gh-108308: Replace PyDict_GetItem() with PyDict_GetItemRef() (#108309)

Replace PyDict_GetItem() calls with PyDict_GetItemRef()
or PyDict_GetItemWithError() to handle errors.

* Replace PyLong_AS_LONG() with _PyLong_AsInt()
  and check for errors.
* Check for PyDict_Contains() error.
* pycore_init_builtins() checks for _PyType_Lookup() failure.

1 files changed, 22 insertions, 8 deletions

diff --git a/Python/flowgraph.c b/Python/flowgraph.c
index 719ed921050..e620e7cf1b9 100644
--- a/Python/flowgraph.c
+++ b/Python/flowgraph.c
@@ -2404,17 +2404,31 @@ build_cellfixedoffsets(_PyCompile_CodeUnitMetadata *umd)
     PyObject *varname, *cellindex;
     Py_ssize_t pos = 0;
     while (PyDict_Next(umd->u_cellvars, &pos, &varname, &cellindex)) {
-        PyObject *varindex = PyDict_GetItem(umd->u_varnames, varname);
-        if (varindex != NULL) {
-            assert(PyLong_AS_LONG(cellindex) < INT_MAX);
-            assert(PyLong_AS_LONG(varindex) < INT_MAX);
-            int oldindex = (int)PyLong_AS_LONG(cellindex);
-            int argoffset = (int)PyLong_AS_LONG(varindex);
-            fixed[oldindex] = argoffset;
+        PyObject *varindex;
+        if (PyDict_GetItemRef(umd->u_varnames, varname, &varindex) < 0) {
+            goto error;
+        }
+        if (varindex == NULL) {
+            continue;
+        }
+
+        int argoffset = _PyLong_AsInt(varindex);
+        Py_DECREF(varindex);
+        if (argoffset == -1 && PyErr_Occurred()) {
+            goto error;
         }
-    }
 
+        int oldindex = _PyLong_AsInt(cellindex);
+        if (oldindex == -1 && PyErr_Occurred()) {
+            goto error;
+        }
+        fixed[oldindex] = argoffset;
+    }
     return fixed;
+
+error:
+    PyMem_Free(fixed);
+    return NULL;
 }
 
 #define IS_GENERATOR(CF) \