[Python-checkins] bpo-33930: Fix segfault with deep recursion when cleaning method objects (GH-27678)

[pablogsal]

https://github.com/python/cpython/commit/bfc2d5a5c4550ab3a2fadeb9459b4bd948ff61a2
commit: bfc2d5a5c4550ab3a2fadeb9459b4bd948ff61a2
branch: main
author: Pablo Galindo Salgado <Pablogsal at gmail.com>
committer: pablogsal <Pablogsal at gmail.com>
date: 2021-08-11T00:34:14+01:00
summary:

bpo-33930: Fix segfault with deep recursion when cleaning method objects (GH-27678)

files:
A Misc/NEWS.d/next/Core and Builtins/2021-08-09-14-29-52.bpo-33930.--5LQ-.rst
M Lib/test/test_exceptions.py
M Objects/methodobject.c

diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 593107f290dc5..8bcb4b0f789a8 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -1169,6 +1169,21 @@ def g():
         self.assertIsInstance(v, RecursionError, type(v))
         self.assertIn("maximum recursion depth exceeded", str(v))
 
+
+    @cpython_only
+    def test_crashcan_recursion(self):
+        # See bpo-33930
+
+        def foo():
+            o = object()
+            for x in range(1_000_000):
+                # Create a big chain of method objects that will trigger
+                # a deep chain of calls when they need to be destructed.
+                o = o.__dir__
+
+        foo()
+        support.gc_collect()
+
     @cpython_only
     def test_recursion_normalizing_exception(self):
         # Issue #22898.
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-08-09-14-29-52.bpo-33930.--5LQ-.rst b/Misc/NEWS.d/next/Core and Builtins/2021-08-09-14-29-52.bpo-33930.--5LQ-.rst
new file mode 100644
index 0000000000000..827dd3f8b6513
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-08-09-14-29-52.bpo-33930.--5LQ-.rst	
@@ -0,0 +1,2 @@
+Fix segmentation fault with deep recursion when cleaning method objects.
+Patch by Augusto Goulart and Pablo Galindo.
diff --git a/Objects/methodobject.c b/Objects/methodobject.c
index 7b430416c5a04..2df63cfdf6a81 100644
--- a/Objects/methodobject.c
+++ b/Objects/methodobject.c
@@ -160,7 +160,10 @@ PyCMethod_GetClass(PyObject *op)
 static void
 meth_dealloc(PyCFunctionObject *m)
 {
-    _PyObject_GC_UNTRACK(m);
+    // The Py_TRASHCAN mechanism requires that we be able to
+    // call PyObject_GC_UnTrack twice on an object.
+    PyObject_GC_UnTrack(m);
+    Py_TRASHCAN_BEGIN(m, meth_dealloc);
     if (m->m_weakreflist != NULL) {
         PyObject_ClearWeakRefs((PyObject*) m);
     }
@@ -170,6 +173,7 @@ meth_dealloc(PyCFunctionObject *m)
     Py_XDECREF(m->m_self);
     Py_XDECREF(m->m_module);
     PyObject_GC_Del(m);
+    Py_TRASHCAN_END;
 }
 
 static PyObject *