Fix unbounded write on negative star precision in format_converter - #247
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A "%.*[diouxX]" conversion with a negative precision was only clamped to -1, which FIX_PRECISION() compares against a size_t: (size_t)-1 turns the zero-padding loop into an unbounded backward write through num_buf and the stack. Treat a negative star precision as omitted in format_converter() only; xbuf_format_converter() keeps -1 as the %H shortest-float sentinel used by serialize_precision.
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Upstream: php#23416 |
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A negative star precision was only clamped to -1, so FIX_PRECISION() treated it as SIZE_MAX and wrote backwards through the buffer. Treat omitted precision that way in format_converter() only. xbuf_format_converter() keeps -1 as the %H shortest-float sentinel used by serialize_precision.