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GH-97592: Fix crash in C remove_done_callback due to evil code #97660

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Merged
merged 4 commits into from
Sep 30, 2022
Merged

GH-97592: Fix crash in C remove_done_callback due to evil code #97660

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bc55838
GH-97592: Anticipate fut_callbacks being cleared by PyObject_RichComp…
gvanrossum Sep 28, 2022
00b9536
Add test
gvanrossum Sep 29, 2022
648a617
📜🤖 Added by blurb_it.
blurb-it[bot] Sep 29, 2022
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Add a link to the news
gvanrossum Sep 30, 2022
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15 changes: 15 additions & 0 deletions Lib/test/test_asyncio/test_futures.py
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Original file line number Diff line number Diff line change
Expand Up @@ -832,6 +832,21 @@ def __eq__(self, other):

fut.remove_done_callback(evil())

def test_remove_done_callbacks_list_clear(self):
# see https://github.com/python/cpython/issues/97592 for details

fut = self._new_future()
fut.add_done_callback(str)

for _ in range(63):
fut.add_done_callback(id)

class evil:
def __eq__(self, other):
fut.remove_done_callback(other)

fut.remove_done_callback(evil())
Comment on lines +844 to +848
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Class names should normally use the CapWords convention.

Suggested change
class evil:
def __eq__(self, other):
fut.remove_done_callback(other)
fut.remove_done_callback(evil())
class Evil:
def __eq__(self, other):
fut.remove_done_callback(other)
fut.remove_done_callback(Evil())

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All callbacks added by fut.add_done_callback() will be cleared when calling fut.remove_done_callback(Evil()), but the return value will be the number of callbacks added last.

I'm not sure if we need to improve the return value of remove done callback further, the current changes are good enough to fix the crash. :)


def test_schedule_callbacks_list_mutation_1(self):
# see http://bugs.python.org/issue28963 for details

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-09-29-23-22-24.gh-issue-97592.tpJg_J.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Avoid a crash in the C version of :meth:`asyncio.Future.remove_done_callback` when an evil argument is passed.
9 changes: 7 additions & 2 deletions Modules/_asynciomodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1052,7 +1052,11 @@ _asyncio_Future_remove_done_callback(FutureObj *self, PyObject *fn)
return NULL;
}

for (i = 0; i < PyList_GET_SIZE(self->fut_callbacks); i++) {
// Beware: PyObject_RichCompareBool below may change fut_callbacks.
// See GH-97592.
for (i = 0;
self->fut_callbacks != NULL && i < PyList_GET_SIZE(self->fut_callbacks);
i++) {
int ret;
PyObject *item = PyList_GET_ITEM(self->fut_callbacks, i);
Py_INCREF(item);
Expand All @@ -1071,7 +1075,8 @@ _asyncio_Future_remove_done_callback(FutureObj *self, PyObject *fn)
}
}

if (j == 0) {
// Note: fut_callbacks may have been cleared.
if (j == 0 || self->fut_callbacks == NULL) {
Py_CLEAR(self->fut_callbacks);
Py_DECREF(newlist);
return PyLong_FromSsize_t(len + cleared_callback0);
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