f194d4b115
## Summary - preserve Linux bubblewrap semantics for `write -> none -> write` filesystem policies by recreating masked mount targets before rebinding narrower writable descendants - add a Linux runtime regression for `/repo = write`, `/repo/a = none`, `/repo/a/b = write` so the nested writable child is exercised under bubblewrap - document the supported legacy Landlock fallback and the split-policy bubblewrap behavior for overlapping carveouts ## Example Given a split filesystem policy like: ```toml "/repo" = "write" "/repo/a" = "none" "/repo/a/b" = "write" ``` this PR keeps `/repo` writable, masks `/repo/a`, and still reopens `/repo/a/b` as writable again under bubblewrap. ## Testing - `just fmt` - `cargo test -p codex-linux-sandbox` - `cargo clippy -p codex-linux-sandbox --tests -- -D warnings`
55 lines
3.2 KiB
Markdown
55 lines
3.2 KiB
Markdown
# codex-linux-sandbox
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This crate is responsible for producing:
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- a `codex-linux-sandbox` standalone executable for Linux that is bundled with the Node.js version of the Codex CLI
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- a lib crate that exposes the business logic of the executable as `run_main()` so that
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- the `codex-exec` CLI can check if its arg0 is `codex-linux-sandbox` and, if so, execute as if it were `codex-linux-sandbox`
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- this should also be true of the `codex` multitool CLI
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On Linux, the bubblewrap pipeline uses the vendored bubblewrap path compiled
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into this binary.
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**Current Behavior**
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- Legacy `SandboxPolicy` / `sandbox_mode` configs remain supported.
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- Bubblewrap is the default filesystem sandbox pipeline and is standardized on
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the vendored path.
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- Legacy Landlock + mount protections remain available as an explicit legacy
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fallback path.
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- Set `features.use_legacy_landlock = true` (or CLI `-c use_legacy_landlock=true`)
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to force the legacy Landlock fallback.
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- The legacy Landlock fallback is used only when the split filesystem policy is
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sandbox-equivalent to the legacy model after `cwd` resolution.
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- Split-only filesystem policies that do not round-trip through the legacy
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`SandboxPolicy` model stay on bubblewrap so nested read-only or denied
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carveouts are preserved.
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- When the default bubblewrap pipeline is active, the helper applies `PR_SET_NO_NEW_PRIVS` and a
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seccomp network filter in-process.
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- When the default bubblewrap pipeline is active, the filesystem is read-only by default via `--ro-bind / /`.
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- When the default bubblewrap pipeline is active, writable roots are layered with `--bind <root> <root>`.
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- When the default bubblewrap pipeline is active, protected subpaths under writable roots (for
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example `.git`,
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resolved `gitdir:`, and `.codex`) are re-applied as read-only via `--ro-bind`.
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- When the default bubblewrap pipeline is active, overlapping split-policy
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entries are applied in path-specificity order so narrower writable children
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can reopen broader read-only or denied parents while narrower denied subpaths
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still win. For example, `/repo = write`, `/repo/a = none`, `/repo/a/b = write`
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keeps `/repo` writable, denies `/repo/a`, and reopens `/repo/a/b` as
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writable again.
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- When the default bubblewrap pipeline is active, symlink-in-path and non-existent protected paths inside
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writable roots are blocked by mounting `/dev/null` on the symlink or first
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missing component.
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- When the default bubblewrap pipeline is active, the helper explicitly isolates the user namespace via
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`--unshare-user` and the PID namespace via `--unshare-pid`.
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- When the default bubblewrap pipeline is active and network is restricted without proxy routing, the helper also
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isolates the network namespace via `--unshare-net`.
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- In managed proxy mode, the helper uses `--unshare-net` plus an internal
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TCP->UDS->TCP routing bridge so tool traffic reaches only configured proxy
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endpoints.
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- In managed proxy mode, after the bridge is live, seccomp blocks new
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AF_UNIX/socketpair creation for the user command.
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- When the default bubblewrap pipeline is active, it mounts a fresh `/proc` via `--proc /proc` by default, but
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you can skip this in restrictive container environments with `--no-proc`.
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**Notes**
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- The CLI surface still uses legacy names like `codex debug landlock`.
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