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gh-126138: Fix UAF in asyncio.Task when task calls back to user defined cancel function #126305

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Merged
merged 4 commits into from
Nov 2, 2024
Merged

gh-126138: Fix UAF in asyncio.Task when task calls back to user defined cancel function #126305

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ed63507
fix uaf and add blurb
Nico-Posada Nov 1, 2024
f83c4ff
Merge branch 'main' into fix-issue-126138
willingc Nov 1, 2024
eddc044
Address picnixz's changes
Nico-Posada Nov 1, 2024
b4f4187
Update to keep line length under 80 characters
Nico-Posada Nov 1, 2024
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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 @@ -2967,8 +2967,17 @@ 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 @@ -3060,8 +3069,17 @@ 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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