readline.c: Missing NULL check on PyLong_FromLong

[aisk]

Bug report

Bug description:

Original gist: https://gist.github.com/devdanzin/60aed55f44fba133ee2d34d46aa8d197

readline.c: Missing NULL check on PyLong_FromLong in setup_readline

Summary

PyLong_FromLong(0L) at lines 1418-1419 stored in begidx/endidx without NULL check. On OOM during module init, readline.get_begidx() does Py_NewRef(NULL) → segfault.

Reproducer

import _testcapi, sys
if "readline" in sys.modules: del sys.modules["readline"]
for n in range(1, 80):
 if "readline" in sys.modules: del sys.modules["readline"]
 _testcapi.set_nomemory(n, 0)
 try:
 import readline
 _testcapi.remove_mem_hooks()
 break
 except MemoryError:
 _testcapi.remove_mem_hooks()
 except ImportError:
 _testcapi.remove_mem_hooks()
 except:
 _testcapi.remove_mem_hooks()
# Assertion: obj != NULL in PyStackRef_FromPyObjectSteal

The original gist said we should check the result of PyLong_FromLong(0L), but I think this is a false positive, because 0 is small int and should not failed while creating a Python int object from it.

However there are other line of code in this file for calling PyLong_FromLong with begidx/endidx withoud check the result:

cpython/Modules/readline.c

Lines 1330 to 1331 in d333e5a

	state->begidx = PyLong_FromLong((long) start);
	state->endidx = PyLong_FromLong((long) end);

I guess the LLM found a real bug but reported it at the wrong place. Either way, we should fix it.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-154385: Add missing NULL check on PyLong_FromLong in flex_complete in readline.c #154386