gh-131311: Fix additional memory leaks in ctypes (GH-131429)

* Visit keep in StructParam_traverse
* Decref swapped in PyCSimpleType_init
* Decref ob in make_funcptrtype_dict
* Check Pointer_item result while constructing result list in Pointer_subscript

* Fix align and size naming in PyCStructUnionType_update_stginfo
  - as discussed in previous PR

Author: sergey-miryanov

Modules/_ctypes/_ctypes.c

@@ -410,9 +410,11 @@ typedef struct {
 #define _StructParamObject_CAST(op) ((StructParamObject *)(op))
 
 static int
-StructParam_traverse(PyObject *self, visitproc visit, void *arg)
+StructParam_traverse(PyObject *myself, visitproc visit, void *arg)
 {
+    StructParamObject *self = _StructParamObject_CAST(myself);
     Py_VISIT(Py_TYPE(self));
+    Py_VISIT(self->keep);
     return 0;
 }
 
@@ -2378,6 +2380,7 @@ PyCSimpleType_init(PyObject *self, PyObject *args, PyObject *kwds)
         }
         StgInfo *sw_info;
         if (PyStgInfo_FromType(st, swapped, &sw_info) < 0) {
+            Py_DECREF(swapped);
             return -1;
         }
         assert(sw_info);
@@ -2674,6 +2677,7 @@ make_funcptrtype_dict(ctypes_state *st, PyObject *attrdict, StgInfo *stginfo)
     if (ob) {
         StgInfo *info;
         if (PyStgInfo_FromType(st, ob, &info) < 0) {
+            Py_DECREF(ob);
             return -1;
         }
         if (ob != Py_None && !info && !PyCallable_Check(ob)) {
@@ -5650,6 +5654,10 @@ Pointer_subscript(PyObject *myself, PyObject *item)
 
         for (cur = start, i = 0; i < len; cur += step, i++) {
             PyObject *v = Pointer_item(myself, cur);
+            if (!v) {
+                Py_DECREF(np);
+                return NULL;
+            }
             PyList_SET_ITEM(np, i, v);
         }
         return np;

Modules/_ctypes/stgdict.c

@@ -225,8 +225,8 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
     // They're cleared on error.
     PyObject *layout_func = NULL;
     PyObject *kwnames = NULL;
-    PyObject* align = NULL;
-    PyObject* size = NULL;
+    PyObject *align_obj = NULL;
+    PyObject *size_obj = NULL;
     PyObject *layout_fields_obj = NULL;
     PyObject *layout_fields = NULL;
     PyObject *layout = NULL;
@@ -291,12 +291,12 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
         goto error;
     }
 
-    align = PyObject_GetAttr(layout, &_Py_ID(align));
-    if (!align) {
+    align_obj = PyObject_GetAttr(layout, &_Py_ID(align));
+    if (!align_obj) {
         goto error;
     }
-    Py_ssize_t total_align = PyLong_AsSsize_t(align);
-    Py_CLEAR(align);
+    Py_ssize_t total_align = PyLong_AsSsize_t(align_obj);
+    Py_CLEAR(align_obj);
     if (total_align < 0) {
         if (!PyErr_Occurred()) {
             PyErr_SetString(PyExc_ValueError,
@@ -305,12 +305,12 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
         goto error;
     }
 
-    size = PyObject_GetAttr(layout, &_Py_ID(size));
-    if (!size) {
+    size_obj = PyObject_GetAttr(layout, &_Py_ID(size));
+    if (!size_obj) {
         goto error;
     }
-    Py_ssize_t total_size = PyLong_AsSsize_t(size);
-    Py_CLEAR(size);
+    Py_ssize_t total_size = PyLong_AsSsize_t(size_obj);
+    Py_CLEAR(size_obj);
     if (total_size < 0) {
         if (!PyErr_Occurred()) {
             PyErr_SetString(PyExc_ValueError,
@@ -669,8 +669,8 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
 error:
     Py_XDECREF(layout_func);
     Py_XDECREF(kwnames);
-    Py_XDECREF(align);
-    Py_XDECREF(size);
+    Py_XDECREF(align_obj);
+    Py_XDECREF(size_obj);
     Py_XDECREF(layout_fields_obj);
     Py_XDECREF(layout_fields);
     Py_XDECREF(layout);