GNU tar fixed-size tar header writes can overflow on unbounded labels and path concatenation

GNU tar contains multiple string construction sites that rely on strcpy/strcat into buffers sized from metadata-derived lengths. In particular, label writing copies an arbitrary label into the tar header name field, and directory/name assembly concatenates entry data after reallocating using a length check that must exactly match the trailing terminator assumptions. These patterns are risky because archive-controlled or user-controlled names can exceed fixed header field sizes or create off-by-one space mismatches.