CVE-2023-40217.patch

From 0cb0c238d520a8718e313b52cffc356a5a7561bf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Langa?= <lukasz@langa.pl>
Date: Tue, 22 Aug 2023 19:53:15 +0200
Subject: [PATCH] gh-108310: Fix CVE-2023-40217: Check for & avoid the ssl
 pre-close flaw (#108315)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Instances of `ssl.SSLSocket` were vulnerable to a bypass of the TLS handshake
and included protections (like certificate verification) and treating sent
unencrypted data as if it were post-handshake TLS encrypted data.

The vulnerability is caused when a socket is connected, data is sent by the
malicious peer and stored in a buffer, and then the malicious peer closes the
socket within a small timing window before the other peers’ TLS handshake can
begin. After this sequence of events the closed socket will not immediately
attempt a TLS handshake due to not being connected but will also allow the
buffered data to be read as if a successful TLS handshake had occurred.

Co-authored-by: Gregory P. Smith [Google LLC] <greg@krypto.org>
---
 Lib/ssl.py                                    |  31 ++-
 Lib/test/test_ssl.py                          | 211 ++++++++++++++++++
 ...-08-22-17-39-12.gh-issue-108310.fVM3sg.rst |   7 +
 3 files changed, 248 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Security/2023-08-22-17-39-12.gh-issue-108310.fVM3sg.rst

From 64f99350351bc46e016b2286f36ba7cd669b79e3 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 23 Aug 2023 07:26:01 +0200
Subject: [PATCH] gh-108342: Break ref cycle in SSLSocket._create() exc
 (#108344)

Explicitly break a reference cycle when SSLSocket._create() raises an
exception. Clear the variable storing the exception, since the
exception traceback contains the variables and so creates a reference
cycle.

This test leak was introduced by the test added for the fix of #108310.
---
 Lib/ssl.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Backport:
 * ssl.py:
   * There is no socket.getblocking. In the connected case, we do not retain the
     timeout, because #8524 was never fixed on Python 2.7. In the disconnected
     case, we have to modify the timeout and therefore restore it.
   * Cannot use self.recv in c'tor, because it would access self._sslobj
   * socket.socket raises socket.error rather than OSError
 * test_ssl.py:
   * Merge imports
   * Inline socket_helper.bind_port
   * Delete non_linux_skip_if_other_okay_error: This backport is Linux-only
   * socket.socket isn't a ContextManager yet
   * http.client -> httplib
   * Implement assertRaises
   * Remove use of keyword-only arguments
   * Do not use f"strings"
 * Drop Misc/NEWS.d

diff --git a/Lib/ssl.py b/Lib/ssl.py
index 1d58737264..ff363c75e7 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -994,6 +994,38 @@ def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
             if e.errno != errno.ENOTCONN:
                 raise
             connected = False
+            sock_timeout = self.gettimeout()
+            self.settimeout(0)
+            try:
+                # We are not connected so this is not supposed to block, but
+                # testing revealed otherwise on macOS and Windows so we do
+                # the non-blocking dance regardless. Our raise when any data
+                # is found means consuming the data is harmless.
+                notconn_pre_handshake_data = self._sock.recv(1)
+            except socket_error as e:
+                # EINVAL occurs for recv(1) on non-connected on unix sockets.
+                if e.errno not in (errno.ENOTCONN, errno.EINVAL):
+                    raise
+                notconn_pre_handshake_data = b''
+            self.settimeout(sock_timeout)
+            if notconn_pre_handshake_data:
+                # This prevents pending data sent to the socket before it was
+                # closed from escaping to the caller who could otherwise
+                # presume it came through a successful TLS connection.
+                reason = "Closed before TLS handshake with data in recv buffer."
+                notconn_pre_handshake_data_error = SSLError(e.errno, reason)
+                # Add the SSLError attributes that _ssl.c always adds.
+                notconn_pre_handshake_data_error.reason = reason
+                notconn_pre_handshake_data_error.library = None
+                try:
+                    self.close()
+                except socket_error:
+                    pass
+                try:
+                    raise notconn_pre_handshake_data_error
+                finally:
+                    # Explicitly break the reference cycle.
+                    notconn_pre_handshake_data_error = None
         else:
             connected = True
 
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 6117ca3fdb..ad5377ec05 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -10,9 +10,11 @@
 import asyncore
 import socket
 import select
+import struct
 import time
 import datetime
 import gc
+import httplib
 import os
 import errno
 import pprint
@@ -4659,5 +4662,196 @@ def sni_cb(sock, servername, ctx):
         if _have_threads:
             support.threading_cleanup(*thread_info)
 
+def set_socket_so_linger_on_with_zero_timeout(sock):
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack('ii', 1, 0))
+
+
+class TestPreHandshakeClose(unittest.TestCase):
+    """Verify behavior of close sockets with received data before to the handshake.
+    """
+
+    class SingleConnectionTestServerThread(threading.Thread):
+
+        def __init__(self, name, call_after_accept):
+            self.call_after_accept = call_after_accept
+            self.received_data = b''  # set by .run()
+            self.wrap_error = None  # set by .run()
+            self.listener = None  # set by .start()
+            self.port = None  # set by .start()
+            super().__init__(name=name)
+
+        def __enter__(self):
+            self.start()
+            return self
+
+        def __exit__(self, *args):
+            try:
+                if self.listener:
+                    self.listener.close()
+            except OSError:
+                pass
+            self.join()
+            self.wrap_error = None  # avoid dangling references
+
+        def start(self):
+            self.ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
+            self.ssl_ctx.verify_mode = ssl.CERT_REQUIRED
+            self.ssl_ctx.load_verify_locations(cafile=ONLYCERT)
+            self.ssl_ctx.load_cert_chain(certfile=ONLYCERT, keyfile=ONLYKEY)
+            self.listener = socket.socket()
+            self.listener.bind((None, 0))
+            self.port = self.listener.getsockname()[1]
+            self.listener.settimeout(2.0)
+            self.listener.listen(1)
+            super().start()
+
+        def run(self):
+            conn, address = self.listener.accept()
+            self.listener.close()
+            with conn:
+                if self.call_after_accept(conn):
+                    return
+                try:
+                    tls_socket = self.ssl_ctx.wrap_socket(conn, server_side=True)
+                except OSError as err:  # ssl.SSLError inherits from OSError
+                    self.wrap_error = err
+                else:
+                    try:
+                        self.received_data = tls_socket.recv(400)
+                    except OSError:
+                        pass  # closed, protocol error, etc.
+
+    def test_preauth_data_to_tls_server(self):
+        server_accept_called = threading.Event()
+        ready_for_server_wrap_socket = threading.Event()
+
+        def call_after_accept(unused):
+            server_accept_called.set()
+            if not ready_for_server_wrap_socket.wait(2.0):
+                raise RuntimeError("wrap_socket event never set, test may fail.")
+            return False  # Tell the server thread to continue.
+
+        server = self.SingleConnectionTestServerThread(
+                call_after_accept=call_after_accept,
+                name="preauth_data_to_tls_server")
+        self.enterContext(server)  # starts it & unittest.TestCase stops it.
+
+        with closing(socket.socket()) as client:
+            client.connect(server.listener.getsockname())
+            # This forces an immediate connection close via RST on .close().
+            set_socket_so_linger_on_with_zero_timeout(client)
+            client.setblocking(False)
+
+            server_accept_called.wait()
+            client.send(b"DELETE /data HTTP/1.0\r\n\r\n")
+            client.close()  # RST
+
+        ready_for_server_wrap_socket.set()
+        server.join()
+        wrap_error = server.wrap_error
+        self.assertEqual(b"", server.received_data)
+        self.assertIsInstance(wrap_error, OSError)  # All platforms.
+        self.assertIsInstance(wrap_error, ssl.SSLError)
+        self.assertIn("before TLS handshake with data", wrap_error.args[1])
+        self.assertIn("before TLS handshake with data", wrap_error.reason)
+        self.assertNotEqual(0, wrap_error.args[0])
+        self.assertIsNone(wrap_error.library, msg="attr must exist")
+
+    def test_preauth_data_to_tls_client(self):
+        client_can_continue_with_wrap_socket = threading.Event()
+
+        def call_after_accept(conn_to_client):
+            # This forces an immediate connection close via RST on .close().
+            set_socket_so_linger_on_with_zero_timeout(conn_to_client)
+            conn_to_client.send(
+                    b"HTTP/1.0 307 Temporary Redirect\r\n"
+                    b"Location: https://example.com/someone-elses-server\r\n"
+                    b"\r\n")
+            conn_to_client.close()  # RST
+            client_can_continue_with_wrap_socket.set()
+            return True  # Tell the server to stop.
+
+        server = self.SingleConnectionTestServerThread(
+                call_after_accept=call_after_accept,
+                name="preauth_data_to_tls_client")
+        self.enterContext(server)  # starts it & unittest.TestCase stops it.
+        # Redundant; call_after_accept sets SO_LINGER on the accepted conn.
+        set_socket_so_linger_on_with_zero_timeout(server.listener)
+
+        with closing(socket.socket()) as client:
+            client.connect(server.listener.getsockname())
+            if not client_can_continue_with_wrap_socket.wait(2.0):
+                self.fail("test server took too long.")
+            ssl_ctx = ssl.create_default_context()
+            try:
+                tls_client = ssl_ctx.wrap_socket(
+                        client, server_hostname="localhost")
+            except OSError as err:  # SSLError inherits from OSError
+                wrap_error = err
+                received_data = b""
+            else:
+                wrap_error = None
+                received_data = tls_client.recv(400)
+                tls_client.close()
+
+        server.join()
+        self.assertEqual(b"", received_data)
+        self.assertIsInstance(wrap_error, OSError)  # All platforms.
+        self.assertIsInstance(wrap_error, ssl.SSLError)
+        self.assertIn("before TLS handshake with data", wrap_error.args[1])
+        self.assertIn("before TLS handshake with data", wrap_error.reason)
+        self.assertNotEqual(0, wrap_error.args[0])
+        self.assertIsNone(wrap_error.library, msg="attr must exist")
+
+    def test_https_client_non_tls_response_ignored(self):
+
+        server_responding = threading.Event()
+
+        class SynchronizedHTTPSConnection(httplib.HTTPSConnection):
+            def connect(self):
+                httplib.HTTPConnection.connect(self)
+                # Wait for our fault injection server to have done its thing.
+                if not server_responding.wait(1.0) and support.verbose:
+                    sys.stdout.write("server_responding event never set.")
+                self.sock = self._context.wrap_socket(
+                        self.sock, server_hostname=self.host)
+
+        def call_after_accept(conn_to_client):
+            # This forces an immediate connection close via RST on .close().
+            set_socket_so_linger_on_with_zero_timeout(conn_to_client)
+            conn_to_client.send(
+                    b"HTTP/1.0 402 Payment Required\r\n"
+                    b"\r\n")
+            conn_to_client.close()  # RST
+            server_responding.set()
+            return True  # Tell the server to stop.
+
+        server = self.SingleConnectionTestServerThread(
+                call_after_accept=call_after_accept,
+                name="non_tls_http_RST_responder")
+        self.enterContext(server)  # starts it & unittest.TestCase stops it.
+        # Redundant; call_after_accept sets SO_LINGER on the accepted conn.
+        set_socket_so_linger_on_with_zero_timeout(server.listener)
+
+        connection = SynchronizedHTTPSConnection(
+                "localhost",
+                port=server.port,
+                context=ssl.create_default_context(),
+                timeout=2.0,
+        )
+        # There are lots of reasons this raises as desired, long before this
+        # test was added. Sending the request requires a successful TLS wrapped
+        # socket; that fails if the connection is broken. It may seem pointless
+        # to test this. It serves as an illustration of something that we never
+        # want to happen... properly not happening.
+        try:
+            connection.request("HEAD", "/test", headers={"Host": "localhost"})
+            response = connection.getresponse()
+        except OSError:
+            pass
+        else:
+            self.fail("http request did not raise OSError")
+
+
 if __name__ == "__main__":
     test_main()
-- 
2.40.1