bpo-38275: Skip ssl tests for disabled versions (GH-16386)

test_ssl now handles disabled TLS/SSL versions better. OpenSSL's crypto
policy and run-time settings are recognized and tests for disabled versions
are skipped.

Signed-off-by: Christian Heimes <christian@python.org>



https://bugs.python.org/issue38275

2 files changed, 147 insertions, 51 deletions

diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 737a969..8bb74b4 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -19,6 +19,7 @@ import asyncore
 import weakref
 import platform
 import sysconfig
+import functools
 try:
     import ctypes
 except ImportError:
@@ -146,6 +147,85 @@ OP_CIPHER_SERVER_PREFERENCE = getattr(ssl, "OP_CIPHER_SERVER_PREFERENCE", 0)
 OP_ENABLE_MIDDLEBOX_COMPAT = getattr(ssl, "OP_ENABLE_MIDDLEBOX_COMPAT", 0)
 
 
+def has_tls_protocol(protocol):
+    """Check if a TLS protocol is available and enabled
+
+    :param protocol: enum ssl._SSLMethod member or name
+    :return: bool
+    """
+    if isinstance(protocol, str):
+        assert protocol.startswith('PROTOCOL_')
+        protocol = getattr(ssl, protocol, None)
+        if protocol is None:
+            return False
+    if protocol in {
+        ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS_SERVER,
+        ssl.PROTOCOL_TLS_CLIENT
+    }:
+        # auto-negotiate protocols are always available
+        return True
+    name = protocol.name
+    return has_tls_version(name[len('PROTOCOL_'):])
+
+
+@functools.lru_cache
+def has_tls_version(version):
+    """Check if a TLS/SSL version is enabled
+
+    :param version: TLS version name or ssl.TLSVersion member
+    :return: bool
+    """
+    if version == "SSLv2":
+        # never supported and not even in TLSVersion enum
+        return False
+
+    if isinstance(version, str):
+        version = ssl.TLSVersion.__members__[version]
+
+    # check compile time flags like ssl.HAS_TLSv1_2
+    if not getattr(ssl, f'HAS_{version.name}'):
+        return False
+
+    # check runtime and dynamic crypto policy settings. A TLS version may
+    # be compiled in but disabled by a policy or config option.
+    ctx = ssl.SSLContext()
+    if (
+            ctx.minimum_version != ssl.TLSVersion.MINIMUM_SUPPORTED and
+            version < ctx.minimum_version
+    ):
+        return False
+    if (
+        ctx.maximum_version != ssl.TLSVersion.MAXIMUM_SUPPORTED and
+        version > ctx.maximum_version
+    ):
+        return False
+
+    return True
+
+
+def requires_tls_version(version):
+    """Decorator to skip tests when a required TLS version is not available
+
+    :param version: TLS version name or ssl.TLSVersion member
+    :return:
+    """
+    def decorator(func):
+        @functools.wraps(func)
+        def wrapper(*args, **kw):
+            if not has_tls_version(version):
+                raise unittest.SkipTest(f"{version} is not available.")
+            else:
+                return func(*args, **kw)
+        return wrapper
+    return decorator
+
+
+requires_minimum_version = unittest.skipUnless(
+    hasattr(ssl.SSLContext, 'minimum_version'),
+    "required OpenSSL >= 1.1.0g"
+)
+
+
 def handle_error(prefix):
     exc_format = ' '.join(traceback.format_exception(*sys.exc_info()))
     if support.verbose:
@@ -1107,20 +1187,23 @@ class ContextTests(unittest.TestCase):
             with self.assertRaises(AttributeError):
                 ctx.hostname_checks_common_name = True
 
-    @unittest.skipUnless(hasattr(ssl.SSLContext, 'minimum_version'),
-                         "required OpenSSL 1.1.0g")
+    @requires_minimum_version
     @unittest.skipIf(IS_LIBRESSL, "see bpo-34001")
     def test_min_max_version(self):
         ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
         # OpenSSL default is MINIMUM_SUPPORTED, however some vendors like
         # Fedora override the setting to TLS 1.0.
+        minimum_range = {
+            # stock OpenSSL
+            ssl.TLSVersion.MINIMUM_SUPPORTED,
+            # Fedora 29 uses TLS 1.0 by default
+            ssl.TLSVersion.TLSv1,
+            # RHEL 8 uses TLS 1.2 by default
+            ssl.TLSVersion.TLSv1_2
+        }
+
         self.assertIn(
-            ctx.minimum_version,
-            {ssl.TLSVersion.MINIMUM_SUPPORTED,
-             # Fedora 29 uses TLS 1.0 by default
-             ssl.TLSVersion.TLSv1,
-             # RHEL 8 uses TLS 1.2 by default
-             ssl.TLSVersion.TLSv1_2}
+            ctx.minimum_version, minimum_range
         )
         self.assertEqual(
             ctx.maximum_version, ssl.TLSVersion.MAXIMUM_SUPPORTED
@@ -1166,8 +1249,8 @@ class ContextTests(unittest.TestCase):
 
         ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1_1)
 
-        self.assertEqual(
-            ctx.minimum_version, ssl.TLSVersion.MINIMUM_SUPPORTED
+        self.assertIn(
+            ctx.minimum_version, minimum_range
         )
         self.assertEqual(
             ctx.maximum_version, ssl.TLSVersion.MAXIMUM_SUPPORTED
@@ -2722,6 +2805,8 @@ class ThreadedTests(unittest.TestCase):
         for protocol in PROTOCOLS:
             if protocol in {ssl.PROTOCOL_TLS_CLIENT, ssl.PROTOCOL_TLS_SERVER}:
                 continue
+            if not has_tls_protocol(protocol):
+                continue
             with self.subTest(protocol=ssl._PROTOCOL_NAMES[protocol]):
                 context = ssl.SSLContext(protocol)
                 context.load_cert_chain(CERTFILE)
@@ -3013,7 +3098,7 @@ class ThreadedTests(unittest.TestCase):
             else:
                 self.fail("Use of invalid cert should have failed!")
 
-    @unittest.skipUnless(ssl.HAS_TLSv1_3, "Test needs TLS 1.3")
+    @requires_tls_version('TLSv1_3')
     def test_wrong_cert_tls13(self):
         client_context, server_context, hostname = testing_context()
         # load client cert that is not signed by trusted CA
@@ -3108,8 +3193,7 @@ class ThreadedTests(unittest.TestCase):
                     self.assertIn(msg, repr(e))
                     self.assertIn('certificate verify failed', repr(e))
 
-    @unittest.skipUnless(hasattr(ssl, 'PROTOCOL_SSLv2'),
-                         "OpenSSL is compiled without SSLv2 support")
+    @requires_tls_version('SSLv2')
     def test_protocol_sslv2(self):
         """Connecting to an SSLv2 server with various client options"""
         if support.verbose:
@@ -3118,7 +3202,7 @@ class ThreadedTests(unittest.TestCase):
         try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv2, True, ssl.CERT_OPTIONAL)
         try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv2, True, ssl.CERT_REQUIRED)
         try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_TLS, False)
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv3, False)
         try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_TLSv1, False)
         # SSLv23 client with specific SSL options
@@ -3135,7 +3219,7 @@ class ThreadedTests(unittest.TestCase):
         """Connecting to an SSLv23 server with various client options"""
         if support.verbose:
             sys.stdout.write("\n")
-        if hasattr(ssl, 'PROTOCOL_SSLv2'):
+        if has_tls_version('SSLv2'):
             try:
                 try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_SSLv2, True)
             except OSError as x:
@@ -3144,34 +3228,36 @@ class ThreadedTests(unittest.TestCase):
                     sys.stdout.write(
                         " SSL2 client to SSL23 server test unexpectedly failed:\n %s\n"
                         % str(x))
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_SSLv3, False)
         try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS, True)
-        try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1')
+        if has_tls_version('TLSv1'):
+            try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1')
 
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_SSLv3, False, ssl.CERT_OPTIONAL)
         try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS, True, ssl.CERT_OPTIONAL)
-        try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_OPTIONAL)
+        if has_tls_version('TLSv1'):
+            try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_OPTIONAL)
 
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_SSLv3, False, ssl.CERT_REQUIRED)
         try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS, True, ssl.CERT_REQUIRED)
-        try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_REQUIRED)
+        if has_tls_version('TLSv1'):
+            try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_REQUIRED)
 
         # Server with specific SSL options
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_SSLv3, False,
                            server_options=ssl.OP_NO_SSLv3)
         # Will choose TLSv1
         try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLS, True,
                            server_options=ssl.OP_NO_SSLv2 | ssl.OP_NO_SSLv3)
-        try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, False,
-                           server_options=ssl.OP_NO_TLSv1)
-
+        if has_tls_version('TLSv1'):
+            try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1, False,
+                               server_options=ssl.OP_NO_TLSv1)
 
-    @unittest.skipUnless(hasattr(ssl, 'PROTOCOL_SSLv3'),
-                         "OpenSSL is compiled without SSLv3 support")
+    @requires_tls_version('SSLv3')
     def test_protocol_sslv3(self):
         """Connecting to an SSLv3 server with various client options"""
         if support.verbose:
@@ -3179,7 +3265,7 @@ class ThreadedTests(unittest.TestCase):
         try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_SSLv3, 'SSLv3')
         try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_SSLv3, 'SSLv3', ssl.CERT_OPTIONAL)
         try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_SSLv3, 'SSLv3', ssl.CERT_REQUIRED)
-        if hasattr(ssl, 'PROTOCOL_SSLv2'):
+        if has_tls_version('SSLv2'):
             try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_SSLv2, False)
         try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_TLS, False,
                            client_options=ssl.OP_NO_SSLv3)
@@ -3189,6 +3275,7 @@ class ThreadedTests(unittest.TestCase):
             try_protocol_combo(ssl.PROTOCOL_SSLv3, ssl.PROTOCOL_TLS,
                                False, client_options=ssl.OP_NO_SSLv2)
 
+    @requires_tls_version('TLSv1')
     def test_protocol_tlsv1(self):
         """Connecting to a TLSv1 server with various client options"""
         if support.verbose:
@@ -3196,34 +3283,32 @@ class ThreadedTests(unittest.TestCase):
         try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_TLSv1, 'TLSv1')
         try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_OPTIONAL)
         try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_TLSv1, 'TLSv1', ssl.CERT_REQUIRED)
-        if hasattr(ssl, 'PROTOCOL_SSLv2'):
+        if has_tls_version('SSLv2'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_SSLv2, False)
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_SSLv3, False)
         try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_TLS, False,
                            client_options=ssl.OP_NO_TLSv1)
 
-    @unittest.skipUnless(hasattr(ssl, "PROTOCOL_TLSv1_1"),
-                         "TLS version 1.1 not supported.")
+    @requires_tls_version('TLSv1_1')
     def test_protocol_tlsv1_1(self):
         """Connecting to a TLSv1.1 server with various client options.
            Testing against older TLS versions."""
         if support.verbose:
             sys.stdout.write("\n")
         try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_TLSv1_1, 'TLSv1.1')
-        if hasattr(ssl, 'PROTOCOL_SSLv2'):
+        if has_tls_version('SSLv2'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_SSLv2, False)
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_SSLv3, False)
         try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_TLS, False,
                            client_options=ssl.OP_NO_TLSv1_1)
 
         try_protocol_combo(ssl.PROTOCOL_TLS, ssl.PROTOCOL_TLSv1_1, 'TLSv1.1')
-        try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_TLSv1, False)
-        try_protocol_combo(ssl.PROTOCOL_TLSv1, ssl.PROTOCOL_TLSv1_1, False)
+        try_protocol_combo(ssl.PROTOCOL_TLSv1_1, ssl.PROTOCOL_TLSv1_2, False)
+        try_protocol_combo(ssl.PROTOCOL_TLSv1_2, ssl.PROTOCOL_TLSv1_1, False)
 
-    @unittest.skipUnless(hasattr(ssl, "PROTOCOL_TLSv1_2"),
-                         "TLS version 1.2 not supported.")
+    @requires_tls_version('TLSv1_2')
     def test_protocol_tlsv1_2(self):
         """Connecting to a TLSv1.2 server with various client options.
            Testing against older TLS versions."""
@@ -3232,9 +3317,9 @@ class ThreadedTests(unittest.TestCase):
         try_protocol_combo(ssl.PROTOCOL_TLSv1_2, ssl.PROTOCOL_TLSv1_2, 'TLSv1.2',
                            server_options=ssl.OP_NO_SSLv3|ssl.OP_NO_SSLv2,
                            client_options=ssl.OP_NO_SSLv3|ssl.OP_NO_SSLv2,)
-        if hasattr(ssl, 'PROTOCOL_SSLv2'):
+        if has_tls_version('SSLv2'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1_2, ssl.PROTOCOL_SSLv2, False)
-        if hasattr(ssl, 'PROTOCOL_SSLv3'):
+        if has_tls_version('SSLv3'):
             try_protocol_combo(ssl.PROTOCOL_TLSv1_2, ssl.PROTOCOL_SSLv3, False)
         try_protocol_combo(ssl.PROTOCOL_TLSv1_2, ssl.PROTOCOL_TLS, False,
                            client_options=ssl.OP_NO_TLSv1_2)
@@ -3677,7 +3762,7 @@ class ThreadedTests(unittest.TestCase):
                 self.assertIs(s.version(), None)
                 self.assertIs(s._sslobj, None)
                 s.connect((HOST, server.port))
-                if IS_OPENSSL_1_1_1 and ssl.HAS_TLSv1_3:
+                if IS_OPENSSL_1_1_1 and has_tls_version('TLSv1_3'):
                     self.assertEqual(s.version(), 'TLSv1.3')
                 elif ssl.OPENSSL_VERSION_INFO >= (1, 0, 2):
                     self.assertEqual(s.version(), 'TLSv1.2')
@@ -3686,8 +3771,7 @@ class ThreadedTests(unittest.TestCase):
             self.assertIs(s._sslobj, None)
             self.assertIs(s.version(), None)
 
-    @unittest.skipUnless(ssl.HAS_TLSv1_3,
-                         "test requires TLSv1.3 enabled OpenSSL")
+    @requires_tls_version('TLSv1_3')
     def test_tls1_3(self):
         context = ssl.SSLContext(ssl.PROTOCOL_TLS)
         context.load_cert_chain(CERTFILE)
@@ -3704,9 +3788,9 @@ class ThreadedTests(unittest.TestCase):
                 })
                 self.assertEqual(s.version(), 'TLSv1.3')
 
-    @unittest.skipUnless(hasattr(ssl.SSLContext, 'minimum_version'),
-                         "required OpenSSL 1.1.0g")
-    def test_min_max_version(self):
+    @requires_minimum_version
+    @requires_tls_version('TLSv1_2')
+    def test_min_max_version_tlsv1_2(self):
         client_context, server_context, hostname = testing_context()
         # client TLSv1.0 to 1.2
         client_context.minimum_version = ssl.TLSVersion.TLSv1
@@ -3721,7 +3805,13 @@ class ThreadedTests(unittest.TestCase):
                 s.connect((HOST, server.port))
                 self.assertEqual(s.version(), 'TLSv1.2')
 
+    @requires_minimum_version
+    @requires_tls_version('TLSv1_1')
+    def test_min_max_version_tlsv1_1(self):
+        client_context, server_context, hostname = testing_context()
         # client 1.0 to 1.2, server 1.0 to 1.1
+        client_context.minimum_version = ssl.TLSVersion.TLSv1
+        client_context.maximum_version = ssl.TLSVersion.TLSv1_2
         server_context.minimum_version = ssl.TLSVersion.TLSv1
         server_context.maximum_version = ssl.TLSVersion.TLSv1_1
 
@@ -3731,6 +3821,10 @@ class ThreadedTests(unittest.TestCase):
                 s.connect((HOST, server.port))
                 self.assertEqual(s.version(), 'TLSv1.1')
 
+    @requires_minimum_version
+    @requires_tls_version('TLSv1_2')
+    def test_min_max_version_mismatch(self):
+        client_context, server_context, hostname = testing_context()
         # client 1.0, server 1.2 (mismatch)
         server_context.maximum_version = ssl.TLSVersion.TLSv1_2
         server_context.minimum_version = ssl.TLSVersion.TLSv1_2
@@ -3743,10 +3837,8 @@ class ThreadedTests(unittest.TestCase):
                     s.connect((HOST, server.port))
                 self.assertIn("alert", str(e.exception))
 
-
-    @unittest.skipUnless(hasattr(ssl.SSLContext, 'minimum_version'),
-                         "required OpenSSL 1.1.0g")
-    @unittest.skipUnless(ssl.HAS_SSLv3, "requires SSLv3 support")
+    @requires_minimum_version
+    @requires_tls_version('SSLv3')
     def test_min_max_version_sslv3(self):
         client_context, server_context, hostname = testing_context()
         server_context.minimum_version = ssl.TLSVersion.SSLv3
@@ -4270,7 +4362,7 @@ class ThreadedTests(unittest.TestCase):
                                  'Session refers to a different SSLContext.')
 
 
-@unittest.skipUnless(ssl.HAS_TLSv1_3, "Test needs TLS 1.3")
+@unittest.skipUnless(has_tls_version('TLSv1_3'), "Test needs TLS 1.3")
 class TestPostHandshakeAuth(unittest.TestCase):
     def test_pha_setter(self):
         protocols = [
diff --git a/Misc/NEWS.d/next/Tests/2019-09-25-14-40-57.bpo-38275.-kdveI.rst b/Misc/NEWS.d/next/Tests/2019-09-25-14-40-57.bpo-38275.-kdveI.rst
new file mode 100644
index 0000000..893c0f1
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2019-09-25-14-40-57.bpo-38275.-kdveI.rst
@@ -0,0 +1,4 @@
+test_ssl now handles disabled TLS/SSL versions better. OpenSSL's crypto
+policy and run-time settings are recognized and tests for disabled versions
+are skipped. Tests also accept more TLS minimum_versions for platforms that
+override OpenSSL's default with strict settings.