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[3.12] GH-115874: Fix segfault in FutureIter_dealloc (GH-117741) #118114

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Merged
brandtbucher merged 1 commit into from
Apr 19, 2024
+17 −2
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[3.12] GH-115874: Fix segfault in FutureIter_dealloc (GH-117741) #118114

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2024-04-13-18-59-25.gh-issue-115874.c3xG-E.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fixed a possible segfault during garbage collection of ``_asyncio.FutureIter`` objects
18 changes: 16 additions & 2 deletions Modules/_asynciomodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1590,11 +1590,25 @@ static void
FutureIter_dealloc(futureiterobject *it)
{
PyTypeObject *tp = Py_TYPE(it);
asyncio_state *state = get_asyncio_state_by_def((PyObject *)it);

// FutureIter is a heap type so any subclass must also be a heap type.
assert(_PyType_HasFeature(tp, Py_TPFLAGS_HEAPTYPE));

PyObject *module = ((PyHeapTypeObject*)tp)->ht_module;
asyncio_state *state = NULL;

PyObject_GC_UnTrack(it);
tp->tp_clear((PyObject *)it);

if (state->fi_freelist_len < FI_FREELIST_MAXLEN) {
// GH-115874: We can't use PyType_GetModuleByDef here as the type might have
// already been cleared, which is also why we must check if ht_module != NULL.
// Due to this restriction, subclasses that belong to a different module
// will not be able to use the free list.
if (module && _PyModule_GetDef(module) == &_asynciomodule) {
state = get_asyncio_state(module);
}

if (state && state->fi_freelist_len < FI_FREELIST_MAXLEN) {
state->fi_freelist_len++;
it->future = (FutureObj*) state->fi_freelist;
state->fi_freelist = it;
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