Merge remote-tracking branch 'public/pr/1915' into iotssl-165-dtls-hs-fragmentation-new

* public/pr/1915:
  Adapt ChangeLog
  Fix mbedtls_ssl_get_record_expansion() for ChaChaPoly and CBC

ChangeLog

@@ -15,6 +15,9 @@ Bugfix
      interoperability issues with BouncyCastle. Raised by milenamil in #1157.
    * Fix potential use-after-free in mbedtls_ssl_get_max_frag_len()
      and mbedtls_ssl_get_record_expansion() after a session reset. Fixes #1941.
+   * Fix a miscalculation of the maximum record expansion in
+     mbedtls_ssl_get_record_expansion() in case of ChachaPoly ciphersuites,
+     or CBC ciphersuites in (D)TLS versions 1.1 or higher. Fixes #1913, #1914.
 
 Changes
    * Copy headers preserving timestamps when doing a "make install".

library/ssl_tls.c

@@ -7005,6 +7005,7 @@ int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
 {
     size_t transform_expansion;
     const mbedtls_ssl_transform *transform = ssl->transform_out;
+    unsigned block_size;
 
     if( transform == NULL )
         return( (int) mbedtls_ssl_hdr_len( ssl ) );
@@ -7019,13 +7020,33 @@ int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
     {
         case MBEDTLS_MODE_GCM:
         case MBEDTLS_MODE_CCM:
+        case MBEDTLS_MODE_CHACHAPOLY:
         case MBEDTLS_MODE_STREAM:
             transform_expansion = transform->minlen;
             break;
 
         case MBEDTLS_MODE_CBC:
-            transform_expansion = transform->maclen
+
-                      + mbedtls_cipher_get_block_size( &transform->cipher_ctx_enc );
+            block_size = mbedtls_cipher_get_block_size(
+                &transform->cipher_ctx_enc );
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+            if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
+            {
+                /* Expansion due to addition of
+                 * - MAC
+                 * - CBC padding (theoretically up to 256 bytes, but
+                 *                we never use more than block_size)
+                 * - explicit IV
+                 */
+                transform_expansion = transform->maclen + 2 * block_size;
+            }
+            else
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */
+            {
+                /* No explicit IV prior to TLS 1.1. */
+                transform_expansion = transform->maclen + block_size;
+            }
             break;
 
         default: