[3.11] GH-97752: Clear the previous member of newly-created generator/coroutine frames (GH-97812)

miss-islington · pablogsal · commit 585c95df9578 · 2022-10-22T20:10:18.000+01:00
(cherry picked from commit 93fcc1f)
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
@@ -69,6 +69,9 @@ _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 @@`
	`1`	+Fix possible data corruption or crashes when accessing the ``f_back`` member
	`2`	`+of newly-created generator or coroutine frames.`
Original file line number	Diff line number	Diff line change
`@@ -69,6 +69,9 @@ _PyFrame_Copy(_PyInterpreterFrame src, _PyInterpreterFrame dest)`
`69`	`69`	`assert(src->stacktop >= src->f_code->co_nlocalsplus);`
`70`	`70`	`Py_ssize_t size = ((char)&src->localsplus[src->stacktop]) - (char )src;`
`71`	`71`	`memcpy(dest, src, size);`
	`72`	`+ // Don't leave a dangling pointer to the old frame when creating generators`
	`73`	`+ // and coroutines:`
	`74`	`+ dest->previous = NULL;`
`72`	`75`	`}`
`73`	`76`
`74`	`77`