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fix(sandbox): report Windows ACL limits

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Tianyi Cui
2026-08-10 14:59:38 +08:00
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packages/sandbox/sandbox-windows-acl/README.md
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English | [中文](README.zh.md)
Windows write-restriction sandbox backend for the [harness sandbox seam](../sandbox/): a Node.js/[koffi](https://koffi.dev/) port of the mechanism in [huoyaoyuan/windows-acl-restrict-poc](https://github.com/huoyaoyuan/windows-acl-restrict-poc) (`10e4dfb`, the fixed revision), mounted as the win32 rung of the [`@deepseek-ai/dsh-sandbox-local`](../sandbox-local/) chain (`workspace-write` / `read-only` modes); the same package carries the Linux/macOS backends.
Windows write-restriction sandbox backend for the [harness sandbox seam](../sandbox/): a Node.js/[koffi](https://koffi.dev/) port of the mechanism in [huoyaoyuan/windows-acl-restrict-poc](https://github.com/huoyaoyuan/windows-acl-restrict-poc) (`10e4dfb`, the fixed revision), mounted as the `enforcement: 'partial'` win32 rung of the [`@deepseek-ai/dsh-sandbox-local`](../sandbox-local/) chain (`workspace-write` / `read-only` modes); the same package carries the Linux/macOS backends.
Mechanism in one line: the caller's token is duplicated into a `WRITE_RESTRICTED` token whose restricting SIDs include a write SID (`S-1-4-x-y`) whose Write ACEs exist only on the workspace and the session's private temp directory. The write SID is the per-WORKSPACE identity, derived deterministically from the canonical workspace path (`workspaceWriteSid`), so the workspace-root ACE materializes once per workspace per machine — every later session, call, or restart hits the exact-ACE skip — instead of once per session (see [The confinement runner](#the-confinement-runner)). Windows then grants a write only where BOTH the caller's normal access AND the restricting-SID intersection allow it — the write SID is the write allowlist, and it grants nothing anywhere else on the system; the token's write check also inherits the ambient write ACEs of the OTHER restricting SIDs (the keep-alive group logon SID + Everyone — the Modes section below is the complete boundary).
Mechanism in one line: the caller's token is duplicated into a `WRITE_RESTRICTED` token whose restricting SIDs include a write SID (`S-1-4-x-y`) whose Write ACEs exist only on the workspace and the session's private temp directory. The write SID is the per-WORKSPACE identity, derived deterministically from the canonical workspace path (`workspaceWriteSid`), so the workspace-root ACE materializes once per workspace per machine — every later session, call, or restart hits the exact-ACE skip — instead of once per session (see [The confinement runner](#the-confinement-runner)). Windows then grants a write only where BOTH the caller's normal access AND the restricting-SID intersection allow it. The write SID is the primary allowlist and grants nothing elsewhere, but the check also inherits ambient write ACEs of the OTHER restricting SIDs (the keep-alive group logon SID + Everyone), and NTFS ACLs belong to file objects rather than paths; the Everyone and hard-link boundaries are why the rung reports partial rather than full enforcement.
Building directly on the raw ACL mechanism is the recorded design choice: it implements both confinement modes without the problems the rejected container options carry — see the [design note](../../../.agents/notes/implemented/feature/2026-08-08-windows-acl-restricted-token-sandbox.md) ([mxc](https://github.com/microsoft/mxc/blob/main/docs/process-container/os-version-support.md) needs an OS floor of Windows 11 24H2 and wholesale host DACL writes for arbitrary-path reads; AppContainer cannot do arbitrary-path reads at all).
@@ -42,8 +42,8 @@ The runner creates the restricted token, spawns the wrapped argv under it with t
**Workspace grant reuse** (`--write-sid`): the write SID is DERIVED from the workspace path — no SID or temp-dir state is stored anywhere (the previous per-session random SID and its tamper surface are gone). The seam materializes the workspace ACE STANDING (once per workspace per server lifetime, never revoked — it is the reuse cache) and the temp ACE revocably (revoked on provider dispose), both lazily at the session's first confined execution. The session's private temp subdirectory is DERIVED from the session id + workspace (sha256, 16 hex) instead of stored: a resumed session derives the same directory and re-grants it (the exact-ACE skip keeps that O(1)), while a fork's different session id derives a fresh one. The directory is created EXCLUSIVELY — a pre-existing entry or a reparse point fails the first confined run loudly, so the grant never lands on a foreign object — and removed again on provider dispose. Under `--write-sid` the runner neither grants nor revokes (`manageDacls: false`) — the flag's presence marks the seam-managed contract, its value is the derived SID; without it (standalone use) the runner self-manages with the SAME derived SID (workspace ACEs standing, temp ACE revocable per call). Re-granting after a restart is idempotent: `grantWrite` reads the current DACL and SKIPS the `SetNamedSecurityInfoW` apply when the exact ACE already stands (that apply eagerly re-propagates the identical ACE across the whole tree — minutes on large workspaces). Standing ACEs from an unclean shutdown need no garbage collection — they ARE the cache; the same derived SID re-hits them forever. Known cost: materializing the grant on a big workspace tree blocks for the full eager propagation once per workspace per machine (the first confined write ever on this host).
Modes (the token's restricting-SID list follows the mode; the keep-alive group is logon SID + Everyone in BOTH modes — early DLL init dies with `0xC0000142` and CNG crashes pwsh with `0xE0434352` without them):
- `workspace-write` (logon SID, Everyone, write SID): the workspace and the session's PRIVATE temp subdirectory carry the write-SID Write grant; every other write is denied by the token intersection.
- `read-only` (logon SID, Everyone — NO write SID): STRICT zero grants — nothing is writable. The write SID stays OUT of the list on purpose: the standing workspace grant ACE from an earlier workspace-write period (a `/permission` downgrade, or a crash-resumed session) remains INERT under read-only because the write-restricted pass-2 check grants only what the restricting list carries — while the standing ACE keeps the re-upgrade free of re-propagation. NUL writes are AMBIENT, not granted: the device DACL grants Everyone read+write+execute (`0x1201BF`), so openers whose mask fits it (cmd `> NUL`, node `\\.\NUL`) can write it in BOTH modes — the sandbox cannot zero-grant the NUL device while Everyone stays in the keep-alive group. `Set-Content NUL` fails in both modes (a PowerShell/.NET-layer effect, pinned by the read-only suite — the device DACL is not the denying party); PowerShell's `> $null` redirection keeps working (it discards without opening NUL).
- `workspace-write` (logon SID, Everyone, write SID): the workspace and the session's PRIVATE temp subdirectory carry the write-SID Write grant; other ACL-addressable writes are denied except for the documented Everyone and hard-link boundaries.
- `read-only` (logon SID, Everyone — NO write SID): no explicit write-SID grants. The write SID stays OUT of the list on purpose: the standing workspace grant ACE from an earlier workspace-write period (a `/permission` downgrade, or a crash-resumed session) remains INERT under read-only because the write-restricted pass-2 check grants only what the restricting list carries — while the standing ACE keeps the re-upgrade free of re-propagation. Everyone's ambient rights remain the documented partial boundary. NUL writes are AMBIENT, not granted: the device DACL grants Everyone read+write+execute (`0x1201BF`), so openers whose mask fits it (cmd `> NUL`, node `\\.\NUL`) can write it in BOTH modes — the sandbox cannot zero-grant the NUL device while Everyone stays in the keep-alive group. `Set-Content NUL` fails in both modes (a PowerShell/.NET-layer effect, pinned by the read-only suite — the device DACL is not the denying party); PowerShell's `> $null` redirection keeps working (it discards without opening NUL).
Authenticated Users is absent from BOTH lists — the WMI namespace security check fails (`0x80041003`), so CIM cmdlets and `Get-ComputerInfo` (which silently returns incomplete results rather than an error) are unavailable in EVERY confined mode, and the C:\-root tree-creation escape (standing `AU:(AD)` + `AU:(OI)(CI)(IO)(M)` ACEs) is closed in both — the model-facing surface documents that contract, not a prompt promise. INTERACTIVE/LOCAL are absent from BOTH lists too: the host's Public tree grants write to INTERACTIVE, so Public writes are denied — pinned by the runner's ambient-writable Public-probe regression (see the design note).
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## Verified boundaries (inherent to restricted tokens, not this port)
- **Everyone grants remain ambient write authority.** Everyone must stay in both restricting lists: removing it breaks early DLL initialization and CNG. An external NTFS object whose normal DACL grants Everyone a requested write right therefore clears both access checks and stays writable under both modes. The real runner suite provisions an external `Everyone:Modify` directory and pins that behavior; the provider reports `enforcement: 'partial'` so callers can reject or surface the weaker boundary.
- **Hard links are file-object aliases, not path aliases.** An inheritable workspace ACE propagated onto an existing NTFS hard link changes the one underlying file security descriptor, so the same object is writable through an external alias. Rejecting every multiply-linked workspace file is not viable for ordinary pnpm installations, which use hard links into their content-addressable store; the native runner suite pins the gap and the provider's partial report names its consequence.
- **Writes are restricted; reads, network, and process visibility are not.** `WRITE_RESTRICTED` intersects write accesses only, so a confined child can read any caller-readable file and open sockets. `read-only` mode therefore cannot be expressed by this mechanism alone; pair it with a read-side policy or an AppContainer/`S-1-15-2` capability token for stronger confinement.
- **Console isolation is unavailable.** Under the restricted token, children created with `CREATE_NO_WINDOW` / `CREATE_NEW_CONSOLE` die during DLL initialization with `STATUS_DLL_INIT_FAILED` (`0xC0000142`). The POC tried to fix this by adding the console logon SID (`S-1-2-1`) to the restricting list; on Windows 11 26200 `CreateWellKnownSid(WinLocalLogonSid)` fails with `ERROR_INVALID_PARAMETER` (87), the correct `WinConsoleLogonSid` yields a valid `S-1-2-1` but the child still dies, and the POC's final revision removed both the SID and console isolation. Children therefore share the host console; stdio redirection is pipe-based and unaffected.
- **ACL grants are standing directory mutations.** They persist if the process dies mid-run; workspace ACEs are standing BY DESIGN (never revoked — the reuse cache), temp ACEs are revoked by `dispose()` (`init()` also revokes an already-applied temp grant when a later step fails). The POC's documented manual cleanup (`icacls <dir> /remove '*S-1-4-…'`) fails on this platform with `ERROR_NONE_MAPPED` (1332) — revoke through this module instead. An unclean shutdown needs no self-healing for the workspace ACE: the derived SID re-hits the standing ACE on the next provision (skipping the apply); the write-SID ACE never accumulates a second identity per restart because the identity IS the workspace.
@@ -71,7 +73,7 @@ The koffi struct definitions assert their sizes against the probe at module load
## Model Experience
Indirectly, through [`dsh-bash-sandbox`](../../bash/bash-sandbox/README.md), [`dsh-pwsh-sandbox`](../../bash/pwsh-sandbox/README.md), and their tools, which render this backend's enforcement and denial facts (the confined stderr the tool layer classifies through `denialSignatures`) while the [`dsh-sandbox`](../sandbox/README.md) seam owns the `SANDBOX_UNAVAILABLE` text and runner selection.
Indirectly, through [`dsh-bash-sandbox`](../../bash/bash-sandbox/README.md), [`dsh-pwsh-sandbox`](../../bash/pwsh-sandbox/README.md), and their tools, which render this backend's partial-enforcement and denial facts (the confined stderr the tool layer classifies through `denialSignatures`) while the [`dsh-sandbox`](../sandbox/README.md) seam owns the `SANDBOX_UNAVAILABLE` text and runner selection.
#### KV Cache effect