8000 [3.12] GH-125789: fix `fut._callbacks` to always return a copy of cal… · python/cpython@42927f7 · GitHub
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[3.12] GH-125789: fix fut._callbacks to always return a copy of callbacks (GH-125922) (#125977)
GH-125789: fix `fut._callbacks` to always return a copy of callbacks (GH-125922) Fix `asyncio.Future._callbacks` to always return a copy of the internal list of callbacks to avoid mutation from user code affecting the internal state. Co-authored-by: Kumar Aditya <kumaraditya@python.org> (cherry picked from commit cae853e)
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‎Lib/test/test_asyncio/test_futures.py

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Original file line numberDiff line numberDiff line change
@@ -686,6 +686,24 @@ def test_future_iter_get_referents_segfault(self):
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evil = gc.get_referents(_asyncio)
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gc.collect()
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def test_callbacks_copy(self):
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# See https://github.com/python/cpython/issues/125789
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# In C implementation, the `_callbacks` attribute
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# always returns a new list to avoid mutations of internal state
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fut = self._new_future(loop=self.loop)
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f1 = lambda _: 1
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f2 = lambda _: 2
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fut.add_done_callback(f1)
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fut.add_done_callback(f2)
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callbacks = fut._callbacks
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self.assertIsNot(callbacks, fut._callbacks)
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fut.remove_done_callback(f1)
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callbacks = fut._callbacks
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self.assertIsNot(callbacks, fut._callbacks)
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fut.remove_done_callback(f2)
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self.assertIsNone(fut._callbacks)
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@unittest.skipUnless(hasattr(futures, '_CFuture'),
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'requires the C _asyncio module')

‎Misc/NEWS.d/next/Library/2024-10-24-14-08-10.gh-issue-125789.eaiAMw.rst

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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.

‎Modules/_asynciomodule.c

Lines changed: 25 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -1290,52 +1290,49 @@ static PyObject *
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FutureObj_get_callbacks(FutureObj *fut, void *Py_UNUSED(ignored))
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{
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asyncio_state *state = get_asyncio_state_by_def((PyObject *)fut);
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Py_ssize_t i;
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ENSURE_FUTURE_ALIVE(state, fut)
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1297-
if (fut->fut_callback0 == NULL) {
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if (fut->fut_callbacks == NULL) {
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Py_RETURN_NONE;
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}
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return Py_NewRef(fut->fut_callbacks);
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Py_ssize_t len = 0;
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if (fut->fut_callback0 != NULL) {
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len++;
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}
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Py_ssize_t len = 1;
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if (fut->fut_callbacks != NULL) {
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len += PyList_GET_SIZE(fut->fut_callbacks);
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}
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PyObject *new_list = PyList_New(len);
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if (new_list == NULL) {
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return NULL;
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if (len == 0) {
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Py_RETURN_NONE;
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}
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1316-
PyObject *tup0 = PyTuple_New(2);
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if (tup0 == NULL) {
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Py_DECREF(new_list);
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PyObject *callbacks = PyList_New(len);
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if (callbacks == NULL) {
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return NULL;
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}
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1322-
Py_INCREF(fut->fut_callback0);
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PyTuple_SET_ITEM(tup0, 0, fut->fut_callback0);
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assert(fut->fut_context0 != NULL);
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Py_INCREF(fut->fut_context0);
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PyTuple_SET_ITEM(tup0, 1, (PyObject *)fut->fut_context0);
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PyList_SET_ITEM(new_list, 0, tup0);
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Py_ssize_t i = 0;
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if (fut->fut_callback0 != NULL) {
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PyObject *tup0 = PyTuple_New(2);
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if (tup0 == NULL) {
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Py_DECREF(callbacks);
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return NULL;
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}
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PyTuple_SET_ITEM(tup0, 0, Py_NewRef(fut->fut_callback0));
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assert(fut->fut_context0 != NULL);
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PyTuple_SET_ITEM(tup0, 1, Py_NewRef(fut->fut_context0));
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PyList_SET_ITEM(callbacks, i, tup0);
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i++;
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}
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if (fut->fut_callbacks != NULL) {
1331-
for (i = 0; i < PyList_GET_SIZE(fut->fut_callbacks); i++) {
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PyObject *cb = PyList_GET_ITEM(fut->fut_callbacks, i);
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for (Py_ssize_t j = 0; j < PyList_GET_SIZE(fut->fut_callbacks); j++) {
1328+
PyObject *cb = PyList_GET_ITEM(fut->fut_callbacks, j);
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Py_INCREF(cb);
1334-
PyList_SET_ITEM(new_list, i + 1, cb);
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PyList_SET_ITEM(callbacks, i, cb);
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i++;
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}
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}
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1338-
return new_list;
1335+
return callbacks;
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}
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static PyObject *

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