python · markshannon · Oct 3, 2022 · Oct 3, 2022 · Oct 3, 2022 · Oct 3, 2022
diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
@@ -206,6 +206,25 @@ def __del__(self):
        finally:
            gc.set_threshold(*thresholds)

+    def test_ag_frame_f_back(self):
+        async def f():
+            yield
+        ag = f()
+        self.assertIsNone(ag.ag_frame.f_back)
+
+    def test_cr_frame_f_back(self):
+        async def f():
+            pass
+        cr = f()
+        self.assertIsNone(cr.cr_frame.f_back)
+        cr.close()  # Suppress RuntimeWarning.
+
+    def test_gi_frame_f_back(self):
+        def f():
+            yield
+        gi = f()
+        self.assertIsNone(gi.gi_frame.f_back)
+


 class ExceptionTest(unittest.TestCase):

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-10-03-13-35-48.gh-issue-97752.0xTjJY.rst b/Misc/NEWS.d/next/Core and Builtins/2022-10-03-13-35-48.gh-issue-97752.0xTjJY.rst
@@ -0,0 +1,2 @@
+Fix possible data corruption or crashes when accessing the ``f_back`` member
+of newly-created generator or coroutine frames.
diff --git a/Python/frame.c b/Python/frame.c
@@ -54,6 +54,9 @@ _PyFrame_Copy(_PyInterpreterFrame *src, _PyInterpreterFrame *dest)
    assert(src->stacktop >= src->f_code->co_nlocalsplus);
    Py_ssize_t size = ((char*)&src->localsplus[src->stacktop]) - (char *)src;
    memcpy(dest, src, size);
+    // Don't leave a dangling pointer to the old frame when creating generators
+    // and coroutines:
+    dest->previous = NULL;
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix possible data corruption or crashes when accessing the ``f_back`` member
		of newly-created generator or coroutine frames.