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codex/codex-rs/linux-sandbox/README.md
viyatb-oai cb870a169a fix(sandboxing): reject WSL1 bubblewrap sandboxing (#17559)
## Summary

- detect WSL1 before Codex probes or invokes the Linux bubblewrap
sandbox
- fail early with a clear unsupported-operation message when a command
would require bubblewrap on WSL1
- document that WSL2 follows the normal Linux bubblewrap path while WSL1
is unsupported

## Why

Codex 0.115.0 made bubblewrap the default Linux sandbox. WSL1 cannot
create the user namespaces that bubblewrap needs, so shell commands
currently fail later with a raw bwrap namespace error. This makes the
unsupported environment explicit and keeps non-bubblewrap paths
unchanged.

The WSL detection reads /proc/version, lets an explicit WSL<version>
marker decide WSL1 vs WSL2+, and only treats a bare Microsoft marker as
WSL1 when no explicit WSL version is present.

addresses https://github.com/openai/codex/issues/16076

---------

Co-authored-by: Codex <noreply@openai.com>
2026-04-12 14:08:14 -07:00

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Markdown

# 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 first `bwrap` found on `PATH`
outside the current working directory whenever it is available. If `bwrap` is
present but too old to support
`--argv0`, the helper keeps using system bubblewrap and switches to a
no-`--argv0` compatibility path for the inner re-exec. If `bwrap` is missing,
the helper falls back to the vendored bubblewrap path compiled into this
binary.
Codex also surfaces a startup warning when `bwrap` is missing so users know it
is falling back to the vendored helper. Codex surfaces the same startup warning
path when bubblewrap cannot create user namespaces. WSL2 follows the normal
Linux bubblewrap path. WSL1 is not supported for bubblewrap sandboxing because
it cannot create the required user namespaces, so Codex rejects sandboxed shell
commands that would enter the bubblewrap path.
**Current Behavior**
- Legacy `SandboxPolicy` / `sandbox_mode` configs remain supported.
- Bubblewrap is the default filesystem sandbox pipeline.
- If `bwrap` is present on `PATH` outside the current working directory, the
helper uses it.
- If `bwrap` is present but too old to support `--argv0`, the helper uses a
no-`--argv0` compatibility path for the inner re-exec.
- If `bwrap` is missing, the helper falls back to the vendored bubblewrap
path.
- If `bwrap` is missing, Codex also surfaces a startup warning instead of
printing directly from the sandbox helper.
- If bubblewrap cannot create user namespaces, Codex surfaces a startup warning
instead of waiting for a runtime sandbox failure.
- WSL2 uses the normal Linux bubblewrap path.
- WSL1 is not supported for bubblewrap sandboxing; Codex rejects sandboxed
shell commands that would require the bubblewrap path before invoking `bwrap`.
- 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`.