python: Safely clear structure members

Using Py_CLEAR() ensures that these structures are observed in a
consistent state by any Python code that may run during deconstruction.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

5 files changed, 15 insertions, 23 deletions

diff --git a/lib/ldb/pyldb.c b/lib/ldb/pyldb.c
index aa38e115ce4..11d093c0429 100644
--- a/lib/ldb/pyldb.c
+++ b/lib/ldb/pyldb.c
@@ -2134,10 +2134,7 @@ static int py_ldb_search_iterator_reply_destructor(struct py_ldb_search_iterator
 		reply->py_iter = NULL;
 	}
 
-	if (reply->obj != NULL) {
-		Py_DECREF(reply->obj);
-		reply->obj = NULL;
-	}
+	Py_CLEAR(reply->obj);
 
 	return 0;
 }
@@ -2679,9 +2676,9 @@ static PyTypeObject PyLdb = {
 static void py_ldb_result_dealloc(PyLdbResultObject *self)
 {
 	talloc_free(self->mem_ctx);
-	Py_DECREF(self->msgs);
-	Py_DECREF(self->referals);
-	Py_DECREF(self->controls);
+	Py_CLEAR(self->msgs);
+	Py_CLEAR(self->referals);
+	Py_CLEAR(self->controls);
 	Py_TYPE(self)->tp_free(self);
 }
 
@@ -2775,10 +2772,10 @@ static PyTypeObject PyLdbResult = {
 
 static void py_ldb_search_iterator_dealloc(PyLdbSearchIteratorObject *self)
 {
-	Py_XDECREF(self->state.exception);
+	Py_CLEAR(self->state.exception);
 	TALLOC_FREE(self->mem_ctx);
 	ZERO_STRUCT(self->state);
-	Py_DECREF(self->ldb);
+	Py_CLEAR(self->ldb);
 	Py_TYPE(self)->tp_free(self);
 }
 
@@ -2885,7 +2882,7 @@ static PyObject *py_ldb_search_iterator_abandon(PyLdbSearchIteratorObject *self,
 		return NULL;
 	}
 
-	Py_XDECREF(self->state.exception);
+	Py_CLEAR(self->state.exception);
 	TALLOC_FREE(self->mem_ctx);
 	ZERO_STRUCT(self->state);
 	Py_RETURN_NONE;
@@ -4289,7 +4286,7 @@ static int py_module_del_transaction(struct ldb_module *mod)
 
 static int py_module_destructor(struct ldb_module *mod)
 {
-	Py_DECREF((PyObject *)mod->private_data);
+	Py_CLEAR(mod->private_data);
 	return 0;
 }
 
diff --git a/lib/tdb/pytdb.c b/lib/tdb/pytdb.c
index 85df1b18621..ed22803328c 100644
--- a/lib/tdb/pytdb.c
+++ b/lib/tdb/pytdb.c
@@ -450,7 +450,7 @@ static PyObject *tdb_iter_next(PyTdbIteratorObject *self)
 
 static void tdb_iter_dealloc(PyTdbIteratorObject *self)
 {
-	Py_DECREF(self->iteratee);
+	Py_CLEAR(self->iteratee);
 	PyObject_Del(self);
 }
 
diff --git a/lib/tevent/pytevent.c b/lib/tevent/pytevent.c
index 1af6f16c0fb..aa2331c1d6c 100644
--- a/lib/tevent/pytevent.c
+++ b/lib/tevent/pytevent.c
@@ -241,7 +241,7 @@ static void py_tevent_timer_dealloc(TeventTimer_Object *self)
 	if (self->timer) {
 		talloc_free(self->timer);
 	}
-	Py_DECREF(self->callback);
+	Py_CLEAR(self->callback);
 	PyObject_Del(self);
 }
 
@@ -282,7 +282,7 @@ struct TeventTimer_Object_ref {
 static int TeventTimer_Object_ref_destructor(struct TeventTimer_Object_ref *ref)
 {
 	ref->obj->timer = NULL;
-	Py_DECREF(ref->obj);
+	Py_CLEAR(ref->obj);
 	return 0;
 }
 
diff --git a/source3/libsmb/pylibsmb.c b/source3/libsmb/pylibsmb.c
index 571681aee91..bace98ddd3a 100644
--- a/source3/libsmb/pylibsmb.c
+++ b/source3/libsmb/pylibsmb.c
@@ -1668,10 +1668,7 @@ struct py_cli_notify_state {
 static void py_cli_notify_state_dealloc(struct py_cli_notify_state *self)
 {
 	TALLOC_FREE(self->req);
-	if (self->py_cli_state != NULL) {
-		Py_DECREF(self->py_cli_state);
-		self->py_cli_state = NULL;
-	}
+	Py_CLEAR(self->py_cli_state);
 	Py_TYPE(self)->tp_free(self);
 }
 
@@ -1823,8 +1820,7 @@ static PyObject *py_cli_notify_get_changes(struct py_cli_notify_state *self,
 
 	ok = py_tevent_req_wait_exc(py_cli_state, req);
 	self->req = NULL;
-	Py_DECREF(self->py_cli_state);
-	self->py_cli_state = NULL;
+	Py_CLEAR(self->py_cli_state);
 	if (!ok) {
 		return NULL;
 	}
diff --git a/source4/librpc/rpc/pyrpc.c b/source4/librpc/rpc/pyrpc.c
index 7b6bcef9eba..61b3c6357b0 100644
--- a/source4/librpc/rpc/pyrpc.c
+++ b/source4/librpc/rpc/pyrpc.c
@@ -492,8 +492,7 @@ static void py_dcerpc_ndr_pointer_dealloc(PyObject* self)
 	struct py_dcerpc_ndr_pointer *obj =
 		pytalloc_get_type(self, struct py_dcerpc_ndr_pointer);
 
-	Py_DECREF(obj->value);
-	obj->value = NULL;
+	Py_CLEAR(obj->value);
 
 	self->ob_type->tp_free(self);
 }
@@ -512,7 +511,7 @@ static int py_dcerpc_ndr_pointer_set_value(PyObject *self, PyObject *value, void
 	struct py_dcerpc_ndr_pointer *obj =
 		pytalloc_get_type(self, struct py_dcerpc_ndr_pointer);
 
-	Py_DECREF(obj->value);
+	Py_CLEAR(obj->value);
 	obj->value = value;
 	Py_INCREF(obj->value);
 	return 0;