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viyatb-oai 937cb5081d fix: fix old system bubblewrap compatibility without falling back to vendored bwrap (#15693 )

Fixes #15283.

## Summary
Older system bubblewrap builds reject `--argv0`, which makes our Linux
sandbox fail before the helper can re-exec. This PR keeps using system
`/usr/bin/bwrap` whenever it exists and only falls back to vendored
bwrap when the system binary is missing. That matters on stricter
AppArmor hosts, where the distro bwrap package also provides the policy
setup needed for user namespaces.

For old system bwrap, we avoid `--argv0` instead of switching binaries:
- pass the sandbox helper a full-path `argv0`,
- keep the existing `current_exe() + --argv0` path when the selected
launcher supports it,
- otherwise omit `--argv0` and re-exec through the helper's own
`argv[0]` path, whose basename still dispatches as
`codex-linux-sandbox`.

Also updates the launcher/warning tests and docs so they match the new
behavior: present-but-old system bwrap uses the compatibility path, and
only absent system bwrap falls back to vendored.

### Validation

1. Install Ubuntu 20.04 in a VM
2. Compile codex and run without bubblewrap installed - see a warning
about falling back to the vendored bwrap
3. Install bwrap and verify version is 0.4.0 without `argv0` support
4. run codex and use apply_patch tool without errors

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<img width="812" height="635" alt="Screenshot 2026-03-25 at 11 45 45 PM"
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---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

2026-03-25 23:51:39 -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. If /usr/bin/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 /usr/bin/bwrap is missing, 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 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 present but too old to support --argv0, the helper uses a no---argv0 compatibility path for the inner re-exec.
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.

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codex-linux-sandbox

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