gh-142516: fix reference leaks in ssl.SSLContext objects (#143685)

Lib/test/test_ssl.py

@@ -57,6 +57,16 @@
 CAN_GET_SELECTED_OPENSSL_SIGALG = ssl.OPENSSL_VERSION_INFO >= (3, 5)
 PY_SSL_DEFAULT_CIPHERS = sysconfig.get_config_var('PY_SSL_DEFAULT_CIPHERS')
 
+HAS_KEYLOG = hasattr(ssl.SSLContext, 'keylog_filename')
+requires_keylog = unittest.skipUnless(
+    HAS_KEYLOG, 'test requires OpenSSL 1.1.1 with keylog callback')
+CAN_SET_KEYLOG = HAS_KEYLOG and os.name != "nt"
+requires_keylog_setter = unittest.skipUnless(
+    CAN_SET_KEYLOG,
+    "cannot set 'keylog_filename' on Windows"
+)
+
+
 PROTOCOL_TO_TLS_VERSION = {}
 for proto, ver in (
     ("PROTOCOL_SSLv3", "SSLv3"),
@@ -266,34 +276,69 @@ def utc_offset(): #NOTE: ignore issues like #1647654
 )
 
 
-def test_wrap_socket(sock, *,
-                     cert_reqs=ssl.CERT_NONE, ca_certs=None,
-                     ciphers=None, ciphersuites=None,
-                     min_version=None, max_version=None,
-                     certfile=None, keyfile=None,
-                     **kwargs):
-    if not kwargs.get("server_side"):
-        kwargs["server_hostname"] = SIGNED_CERTFILE_HOSTNAME
-        context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
-    else:
+def make_test_context(
+    *,
+    server_side=False,
+    check_hostname=None,
+    cert_reqs=ssl.CERT_NONE,
+    ca_certs=None, certfile=None, keyfile=None,
+    ciphers=None, ciphersuites=None,
+    min_version=None, max_version=None,
+):
+    if server_side:
         context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
-    if cert_reqs is not None:
+    else:
+        context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+
+    if check_hostname is None:
         if cert_reqs == ssl.CERT_NONE:
             context.check_hostname = False
+    else:
+        context.check_hostname = check_hostname
+
+    if cert_reqs is not None:
         context.verify_mode = cert_reqs
+
     if ca_certs is not None:
         context.load_verify_locations(ca_certs)
     if certfile is not None or keyfile is not None:
         context.load_cert_chain(certfile, keyfile)
+
     if ciphers is not None:
         context.set_ciphers(ciphers)
     if ciphersuites is not None:
         context.set_ciphersuites(ciphersuites)
+
     if min_version is not None:
         context.minimum_version = min_version
     if max_version is not None:
         context.maximum_version = max_version
-    return context.wrap_socket(sock, **kwargs)
+
+    return context
+
+
+def test_wrap_socket(
+    sock,
+    *,
+    server_side=False,
+    check_hostname=None,
+    cert_reqs=ssl.CERT_NONE,
+    ca_certs=None, certfile=None, keyfile=None,
+    ciphers=None, ciphersuites=None,
+    min_version=None, max_version=None,
+    **kwargs,
+):
+    context = make_test_context(
+        server_side=server_side,
+        check_hostname=check_hostname,
+        cert_reqs=cert_reqs,
+        ca_certs=ca_certs, certfile=certfile, keyfile=keyfile,
+        ciphers=ciphers, ciphersuites=ciphersuites,
+        min_version=min_version, max_version=max_version,
+    )
+    if not server_side:
+        kwargs.setdefault("server_hostname", SIGNED_CERTFILE_HOSTNAME)
+    return context.wrap_socket(sock, server_side=server_side, **kwargs)
 
 
 USE_SAME_TEST_CONTEXT = False
@@ -1741,6 +1786,39 @@ def test_num_tickest(self):
         with self.assertRaises(ValueError):
             ctx.num_tickets = 1
 
+    @support.cpython_only
+    def test_refcycle_msg_callback(self):
+        # See https://github.com/python/cpython/issues/142516.
+        ctx = make_test_context()
+        def msg_callback(*args, _=ctx, **kwargs): ...
+        ctx._msg_callback = msg_callback
+
+    @support.cpython_only
+    @requires_keylog_setter
+    def test_refcycle_keylog_filename(self):
+        # See https://github.com/python/cpython/issues/142516.
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+        ctx = make_test_context()
+        class KeylogFilename(str): ...
+        ctx.keylog_filename = KeylogFilename(os_helper.TESTFN)
+        ctx.keylog_filename._ = ctx
+
+    @support.cpython_only
+    @unittest.skipUnless(ssl.HAS_PSK, 'requires TLS-PSK')
+    def test_refcycle_psk_client_callback(self):
+        # See https://github.com/python/cpython/issues/142516.
+        ctx = make_test_context()
+        def psk_client_callback(*args, _=ctx, **kwargs): ...
+        ctx.set_psk_client_callback(psk_client_callback)
+
+    @support.cpython_only
+    @unittest.skipUnless(ssl.HAS_PSK, 'requires TLS-PSK')
+    def test_refcycle_psk_server_callback(self):
+        # See https://github.com/python/cpython/issues/142516.
+        ctx = make_test_context(server_side=True)
+        def psk_server_callback(*args, _=ctx, **kwargs): ...
+        ctx.set_psk_server_callback(psk_server_callback)
+
 
 class SSLErrorTests(unittest.TestCase):
 
@@ -5174,10 +5252,6 @@ def test_internal_chain_server(self):
                 self.assertEqual(res, b'\x02\n')
 
 
-HAS_KEYLOG = hasattr(ssl.SSLContext, 'keylog_filename')
-requires_keylog = unittest.skipUnless(
-    HAS_KEYLOG, 'test requires OpenSSL 1.1.1 with keylog callback')
-
 class TestSSLDebug(unittest.TestCase):
 
     def keylog_lines(self, fname=os_helper.TESTFN):

Misc/NEWS.d/next/Library/2026-01-11-13-03-32.gh-issue-142516.u7An-s.rst

@@ -0,0 +1,2 @@
+:mod:`ssl`: fix reference leaks in :class:`ssl.SSLContext` objects. Patch by
+Bénédikt Tran.

Modules/_ssl.c

@@ -331,7 +331,7 @@ typedef struct {
     int post_handshake_auth;
 #endif
     PyObject *msg_cb;
-    PyObject *keylog_filename;
+    PyObject *keylog_filename;  // can be anything accepted by Py_fopen()
     BIO *keylog_bio;
     /* Cached module state, also used in SSLSocket and SSLSession code. */
     _sslmodulestate *state;
@@ -361,7 +361,7 @@ typedef struct {
     PySSLContext *ctx; /* weakref to SSL context */
     char shutdown_seen_zero;
     enum py_ssl_server_or_client socket_type;
-    PyObject *owner; /* Python level "owner" passed to servername callback */
+    PyObject *owner; /* weakref to Python level "owner" passed to servername callback */
     PyObject *server_hostname;
 } PySSLSocket;
 
@@ -2436,6 +2436,17 @@ PySSL_traverse(PyObject *op, visitproc visit, void *arg)
     return 0;
 }
 
+static int
+PySSL_clear(PyObject *op)
+{
+    PySSLSocket *self = PySSLSocket_CAST(op);
+    Py_CLEAR(self->Socket);
+    Py_CLEAR(self->ctx);
+    Py_CLEAR(self->owner);
+    Py_CLEAR(self->server_hostname);
+    return 0;
+}
+
 static void
 PySSL_dealloc(PyObject *op)
 {
@@ -2456,10 +2467,7 @@ PySSL_dealloc(PyObject *op)
         SSL_set_shutdown(self->ssl, SSL_SENT_SHUTDOWN | SSL_get_shutdown(self->ssl));
         SSL_free(self->ssl);
     }
-    Py_XDECREF(self->Socket);
-    Py_XDECREF(self->ctx);
-    Py_XDECREF(self->server_hostname);
-    Py_XDECREF(self->owner);
+    (void)PySSL_clear(op);
     PyObject_GC_Del(self);
     Py_DECREF(tp);
 }
@@ -3568,6 +3576,11 @@ context_traverse(PyObject *op, visitproc visit, void *arg)
     PySSLContext *self = PySSLContext_CAST(op);
     Py_VISIT(self->set_sni_cb);
     Py_VISIT(self->msg_cb);
+    Py_VISIT(self->keylog_filename);
+#ifndef OPENSSL_NO_PSK
+    Py_VISIT(self->psk_client_callback);
+    Py_VISIT(self->psk_server_callback);
+#endif
     Py_VISIT(Py_TYPE(self));
     return 0;
 }