str_repeat() sign mismatch based memory corruption

OVERVIEW str_repeat() suffers from a sign mismatch based integer overflow that results in creation of corrupted ZVALs; this condition, depending on the context, can be abused to bypass PHP-level checks or trigger any kind of memory error: a successful exploitation of this issue is likely to produce …

    /* Initialize the result string */
4907    result_len = input_len * mult;
which then, on line 4930 is passed as argument for RETURN_STRINGL() macro.
It should be noticed that while RETURN_STRINGL() ends up calling ZVAL_STRINGL(), which expects the length argument to be a signed int, result_len …