From 178a238f25ab8aff7689d7a09d66dc1583ecd6cb Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 4 May 2022 03:23:29 -0700
Subject: [PATCH] gh-92036: Fix gc_fini_untrack() (GH-92037)

Fix a crash in subinterpreters related to the garbage collector. When
a subinterpreter is deleted, untrack all objects tracked by its GC.
To prevent a crash in deallocator functions expecting objects to be
tracked by the GC, leak a strong reference to these objects on
purpose, so they are never deleted and their deallocator functions
are not called.
(cherry picked from commit 14243369b5f80613628a565c224bba7fb3fcacd8)

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 .../2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst           | 5 +++++
 Modules/gcmodule.c                                          | 6 ++++++
 2 files changed, 11 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst b/Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst
new file mode 100644
index 0000000000000..78094c5e4fea7
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-04-28-23-37-30.gh-issue-92036.GZJAC9.rst	
@@ -0,0 +1,5 @@
+Fix a crash in subinterpreters related to the garbage collector. When a
+subinterpreter is deleted, untrack all objects tracked by its GC. To prevent a
+crash in deallocator functions expecting objects to be tracked by the GC, leak
+a strong reference to these objects on purpose, so they are never deleted and
+their deallocator functions are not called. Patch by Victor Stinner.
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 805a159d53d60..43ae6fa98beb9 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -2170,6 +2170,12 @@ gc_fini_untrack(PyGC_Head *list)
     for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(list)) {
         PyObject *op = FROM_GC(gc);
         _PyObject_GC_UNTRACK(op);
+        // gh-92036: If a deallocator function expect the object to be tracked
+        // by the GC (ex: func_dealloc()), it can crash if called on an object
+        // which is no longer tracked by the GC. Leak one strong reference on
+        // purpose so the object is never deleted and its deallocator is not
+        // called.
+        Py_INCREF(op);
     }
 }
 
