Prevents sandboxed processes from creating user namespaces to gain fake
root, the standard entry point for kernel privilege-escalation exploits.
Matches Docker and Podman's default seccomp policy.
clone3 remains fully denied (not in the allowlist) so glibc falls back
to clone where this argument filter applies.
Also switches hand-written ioctl constants to libc::{TIOCSTI,TIOCLINUX}.
Derived from Podman's default profile, stripped of capability-conditional
rules (we never grant capabilities), argument filters, and the explicit
EPERM block. Dangerous syscalls (mount, unshare, ptrace, bpf,
perf_event_open, io_uring_*, keyctl, kexec_*, ...) fall through to the
default ENOSYS action, which also keeps glibc's clone3 -> clone fallback
working. x86_64 and aarch64 are supported; other archs error out.
Toggle with --seccomp / --no-seccomp or seccomp = <bool> in config.
mrtoth