bpo-43577: Fix deadlock with SSLContext._msg_callback and sni_callback (GH-24957)

tiran · web-flow · commit 77cde5042a2f · 2021-03-21T16:13:09.000+01:00
OpenSSL copies the internal message callback from SSL_CTX-&gt;msg_callback to
SSL-&gt;msg_callback. SSL_set_SSL_CTX() does not update SSL-&gt;msg_callback
to use the callback value of the new context.

PySSL_set_context() now resets the callback and _PySSL_msg_callback()
resets thread state in error path.

Signed-off-by: Christian Heimes &lt;christian@python.org&gt;
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
@@ -4764,6 +4764,28 @@ def msg_cb(conn, direction, version, content_type, msg_type, data):
             msg
         )
 
+    def test_msg_callback_deadlock_bpo43577(self):
+        client_context, server_context, hostname = testing_context()
+        server_context2 = testing_context()[1]
+
+        def msg_cb(conn, direction, version, content_type, msg_type, data):
+            pass
+
+        def sni_cb(sock, servername, ctx):
+            sock.context = server_context2
+
+        server_context._msg_callback = msg_cb
+        server_context.sni_callback = sni_cb
+
+        server = ThreadedEchoServer(context=server_context, chatty=False)
+        with server:
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+            with client_context.wrap_socket(socket.socket(),
+                                            server_hostname=hostname) as s:
+                s.connect((HOST, server.port))
+
 
 def test_main(verbose=False):
     if support.verbose:
diff --git a/Misc/NEWS.d/next/Library/2021-03-21-10-13-17.bpo-43577.m7JnAV.rst b/Misc/NEWS.d/next/Library/2021-03-21-10-13-17.bpo-43577.m7JnAV.rst
@@ -0,0 +1 @@
+Fix deadlock when using :class:`ssl.SSLContext` debug callback with :meth:`ssl.SSLContext.sni_callback`.
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
@@ -2202,6 +2202,11 @@ static int PySSL_set_context(PySSLSocket *self, PyObject *value,
         Py_INCREF(value);
         Py_SETREF(self->ctx, (PySSLContext *)value);
         SSL_set_SSL_CTX(self->ssl, self->ctx->ctx);
+        /* Set SSL* internal msg_callback to state of new context's state */
+        SSL_set_msg_callback(
+            self->ssl,
+            self->ctx->msg_cb ? _PySSL_msg_callback : NULL
+        );
 #endif
     } else {
         PyErr_SetString(PyExc_TypeError, "The value must be a SSLContext");
diff --git a/Modules/_ssl/debughelpers.c b/Modules/_ssl/debughelpers.c
@@ -23,6 +23,7 @@ _PySSL_msg_callback(int write_p, int version, int content_type,
     ssl_obj = (PySSLSocket *)SSL_get_app_data(ssl);
     assert(PySSLSocket_Check(ssl_obj));
     if (ssl_obj->ctx->msg_cb == NULL) {
+        PyGILState_Release(threadstate);
         return;
     }
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix deadlock when using :class:`ssl.SSLContext` debug callback with :meth:`ssl.SSLContext.sni_callback`.
Original file line number	Diff line number	Diff line change
`@@ -23,6 +23,7 @@ _PySSL_msg_callback(int write_p, int version, int content_type,`
`23`	`23`	`ssl_obj = (PySSLSocket *)SSL_get_app_data(ssl);`
`24`	`24`	`assert(PySSLSocket_Check(ssl_obj));`
`25`	`25`	`if (ssl_obj->ctx->msg_cb == NULL) {`
	`26`	`+ PyGILState_Release(threadstate);`
`26`	`27`	`return;`
`27`	`28`	`}`
`28`	`29`