,6 +100,7 @@
  * ECP       4   10 (Started from top)
  * MD        5   5
  * HKDF      5   1 (Started from top)
+ * SSL       5   1 (Started from 0x5F00)
  * CIPHER    6   8 (Started from 0x6080)
  * SSL       6   24 (Started from top, plus 0x6000)
  * SSL       7   32

include/mbedtls/ssl.h

@@ -127,6 +127,7 @@
 #define MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS                 -0x6500  /**< The asynchronous operation is not completed yet. */
 #define MBEDTLS_ERR_SSL_EARLY_MESSAGE                     -0x6480  /**< Internal-only message signaling that a message arrived early. */
 #define MBEDTLS_ERR_SSL_UNEXPECTED_CID                    -0x6000  /**< An encrypted DTLS-frame with an unexpected CID was received. */
+#define MBEDTLS_ERR_SSL_VERSION_MISMATCH                  -0x5F00  /**< An operation failed due to an unexpected version or configuration. */
 #define MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS                -0x7000  /**< A cryptographic operation is in progress. Try again later. */
 
 /*
@@ -2382,6 +2383,9 @@ int mbedtls_ssl_set_session( mbedtls_ssl_context *ssl, const mbedtls_ssl_session
  * \return         \c 0 if successful.
  * \return         #MBEDTLS_ERR_SSL_ALLOC_FAILED if memory allocation failed.
  * \return         #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.
+ * \return         #MBEDTLS_ERR_SSL_VERSION_MISMATCH if the serialized data
+ *                 was generated in a different version or configuration of
+ *                 Mbed TLS.
  * \return         Another negative value for other kinds of errors (for
  *                 example, unsupported features in the embedded certificate).
  */

library/error.c

@@ -525,6 +525,8 @@ void mbedtls_strerror( int ret, char *buf, size_t buflen )
             mbedtls_snprintf( buf, buflen, "SSL - Internal-only message signaling that a message arrived early" );
         if( use_ret == -(MBEDTLS_ERR_SSL_UNEXPECTED_CID) )
             mbedtls_snprintf( buf, buflen, "SSL - An encrypted DTLS-frame with an unexpected CID was received" );
+        if( use_ret == -(MBEDTLS_ERR_SSL_VERSION_MISMATCH) )
+            mbedtls_snprintf( buf, buflen, "SSL - An operation failed due to an unexpected version or configuration" );
         if( use_ret == -(MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS) )
             mbedtls_snprintf( buf, buflen, "SSL - A cryptographic operation is in progress. Try again later" );
 #endif /* MBEDTLS_SSL_TLS_C */

library/ssl_tls.c

@@ -10184,8 +10184,7 @@ static int ssl_session_load( mbedtls_ssl_session *session,
     if( memcmp( p, ssl_serialized_session_header,
                 sizeof( ssl_serialized_session_header ) ) != 0 )
     {
-        /* A more specific error code might be used here. */
+        return( MBEDTLS_ERR_SSL_VERSION_MISMATCH );
-        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
     }
     p += sizeof( ssl_serialized_session_header );
 

tests/suites/test_suite_ssl.function

@@ -975,7 +975,7 @@ void ssl_session_serialize_version_check( int corrupt_major,
             TEST_ASSERT( mbedtls_ssl_session_load( &session,
                                                    serialized_session,
                                                    serialized_session_len ) ==
-                         MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+                         MBEDTLS_ERR_SSL_VERSION_MISMATCH );
 
             /* Undo the change */
             *byte ^= corrupted_bit;