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[3.12] [3.13] GH-125789: fix fut._callbacks to always return a copy of callbacks (GH-125922) (GH-125976) #125977

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Oct 25, 2024
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18 changes: 18 additions & 0 deletions Lib/test/test_asyncio/test_futures.py
Original file line number Diff line number Diff line change
Expand Up @@ -686,6 +686,24 @@ def test_future_iter_get_referents_segfault(self):
evil = gc.get_referents(_asyncio)
gc.collect()

def test_callbacks_copy(self):
# See https://github.com/python/cpython/issues/125789
# In C implementation, the `_callbacks` attribute
# always returns a new list to avoid mutations of internal state

fut = self._new_future(loop=self.loop)
f1 = lambda _: 1
f2 = lambda _: 2
fut.add_done_callback(f1)
fut.add_done_callback(f2)
callbacks = fut._callbacks
self.assertIsNot(callbacks, fut._callbacks)
fut.remove_done_callback(f1)
callbacks = fut._callbacks
self.assertIsNot(callbacks, fut._callbacks)
fut.remove_done_callback(f2)
self.assertIsNone(fut._callbacks)


@unittest.skipUnless(hasattr(futures, '_CFuture'),
'requires the C _asyncio module')
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix possible crash when mutating list of callbacks returned by :attr:`!asyncio.Future._callbacks`. It now always returns a new copy in C implementation :mod:`!_asyncio`. Patch by Kumar Aditya.
53 changes: 25 additions & 28 deletions Modules/_asynciomodule.c
Original file line number Diff line number Diff line change
Expand Up @@ -1290,52 +1290,49 @@ static PyObject *
FutureObj_get_callbacks(FutureObj *fut, void *Py_UNUSED(ignored))
{
asyncio_state *state = get_asyncio_state_by_def((PyObject *)fut);
Py_ssize_t i;

ENSURE_FUTURE_ALIVE(state, fut)

if (fut->fut_callback0 == NULL) {
if (fut->fut_callbacks == NULL) {
Py_RETURN_NONE;
}

return Py_NewRef(fut->fut_callbacks);
Py_ssize_t len = 0;
if (fut->fut_callback0 != NULL) {
len++;
}

Py_ssize_t len = 1;
if (fut->fut_callbacks != NULL) {
len += PyList_GET_SIZE(fut->fut_callbacks);
}


PyObject *new_list = PyList_New(len);
if (new_list == NULL) {
return NULL;
if (len == 0) {
Py_RETURN_NONE;
}

PyObject *tup0 = PyTuple_New(2);
if (tup0 == NULL) {
Py_DECREF(new_list);
PyObject *callbacks = PyList_New(len);
if (callbacks == NULL) {
return NULL;
}

Py_INCREF(fut->fut_callback0);
PyTuple_SET_ITEM(tup0, 0, fut->fut_callback0);
assert(fut->fut_context0 != NULL);
Py_INCREF(fut->fut_context0);
PyTuple_SET_ITEM(tup0, 1, (PyObject *)fut->fut_context0);

PyList_SET_ITEM(new_list, 0, tup0);
Py_ssize_t i = 0;
if (fut->fut_callback0 != NULL) {
PyObject *tup0 = PyTuple_New(2);
if (tup0 == NULL) {
Py_DECREF(callbacks);
return NULL;
}
PyTuple_SET_ITEM(tup0, 0, Py_NewRef(fut->fut_callback0));
assert(fut->fut_context0 != NULL);
PyTuple_SET_ITEM(tup0, 1, Py_NewRef(fut->fut_context0));
PyList_SET_ITEM(callbacks, i, tup0);
i++;
}

if (fut->fut_callbacks != NULL) {
for (i = 0; i < PyList_GET_SIZE(fut->fut_callbacks); i++) {
PyObject *cb = PyList_GET_ITEM(fut->fut_callbacks, i);
for (Py_ssize_t j = 0; j < PyList_GET_SIZE(fut->fut_callbacks); j++) {
PyObject *cb = PyList_GET_ITEM(fut->fut_callbacks, j);
Py_INCREF(cb);
PyList_SET_ITEM(new_list, i + 1, cb);
PyList_SET_ITEM(callbacks, i, cb);
i++;
}
}

return new_list;
return callbacks;
}

static PyObject *
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