Fix SpyMessage attribute deletion crashes

src/object_spy_message.cpp

@@ -138,6 +138,11 @@ static PyObject* spy_message_object_getattr(PyObject* o, PyObject* attr_name)
 
 static int spy_message_object_setattr(PyObject* o, PyObject* name, PyObject* value)
 {
+    // tp_setattro receives NULL for deletion. Let descriptors reject deletion
+    // before any custom setter inspects the value or changes message storage.
+    if (value == NULL)
+        return PyObject_GenericSetAttr(o, name, value);
+
     spy_message_object* obj = (spy_message_object*)o;
     if (PyUnicode_CompareWithASCIIString(name, "Data") == 0) {
         Py_ssize_t length = _copy_byte_tuple(value, name, obj->msg.Data, sizeof(obj->msg.Data));
@@ -484,4 +489,4 @@ bool setup_spy_message_object(PyObject* module)
     Py_INCREF(&spy_message_j1850_object_type);
     PyModule_AddObject(module, SPY_MESSAGE_J1850_OBJECT_NAME, (PyObject*)&spy_message_j1850_object_type);
     return true;
-}
+}

tests/test_spy_message.py

@@ -1,7 +1,48 @@
+import os
+import subprocess
+import sys
+import textwrap
+
 import pytest
 import ics
 
 
+@pytest.mark.parametrize("message_type", ["SpyMessage", "SpyMessageJ1850"])
+@pytest.mark.parametrize("attribute", ["Data", "AckBytes", "Header", "ExtraDataPtr", "Protocol", "ExtraDataPtrEnabled"])
+@pytest.mark.parametrize("initialized", [False, True])
+def test_attribute_deletion_is_safe(message_type, attribute, initialized):
+    # Isolate native crashes so every affected attribute/type is reported.
+    code = textwrap.dedent(f"""
+        import ics
+
+        msg = ics.{message_type}()
+        if {initialized!r}:
+            msg.Protocol = ics.SPY_PROTOCOL_CANFD
+            msg.Data = (1, 2, 3)
+            msg.AckBytes = (4, 5)
+            msg.Header = (6, 7)
+            msg.ExtraDataPtr = (8, 9, 10)
+        fields = ("Data", "AckBytes", "Header", "ExtraDataPtr", "Protocol",
+                  "ExtraDataPtrEnabled", "NumberBytesData", "NumberBytesHeader")
+        before = tuple(getattr(msg, field) for field in fields)
+        try:
+            delattr(msg, {attribute!r})
+        except (AttributeError, TypeError):
+            pass
+        else:
+            raise AssertionError("deletion should be rejected")
+        assert tuple(getattr(msg, field) for field in fields) == before
+        # The message remains usable, including replacing and freeing its buffer.
+        msg.ExtraDataPtr = (11, 12)
+        assert msg.ExtraDataPtr == (11, 12)
+        del msg
+    """)
+    env = os.environ.copy()
+    env["PYTHONPATH"] = os.pathsep.join(str(path) for path in sys.path)
+    result = subprocess.run([sys.executable, "-c", code], env=env, capture_output=True, text=True, timeout=30)
+    assert result.returncode == 0, f"exit {result.returncode}\n{result.stdout}\n{result.stderr}"
+
+
 def test_data_roundtrip():
     msg = ics.SpyMessage()
     msg.Data = (1, 2, 3, 4, 5, 6, 7, 8)