bpo-32947: Fixes for TLS 1.3 and OpenSSL 1.1.1 (GH-8761)

Backport of TLS 1.3 related fixes from 3.7.

Misc fixes and workarounds for compatibility with OpenSSL 1.1.1 from git
master and TLS 1.3 support. With OpenSSL 1.1.1, Python negotiates TLS 1.3 by
default. Some test cases only apply to TLS 1.2.

OpenSSL 1.1.1 has added a new option OP_ENABLE_MIDDLEBOX_COMPAT for TLS
1.3. The feature is enabled by default for maximum compatibility with
broken middle boxes. Users should be able to disable the hack and CPython's test suite needs
it to verify default options

Signed-off-by: Christian Heimes <[email protected]>

Author: tiran

Doc/library/ssl.rst

@@ -821,6 +821,15 @@ Constants
 
    .. versionadded:: 3.3
 
+.. data:: OP_ENABLE_MIDDLEBOX_COMPAT
+
+   Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make
+   a TLS 1.3 connection look more like a TLS 1.2 connection.
+
+   This option is only available with OpenSSL 1.1.1 and later.
+
+   .. versionadded:: 3.6.7
+
 .. data:: OP_NO_COMPRESSION
 
    Disable compression on the SSL channel.  This is useful if the application

Lib/test/test_asyncio/test_events.py

@@ -1187,7 +1187,11 @@ def test_create_server_ssl_match_failed(self):
                     self.loop.run_until_complete(f_c)
 
         # close connection
-        proto.transport.close()
+        # transport may be None with TLS 1.3, because connection is
+        # interrupted, server is unable to send session tickets, and
+        # transport is closed.
+        if proto.transport is not None:
+            proto.transport.close()
         server.close()
 
     def test_legacy_create_server_ssl_match_failed(self):

Lib/test/test_ssl.py

@@ -89,6 +89,7 @@ def data_file(*name):
 OP_SINGLE_DH_USE = getattr(ssl, "OP_SINGLE_DH_USE", 0)
 OP_SINGLE_ECDH_USE = getattr(ssl, "OP_SINGLE_ECDH_USE", 0)
 OP_CIPHER_SERVER_PREFERENCE = getattr(ssl, "OP_CIPHER_SERVER_PREFERENCE", 0)
+OP_ENABLE_MIDDLEBOX_COMPAT = getattr(ssl, "OP_ENABLE_MIDDLEBOX_COMPAT", 0)
 
 
 def handle_error(prefix):
@@ -181,8 +182,8 @@ def test_constants(self):
         ssl.OP_NO_TLSv1
         ssl.OP_NO_TLSv1_3
     if ssl.OPENSSL_VERSION_INFO >= (1, 0, 1):
-            ssl.OP_NO_TLSv1_1
-            ssl.OP_NO_TLSv1_2
+        ssl.OP_NO_TLSv1_1
+        ssl.OP_NO_TLSv1_2
 
     def test_str_for_enums(self):
         # Make sure that the PROTOCOL_* constants have enum-like string
@@ -899,12 +900,13 @@ def test_get_ciphers(self):
 
     @skip_if_broken_ubuntu_ssl
     def test_options(self):
-        ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
+        ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
         # OP_ALL | OP_NO_SSLv2 | OP_NO_SSLv3 is the default value
         default = (ssl.OP_ALL | ssl.OP_NO_SSLv2 | ssl.OP_NO_SSLv3)
         # SSLContext also enables these by default
         default |= (OP_NO_COMPRESSION | OP_CIPHER_SERVER_PREFERENCE |
-                    OP_SINGLE_DH_USE | OP_SINGLE_ECDH_USE)
+                    OP_SINGLE_DH_USE | OP_SINGLE_ECDH_USE |
+                    OP_ENABLE_MIDDLEBOX_COMPAT)
         self.assertEqual(default, ctx.options)
         ctx.options |= ssl.OP_NO_TLSv1
         self.assertEqual(default | ssl.OP_NO_TLSv1, ctx.options)
@@ -1857,11 +1859,23 @@ def wrap_conn(self):
                         self.sock, server_side=True)
                     self.server.selected_npn_protocols.append(self.sslconn.selected_npn_protocol())
                     self.server.selected_alpn_protocols.append(self.sslconn.selected_alpn_protocol())
-                except (ssl.SSLError, ConnectionResetError, OSError) as e:
+                except (ConnectionResetError, BrokenPipeError) as e:
                     # We treat ConnectionResetError as though it were an
                     # SSLError - OpenSSL on Ubuntu abruptly closes the
                     # connection when asked to use an unsupported protocol.
                     #
+                    # BrokenPipeError is raised in TLS 1.3 mode, when OpenSSL
+                    # tries to send session tickets after handshake.
+                    # https://github.com/openssl/openssl/issues/6342
+                    self.server.conn_errors.append(str(e))
+                    if self.server.chatty:
+                        handle_error(
+                            "\n server:  bad connection attempt from " + repr(
+                                self.addr) + ":\n")
+                    self.running = False
+                    self.close()
+                    return False
+                except (ssl.SSLError, OSError) as e:
                     # OSError may occur with wrong protocols, e.g. both
                     # sides use PROTOCOL_TLS_SERVER.
                     #
@@ -3042,14 +3056,16 @@ def serve():
                 # Block on the accept and wait on the connection to close.
                 evt.set()
                 remote, peer = server.accept()
-                remote.recv(1)
+                remote.send(remote.recv(4))
 
             t = threading.Thread(target=serve)
             t.start()
             # Client wait until server setup and perform a connect.
             evt.wait()
             client = context.wrap_socket(socket.socket())
             client.connect((host, port))
+            client.send(b'data')
+            client.recv()
             client_addr = client.getsockname()
             client.close()
             t.join()

Misc/NEWS.d/next/Library/2018-08-14-08-57-01.bpo-32947.mqStVW.rst

@@ -0,0 +1,2 @@
+Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround for TLSv1.3 for future
+compatibility with OpenSSL 1.1.1.

Modules/_ssl.c

@@ -5486,6 +5486,10 @@ PyInit__ssl(void)
     PyModule_AddIntConstant(m, "OP_NO_COMPRESSION",
                             SSL_OP_NO_COMPRESSION);
 #endif
+#ifdef SSL_OP_ENABLE_MIDDLEBOX_COMPAT
+    PyModule_AddIntConstant(m, "OP_ENABLE_MIDDLEBOX_COMPAT",
+                            SSL_OP_ENABLE_MIDDLEBOX_COMPAT);
+#endif
 
 #if HAVE_SNI
     r = Py_True;