Merge branch 'mbedtls_ssl_get_key_exchange_md_ssl_tls-return_hashlen' into tls_async_server-2.9

Conflict resolution:
* ChangeLog: put the new entry from my branch in the proper place.
* include/mbedtls/error.h: counted high-level module error codes again.
* include/mbedtls/ssl.h: picked different numeric codes for the
  concurrently added errors; made the new error a full sentence per
  current standards.
* library/error.c: ran scripts/generate_errors.pl.
* library/ssl_srv.c:
    * ssl_prepare_server_key_exchange "DHE key exchanges": the conflict
      was due to style corrections in development
      (4cb1f4d49c) which I merged with
      my refactoring.
    * ssl_prepare_server_key_exchange "For key exchanges involving the
      server signing", first case, variable declarations: merged line
      by line:
        * dig_signed_len: added in async
        * signature_len: removed in async
        * hashlen: type changed to size_t in development
        * hash: size changed to MBEDTLS_MD_MAX_SIZE in async
        * ret: added in async
    * ssl_prepare_server_key_exchange "For key exchanges involving the
      server signing", first cae comment: the conflict was due to style
      corrections in development (4cb1f4d49c)
      which I merged with my comment changes made as part of refactoring
      the function.
    * ssl_prepare_server_key_exchange "Compute the hash to be signed" if
      `md_alg != MBEDTLS_MD_NONE`: conflict between
      ebd652fe2d
      "ssl_write_server_key_exchange: calculate hashlen explicitly" and
      46f5a3e9b4 "Check return codes from
      MD in ssl code". I took the code from commit
      ca1d742904 made on top of development
      which makes mbedtls_ssl_get_key_exchange_md_ssl_tls return the
      hash length.
* programs/ssl/ssl_server2.c: multiple conflicts between the introduction
  of MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS and new auxiliary functions and
  definitions for async support, and the introduction of idle().
    * definitions before main: concurrent additions, kept both.
    * main, just after `handshake:`: in the loop around
      mbedtls_ssl_handshake(), merge the addition of support for
      MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS and SSL_ASYNC_INJECT_ERROR_CANCEL
      with the addition of the idle() call.
    * main, if `opt.transport == MBEDTLS_SSL_TRANSPORT_STREAM`: take the
      code from development and add a check for
      MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS.
    * main, loop around mbedtls_ssl_read() in the datagram case:
      take the code from development and add a check for
      MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS; revert to a do...while loop.
    * main, loop around mbedtls_ssl_write() in the datagram case:
      take the code from development and add a check for
      MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS; revert to a do...while loop.

include/mbedtls/ssl_internal.h

@@ -1,8 +1,9 @@
 /**
- * \file ssl_ticket.h
+ * \file ssl_internal.h
  *
  * \brief Internal functions shared by the SSL modules
- *
+ */
+/*
  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
@@ -24,6 +25,7 @@
 #define MBEDTLS_SSL_INTERNAL_H
 
 #include "ssl.h"
+#include "cipher.h"
 
 #if defined(MBEDTLS_MD5_C)
 #include "md5.h"
@@ -69,6 +71,9 @@
 #endif /* MBEDTLS_SSL_PROTO_TLS1   */
 #endif /* MBEDTLS_SSL_PROTO_SSL3   */
 
+#define MBEDTLS_SSL_MIN_VALID_MINOR_VERSION MBEDTLS_SSL_MINOR_VERSION_1
+#define MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION MBEDTLS_SSL_MAJOR_VERSION_3
+
 /* Determine maximum supported version */
 #define MBEDTLS_SSL_MAX_MAJOR_VERSION           MBEDTLS_SSL_MAJOR_VERSION_3
 
@@ -138,13 +143,33 @@
 #define MBEDTLS_SSL_PADDING_ADD              0
 #endif
 
-#define MBEDTLS_SSL_BUFFER_LEN  ( MBEDTLS_SSL_MAX_CONTENT_LEN               \
-                        + MBEDTLS_SSL_COMPRESSION_ADD               \
-                        + 29 /* counter + header + IV */    \
-                        + MBEDTLS_SSL_MAC_ADD                       \
-                        + MBEDTLS_SSL_PADDING_ADD                   \
+#define MBEDTLS_SSL_PAYLOAD_LEN ( MBEDTLS_SSL_MAX_CONTENT_LEN    \
+                        + MBEDTLS_SSL_COMPRESSION_ADD            \
+                        + MBEDTLS_MAX_IV_LENGTH                  \
+                        + MBEDTLS_SSL_MAC_ADD                    \
+                        + MBEDTLS_SSL_PADDING_ADD                \
                         )
 
+/*
+ * Check that we obey the standard's message size bounds
+ */
+
+#if MBEDTLS_SSL_MAX_CONTENT_LEN > 16384
+#error Bad configuration - record content too large.
+#endif
+
+#if MBEDTLS_SSL_PAYLOAD_LEN > 16384 + 2048
+#error Bad configuration - protected record payload too large.
+#endif
+
+/* Note: Even though the TLS record header is only 5 bytes
+   long, we're internally using 8 bytes to store the
+   implicit sequence number. */
+#define MBEDTLS_SSL_HEADER_LEN 13
+
+#define MBEDTLS_SSL_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_PAYLOAD_LEN ) )
+
 /*
  * TLS extension flags (for extensions with outgoing ServerHello content
  * that need it (e.g. for RENEGOTIATION_INFO the server already knows because
@@ -606,9 +631,9 @@ void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
 static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
 {
     size_t i;
-    const unsigned char *A = (const unsigned char *) a;
-    const unsigned char *B = (const unsigned char *) b;
-    unsigned char diff = 0;
+    volatile const unsigned char *A = (volatile const unsigned char *) a;
+    volatile const unsigned char *B = (volatile const unsigned char *) b;
+    volatile unsigned char diff = 0;
 
     for( i = 0; i < n; i++ )
         diff |= A[i] ^ B[i];
@@ -616,6 +641,23 @@ static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t
     return( diff );
 }
 
+#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_1)
+int mbedtls_ssl_get_key_exchange_md_ssl_tls( mbedtls_ssl_context *ssl,
+                                        unsigned char *output,
+                                        unsigned char *data, size_t data_len );
+#endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 || \
+          MBEDTLS_SSL_PROTO_TLS1_1 */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2)
+int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
+                                            unsigned char *hash, size_t *hashlen,
+                                            unsigned char *data, size_t data_len,
+                                            mbedtls_md_type_t md_alg );
+#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
+          MBEDTLS_SSL_PROTO_TLS1_2 */
+
 #ifdef __cplusplus
 }
 #endif