8000 bpo-46417: PyWeakref_GET_OBJECT() uses PyWeakref_CheckRef() by vstinner · Pull Request #30763 · python/cpython · GitHub
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bpo-46417: PyWeakref_GET_OBJECT() uses PyWeakref_CheckRef() #30763

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bpo-46417: PyWeakref_GET_OBJECT() uses PyWeakref_CheckRef() 
PyWeakref_GET_OBJECT() now ensures that the its argument is valid
using PyWeakref_CheckRef().

* Convert PyWeakref_GET_OBJECT() macro to a static inline function.
* Remove now redundant assert(PyWeakref_CheckRef(ref)) before
  PyWeakref_GET_OBJECT(ref) calls.
* Add proxy_get_object() to proxy functions.
* _ctypes PyDict_GetItemProxy() uses the private
  _PyWeakref_GET_OBJECT() function.
* Cleanup weakrefobject.c.
  • Loading branch information
@vstinner
vstinner committed Jan 21, 2022
commit 6822ad09bbc9c1515d7f0ab7f7552bb0c6529814
4 changes: 2 additions & 2 deletions Doc/c-api/weakref.rst
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Expand Up @@ -66,5 +66,5 @@ as much as it can.

.. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref)

Similar to :c:func:`PyWeakref_GetObject`, but implemented as a macro that does no
error checking.
Similar to :c:func:`PyWeakref_GetObject`, but implemented as a static inline
function which only check errors with assertions.
35 changes: 25 additions & 10 deletions Include/cpython/weakrefobject.h
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Expand Up @@ -35,13 +35,28 @@ PyAPI_FUNC(Py_ssize_t) _PyWeakref_GetWeakrefCount(PyWeakReference *head);

PyAPI_FUNC(void) _PyWeakref_ClearRef(PyWeakReference *self);

/* Explanation for the Py_REFCNT() check: when a weakref's target is part
of a long chain of deallocations which triggers the trashcan mechanism,
clearing the weakrefs can be delayed long after the target's refcount
has dropped to zero. In the meantime, code accessing the weakref will
be able to "see" the target object even though it is supposed to be
unreachable. See issue #16602. */
#define PyWeakref_GET_OBJECT(ref) \
(Py_REFCNT(((PyWeakReference *)(ref))->wr_object) > 0 \
? ((PyWeakReference *)(ref))->wr_object \
: Py_None)

static inline PyObject* _PyWeakref_GET_OBJECT(PyWeakReference *ref)
{
PyObject *obj = ref->wr_object;
assert(obj != NULL);
/* Explanation for the Py_REFCNT() check: when a weakref's target is part
of a long chain of deallocations which triggers the trashcan mechanism,
clearing the weakrefs can be delayed long after the target's refcount
has dropped to zero. In the meantime, code accessing the weakref will
be able to "see" the target object even though it is supposed to be
unreachable. See issue #16602. */
if (Py_REFCNT(obj) > 0) {
return obj;
}
else {
return Py_None;
}
}

static inline PyObject* PyWeakref_GET_OBJECT(PyWeakReference *ref)
{
assert(PyWeakref_CheckRef(ref));
return _PyWeakref_GET_OBJECT(ref);
}
#define PyWeakref_GET_OBJECT(ref) PyWeakref_GET_OBJECT((PyWeakReference*)(ref))
4 changes: 1 addition & 3 deletions Modules/_abc.c
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Expand Up @@ -155,8 +155,7 @@ _in_weak_set(PyObject *set, PyObject *obj)
static PyObject *
_destroy(PyObject *setweakref, PyObject *objweakref)
{
PyObject *set;
set = PyWeakref_GET_OBJECT(setweakref);
PyObject *set = PyWeakref_GET_OBJECT(setweakref);
if (set == Py_None) {
Py_RETURN_NONE;
}
Expand Down Expand Up @@ -502,7 +501,6 @@ set_collection_flag_recursive(PyTypeObject *child, unsigned long flag)
assert(PyDict_CheckExact(grandchildren));
Py_ssize_t i = 0;
while (PyDict_Next(grandchildren, &i, NULL, &grandchildren)) {
assert(PyWeakref_CheckRef(grandchildren));
PyObject *grandchild = PyWeakref_GET_OBJECT(grandchildren);
if (PyType_Check(grandchild)) {
set_collection_flag_recursive((PyTypeObject *)grandchild, flag);
Expand Down
4 changes: 2 additions & 2 deletions Modules/_ctypes/_ctypes.c
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Expand Up @@ -246,7 +246,7 @@ PyDict_SetItemProxy(PyObject *dict, PyObject *key, PyObject *item)
return result;
}

PyObject *
static PyObject *
PyDict_GetItemProxy(PyObject *dict, PyObject *key)
{
PyObject *result;
Expand All @@ -256,7 +256,7 @@ PyDict_GetItemProxy(PyObject *dict, PyObject *key)
return NULL;
if (!PyWeakref_CheckProxy(item))
return item;
result = PyWeakref_GET_OBJECT(item);
result = _PyWeakref_GET_OBJECT((PyWeakReference*)item);
if (result == Py_None)
return NULL;
return result;
Expand Down
1 change: 0 additions & 1 deletion Modules/_threadmodule.c
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Expand Up @@ -1031,7 +1031,6 @@ local_getattro(localobject *self, PyObject *name)
static PyObject *
_localdummy_destroyed(PyObject *localweakref, PyObject *dummyweakref)
{
assert(PyWeakref_CheckRef(localweakref));
PyObject *obj = PyWeakref_GET_OBJECT(localweakref);
if (obj == Py_None) {
Py_RETURN_NONE;
Expand Down
4 changes: 0 additions & 4 deletions Objects/typeobject.c
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Expand Up @@ -339,7 +339,6 @@ PyType_Modified(PyTypeObject *type)
assert(PyDict_CheckExact(raw));
i = 0;
while (PyDict_Next(raw, &i, NULL, &ref)) {
assert(PyWeakref_CheckRef(ref));
ref = PyWeakref_GET_OBJECT(ref);
if (ref != Py_None) {
PyType_Modified(_PyType_CAST(ref));
Expand Down Expand Up @@ -4146,7 +4145,6 @@ type___subclasses___impl(PyTypeObject *self)
assert(PyDict_CheckExact(raw));
i = 0;
while (PyDict_Next(raw, &i, NULL, &ref)) {
assert(PyWeakref_CheckRef(ref));
ref = PyWeakref_GET_OBJECT(ref);
if (ref != Py_None) {
if (PyList_Append(list, ref) < 0) {
Expand Down Expand Up @@ -8647,9 +8645,7 @@ recurse_down_subclasses(PyTypeObject *type, PyObject *name,
assert(PyDict_CheckExact(subclasses));
i = 0;
while (PyDict_Next(subclasses, &i, NULL, &ref)) {
assert(PyWeakref_CheckRef(ref));
PyObject *obj = PyWeakref_GET_OBJECT(ref);
assert(obj != NULL);
if (obj == Py_None) {
continue;
}
Expand Down
75 changes: 37 additions & 38 deletions Objects/weakrefobject.c
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Expand Up @@ -131,22 +131,22 @@ static PyObject *
weakref_call(PyWeakReference *self, PyObject *args, PyObject *kw)
{
static char *kwlist[] = {NULL};

if (PyArg_ParseTupleAndKeywords(args, kw, ":__call__", kwlist)) {
PyObject *object = PyWeakref_GET_OBJECT(self);
Py_INCREF(object);
return (object);
if (!PyArg_ParseTupleAndKeywords(args, kw, ":__call__", kwlist)) {
return NULL;
}
return NULL;

return Py_NewRef(PyWeakref_GET_OBJECT(self));
}


static Py_hash_t
weakref_hash(PyWeakReference *self)
{
if (self->hash != -1)
if (self->hash != -1) {
return self->hash;
PyObject* obj = PyWeakref_GET_OBJECT(self);
}

PyObject *obj = PyWeakref_GET_OBJECT(self);
if (obj == Py_None) {
PyErr_SetString(PyExc_TypeError, "weak object has gone away");
return -1;
Expand All @@ -163,7 +163,7 @@ weakref_repr(PyWeakReference *self)
{
PyObject *name, *repr;
_Py_IDENTIFIER(__name__);
PyObject* obj = PyWeakref_GET_OBJECT(self);
PyObject *obj = PyWeakref_GET_OBJECT(self);

if (obj == Py_None) {
return PyUnicode_FromFormat("<weakref at %p; dead>", self);
Expand All @@ -177,17 +177,12 @@ weakref_repr(PyWeakReference *self)
if (name == NULL || !PyUnicode_Check(name)) {
repr = PyUnicode_FromFormat(
"<weakref at %p; to '%s' at %p>",
self,
Py_TYPE(PyWeakref_GET_OBJECT(self))->tp_name,
obj);
self, Py_TYPE(obj)->tp_name, obj);
}
else {
repr = PyUnicode_FromFormat(
"<weakref at %p; to '%s' at %p (%U)>",
self,
Py_TYPE(PyWeakref_GET_OBJECT(self))->tp_name,
obj,
name);
self, Py_TYPE(obj)->tp_name, obj, name);
}
Py_DECREF(obj);
Py_XDECREF(name);
Expand All @@ -206,8 +201,9 @@ weakref_richcompare(PyWeakReference* self, PyWeakReference* other, int op)
!PyWeakref_Check(other)) {
Py_RETURN_NOTIMPLEMENTED;
}
if (PyWeakref_GET_OBJECT(self) == Py_None
|| PyWeakref_GET_OBJECT(other) == Py_None) {
PyObject* obj = PyWeakref_GET_OBJECT(self);
PyObject* other_obj = PyWeakref_GET_OBJECT(other);
if (obj == Py_None || other_obj == Py_None) {
int res = (self == other);
if (op == Py_NE)
res = !res;
Expand All @@ -216,8 +212,6 @@ weakref_richcompare(PyWeakReference* self, PyWeakReference* other, int op)
else
Py_RETURN_FALSE;
}
PyObject* obj = PyWeakref_GET_OBJECT(self);
PyObject* other_obj = PyWeakref_GET_OBJECT(other);
Py_INCREF(obj);
Py_INCREF(other_obj);
PyObject* res = PyObject_RichCompare(obj, other_obj, op);
Expand Down Expand Up @@ -413,10 +407,18 @@ _PyWeakref_RefType = {
};


static inline PyObject*
proxy_get_object(PyWeakReference *ref)
{
assert(PyWeakref_CheckProxy(ref));
return _PyWeakref_GET_OBJECT(ref);
}


static int
proxy_checkref(PyWeakReference *proxy)
{
if (PyWeakref_GET_OBJECT(proxy) == Py_None) {
if (proxy_get_object(proxy) == Py_None) {
PyErr_SetString(PyExc_ReferenceError,
"weakly-referenced object no longer exists");
return 0;
Expand All @@ -431,9 +433,10 @@ proxy_checkref(PyWeakReference *proxy)
*/
#define UNWRAP(o) \
if (PyWeakref_CheckProxy(o)) { \
if (!proxy_checkref((PyWeakReference *)o)) \
PyWeakReference *_proxy = (PyWeakReference *)o; \
if (!proxy_checkref(_proxy)) \
return NULL; \
o = PyWeakref_GET_OBJECT(o); \
o = proxy_get_object(_proxy); \
}

#define WRAP_UNARY(method, generic) \
Expand Down Expand Up @@ -500,20 +503,20 @@ WRAP_TERNARY(proxy_call, PyObject_Call)
static PyObject *
proxy_repr(PyWeakReference *proxy)
{
PyObject *obj = proxy_get_object(proxy);
return PyUnicode_FromFormat(
"<weakproxy at %p to %s at %p>",
proxy,
Py_TYPE(PyWeakref_GET_OBJECT(proxy))->tp_name,
PyWeakref_GET_OBJECT(proxy));
proxy, Py_TYPE(obj)->tp_name, obj);
}


static int
proxy_setattr(PyWeakReference *proxy, PyObject *name, PyObject *value)
{
if (!proxy_checkref(proxy))
if (!proxy_checkref(proxy)) {
return -1;
PyObject *obj = PyWeakref_GET_OBJECT(proxy);
}
PyObject *obj = proxy_get_object(proxy);
Py_INCREF(obj);
int res = PyObject_SetAttr(obj, name, value);
Py_DECREF(obj);
Expand Down Expand Up @@ -567,7 +570,7 @@ WRAP_BINARY(proxy_imatmul, PyNumber_InPlaceMatrixMultiply)
static int
proxy_bool(PyWeakReference *proxy)
{
PyObject *o = PyWeakref_GET_OBJECT(proxy);
PyObject *o = proxy_get_object(proxy);
if (!proxy_checkref(proxy)) {
return -1;
}
Expand All @@ -594,8 +597,7 @@ proxy_contains(PyWeakReference *proxy, PyObject *value)
if (!proxy_checkref(proxy))
return -1;

PyObject *obj = PyWeakref_GET_OBJECT(proxy);
Py_INCREF(obj);
PyObject *obj = Py_NewRef(proxy_get_object(proxy));
int res = PySequence_Contains(obj, value);
Py_DECREF(obj);
return res;
Expand All @@ -609,8 +611,7 @@ proxy_length(PyWeakReference *proxy)
if (!proxy_checkref(proxy))
return -1;

PyObject *obj = PyWeakref_GET_OBJECT(proxy);
Py_INCREF(obj);
PyObject *obj = Py_NewRef(proxy_get_object(proxy));
Py_ssize_t res = PyObject_Length(obj);
Py_DECREF(obj);
return res;
Expand All @@ -624,8 +625,7 @@ proxy_setitem(PyWeakReference *proxy, PyObject *key, PyObject *value)
if (!proxy_checkref(proxy))
return -1;

PyObject *obj = PyWeakref_GET_OBJECT(proxy);
Py_INCREF(obj);
PyObject *obj = Py_NewRef(proxy_get_object(proxy));
int res;
if (value == NULL) {
res = PyObject_DelItem(obj, key);
Expand All @@ -643,8 +643,7 @@ proxy_iter(PyWeakReference *proxy)
{
if (!proxy_checkref(proxy))
return NULL;
PyObject *obj = PyWeakref_GET_OBJECT(proxy);
Py_INCREF(obj);
PyObject *obj = Py_NewRef(proxy_get_object(proxy));
PyObject* res = PyObject_GetIter(obj);
Py_DECREF(obj);
return res;
Expand All @@ -656,7 +655,7 @@ proxy_iternext(PyWeakReference *proxy)
if (!proxy_checkref(proxy))
return NULL;

PyObject *obj = PyWeakref_GET_OBJECT(proxy);
PyObject *obj = proxy_get_object(proxy);
if (!PyIter_Check(obj)) {
PyErr_Format(PyExc_TypeError,
"Weakref proxy referenced a non-iterator '%.200s' object",
Expand Down
0