[Python-checkins] bpo-30570: Use Py_EnterRecursiveCall() in issubclass() (GH-29048) (GH-29178)

[ambv]

https://github.com/python/cpython/commit/1e29dce1138a39e095ba47ab4c1e445fd08716e2
commit: 1e29dce1138a39e095ba47ab4c1e445fd08716e2
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2021-11-04T21:20:21+01:00
summary:

bpo-30570: Use Py_EnterRecursiveCall() in issubclass() (GH-29048) (GH-29178)

* Use Py_EnterRecursiveCall() in issubclass()

Reviewed-by: Gregory P. Smith <greg at krypto.org> [Google]
(cherry picked from commit 423fa1c1817abfa8c3d1bc308ddbbd8f28b69d68)

Co-authored-by: Dennis Sweeney <36520290+sweeneyde at users.noreply.github.com>

files:
A Misc/NEWS.d/next/Core and Builtins/2021-10-19-01-04-08.bpo-30570._G30Ms.rst
M Lib/test/test_isinstance.py
M Objects/abstract.c

diff --git a/Lib/test/test_isinstance.py b/Lib/test/test_isinstance.py
index 31b38996930cc..34082a1a4b361 100644
--- a/Lib/test/test_isinstance.py
+++ b/Lib/test/test_isinstance.py
@@ -281,6 +281,36 @@ def __bases__(self):
         self.assertRaises(RecursionError, issubclass, int, X())
         self.assertRaises(RecursionError, isinstance, 1, X())
 
+    def test_infinite_recursion_via_bases_tuple(self):
+        """Regression test for bpo-30570."""
+        class Failure(object):
+            def __getattr__(self, attr):
+                return (self, None)
+
+        with self.assertRaises(RecursionError):
+            issubclass(Failure(), int)
+
+    def test_infinite_cycle_in_bases(self):
+        """Regression test for bpo-30570."""
+        class X:
+            @property
+            def __bases__(self):
+                return (self, self, self)
+        self.assertRaises(RecursionError, issubclass, X(), int)
+
+    def test_infinitely_many_bases(self):
+        """Regression test for bpo-30570."""
+        class X:
+            def __getattr__(self, attr):
+                self.assertEqual(attr, "__bases__")
+                class A:
+                    pass
+                class B:
+                    pass
+                A.__getattr__ = B.__getattr__ = X.__getattr__
+                return (A(), B())
+        self.assertRaises(RecursionError, issubclass, X(), int)
+
 
 def blowstack(fxn, arg, compare_to):
     # Make sure that calling isinstance with a deeply nested tuple for its
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-10-19-01-04-08.bpo-30570._G30Ms.rst b/Misc/NEWS.d/next/Core and Builtins/2021-10-19-01-04-08.bpo-30570._G30Ms.rst
new file mode 100644
index 0000000000000..d9ab60cd08f56
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-10-19-01-04-08.bpo-30570._G30Ms.rst	
@@ -0,0 +1 @@
+Fixed a crash in ``issubclass()`` from infinite recursion when searching pathological ``__bases__`` tuples.
\ No newline at end of file
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 1922619ad85db..a5cbb12ff87c6 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2417,14 +2417,22 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
             derived = PyTuple_GET_ITEM(bases, 0);
             continue;
         }
-        for (i = 0; i < n; i++) {
-            r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
-            if (r != 0)
-                break;
-        }
+        break;
+    }
+    assert(n >= 2);
+    if (Py_EnterRecursiveCall(" in __issubclass__")) {
         Py_DECREF(bases);
-        return r;
+        return -1;
     }
+    for (i = 0; i < n; i++) {
+        r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
+        if (r != 0) {
+            break;
+        }
+    }
+    Py_LeaveRecursiveCall();
+    Py_DECREF(bases);
+    return r;
 }
 
 static int