static CYTHON_INLINE PyObject* __Pyx_decode_c_string(
         const char* cstring, Py_ssize_t start, Py_ssize_t stop,
         const char* encoding, const char* errors,
         PyObject* (*decode_func)(const char *s, Py_ssize_t size, const char *errors)) {
    Py_ssize_t length;
    if (unlikely((start < 0) | (stop < 0))) {
        size_t slen = strlen(cstring);
        if (unlikely(slen > (size_t) PY_SSIZE_T_MAX)) {
            PyErr_SetString(PyExc_OverflowError,
                            "c-string too long to convert to Python");
            return NULL;
        }
        length = (Py_ssize_t) slen;
        if (start < 0) {
            start += length;
            if (start < 0)
                start = 0;
        }
        if (stop < 0)
            stop += length;
    }
    if (unlikely(stop <= start))
        return PyUnicode_FromUnicode(NULL, 0);
    length = stop - start;
    cstring += start;
    if (decode_func) {
        return decode_func(cstring, length, errors);
    } else {
        return PyUnicode_Decode(cstring, length, encoding, errors);
    }
}
The program copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow.