From 66aa78cbe604a7c5731f074b869f92174a8e3b64 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marta=20G=C3=B3mez=20Mac=C3=ADas?= <mgmacias@google.com>
Date: Sun, 5 Mar 2023 12:00:41 +0100
Subject: gh-102356: Add thrashcan macros to filter object dealloc (#102426)

Add thrashcan macros to the deallocator of the filter objects to protect against deeply nested destruction of chains of nested filters.
---
 Lib/test/test_builtin.py                                       | 10 ++++++++++
 Misc/ACKS                                                      |  1 +
 .../2023-03-04-20-56-12.gh-issue-102356.07KvUd.rst             |  2 ++
 Python/bltinmodule.c                                           |  2 ++
 4 files changed, 15 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-03-04-20-56-12.gh-issue-102356.07KvUd.rst

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 9e19af0..e7a79bc 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -926,6 +926,16 @@ class BuiltinTest(unittest.TestCase):
             f2 = filter(filter_char, "abcdeabcde")
             self.check_iter_pickle(f1, list(f2), proto)
 
+    def test_filter_dealloc(self):
+        # Tests recursive deallocation of nested filter objects using the
+        # thrashcan mechanism. See gh-102356 for more details.
+        max_iters = 1000000
+        i = filter(bool, range(max_iters))
+        for _ in range(max_iters):
+            i = filter(bool, i)
+        del i
+        gc.collect()
+
     def test_getattr(self):
         self.assertTrue(getattr(sys, 'stdout') is sys.stdout)
         self.assertRaises(TypeError, getattr)
diff --git a/Misc/ACKS b/Misc/ACKS
index c591cd3..7bbde3a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -637,6 +637,7 @@ Tim Golden
 Yonatan Goldschmidt
 Mark Gollahon
 Mikhail Golubev
+Marta Gómez Macías
 Guilherme Gonçalves
 Tiago Gonçalves
 Chris Gonnerman
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-03-04-20-56-12.gh-issue-102356.07KvUd.rst b/Misc/NEWS.d/next/Core and Builtins/2023-03-04-20-56-12.gh-issue-102356.07KvUd.rst
new file mode 100644
index 0000000..c03fd52
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-03-04-20-56-12.gh-issue-102356.07KvUd.rst	
@@ -0,0 +1,2 @@
+Fix a bug that caused a crash when deallocating deeply nested filter
+objects. Patch by Marta Gómez Macías.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 53439ab..12ca0ba 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -553,9 +553,11 @@ static void
 filter_dealloc(filterobject *lz)
 {
     PyObject_GC_UnTrack(lz);
+    Py_TRASHCAN_BEGIN(lz, filter_dealloc)
     Py_XDECREF(lz->func);
     Py_XDECREF(lz->it);
     Py_TYPE(lz)->tp_free(lz);
+    Py_TRASHCAN_END
 }
 
 static int
-- 
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