[3.13] gh-126980: Fix bytearray.__buffer__ crash on PyBUF_{READ,WRITE} (GH-126981)

Lib/test/test_buffer.py

@@ -4439,6 +4439,14 @@ def test_issue_7385(self):
         x = ndarray([1,2,3], shape=[3], flags=ND_GETBUF_FAIL)
         self.assertRaises(BufferError, memoryview, x)
 
+    def test_bytearray_release_buffer_read_flag(self):
+        # See https://github.com/python/cpython/issues/126980
+        obj = bytearray(b'abc')
+        with self.assertRaises(SystemError):
+            obj.__buffer__(inspect.BufferFlags.READ)
+        with self.assertRaises(SystemError):
+            obj.__buffer__(inspect.BufferFlags.WRITE)
+
     @support.cpython_only
     def test_pybuffer_size_from_format(self):
         # basic tests

Misc/NEWS.d/next/Core_and_Builtins/2024-11-18-23-18-17.gh-issue-126980.r8QHdi.rst

@@ -0,0 +1,3 @@
+Fix :meth:`~object.__buffer__` of :class:`bytearray` crashing when
+:attr:`~inspect.BufferFlags.READ` or :attr:`~inspect.BufferFlags.WRITE` are
+passed as flags.

Objects/bytearrayobject.c

@@ -44,15 +44,15 @@ _getbytevalue(PyObject* arg, int *value)
 static int
 bytearray_getbuffer(PyByteArrayObject *obj, Py_buffer *view, int flags)
 {
-    void *ptr;
     if (view == NULL) {
         PyErr_SetString(PyExc_BufferError,
             "bytearray_getbuffer: view==NULL argument is obsolete");
         return -1;
     }
-    ptr = (void *) PyByteArray_AS_STRING(obj);
-    /* cannot fail if view != NULL and readonly == 0 */
-    (void)PyBuffer_FillInfo(view, (PyObject*)obj, ptr, Py_SIZE(obj), 0, flags);
+    void *ptr = (void *) PyByteArray_AS_STRING(obj);
+    if (PyBuffer_FillInfo(view, (PyObject*)obj, ptr, Py_SIZE(obj), 0, flags) < 0) {
+        return -1;
+    }
     obj->ob_exports++;
     return 0;
 }