# DF-2768 fix validation (patched kernel #1: Tue Sep  1 00:17:25 UTC 2026,
# combined patch = DF-2768 (MAXPTYS-1) + DF-2769 (PF_SOPEN fence) hunks)
$ su -m nobody -c /tmp/ptmx_limit_offbyone; echo rc=$?
opened 1000 ptmx master fds (expect <= 1000), last error=Operation not supported by device(19)
not vulnerable: /dev/pts/1000 absent
rc=0
# baseline (stock #0): identical run created /dev/pts/1000 and reported VULNERABLE (rc=2)