@deepseek-ai/dsh-sandbox-windows-acl

@deepseek-ai/dsh-sandbox-windows-acl

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Windows write-restriction sandbox backend for the harness sandbox seam: a Node.js/koffi port of the mechanism in huoyaoyuan/windows-acl-restrict-poc (10e4dfb, the fixed revision), mounted as the win32 rung of the @deepseek-ai/dsh-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). 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).

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 (mxc 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).

Usage

import { AclSandbox, workspaceWriteSid } from '@deepseek-ai/dsh-sandbox-windows-acl'

const workspaceRoot = process.cwd()

// mode selects the token's restricting-SID list (see Modes below) and must
// match the grant shape: read-only pairs with zero grants. workspace-write
// REQUIRES the workspace's write SID — the per-workspace identity.
const sandbox = new AclSandbox({ writableDirs: [workspaceRoot], writeSid: workspaceWriteSid(workspaceRoot), mode: 'workspace-write' })
await sandbox.init() // throws on ANY Win32 failure — never spawns unrestricted

const child = sandbox.spawn({ command: 'pwsh', args: ['-NoProfile', '-Command', '...'], cwd: workspaceRoot })
const { stdout, stderr, exitCode } = await child.wait()

sandbox.dispose() // revokes the revocable (temp) grant, keeps the standing workspace ACE; reports every cleanup failure

A direct AclSandbox grants the workspace ACEs STANDING (dispose() leaves them — they are the cross-instance reuse cache) and the temp ACE revocably (dispose() revokes it, so an inheritable ACE never outlives the instance on the ambient temp root). The server-side reuse is the AclWriteGrant class: add(path, standing) per directory, dispose() revokes the revocable paths and frees the SID — see the runner contract below. Every Win32 API call in this package is checked; failures throw Win32Error carrying the API name, the exact Win32 code, the FormatMessageW system text, and the failing path/context. This is deliberate: the POC ignored every return value and, when CreateRestrictedToken failed, silently ran the child with the FULL unrestricted token (fail-open). This port fails closed by construction.

The confinement runner

The seam-facing shape is the runner entry (./runner), the argv-prefix wrapper @deepseek-ai/dsh-sandbox-local spawns in place of the caller's command — the same architecture as bwrap/landlock-run/sandbox-exec, so the sandbox seam's confine() contract needs no change. Stable argv contract:

node runner.js --workspace <dir> --temp <dir> --mode <read-only|workspace-write> [--write-sid <S-1-4-…>] -- <argv...>

The runner creates the restricted token, spawns the wrapped argv under it with the caller's stdio passed straight through (the caller's pipes, made inheritable around the spawn — Node clears stdio inheritability at startup, which raw spawns must compensate for), wraps the child in a KILL_ON_JOB_CLOSE job (a dead runner kills the child), ignores its own console Ctrl+C so the child handles its own, mirrors the child's exit code, and revokes its temp grant on exit (workspace ACEs stand). Every runner-side failure prints windows-acl-run: <detail> to stderr and exits 127 — the seam's RUNNER_FAILURE_RULES match that signature, so a runner refusal is never mistaken for a denial.

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).

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).

The AclSandbox class (tempDir: null disables the temp grant) remains the programmatic API for direct spawns; AclWriteGrant is the server-side materialization half of the grant lifecycle.

Header verification

All constants, signatures, and struct layouts were verified against the Windows headers on the development machine (MinGW winnt.h / accctrl.h / aclapi.h / securitybaseapi.h / sddl.h / processthreadsapi.h / fileapi.h / namedpipeapi.h / synchapi.h / winbase.h) and are cross-checked at runtime by verify/abi-probe.cpp (sizes, offsets, enum values, static asserts):

g++ -std=c++20 -municode -O2 -o abi-probe.exe verify/abi-probe.cpp -ladvapi32 && ./abi-probe.exe

The koffi struct definitions assert their sizes against the probe at module load, so a header/koffi layout drift fails loudly instead of corrupting memory.

Verified boundaries (inherent to restricted tokens, not this port)

• 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.
• Granted directories must be caller-owned. The owner's implicit WRITE_DAC is what lets the sandbox edit the DACL without elevation.
• The temp grant follows GetTempPathW — pass tempDir explicitly whenever possible. GetTempPathW reads the NATIVE environment block, which host runtimes that manage process.env through worker pools may not keep in sync (verified with vitest: a worker-side process.env.TMP change never reached the native block). The seam passes the session's PRIVATE subdirectory (<temp>\dsh-<16 hex> derived from the session id + workspace, created exclusively — a pre-existing entry or reparse point fails loudly); a defaulted grant landing on the real temp dir inherits (OI)(CI) over every subdirectory of temp, silently widening the allowlist — point it at a per-sandbox directory instead.
• The confined child's temp root is private per session (workspace-write + --write-sid): the runner rewrites TMP/TEMP via SetEnvironmentVariableW to the session's private subdirectory before the spawn and the child inherits the rewritten block (bwrap --tmpfs /tmp semantics). Read-only leaves the ambient temp entries untouched — writes there are denied anyway. The subdirectory is removed on provider dispose; after a crash it may survive as plain %TEMP% litter until OS temp hygiene (or manual removal) reclaims it — a later resume then fails loudly at the exclusive creation.
• whoami and token-inspection cmdlets fail under the restricted token. GetTokenInformation on the duplicate is partially unavailable to the child, so whoami /all reports errors — diagnostic noise of the restriction scheme, not an operational failure; the denial surfaces that matter (file writes) are unaffected.

Model Experience

Indirectly, through dsh-bash-sandbox, dsh-pwsh-sandbox, 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 seam owns the SANDBOX_UNAVAILABLE text and runner selection.

KV Cache effect

None directly; the denial surface belongs to the tool layer.

Known Limitations and Deferred Work

• One write allowlist per workspace — the write SID is the unit of the allowlist and IS the workspace identity; reusing one sandbox instance across two workspaces widens both grants to both roots (the same SID would then name two roots). Create one instance per workspace root — the seam does exactly this, keyed by the workspace path.
• Cleanup is best-effort by design — dispose() attempts every temp revocation and aggregates failures into an AggregateError; a cleanup failure leaves a standing (but write-SID-only) temp ACE that this process's next init()/dispose() cycle or icacls (via the ACE, not the trustee name) can still remove.
• Standing workspace ACEs are invisible residue. Renaming a workspace derives a new SID; the old ACEs on the old path stay (inert, write-SID-only). A future cleanup command may reap them; nothing re-propagates because of them.
• NULL-DACL directories are not identity-preserving under grant+revoke. A directory with a NULL DACL (rare — Windows-created directories carry real DACLs) means "everyone full control"; grantWrite builds the new ACL from that null, and the revoke round-trip leaves an EMPTY (deny-all) DACL rather than the original NULL DACL. The POC shares the behavior; real workspace and temp directories carry real DACLs, so this stays a documented edge rather than a guarded path.
• Piped stdio capture is impossible for confined grandchildren (the named-pipe default SD template). libuv's pipe stdio uses NAMED pipes; CreateNamedPipeW without security attributes installs the Win32 layer's user-mode default SD template (built by KernelBase — owner/SYSTEM/Admins full, Everyone/ANONYMOUS read-only, the fixed template MS documents) — NOT the token default DACL, which is what the kernel applies to a raw SD-null create — so the client-end open requests write access no restricting SID is granted: spawn(..., { stdio: 'pipe' }) inside a confined process fails with EPERM, the POC-documented "no output redirection" boundary of WRITE_RESTRICTED tokens. Inherited (inherit/fd) and ignored (ignore) stdio spawns work, and anonymous pipes (CreatePipe — a token-default-DACL consumer, e.g. PowerShell pipelines) work because the restricted token's default DACL carries a full-access restricting-SID ACE (set at init). A confined process therefore cannot capture a grandchild's output through a pipe; tools that must capture output cannot run confined.
• Grant materialization is an eager full-tree propagation. SetNamedSecurityInfoW on a directory with inheritable ACEs walks every descendant immediately (NOT lazily per access — measured at tens of seconds on large workspace trees plus the real temp root). The per-workspace identity pays it once per workspace per machine (lazily at the first confined execution ever, skipped entirely on every later provision when the exact ACE stands). If a workspace is huge, the first confined write on this host is correspondingly slow.
• Resuming one session concurrently in two server processes fails the second at its first confined write. Both processes derive the same private temp directory; the second one's exclusive creation hits the first one's directory and fails loudly. Single-writer session usage (the normal deployment) never sees this.
• Read-side confinement and network policy are out of scope — WRITE_RESTRICTED intersects write accesses only; pair this backend with a read-side policy for stronger confinement.
• Wide-directory and FAT-volume warnings are deferred; FAT-class targets stay writable. The UI-side warnings for granting unusually wide directories or FAT-class (non-ACL) volumes are not yet implemented, and a FAT volume as a grant ROOT simply fails the grant loudly (no ACL support). A FAT-class target OUTSIDE the granted roots is different: it has no security descriptors, so the restricted token's write check passes (Everyone sits in both lists) and such targets are writable under BOTH confined modes. FAT is treated as a legacy residue — unsupported and not engineered around; this warn-only posture is documented here rather than mitigated.
• Both confined modes run pwsh in ConstrainedLanguage. The restricted token trips PowerShell's lockdown detection, so under read-only AND workspace-write the language mode is ConstrainedLanguage: Add-Type (C# compile, P/Invoke), non-core .NET static calls ([System.IO.*]::, [math]::, [Environment]::), COM objects, and reflection fail with Cannot create type / Cannot invoke method ("only core types") errors, and $ExecutionContext.SessionState.LanguageMode = 'FullLanguage' is refused. Core cmdlets, core types ([string], [datetime], [regex], [guid]), -f formatting, and property access keep working. The pwsh tool description teaches this contract to the model; danger-full-access calls run unconfined at FullLanguage.