GH-113462: Limit the number of versions that a single class can use. (GH-114900)

markshannon · web-flow · commit 992446dd5bd3 · 2024-02-05T16:20:54.000Z
diff --git a/Include/cpython/object.h b/Include/cpython/object.h
@@ -229,6 +229,7 @@ struct _typeobject {
 
     /* bitset of which type-watchers care about this type */
     unsigned char tp_watched;
+    uint16_t tp_versions_used;
 };
 
 /* This struct is used by the specializer
diff --git a/Lib/test/test_type_cache.py b/Lib/test/test_type_cache.py
@@ -79,6 +79,19 @@ class C:
 
         _clear_type_cache()
 
+    def test_per_class_limit(self):
+        class C:
+            x = 0
+
+        type_assign_version(C)
+        orig_version = type_get_version(C)
+        for i in range(1001):
+            C.x = i
+            type_assign_version(C)
+
+        new_version = type_get_version(C)
+        self.assertEqual(new_version, 0)
+
 
 @support.cpython_only
 class TypeCacheWithSpecializationTests(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-02-02-05-27-48.gh-issue-113462.VMml8q.rst b/Misc/NEWS.d/next/Core and Builtins/2024-02-02-05-27-48.gh-issue-113462.VMml8q.rst
@@ -0,0 +1,2 @@
+Limit the number of versions that a single class can use. Prevents a few
+wayward classes using up all the version numbers.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -908,6 +908,8 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {
     }
 }
 
+#define MAX_VERSIONS_PER_CLASS 1000
+
 static int
 assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
 {
@@ -922,7 +924,10 @@ assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
     if (!_PyType_HasFeature(type, Py_TPFLAGS_READY)) {
         return 0;
     }
-
+    if (type->tp_versions_used >= MAX_VERSIONS_PER_CLASS) {
+        return 0;
+    }
+    type->tp_versions_used++;
     if (type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) {
         /* static types */
         if (NEXT_GLOBAL_VERSION_TAG > _Py_MAX_GLOBAL_TYPE_VERSION_TAG) {

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+Limit the number of versions that a single class can use. Prevents a few`
	`2`	`+wayward classes using up all the version numbers.`
Original file line number	Diff line number	Diff line change
`@@ -908,6 +908,8 @@ type_mro_modified(PyTypeObject type, PyObject bases) {`
`908`	`908`	`}`
`909`	`909`	`}`
`910`	`910`
	`911`	`+#define MAX_VERSIONS_PER_CLASS 1000`
	`912`	`+`
`911`	`913`	`static int`
`912`	`914`	`assign_version_tag(PyInterpreterState interp, PyTypeObject type)`
`913`	`915`	`{`
`@@ -922,7 +924,10 @@ assign_version_tag(PyInterpreterState interp, PyTypeObject type)`
`922`	`924`	`if (!_PyType_HasFeature(type, Py_TPFLAGS_READY)) {`
`923`	`925`	`return 0;`
`924`	`926`	`}`
`925`		`-`
	`927`	`+ if (type->tp_versions_used >= MAX_VERSIONS_PER_CLASS) {`
	`928`	`+ return 0;`
	`929`	`+ }`
	`930`	`+ type->tp_versions_used++;`
`926`	`931`	`if (type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) {`
`927`	`932`	`/* static types */`
`928`	`933`	`if (NEXT_GLOBAL_VERSION_TAG > _Py_MAX_GLOBAL_TYPE_VERSION_TAG) {`