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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`_csv`: `_set_str()` missing NULL check after `PyUnicode_DecodeASCII()`","articleBody":"# Bug report\n\n### Bug description:\n\nIn `Modules/_csv.c`, `_set_str()` does not check the return value of `PyUnicode_DecodeASCII()` when using the default value. If the allocation fails (OOM), `*target` is set to `NULL` and the function returns `0` (success).\n\nhttps://github.com/python/cpython/blob/main/Modules/_csv.c#L315-L329\n\n```c\nstatic int\n_set_str(const char *name, PyObject **target, PyObject *src, const char *dflt)\n{\n    if (src == NULL)\n        *target = PyUnicode_DecodeASCII(dflt, strlen(dflt), NULL);\n        // ^^^ no NULL check \n    else {\n        ...\n    }\n    return 0; // Returns 0 even if allocation failed\n}\n```\n\nThis function is called for `lineterminator`:\n```c\nDIASET(_set_str, \"lineterminator\", \u0026self-\u003elineterminator, lineterminator, \"\\r\\n\");\n```\n\nIf allocation fails, `self-\u003elineterminator` is `NULL`. Subsequent calls to `PyUnicode_GET_LENGTH(dialect-\u003elineterminator)` (e.g. in `join_append_data` at line 1183 or `join_append_lineterminator` at line 1299) will dereference `NULL`.\n\n## Fix\n\n```c\nstatic int\n_set_str(const char *name, PyObject **target, PyObject *src, const char *dflt)\n{\n    if (src == NULL) {\n        *target = PyUnicode_DecodeASCII(dflt, strlen(dflt), NULL);\n        if (*target == NULL)\n            return -1;\n    }\n    else {\n        if (!PyUnicode_Check(src)) {\n            PyErr_Format(PyExc_TypeError,\n                         \"\\\"%s\\\" must be a string, not %T\", name, src);\n            return -1;\n        }\n        Py_XSETREF(*target, Py_NewRef(src));\n    }\n    return 0;\n}\n```\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nLinux","author":{"url":"https://github.com/raminfp","@type":"Person","name":"raminfp"},"datePublished":"2026-03-15T12:24:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/145978/cpython/issues/145978"}