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Michael Bolin d1088158b8 fix: fall back to vendored bubblewrap when system bwrap lacks --argv0 (#15338 )

## Why

Fixes [#15283](https://github.com/openai/codex/issues/15283), where
sandboxed tool calls fail on older distro `bubblewrap` builds because
`/usr/bin/bwrap` does not understand `--argv0`. The upstream [bubblewrap
v0.9.0 release
notes](https://github.com/containers/bubblewrap/releases/tag/v0.9.0)
explicitly call out `Add --argv0`. Flipping `use_legacy_landlock`
globally works around that compatibility bug, but it also weakens the
default Linux sandbox and breaks proxy-routed and split-policy cases
called out in review.

The follow-up Linux CI failure was in the new launcher test rather than
the launcher logic: the fake `bwrap` helper stayed open for writing, so
Linux would not exec it. This update also closes the user-visibility gap
from review by surfacing the same startup warning when `/usr/bin/bwrap`
is present but too old for `--argv0`, not only when it is missing.

## What Changed

- keep `use_legacy_landlock` default-disabled
- teach `codex-rs/linux-sandbox/src/launcher.rs` to fall back to the
vendored bubblewrap build when `/usr/bin/bwrap` does not advertise
`--argv0` support
- add launcher tests for supported, unsupported, and missing system
`bwrap`
- write the fake `bwrap` test helper to a closed temp path so the
supported-path launcher test works on Linux too
- extend the startup warning path so Codex warns when `/usr/bin/bwrap`
is missing or too old to support `--argv0`
- mirror the warning/fallback wording across
`codex-rs/linux-sandbox/README.md` and `codex-rs/core/README.md`,
including that the fallback is the vendored bubblewrap compiled into the
binary
- cite the upstream `bubblewrap` release that introduced `--argv0`

## Verification

- `bazel test --config=remote --platforms=//:rbe
//codex-rs/linux-sandbox:linux-sandbox-unit-tests
--test_filter=launcher::tests::prefers_system_bwrap_when_help_lists_argv0
--test_output=errors`
- `cargo test -p codex-core system_bwrap_warning`
- `cargo check -p codex-exec -p codex-tui -p codex-tui-app-server -p
codex-app-server`
- `just argument-comment-lint`

2026-03-23 09:46:51 -07:00

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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 and supports the required argv-rewrite flags. If /usr/bin/bwrap is missing or too old to support the required flags, the helper falls back to the vendored bubblewrap path compiled into this binary. Codex also surfaces a startup warning when /usr/bin/bwrap is missing or too old to support the required flags 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 and supports the required argv-rewrite flags, the helper uses it.
If /usr/bin/bwrap is missing or too old to support the required flags, the helper falls back to the vendored bubblewrap path.
If /usr/bin/bwrap is missing or too old to support the required flags, 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.

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codex-linux-sandbox

4.0 KiB

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