GNU tar: unbounded strcpy into fixed-size archive header field

A tar archive creation path copies attacker-influenced strings into fixed-size tar header fields with strcpy, relying on prior assumptions that the source has already been bounded. In the GNU tar source snapshot, _write_volume_label() writes the volume label directly into label->header.name, and add_volume_label() builds a label string before passing it there. Similar patterns exist in other header-building helpers that target fixed-width tar fields.