bpo-41654: Fix deallocator of MemoryError to account for subclasses (GH-22020)
When allocating MemoryError classes, there is some logic to use
pre-allocated instances in a freelist only if the type that is being
allocated is not a subclass of MemoryError. Unfortunately in the
destructor this logic is not present so the freelist is altered even
with subclasses of MemoryError.
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 2ffe8ca..1ec4468 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -1,6 +1,7 @@
# Python test set -- part 5, built-in exceptions
import copy
+import gc
import os
import sys
import unittest
@@ -1330,6 +1331,36 @@
del AssertionError
self.fail('Expected exception')
+ def test_memory_error_subclasses(self):
+ # bpo-41654: MemoryError instances use a freelist of objects that are
+ # linked using the 'dict' attribute when they are inactive/dead.
+ # Subclasses of MemoryError should not participate in the freelist
+ # schema. This test creates a MemoryError object and keeps it alive
+ # (therefore advancing the freelist) and then it creates and destroys a
+ # subclass object. Finally, it checks that creating a new MemoryError
+ # succeeds, proving that the freelist is not corrupted.
+
+ class TestException(MemoryError):
+ pass
+
+ try:
+ raise MemoryError
+ except MemoryError as exc:
+ inst = exc
+
+ try:
+ raise TestException
+ except Exception:
+ pass
+
+ for _ in range(10):
+ try:
+ raise MemoryError
+ except MemoryError as exc:
+ pass
+
+ gc_collect()
+
class ImportErrorTests(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-08-30-20-38-33.bpo-41654.HtnhAM.rst b/Misc/NEWS.d/next/Core and Builtins/2020-08-30-20-38-33.bpo-41654.HtnhAM.rst
new file mode 100644
index 0000000..e05c313
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-08-30-20-38-33.bpo-41654.HtnhAM.rst
@@ -0,0 +1,2 @@
+Fix a crash that occurred when destroying subclasses of
+:class:`MemoryError`. Patch by Pablo Galindo.
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 1195ba1..b08cbdd 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2286,8 +2286,11 @@
{
PyBaseExceptionObject *self;
- if (type != (PyTypeObject *) PyExc_MemoryError)
+ /* If this is a subclass of MemoryError, don't use the freelist
+ * and just return a fresh object */
+ if (type != (PyTypeObject *) PyExc_MemoryError) {
return BaseException_new(type, args, kwds);
+ }
struct _Py_exc_state *state = get_exc_state();
if (state->memerrors_freelist == NULL) {
@@ -2313,9 +2316,16 @@
static void
MemoryError_dealloc(PyBaseExceptionObject *self)
{
- _PyObject_GC_UNTRACK(self);
BaseException_clear(self);
+ /* If this is a subclass of MemoryError, we don't need to
+ * do anything in the free-list*/
+ if (!Py_IS_TYPE(self, (PyTypeObject *) PyExc_MemoryError)) {
+ return Py_TYPE(self)->tp_free((PyObject *)self);
+ }
+
+ _PyObject_GC_UNTRACK(self);
+
struct _Py_exc_state *state = get_exc_state();
if (state->memerrors_numfree >= MEMERRORS_SAVE) {
Py_TYPE(self)->tp_free((PyObject *)self);