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codex-linux-sandbox

codex-rs/linux-sandbox/README.md

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codex-linux-sandbox

This crate is responsible for producing:

  • a codex-linux-sandbox standalone executable for Linux that is bundled with the Node.js version of the Codex CLI
  • a lib crate that exposes the business logic of the executable as run_main() so that
    • the codex-exec CLI can check if its arg0 is codex-linux-sandbox and, if so, execute as if it were codex-linux-sandbox
    • this should also be true of the codex multitool CLI

On Linux, the bubblewrap pipeline prefers the system /usr/bin/bwrap whenever it is available. If /usr/bin/bwrap is missing, the helper still falls back to the vendored bubblewrap path compiled into this binary. Codex also surfaces a startup warning when /usr/bin/bwrap is missing so users know it is falling back to the vendored helper.

Current Behavior

  • Legacy SandboxPolicy / sandbox_mode configs remain supported.
  • Bubblewrap is the default filesystem sandbox pipeline.
  • If /usr/bin/bwrap is present, the helper uses it.
  • If /usr/bin/bwrap is missing, the helper falls back to the vendored bubblewrap path.
  • If /usr/bin/bwrap is missing, Codex also surfaces a startup warning instead of printing directly from the sandbox helper.
  • Legacy Landlock + mount protections remain available as an explicit legacy fallback path.
  • Set features.use_legacy_landlock = true (or CLI -c use_legacy_landlock=true) to force the legacy Landlock fallback.
  • The legacy Landlock fallback is used only when the split filesystem policy is sandbox-equivalent to the legacy model after cwd resolution.
  • Split-only filesystem policies that do not round-trip through the legacy SandboxPolicy model stay on bubblewrap so nested read-only or denied carveouts are preserved.
  • When the default bubblewrap pipeline is active, the helper applies PR_SET_NO_NEW_PRIVS and a seccomp network filter in-process.
  • When the default bubblewrap pipeline is active, the filesystem is read-only by default via --ro-bind / /.
  • When the default bubblewrap pipeline is active, writable roots are layered with --bind <root> <root>.
  • When the default bubblewrap pipeline is active, protected subpaths under writable roots (for example .git, resolved gitdir:, and .codex) are re-applied as read-only via --ro-bind.
  • When the default bubblewrap pipeline is active, overlapping split-policy entries are applied in path-specificity order so narrower writable children can reopen broader read-only or denied parents while narrower denied subpaths still win. For example, /repo = write, /repo/a = none, /repo/a/b = write keeps /repo writable, denies /repo/a, and reopens /repo/a/b as writable again.
  • When the default bubblewrap pipeline is active, symlink-in-path and non-existent protected paths inside writable roots are blocked by mounting /dev/null on the symlink or first missing component.
  • When the default bubblewrap pipeline is active, the helper explicitly isolates the user namespace via --unshare-user and the PID namespace via --unshare-pid.
  • When the default bubblewrap pipeline is active and network is restricted without proxy routing, the helper also isolates the network namespace via --unshare-net.
  • In managed proxy mode, the helper uses --unshare-net plus an internal TCP->UDS->TCP routing bridge so tool traffic reaches only configured proxy endpoints.
  • In managed proxy mode, after the bridge is live, seccomp blocks new AF_UNIX/socketpair creation for the user command.
  • When the default bubblewrap pipeline is active, it mounts a fresh /proc via --proc /proc by default, but you can skip this in restrictive container environments with --no-proc.

Notes

  • The CLI surface still uses legacy names like codex debug landlock.