gh-92930: _pickle.c: Acquire strong references before calling save() (GH-92931)

(cherry picked from commit 4c496f1)

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

Author: miss-islington

Lib/test/pickletester.py

@@ -3032,6 +3032,67 @@ def check_array(arr):
         # 2-D, non-contiguous
         check_array(arr[::2])
 
+    def test_evil_class_mutating_dict(self):
+        # https://github.com/python/cpython/issues/92930
+        from random import getrandbits
+
+        global Bad
+        class Bad:
+            def __eq__(self, other):
+                return ENABLED
+            def __hash__(self):
+                return 42
+            def __reduce__(self):
+                if getrandbits(6) == 0:
+                    collection.clear()
+                return (Bad, ())
+
+        for proto in protocols:
+            for _ in range(20):
+                ENABLED = False
+                collection = {Bad(): Bad() for _ in range(20)}
+                for bad in collection:
+                    bad.bad = bad
+                    bad.collection = collection
+                ENABLED = True
+                try:
+                    data = self.dumps(collection, proto)
+                    self.loads(data)
+                except RuntimeError as e:
+                    expected = "changed size during iteration"
+                    self.assertIn(expected, str(e))
+
+    def test_evil_pickler_mutating_collection(self):
+        # https://github.com/python/cpython/issues/92930
+        if not hasattr(self, "pickler"):
+            raise self.skipTest(f"{type(self)} has no associated pickler type")
+
+        global Clearer
+        class Clearer:
+            pass
+
+        def check(collection):
+            class EvilPickler(self.pickler):
+                def persistent_id(self, obj):
+                    if isinstance(obj, Clearer):
+                        collection.clear()
+                    return None
+            pickler = EvilPickler(io.BytesIO(), proto)
+            try:
+                pickler.dump(collection)
+            except RuntimeError as e:
+                expected = "changed size during iteration"
+                self.assertIn(expected, str(e))
+
+        for proto in protocols:
+            check([Clearer()])
+            check([Clearer(), Clearer()])
+            check({Clearer()})
+            check({Clearer(), Clearer()})
+            check({Clearer(): 1})
+            check({Clearer(): 1, Clearer(): 2})
+            check({1: Clearer(), 2: Clearer()})
+
 
 class BigmemPickleTests:
 

Misc/NEWS.d/next/Core and Builtins/2022-05-18-18-34-45.gh-issue-92930.kpYPOb.rst

@@ -0,0 +1 @@
+Fixed a crash in ``_pickle.c`` from mutating collections during ``__reduce__`` or ``persistent_id``.

Modules/_pickle.c

@@ -3005,7 +3005,10 @@ batch_list_exact(PicklerObject *self, PyObject *obj)
 
     if (PyList_GET_SIZE(obj) == 1) {
         item = PyList_GET_ITEM(obj, 0);
-        if (save(self, item, 0) < 0)
+        Py_INCREF(item);
+        int err = save(self, item, 0);
+        Py_DECREF(item);
+        if (err < 0)
             return -1;
         if (_Pickler_Write(self, &append_op, 1) < 0)
             return -1;
@@ -3020,7 +3023,10 @@ batch_list_exact(PicklerObject *self, PyObject *obj)
             return -1;
         while (total < PyList_GET_SIZE(obj)) {
             item = PyList_GET_ITEM(obj, total);
-            if (save(self, item, 0) < 0)
+            Py_INCREF(item);
+            int err = save(self, item, 0);
+            Py_DECREF(item);
+            if (err < 0)
                 return -1;
             total++;
             if (++this_batch == BATCHSIZE)
@@ -3258,10 +3264,16 @@ batch_dict_exact(PicklerObject *self, PyObject *obj)
     /* Special-case len(d) == 1 to save space. */
     if (dict_size == 1) {
         PyDict_Next(obj, &ppos, &key, &value);
-        if (save(self, key, 0) < 0)
-            return -1;
-        if (save(self, value, 0) < 0)
-            return -1;
+        Py_INCREF(key);
+        Py_INCREF(value);
+        if (save(self, key, 0) < 0) {
+            goto error;
+        }
+        if (save(self, value, 0) < 0) {
+            goto error;
+        }
+        Py_CLEAR(key);
+        Py_CLEAR(value);
         if (_Pickler_Write(self, &setitem_op, 1) < 0)
             return -1;
         return 0;
@@ -3273,10 +3285,16 @@ batch_dict_exact(PicklerObject *self, PyObject *obj)
         if (_Pickler_Write(self, &mark_op, 1) < 0)
             return -1;
         while (PyDict_Next(obj, &ppos, &key, &value)) {
-            if (save(self, key, 0) < 0)
-                return -1;
-            if (save(self, value, 0) < 0)
-                return -1;
+            Py_INCREF(key);
+            Py_INCREF(value);
+            if (save(self, key, 0) < 0) {
+                goto error;
+            }
+            if (save(self, value, 0) < 0) {
+                goto error;
+            }
+            Py_CLEAR(key);
+            Py_CLEAR(value);
             if (++i == BATCHSIZE)
                 break;
         }
@@ -3291,6 +3309,10 @@ batch_dict_exact(PicklerObject *self, PyObject *obj)
 
     } while (i == BATCHSIZE);
     return 0;
+error:
+    Py_XDECREF(key);
+    Py_XDECREF(value);
+    return -1;
 }
 
 static int
@@ -3410,7 +3432,10 @@ save_set(PicklerObject *self, PyObject *obj)
         if (_Pickler_Write(self, &mark_op, 1) < 0)
             return -1;
         while (_PySet_NextEntry(obj, &ppos, &item, &hash)) {
-            if (save(self, item, 0) < 0)
+            Py_INCREF(item);
+            int err = save(self, item, 0);
+            Py_CLEAR(item);
+            if (err < 0)
                 return -1;
             if (++i == BATCHSIZE)
                 break;