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devdanzin/readline_begidx_oom.md

Created March 18, 2026 10:07
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readline.c: Missing NULL check on PyLong_FromLong in setup_readline
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readline_begidx_oom.md

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
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