Test TLS extension ordering

Adding extensions is fragile, with the TLSEXT_TYPE entry needing to be
located at TLSEXT_IDX in the array.

This adds a test to ensure extensions are in the correct order.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19269)

ssl/statem/extensions.c

@@ -103,6 +103,9 @@ typedef struct extensions_definition_st {
  * Definitions of all built-in extensions. NOTE: Changes in the number or order
  * of these extensions should be mirrored with equivalent changes to the
  * indexes ( TLSEXT_IDX_* ) defined in ssl_local.h.
+ * Extensions should be added to test/ext_internal_test.c as well, as that
+ * tests the ordering of the extensions.
+ *
  * Each extension has an initialiser, a client and
  * server side parser and a finaliser. The initialiser is called (if the
  * extension is relevant to the given context) even if we did not see the
@@ -123,7 +126,7 @@ typedef struct extensions_definition_st {
  * NOTE: WebSphere Application Server 7+ cannot handle empty extensions at
  * the end, keep these extensions before signature_algorithm.
  */
-#define INVALID_EXTENSION { 0x10000, 0, NULL, NULL, NULL, NULL, NULL, NULL }
+#define INVALID_EXTENSION { TLSEXT_TYPE_invalid, 0, NULL, NULL, NULL, NULL, NULL, NULL }
 static const EXTENSION_DEFINITION ext_defs[] = {
     {
         TLSEXT_TYPE_renegotiate,
@@ -390,6 +393,17 @@ static const EXTENSION_DEFINITION ext_defs[] = {
     }
 };
 
+/* Returns a TLSEXT_TYPE for the given index */
+unsigned int ossl_get_extension_type(size_t idx)
+{
+    size_t num_exts = OSSL_NELEM(ext_defs);
+
+    if (idx >= num_exts)
+        return TLSEXT_TYPE_out_of_range;
+
+    return ext_defs[idx].type;
+}
+
 /* Check whether an extension's context matches the current context */
 static int validate_context(SSL_CONNECTION *s, unsigned int extctx,
                             unsigned int thisctx)

ssl/statem/statem_local.h

@@ -37,6 +37,11 @@
 /* Dummy message type */
 #define SSL3_MT_DUMMY   -1
 
+/* Invalid extension ID for non-supported extensions */
+#define TLSEXT_TYPE_invalid            0x10000
+#define TLSEXT_TYPE_out_of_range       0x10001
+unsigned int ossl_get_extension_type(size_t idx);
+
 extern const unsigned char hrrrandom[];
 
 /* Message processing return codes */

test/build.info

@@ -845,6 +845,11 @@ IF[{- !$disabled{tests} -}]
     INCLUDE[ssl_old_test]=.. ../include ../apps/include
     DEPEND[ssl_old_test]=../libcrypto.a ../libssl.a libtestutil.a
 
+    PROGRAMS{noinst}=ext_internal_test
+    SOURCE[ext_internal_test]=ext_internal_test.c
+    INCLUDE[ext_internal_test]=.. ../include ../apps/include
+    DEPEND[ext_internal_test]=../libcrypto.a ../libssl.a libtestutil.a
+
     PROGRAMS{noinst}=algorithmid_test
     SOURCE[algorithmid_test]=algorithmid_test.c
     INCLUDE[algorithmid_test]=../include ../apps/include

test/ext_internal_test.c

@@ -0,0 +1,105 @@
+/*
+ * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include "internal/nelem.h"
+#include "../ssl/ssl_local.h"
+#include "../ssl/statem/statem_local.h"
+#include "testutil.h"
+
+#define EXT_ENTRY(name) { TLSEXT_IDX_##name, TLSEXT_TYPE_##name, #name }
+#define EXT_EXCEPTION(name) { TLSEXT_IDX_##name, TLSEXT_TYPE_invalid, #name }
+#define EXT_END(name) { TLSEXT_IDX_##name, TLSEXT_TYPE_out_of_range, #name }
+
+typedef struct {
+    size_t idx;
+    unsigned int type;
+    char *name;
+} EXT_LIST;
+
+/* The order here does matter! */
+static EXT_LIST ext_list[] = {
+
+    EXT_ENTRY(renegotiate),
+    EXT_ENTRY(server_name),
+    EXT_ENTRY(max_fragment_length),
+#ifndef OPENSSL_NO_SRP
+    EXT_ENTRY(srp),
+#else
+    EXT_EXCEPTION(srp),
+#endif
+    EXT_ENTRY(ec_point_formats),
+    EXT_ENTRY(supported_groups),
+    EXT_ENTRY(session_ticket),
+#ifndef OPENSSL_NO_OCSP
+    EXT_ENTRY(status_request),
+#else
+    EXT_EXCEPTION(status_request),
+#endif
+#ifndef OPENSSL_NO_NEXTPROTONEG
+    EXT_ENTRY(next_proto_neg),
+#else
+    EXT_EXCEPTION(next_proto_neg),
+#endif
+    EXT_ENTRY(application_layer_protocol_negotiation),
+#ifndef OPENSSL_NO_SRTP
+    EXT_ENTRY(use_srtp),
+#else
+    EXT_EXCEPTION(use_srtp),
+#endif
+    EXT_ENTRY(encrypt_then_mac),
+#ifndef OPENSSL_NO_CT
+    EXT_ENTRY(signed_certificate_timestamp),
+#else
+    EXT_EXCEPTION(signed_certificate_timestamp),
+#endif
+    EXT_ENTRY(extended_master_secret),
+    EXT_ENTRY(signature_algorithms_cert),
+    EXT_ENTRY(post_handshake_auth),
+    EXT_ENTRY(signature_algorithms),
+    EXT_ENTRY(supported_versions),
+    EXT_ENTRY(psk_kex_modes),
+    EXT_ENTRY(key_share),
+    EXT_ENTRY(cookie),
+    EXT_ENTRY(cryptopro_bug),
+    EXT_ENTRY(early_data),
+    EXT_ENTRY(certificate_authorities),
+    EXT_ENTRY(padding),
+    EXT_ENTRY(psk),
+    EXT_END(num_builtins)
+};
+
+static int test_extension_list(void)
+{
+    size_t n = OSSL_NELEM(ext_list);
+    size_t i;
+    unsigned int type;
+    int retval = 1;
+
+    for (i = 0; i < n; i++) {
+        if (!TEST_size_t_eq(i, ext_list[i].idx)) {
+            retval = 0;
+            TEST_error("TLSEXT_IDX_%s=%zd, found at=%zd\n",
+                       ext_list[i].name, ext_list[i].idx, i);
+        }
+        type = ossl_get_extension_type(ext_list[i].idx);
+        if (!TEST_uint_eq(type, ext_list[i].type)) {
+            retval = 0;
+            TEST_error("TLSEXT_IDX_%s=%zd expected=0x%05X got=0x%05X",
+                       ext_list[i].name, ext_list[i].idx, ext_list[i].type,
+                       type);
+        }
+    }
+    return retval;
+}
+
+int setup_tests(void)
+{
+    ADD_TEST(test_extension_list);
+    return 1;
+}

test/recipes/02-test_internal_exts.t

@@ -0,0 +1,15 @@
+#! /usr/bin/env perl
+# Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the Apache License 2.0 (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+use strict;
+use OpenSSL::Test;
+use OpenSSL::Test::Simple;
+
+setup("test_internal_exts");
+
+simple_test("test_internal_exts", "ext_internal_test");