[2.7] bpo-32947: Fixes for TLS 1.3 and OpenSSL 1.1.1 (GH-8761) (GH-11876)

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 <christian@python.org>
(cherry picked from commit 2a4ee8aa01d61b6a9c8e9c65c211e61bdb471826)

Doc/library/ssl.rst

@@ -742,6 +742,15 @@ Constants
 
    .. versionadded:: 2.7.9
 
+.. 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:: 2.7.16
+
 .. data:: OP_NO_COMPRESSION
 
    Disable compression on the SSL channel.  This is useful if the application

Lib/test/test_ssl.py

@@ -82,6 +82,7 @@ OP_NO_COMPRESSION = getattr(ssl, "OP_NO_COMPRESSION", 0)
 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):
@@ -806,7 +807,8 @@ class ContextTests(unittest.TestCase):
         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)
@@ -1697,11 +1699,31 @@ else:
                         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 socket.error as e:
+                except (ssl.SSLError, socket.error, OSError) as e:
+                    if e.errno in (errno.ECONNRESET, errno.EPIPE, errno.ESHUTDOWN):
+                        # Mimick Python 3:
+                        #
+                        #    except (ConnectionResetError, BrokenPipeError):
+                        #
                         # 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
+                    else:
+                        # OSError may occur with wrong protocols, e.g. both
+                        # sides use PROTOCOL_TLS_SERVER.
+                        #
                         # XXX Various errors can have happened here, for example
                         # a mismatching protocol version, an invalid certificate,
                         # or a low-level bug. This should be made more discriminating.
@@ -2769,7 +2791,7 @@ else:
                 # Block on the accept and wait on the connection to close.
                 evt.set()
                 remote[0], peer[0] = server.accept()
-                remote[0].recv(1)
+                remote[0].send(remote[0].recv(4))
 
             t = threading.Thread(target=serve)
             t.start()
@@ -2777,6 +2799,8 @@ else:
             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

+Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround for TLSv1.3 for future
+compatibility with OpenSSL 1.1.1.

Modules/_ssl.c

@@ -4411,6 +4411,10 @@ init_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;