Add a test for an empty NextProto message

It is valid according to the spec for a NextProto message to have no
protocols listed in it. The OpenSSL implementation however does not allow
us to create such a message. In order to check that we work as expected
when communicating with a client that does generate such messages we have
to use a TLSProxy test.

Follow on from CVE-2024-5535

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24716)

1 files changed, 73 insertions, 0 deletions

diff --git a/test/recipes/70-test_npn.t b/test/recipes/70-test_npn.t
new file mode 100644
index 0000000000..f82e71af6a
--- /dev/null
+++ b/test/recipes/70-test_npn.t
@@ -0,0 +1,73 @@
+#! /usr/bin/env perl
+# Copyright 2024 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 qw/:DEFAULT cmdstr srctop_file/;
+use OpenSSL::Test::Utils;
+
+use TLSProxy::Proxy;
+
+my $test_name = "test_npn";
+setup($test_name);
+
+plan skip_all => "TLSProxy isn't usable on $^O"
+    if $^O =~ /^(VMS)$/;
+
+plan skip_all => "$test_name needs the dynamic engine feature enabled"
+    if disabled("engine") || disabled("dynamic-engine");
+
+plan skip_all => "$test_name needs the sock feature enabled"
+    if disabled("sock");
+
+plan skip_all => "$test_name needs NPN enabled"
+    if disabled("nextprotoneg");
+
+plan skip_all => "$test_name needs TLSv1.2 enabled"
+    if disabled("tls1_2");
+
+my $proxy = TLSProxy::Proxy->new(
+    undef,
+    cmdstr(app(["openssl"]), display => 1),
+    srctop_file("apps", "server.pem"),
+    (!$ENV{HARNESS_ACTIVE} || $ENV{HARNESS_VERBOSE})
+);
+
+$proxy->start() or plan skip_all => "Unable to start up Proxy for tests";
+plan tests => 1;
+
+my $npnseen = 0;
+
+# Test 1: Check sending an empty NextProto message from the client works. This is
+#         valid as per the spec, but OpenSSL does not allow you to send it.
+#         Therefore we must be prepared to receive such a message but we cannot
+#         generate it except via TLSProxy
+$proxy->clear();
+$proxy->filter(\&npn_filter);
+$proxy->clientflags("-nextprotoneg foo -no_tls1_3");
+$proxy->serverflags("-nextprotoneg foo");
+$proxy->start();
+ok($npnseen && TLSProxy::Message->success(), "Empty NPN message");
+
+sub npn_filter
+{
+    my $proxy = shift;
+    my $message;
+
+    # The NextProto message always appears in flight 2
+    return if $proxy->flight != 2;
+
+    foreach my $message (@{$proxy->message_list}) {
+        if ($message->mt == TLSProxy::Message::MT_NEXT_PROTO) {
+            # Our TLSproxy NextProto message support doesn't support parsing of
+            # the message. If we repack it just creates an empty NextProto
+            # message - which is exactly the scenario we want to test here.
+            $message->repack();
+            $npnseen = 1;
+        }
+    }
+}