342 lines
15 KiB
Diff
342 lines
15 KiB
Diff
From f0c1e55dfd28970196768a6997a6dc0eab0f5259 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?=C5=81ukasz=20Langa?= <lukasz@langa.pl>
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Date: Tue, 22 Aug 2023 17:39:17 +0200
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Subject: [PATCH] gh-108310: Fix CVE-2023-40217: Check for & avoid the ssl
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pre-close flaw
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Instances of `ssl.SSLSocket` were vulnerable to a bypass of the TLS handshake
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and included protections (like certificate verification) and treating sent
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unencrypted data as if it were post-handshake TLS encrypted data.
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The vulnerability is caused when a socket is connected, data is sent by the
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malicious peer and stored in a buffer, and then the malicious peer closes the
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socket within a small timing window before the other peers’ TLS handshake can
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begin. After this sequence of events the closed socket will not immediately
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attempt a TLS handshake due to not being connected but will also allow the
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buffered data to be read as if a successful TLS handshake had occurred.
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Co-Authored-By: Gregory P. Smith [Google LLC] <greg@krypto.org>
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---
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Lib/ssl.py | 31 ++-
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Lib/test/test_ssl.py | 215 ++++++++++++++++++
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...-08-22-17-39-12.gh-issue-108310.fVM3sg.rst | 7 +
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3 files changed, 252 insertions(+), 1 deletion(-)
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create mode 100644 Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst
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Index: Python-3.6.15/Lib/ssl.py
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===================================================================
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--- Python-3.6.15.orig/Lib/ssl.py
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+++ Python-3.6.15/Lib/ssl.py
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@@ -771,6 +771,8 @@ class SSLSocket(socket):
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"client mode")
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if self._context.check_hostname and not server_hostname:
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raise ValueError("check_hostname requires server_hostname")
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+ self._closed = False
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+ self._sslobj = None
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self._session = _session
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self.server_side = server_side
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self.server_hostname = server_hostname
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@@ -782,7 +784,7 @@ class SSLSocket(socket):
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type=sock.type,
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proto=sock.proto,
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fileno=sock.fileno())
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- self.settimeout(sock.gettimeout())
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+ sock_timeout = sock.gettimeout()
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sock.detach()
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elif fileno is not None:
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socket.__init__(self, fileno=fileno)
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@@ -796,11 +798,38 @@ class SSLSocket(socket):
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if e.errno != errno.ENOTCONN:
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raise
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connected = False
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+ blocking = self.gettimeout() == 0
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+ self.setblocking(False)
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+ try:
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+ # We are not connected so this is not supposed to block, but
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+ # testing revealed otherwise on macOS and Windows so we do
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+ # the non-blocking dance regardless. Our raise when any data
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+ # is found means consuming the data is harmless.
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+ notconn_pre_handshake_data = self.recv(1)
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+ except OSError as e:
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+ # EINVAL occurs for recv(1) on non-connected on unix sockets.
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+ if e.errno not in (errno.ENOTCONN, errno.EINVAL):
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+ raise
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+ notconn_pre_handshake_data = b''
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+ self.setblocking(blocking)
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+ if notconn_pre_handshake_data:
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+ # This prevents pending data sent to the socket before it was
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+ # closed from escaping to the caller who could otherwise
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+ # presume it came through a successful TLS connection.
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+ reason = "Closed before TLS handshake with data in recv buffer."
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+ notconn_pre_handshake_data_error = SSLError(e.errno, reason)
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+ # Add the SSLError attributes that _ssl.c always adds.
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+ notconn_pre_handshake_data_error.reason = reason
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+ notconn_pre_handshake_data_error.library = None
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+ try:
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+ self.close()
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+ except OSError:
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+ pass
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+ raise notconn_pre_handshake_data_error
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else:
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connected = True
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- self._closed = False
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- self._sslobj = None
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+ self.settimeout(sock_timeout) # Must come after setblocking() calls.
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self._connected = connected
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if connected:
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# create the SSL object
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Index: Python-3.6.15/Lib/test/test_ssl.py
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===================================================================
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--- Python-3.6.15.orig/Lib/test/test_ssl.py
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+++ Python-3.6.15/Lib/test/test_ssl.py
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@@ -3,11 +3,14 @@
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import sys
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import unittest
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from test import support
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+import re
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import socket
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import select
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+import struct
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import time
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import datetime
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import gc
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+import http.client
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import os
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import errno
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import pprint
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@@ -3918,6 +3921,218 @@ class TestPostHandshakeAuth(unittest.Tes
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self.assertIn(b'WRONG_SSL_VERSION', s.recv(1024))
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+def set_socket_so_linger_on_with_zero_timeout(sock):
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+ sock.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack('ii', 1, 0))
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+
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+
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+class TestPreHandshakeClose(unittest.TestCase):
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+ """Verify behavior of close sockets with received data before to the handshake.
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+ """
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+
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+ class SingleConnectionTestServerThread(threading.Thread):
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+
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+ def __init__(self, *, name, call_after_accept):
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+ self.call_after_accept = call_after_accept
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+ self.received_data = b'' # set by .run()
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+ self.wrap_error = None # set by .run()
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+ self.listener = None # set by .start()
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+ self.port = None # set by .start()
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+ super().__init__(name=name)
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+
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+ def __enter__(self):
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+ self.start()
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+ return self
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+
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+ def __exit__(self, *args):
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+ try:
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+ if self.listener:
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+ self.listener.close()
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+ except OSError:
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+ pass
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+ self.join()
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+ self.wrap_error = None # avoid dangling references
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+
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+ def start(self):
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+ self.ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
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+ self.ssl_ctx.verify_mode = ssl.CERT_REQUIRED
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+ self.ssl_ctx.load_verify_locations(cafile=ONLYCERT)
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+ self.ssl_ctx.load_cert_chain(certfile=ONLYCERT, keyfile=ONLYKEY)
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+ self.listener = socket.socket()
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+ self.port = support.bind_port(self.listener)
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+ self.listener.settimeout(2.0)
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+ self.listener.listen(1)
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+ super().start()
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+
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+ def run(self):
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+ conn, address = self.listener.accept()
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+ self.listener.close()
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+ with conn:
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+ if self.call_after_accept(conn):
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+ return
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+ try:
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+ tls_socket = self.ssl_ctx.wrap_socket(conn, server_side=True)
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+ except OSError as err: # ssl.SSLError inherits from OSError
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+ self.wrap_error = err
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+ else:
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+ try:
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+ self.received_data = tls_socket.recv(400)
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+ except OSError:
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+ pass # closed, protocol error, etc.
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+
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+ def non_linux_skip_if_other_okay_error(self, err):
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+ if sys.platform == "linux":
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+ return # Expect the full test setup to always work on Linux.
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+ if (isinstance(err, ConnectionResetError) or
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+ (isinstance(err, OSError) and err.errno == errno.EINVAL) or
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+ re.search('wrong.version.number', getattr(err, "reason", ""), re.I)):
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+ # On Windows the TCP RST leads to a ConnectionResetError
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+ # (ECONNRESET) which Linux doesn't appear to surface to userspace.
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+ # If wrap_socket() winds up on the "if connected:" path and doing
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+ # the actual wrapping... we get an SSLError from OpenSSL. Typically
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+ # WRONG_VERSION_NUMBER. While appropriate, neither is the scenario
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+ # we're specifically trying to test. The way this test is written
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+ # is known to work on Linux. We'll skip it anywhere else that it
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+ # does not present as doing so.
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+ self.skipTest(f"Could not recreate conditions on {sys.platform}:"
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+ f" {err}")
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+ # If maintaining this conditional winds up being a problem.
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+ # just turn this into an unconditional skip anything but Linux.
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+ # The important thing is that our CI has the logic covered.
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+
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+ def test_preauth_data_to_tls_server(self):
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+ server_accept_called = threading.Event()
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+ ready_for_server_wrap_socket = threading.Event()
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+
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+ def call_after_accept(unused):
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+ server_accept_called.set()
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+ if not ready_for_server_wrap_socket.wait(2.0):
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+ raise RuntimeError("wrap_socket event never set, test may fail.")
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+ return False # Tell the server thread to continue.
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+
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+ server = self.SingleConnectionTestServerThread(
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+ call_after_accept=call_after_accept,
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+ name="preauth_data_to_tls_server")
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+ server.__enter__() # starts it
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+ self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it.
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+
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+ with socket.socket() as client:
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+ client.connect(server.listener.getsockname())
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+ # This forces an immediate connection close via RST on .close().
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+ set_socket_so_linger_on_with_zero_timeout(client)
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+ client.setblocking(False)
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+
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+ server_accept_called.wait()
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+ client.send(b"DELETE /data HTTP/1.0\r\n\r\n")
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+ client.close() # RST
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+
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+ ready_for_server_wrap_socket.set()
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+ server.join()
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+ wrap_error = server.wrap_error
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+ self.assertEqual(b"", server.received_data)
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+ self.assertIsInstance(wrap_error, OSError) # All platforms.
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+ self.non_linux_skip_if_other_okay_error(wrap_error)
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+ self.assertIsInstance(wrap_error, ssl.SSLError)
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+ self.assertIn("before TLS handshake with data", wrap_error.args[1])
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+ self.assertIn("before TLS handshake with data", wrap_error.reason)
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+ self.assertNotEqual(0, wrap_error.args[0])
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+ self.assertIsNone(wrap_error.library, msg="attr must exist")
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+
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+ def test_preauth_data_to_tls_client(self):
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+ client_can_continue_with_wrap_socket = threading.Event()
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+
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+ def call_after_accept(conn_to_client):
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+ # This forces an immediate connection close via RST on .close().
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+ set_socket_so_linger_on_with_zero_timeout(conn_to_client)
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+ conn_to_client.send(
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+ b"HTTP/1.0 307 Temporary Redirect\r\n"
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+ b"Location: https://example.com/someone-elses-server\r\n"
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+ b"\r\n")
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+ conn_to_client.close() # RST
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+ client_can_continue_with_wrap_socket.set()
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+ return True # Tell the server to stop.
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+
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+ server = self.SingleConnectionTestServerThread(
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+ call_after_accept=call_after_accept,
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+ name="preauth_data_to_tls_client")
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+ server.__enter__() # starts it
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+ self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it.
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+
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+ # Redundant; call_after_accept sets SO_LINGER on the accepted conn.
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+ set_socket_so_linger_on_with_zero_timeout(server.listener)
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+
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+ with socket.socket() as client:
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+ client.connect(server.listener.getsockname())
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+ if not client_can_continue_with_wrap_socket.wait(2.0):
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+ self.fail("test server took too long.")
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+ ssl_ctx = ssl.create_default_context()
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+ try:
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+ tls_client = ssl_ctx.wrap_socket(
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+ client, server_hostname="localhost")
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+ except OSError as err: # SSLError inherits from OSError
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+ wrap_error = err
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+ received_data = b""
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+ else:
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+ wrap_error = None
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+ received_data = tls_client.recv(400)
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+ tls_client.close()
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+
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+ server.join()
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+ self.assertEqual(b"", received_data)
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+ self.assertIsInstance(wrap_error, OSError) # All platforms.
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+ self.non_linux_skip_if_other_okay_error(wrap_error)
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+ self.assertIsInstance(wrap_error, ssl.SSLError)
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+ self.assertIn("before TLS handshake with data", wrap_error.args[1])
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+ self.assertIn("before TLS handshake with data", wrap_error.reason)
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+ self.assertNotEqual(0, wrap_error.args[0])
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+ self.assertIsNone(wrap_error.library, msg="attr must exist")
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+
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+ def test_https_client_non_tls_response_ignored(self):
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+
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+ server_responding = threading.Event()
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+
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+ class SynchronizedHTTPSConnection(http.client.HTTPSConnection):
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+ def connect(self):
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+ http.client.HTTPConnection.connect(self)
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+ # Wait for our fault injection server to have done its thing.
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+ if not server_responding.wait(1.0) and support.verbose:
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+ sys.stdout.write("server_responding event never set.")
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+ self.sock = self._context.wrap_socket(
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+ self.sock, server_hostname=self.host)
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+
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+ def call_after_accept(conn_to_client):
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+ # This forces an immediate connection close via RST on .close().
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+ set_socket_so_linger_on_with_zero_timeout(conn_to_client)
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+ conn_to_client.send(
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+ b"HTTP/1.0 402 Payment Required\r\n"
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+ b"\r\n")
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+ conn_to_client.close() # RST
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+ server_responding.set()
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+ return True # Tell the server to stop.
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+
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+ server = self.SingleConnectionTestServerThread(
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+ call_after_accept=call_after_accept,
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+ name="non_tls_http_RST_responder")
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+ server.__enter__() # starts it
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+ self.addCleanup(server.__exit__) # ... & unittest.TestCase stops it.
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+ # Redundant; call_after_accept sets SO_LINGER on the accepted conn.
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+ set_socket_so_linger_on_with_zero_timeout(server.listener)
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+
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+ connection = SynchronizedHTTPSConnection(
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+ f"localhost",
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+ port=server.port,
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+ context=ssl.create_default_context(),
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+ timeout=2.0,
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+ )
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+ # There are lots of reasons this raises as desired, long before this
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+ # test was added. Sending the request requires a successful TLS wrapped
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+ # socket; that fails if the connection is broken. It may seem pointless
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+ # to test this. It serves as an illustration of something that we never
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+ # want to happen... properly not happening.
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+ with self.assertRaises(OSError) as err_ctx:
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+ connection.request("HEAD", "/test", headers={"Host": "localhost"})
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+ response = connection.getresponse()
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+
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+
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def test_main(verbose=False):
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if support.verbose:
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import warnings
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Index: Python-3.6.15/Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst
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===================================================================
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--- /dev/null
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+++ Python-3.6.15/Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst
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@@ -0,0 +1,7 @@
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+Fixed an issue where instances of :class:`ssl.SSLSocket` were vulnerable to
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+a bypass of the TLS handshake and included protections (like certificate
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+verification) and treating sent unencrypted data as if it were
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+post-handshake TLS encrypted data. Security issue reported as
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+`CVE-2023-40217
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+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-40217>`_ by
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+Aapo Oksman. Patch by Gregory P. Smith.
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