gh-123431: Harmonize extension code checks in pickle (GH-123434)

This checks are redundant in normal circumstances and can only work if
the extension registry was intentionally broken.

* The Python implementation now raises exception for the extension code
  with false boolean value.
* Simplify the C code. RuntimeError is now raised in explicit checks.
* Add many tests.

1 files changed, 11 insertions, 21 deletions

diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index dc0ef0a..3efc05e 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -3650,34 +3650,24 @@ save_global(PickleState *st, PicklerObject *self, PyObject *obj,
         if (extension_key == NULL) {
             goto error;
         }
-        code_obj = PyDict_GetItemWithError(st->extension_registry,
-                                           extension_key);
+        if (PyDict_GetItemRef(st->extension_registry, extension_key, &code_obj) < 0) {
+            Py_DECREF(extension_key);
+            goto error;
+        }
         Py_DECREF(extension_key);
-        /* The object is not registered in the extension registry.
-           This is the most likely code path. */
         if (code_obj == NULL) {
-            if (PyErr_Occurred()) {
-                goto error;
-            }
+            /* The object is not registered in the extension registry.
+               This is the most likely code path. */
             goto gen_global;
         }
 
-        /* XXX: pickle.py doesn't check neither the type, nor the range
-           of the value returned by the extension_registry. It should for
-           consistency. */
-
-        /* Verify code_obj has the right type and value. */
-        if (!PyLong_Check(code_obj)) {
-            PyErr_Format(st->PicklingError,
-                         "Can't pickle %R: extension code %R isn't an integer",
-                         obj, code_obj);
-            goto error;
-        }
-        code = PyLong_AS_LONG(code_obj);
+        code = PyLong_AsLong(code_obj);
+        Py_DECREF(code_obj);
         if (code <= 0 || code > 0x7fffffffL) {
+            /* Should never happen in normal circumstances, since the type and
+               the value of the code are checked in copyreg.add_extension(). */
             if (!PyErr_Occurred())
-                PyErr_Format(st->PicklingError, "Can't pickle %R: extension "
-                             "code %ld is out of range", obj, code);
+                PyErr_Format(PyExc_RuntimeError, "extension code %ld is out of range", code);
             goto error;
         }