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[3.12] gh-126138: Fix use-after-free in _asyncio.Task by evil __getattribute__ (GH-126305) #126325

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Merged
merged 1 commit into from
Nov 2, 2024
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[3.12] gh-126138: Fix use-after-free in _asyncio.Task by evil __getattribute__ (GH-126305) #126325

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2024-11-01-14-31-41.gh-issue-126138.yTniOG.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix a use-after-free crash on :class:`asyncio.Task` objects
whose underlying coroutine yields an object that implements
an evil :meth:`~object.__getattribute__`. Patch by Nico Posada.
22 changes: 20 additions & 2 deletions Modules/_asynciomodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2994,8 +2994,17 @@ task_step_handle_result_impl(asyncio_state *state, TaskObj *task, PyObject *resu
if (task->task_must_cancel) {
PyObject *r;
int is_true;

// Beware: An evil `__getattribute__` could
// prematurely delete task->task_cancel_msg before the
// task is cancelled, thereby causing a UAF crash.
//
// See https://github.com/python/cpython/issues/126138
PyObject *task_cancel_msg = Py_NewRef(task->task_cancel_msg);
r = PyObject_CallMethodOneArg(result, &_Py_ID(cancel),
task->task_cancel_msg);
task_cancel_msg);
Py_DECREF(task_cancel_msg);

if (r == NULL) {
return NULL;
}
Expand Down Expand Up @@ -3087,8 +3096,17 @@ task_step_handle_result_impl(asyncio_state *state, TaskObj *task, PyObject *resu
if (task->task_must_cancel) {
PyObject *r;
int is_true;

// Beware: An evil `__getattribute__` could
// prematurely delete task->task_cancel_msg before the
// task is cancelled, thereby causing a UAF crash.
//
// See https://github.com/python/cpython/issues/126138
PyObject *task_cancel_msg = Py_NewRef(task->task_cancel_msg);
r = PyObject_CallMethodOneArg(result, &_Py_ID(cancel),
task->task_cancel_msg);
task_cancel_msg);
Py_DECREF(task_cancel_msg);

if (r == NULL) {
return NULL;
}
Expand Down
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