[Python-checkins] bpo-45262, asyncio: Fix cache of the running loop holder (GH-28796)

[vstinner]

https://github.com/python/cpython/commit/392a89835371baa0fc4bf79ae479abb80661f57d
commit: 392a89835371baa0fc4bf79ae479abb80661f57d
branch: main
author: Matthias Reichl <github at hias.horus.com>
committer: vstinner <vstinner at python.org>
date: 2021-10-08T00:46:49+02:00
summary:

 bpo-45262, asyncio: Fix cache of the running loop holder (GH-28796)

Prevent use-after-free of running loop holder via cache.

files:
A Misc/NEWS.d/next/Library/2021-10-07-14-04-10.bpo-45262.HqF71Z.rst
M Modules/_asynciomodule.c

diff --git a/Misc/NEWS.d/next/Library/2021-10-07-14-04-10.bpo-45262.HqF71Z.rst b/Misc/NEWS.d/next/Library/2021-10-07-14-04-10.bpo-45262.HqF71Z.rst
new file mode 100644
index 0000000000000..4cd949fe1ed5d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-10-07-14-04-10.bpo-45262.HqF71Z.rst
@@ -0,0 +1 @@
+Prevent use-after-free in asyncio. Make sure the cached running loop holder gets cleared on dealloc to prevent use-after-free in get_running_loop
\ No newline at end of file
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index ecc73d1ca8bf0..56079b0277d1a 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -3239,6 +3239,9 @@ new_running_loop_holder(PyObject *loop)
 static void
 PyRunningLoopHolder_tp_dealloc(PyRunningLoopHolder *rl)
 {
+    if (cached_running_holder == (PyObject *)rl) {
+        cached_running_holder = NULL;
+    }
     Py_CLEAR(rl->rl_loop);
     PyObject_Free(rl);
 }