From 2442255f0d720d76d5016c030dbb4c8113c46c67 Mon Sep 17 00:00:00 2001
From: Janos Follath <janos.follath@arm.com>
Date: Fri, 6 May 2016 13:57:50 +0100
Subject: [PATCH] Fix non compliance SSLv3 in server extension handling.

The server code parses the client hello extensions even when the
protocol is SSLv3 and this behaviour is non compliant with rfc6101.
Also the server sends extensions in the server hello and omitting
them may prevent interoperability problems.
---
 ChangeLog         |  1 +
 library/ssl_srv.c | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 3b32873b2..986eabd67 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -26,6 +26,7 @@ Bugfix
    * Fix issue that caused a crash if invalid curves were passed to
      mbedtls_ssl_conf_curves. #373
    * Fix issue in ssl_fork_server which was preventing it from functioning. #429
+   * Fix non compliance SSLv3 in server extension handling.
 
 Changes
    * On ARM platforms, when compiling with -O0 with GCC, Clang or armcc5,
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 9fc21a5ef..5a51cbbd2 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -1507,6 +1507,12 @@ read_record_header:
         ssl->session_negotiate->compression = MBEDTLS_SSL_COMPRESS_NULL;
 #endif
 
+    /* Do not parse the extensions if the protocol is SSLv3 */
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+    if( ( ssl->major_ver != 3 ) || ( ssl->minor_ver != 0 ) )
+    {
+#endif
+
     /*
      * Check the extension length
      */
@@ -1692,8 +1698,13 @@ read_record_header:
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
             return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
         }
+
     }
 
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+    }
+#endif
+
 #if defined(MBEDTLS_SSL_FALLBACK_SCSV)
     for( i = 0, p = buf + 41 + sess_len; i < ciph_len; i += 2, p += 2 )
     {
@@ -2363,6 +2374,12 @@ static int ssl_write_server_hello( mbedtls_ssl_context *ssl )
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, compress alg.: 0x%02X",
                    ssl->session_negotiate->compression ) );
 
+    /* Do not write the extensions if the protocol is SSLv3 */
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+    if( ( ssl->major_ver != 3 ) || ( ssl->minor_ver != 0 ) )
+    {
+#endif
+
     /*
      *  First write extensions, then the total length
      */
@@ -2419,6 +2436,10 @@ static int ssl_write_server_hello( mbedtls_ssl_context *ssl )
         p += ext_len;
     }
 
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+    }
+#endif
+
     ssl->out_msglen  = p - buf;
     ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
     ssl->out_msg[0]  = MBEDTLS_SSL_HS_SERVER_HELLO;