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fix(sandbox): resolve workspace roots per session

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Tianyi Cui
2026-07-21 00:44:28 +08:00
parent 171a0e2b30
commit ff21f91a39
54 changed files with 664 additions and 305 deletions
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packages/fs/fs-sandbox/README.md
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@@ -2,11 +2,11 @@
`SandboxedFileSystem` extends [`LocalFileSystem`](../fs-local/README.md) and registers as `ctx.fs`. It inherits every text-storage mechanic verbatim (resolve, stat, read/stream, list, the atomic write, the read-match-write edit critical section) and adds only a per-call MODE fence on `writeText`/`editText`. Reads always pass through — every mode permits reading.
Loading it INSTEAD OF `dsh-fs-local`, together with a [`ctx.sandboxPolicy`](../../sandbox/sandbox-policy/README.md), is the whole swap; the model-facing tools (`dsh-tool-fs`) are untouched. Injects `sandboxPolicy` for the default mode and the `workspace-write` boundary root — the SAME policy home bash reads, so the two families never confine to different roots.
Loading it INSTEAD OF `dsh-fs-local`, together with a [`ctx.sandboxPolicy`](../../sandbox/sandbox-policy/README.md), is the whole swap; the model-facing tools (`dsh-tool-fs`) are untouched. The tool layer resolves the calling session's mode and cwd into the SAME per-call policy bash receives, so the two families never confine to different roots.
## The fence
The per-call mode is the tool-stamped effective mode (session override or escalation grant), falling back to the deployment default:
The per-call policy carries the effective mode (session override or escalation grant) together with the calling session's immutable cwd root, falling back to deployment policy only for calls without one:
- `read-only` — denies every mutation with the structured `FS_SANDBOX_DENIED`.
- `workspace-write` — allows a mutation only when the target canonicalizes under a writable root: the workspace root plus the platform temp areas (`/tmp`, `os.tmpdir()`), the SAME set the Seatbelt profile grants, derived from the one [`writableRoots`](../../sandbox/README.md) function so the fs fence and the bash runner cannot drift. The target is re-canonicalized immediately before delegating, so an ancestor symlink swapped since the tool resolved it is caught.
@@ -30,4 +30,4 @@ No direct invalidation; the named consumer owns any request-prefix changes.
- **A policy fence, not a kernel boundary** — the check is trusted code over a model-controlled path, so the residual resolve-to-syscall TOCTOU is narrowed (by the in-place re-canonicalization) but not eliminated; adversarial host processes are out of scope. Kernel-grade isolation of untrusted code stays `ctx.bash`'s.
- **Fence-vs-runner parity is derived, not asserted** — the writable set comes from `writableRoots`, shared with the Seatbelt profile and pinned by a parity test; a runner profile that changed its writable set without that function would drift.
- **Requires `ctx.sandboxPolicy`** — the backend reads the default mode and workspace root from it and does not confine without it composed.
- **Requires `ctx.sandboxPolicy`** — tools use it to resolve each session policy and the backend uses it for agentless-call fallbacks; the backend does not confine without it composed.