d daedalus

Isolation

Isolation

daedalus offers three isolation levels. Levels 0 and 2 are available; level 1 is skipped because level 2 makes it redundant.

Level 0 — LD_LIBRARY_PATH (available)

Extract the rootfs and launch the app with the right environment variables to find its libs:

LD_LIBRARY_PATH = rootfs/lib:rootfs/lib64:rootfs/usr/lib:...
  • ✅ Simple, portable, no privileges required.
  • ✅ Sufficient when the target machine is compatible (same glibc family).
  • ⚠️ The app sees the entire host filesystem (no isolation).
  • ⚠️ The ELF interpreter path (/lib64/ld-linux...) still resolves on the host → cross-distro portability not guaranteed.

Level 2 — User namespaces ✅ (implemented, recommended)

A Linux kernel feature that allows chroot-like isolation without root privileges. This is what Docker uses in rootless mode.

Mechanism (implemented in stub/src/main.rs):

  1. unshare(CLONE_NEWUSER | CLONE_NEWNS) — new user + mount namespaces
  2. UID/GID mapping: write to /proc/self/uid_map, setgroups, gid_map
  3. Bind-mount the rootfs onto itself (MS_BIND | MS_REC, required by pivot_root)
  4. pivot_root(rootfs, rootfs/.old_root) + umount2("/.old_root", MNT_DETACH)
  5. std::env::set_current_dir("/") — CWD in the new root
  6. Install seccomp-bpf denylist (blocks ~14 dangerous syscalls)
  7. execvp(entrypoint) — the app sees only its rootfs

Usage:

daedalus build my-app/ -o my-app.daedalus --isolation 2

Implementation details:

  • The builder preserves symbolic links (e.g. /lib64/ld-linux-x86-64.so.2) in the rootfs so pivot_root resolves them correctly.
  • The ELF analyzer deduplicates .so files that point to the same real file via different symlinks, avoiding duplicates in the rootfs.
  • /etc/hosts is created in the rootfs (127.0.0.1 localhost) to prevent the DNS PTR lookup hang that blocked app startup.
  • The seccomp filter is a conservative denylist — only syscalls with no legitimate use in web/server apps are blocked (ptrace, mount, reboot, kexec, module loading, etc.). All networking, file I/O, memory, and process syscalls pass through.
  • If seccomp is unavailable (kernel without CONFIG_SECCOMP), the launcher prints a warning and continues without the filter.

Level 1 — chroot (skipped)

Make the app think the extracted rootfs is the system root. It only sees its own libs. Limitation: chroot() traditionally requires root, which we don't want to ask for → skip directly to level 2.

Design decision

Isolation is a feature, not the core product. daedalus's value proposition is "one file, it runs". We start at level 0 (which proves the full pipeline) and add isolation without changing the .daedalus format: only the isolation metadata field and the launcher's behavior change.

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