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Commitcae853e

Browse files
GH-125789: fixfut._callbacks to always return a copy of callbacks (#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.
1 parentebcc578 commitcae853e

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3 files changed

+44
-28
lines changed

3 files changed

+44
-28
lines changed

‎Lib/test/test_asyncio/test_futures.py‎

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -697,6 +697,24 @@ def test_future_del_segfault(self):
697697
withself.assertRaises(AttributeError):
698698
delfut._log_traceback
699699

700+
deftest_callbacks_copy(self):
701+
# See https://github.com/python/cpython/issues/125789
702+
# In C implementation, the `_callbacks` attribute
703+
# always returns a new list to avoid mutations of internal state
704+
705+
fut=self._new_future(loop=self.loop)
706+
f1=lambda_:1
707+
f2=lambda_:2
708+
fut.add_done_callback(f1)
709+
fut.add_done_callback(f2)
710+
callbacks=fut._callbacks
711+
self.assertIsNot(callbacks,fut._callbacks)
712+
fut.remove_done_callback(f1)
713+
callbacks=fut._callbacks
714+
self.assertIsNot(callbacks,fut._callbacks)
715+
fut.remove_done_callback(f2)
716+
self.assertIsNone(fut._callbacks)
717+
700718

701719
@unittest.skipUnless(hasattr(futures,'_CFuture'),
702720
'requires the C _asyncio module')
Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
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.

‎Modules/_asynciomodule.c‎

Lines changed: 25 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -1265,52 +1265,49 @@ static PyObject *
12651265
FutureObj_get_callbacks(FutureObj*fut,void*Py_UNUSED(ignored))
12661266
{
12671267
asyncio_state*state=get_asyncio_state_by_def((PyObject*)fut);
1268-
Py_ssize_ti;
1269-
12701268
ENSURE_FUTURE_ALIVE(state,fut)
12711269

1272-
if (fut->fut_callback0==NULL) {
1273-
if (fut->fut_callbacks==NULL) {
1274-
Py_RETURN_NONE;
1275-
}
1276-
1277-
returnPy_NewRef(fut->fut_callbacks);
1270+
Py_ssize_tlen=0;
1271+
if (fut->fut_callback0!=NULL) {
1272+
len++;
12781273
}
1279-
1280-
Py_ssize_tlen=1;
12811274
if (fut->fut_callbacks!=NULL) {
12821275
len+=PyList_GET_SIZE(fut->fut_callbacks);
12831276
}
12841277

1285-
1286-
PyObject*new_list=PyList_New(len);
1287-
if (new_list==NULL) {
1288-
returnNULL;
1278+
if (len==0) {
1279+
Py_RETURN_NONE;
12891280
}
12901281

1291-
PyObject*tup0=PyTuple_New(2);
1292-
if (tup0==NULL) {
1293-
Py_DECREF(new_list);
1282+
PyObject*callbacks=PyList_New(len);
1283+
if (callbacks==NULL) {
12941284
returnNULL;
12951285
}
12961286

1297-
Py_INCREF(fut->fut_callback0);
1298-
PyTuple_SET_ITEM(tup0,0,fut->fut_callback0);
1299-
assert(fut->fut_context0!=NULL);
1300-
Py_INCREF(fut->fut_context0);
1301-
PyTuple_SET_ITEM(tup0,1, (PyObject*)fut->fut_context0);
1302-
1303-
PyList_SET_ITEM(new_list,0,tup0);
1287+
Py_ssize_ti=0;
1288+
if (fut->fut_callback0!=NULL) {
1289+
PyObject*tup0=PyTuple_New(2);
1290+
if (tup0==NULL) {
1291+
Py_DECREF(callbacks);
1292+
returnNULL;
1293+
}
1294+
PyTuple_SET_ITEM(tup0,0,Py_NewRef(fut->fut_callback0));
1295+
assert(fut->fut_context0!=NULL);
1296+
PyTuple_SET_ITEM(tup0,1,Py_NewRef(fut->fut_context0));
1297+
PyList_SET_ITEM(callbacks,i,tup0);
1298+
i++;
1299+
}
13041300

13051301
if (fut->fut_callbacks!=NULL) {
1306-
for (i=0;i<PyList_GET_SIZE(fut->fut_callbacks);i++) {
1307-
PyObject*cb=PyList_GET_ITEM(fut->fut_callbacks,i);
1302+
for (Py_ssize_tj=0;j<PyList_GET_SIZE(fut->fut_callbacks);j++) {
1303+
PyObject*cb=PyList_GET_ITEM(fut->fut_callbacks,j);
13081304
Py_INCREF(cb);
1309-
PyList_SET_ITEM(new_list,i+1,cb);
1305+
PyList_SET_ITEM(callbacks,i,cb);
1306+
i++;
13101307
}
13111308
}
13121309

1313-
returnnew_list;
1310+
returncallbacks;
13141311
}
13151312

13161313
staticPyObject*

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