Process crash via reusable hold buffer shrink

Heap overflow in GNU coreutils split 9.2 through 9.4 allows local users to crash the process via crafted line-oriented input. The line_bytes_split function shrinks its reusable hold buffer after writing a long held line, then a later memcpy exceeds that allocation when long and short lines are mixed. Exploitation requires local invocation of split with --line-bytes; the demonstrated consequence is termination of that process, not a system-wide outage.