Windows sandbox rung: raw ACL restricted tokens over mxc and AppContainer
Windows sandbox rung: raw ACL restricted tokens over mxc and AppContainer
The original [sandbox decision](2026-07-06-sandbox.md) left `PLATFORM_CHAINS.win32` empty, so shipped Windows profiles degraded to danger-full-access because no confining executor existed. The win32 rung must govern the two file-effect modes in the sandbox vocabulary — `read-only` (no explicit writable root) and `workspace-write` (writes under the workspace root plus a backend-defined temp area) — while reporting any
English
Problem
The original sandbox decision left PLATFORM_CHAINS.win32 empty, so shipped Windows profiles degraded to danger-full-access because no confining executor existed. The win32 rung must govern the two file-effect modes in the sandbox vocabulary — read-only (no explicit writable root) and workspace-write (writes under the workspace root plus a backend-defined temp area) — while reporting any effects its mechanism cannot govern; reads, network, and process visibility remain outside this vocabulary.
Decision
Implement the rung directly on the raw ACL mechanism: duplicate the caller's token into a WRITE_RESTRICTED token (CreateRestrictedToken with WRITE_RESTRICTED + DISABLE_MAX_PRIVILEGE + LUA_TOKEN) whose restricting SIDs carry distinct workspace and private-temp capabilities. WRITE_RESTRICTED intersects write accesses only, so reads keep the caller's ambient access while a write must also match one of these capability ACEs. The mechanism is the one huoyaoyuan/windows-acl-restrict-poc (10e4dfb) demonstrates; this port checks every API call and fails closed (the POC fail-opened on ignored failures). The per-workspace SID is derived deterministically from the canonical workspace path (workspaceWriteSid — sha256 → S-1-4-x-y); its standing workspace ACE is the cross-session reuse cache, and an exact-ACE skip prevents repeated eager tree propagation. Each live session/workspace pair instead gets a random private temp directory and a domain-separated SID derived from that path (tempWriteSid); its ACE is revocable, TMP/TEMP point at that directory, and the token default DACL names the temp SID so newly created temp objects do not acquire the shared workspace capability. A fork therefore cannot write its sibling's temp tree. A fresh provider chooses a new path and SID even for the same resumed session, so crash residue is inert litter rather than a collision or inherited capability; agentless calls create and remove the same shape per invocation. The ambient temp root is never an implicit grant. A workspace equal to or containing the temp root fails before any ACL mutation because its inheritable standing ACE would otherwise reach every private child; the direct API rejects overlap in either direction between a writable root and the actual private temp directory. PowerShell can complete its startup AppLocker probe through this private-temp capability, so workspace-write remains FullLanguage absent a host-wide policy; read-only cannot create the probe files and conservatively enters ConstrainedLanguage. That split is PowerShell startup behavior, not part of the ACL boundary. The token lists are read-only = [logon SID, Everyone] and workspace-write = [logon SID, Everyone, workspace SID, optional temp SID]. Logon SID + Everyone are keep-alive invariants (early DLL init dies with 0xC0000142 and CNG crashes pwsh with 0xE0434352 without them). Because Everyone remains, an external object granting Everyone write access clears both checks; because NTFS ACLs belong to file objects, a granted workspace hard link also grants an external alias. Rejecting all hard links would reject ordinary pnpm workspaces, so the provider reports enforcement: 'partial' and the native suite pins both gaps. Read-only carries no capability SID, so standing workspace ACEs remain inert across a mode downgrade. Authenticated Users is absent from both lists — CIM is unavailable, closing the C:-root tree-creation escape — and INTERACTIVE/LOCAL are absent, denying Public-tree writes. New anonymous pipes and sync objects inherit the temp SID (or workspace SID when temp is disabled, Everyone under read-only) through SetTokenInformation(TokenDefaultDacl); named pipes keep the Win32 layer's owner/SYSTEM/Admins-full, Everyone/ANONYMOUS-read-only template, so piped grandchild stdio remains denied. It ships as @deepseek-ai/dsh-sandbox-windows-acl, the win32 rung of dsh-sandbox-local, and @deepseek-ai/dsh-pwsh-sandbox as the confining executor.
How the restriction works (why no new identity)
The identity routes restrict by who runs the child; this rung restricts by token derivation. An identity route (landstrip's restricted-user, AppContainer) runs the child under a fresh account or container SID that starts with zero ACEs on the host's files — everything, reads included, defaults to denied, and every path the child may touch must then be opened back up by writing ACEs for that identity: the wholesale DACL mutation that disqualified both alternatives. The restricted token keeps the caller's own SID and logon session: CreateRestrictedToken derives a token that adds the restricting SIDs and the WRITE_RESTRICTED flag, so Windows performs the access check twice — once against the normal SIDs, once against the restricting SIDs — and grants write-class access only where both checks pass. Reads pass on the normal check alone (the caller's SIDs already carry read access everywhere the caller can read), which is why this rung needs no read grants and no new account; writes must additionally clear the capability-SID check, which only the workspace and temp ACEs satisfy. DISABLE_MAX_PRIVILEGE | LUA_TOKEN synthesize the limited-user effect of a fresh account token-side, so even an elevated caller derives a filtered token. The same primitive could restrict reads (SidsToDisable turning SIDs deny-only), but a read-restricted token would need per-path read grants — reintroducing exactly the cost the identity routes pay — and the sandbox vocabulary never requires read confinement.
Alternatives considered
Why not mxc (Microsoft xContainer)?
Two disqualifiers. First, the OS floor is too new: the mxc OS-version policy sets the product floor at Windows 11 24H2 (build 26100), and the BaseContainer tier (T1, Experimental_CreateProcessInSandbox) exists only on 25H2+ (build 26600+) with the OS feature enabled — on every supported release at or below 25H2 the filesystem policy falls back to T3, AppContainer plus host-side DACL ACE augmentation. Second, supporting arbitrary-path reads under either tier means granting read access by writing ACLs over every path the child may read: a model that reads the whole workspace and arbitrary files would require wholesale host DACL mutation — a standing side effect and a cost a write-only restriction does not need.
Why not AppContainer?
An AppContainer token carries no ambient read access: every readable path must be pre-granted through capabilities or explicit ACEs, so arbitrary-path reads — the harness's read model — are unsupported without the same wholesale grants. The restricted token needs no read grants at all: it intersects write access only.
Why not landstrip?
The landstrip evaluation was rejected before implementation (not battle-tested; the in-house launcher plan won), and its Windows backend is AppContainer-shaped, inheriting the same arbitrary-read problem.
Consequences
Bought: write-only confinement with no new OS floor (CreateRestrictedToken predates the mxc releases by two decades), reads/network/process visibility untouched exactly as the mode vocabulary requires, and fail-closed errors carrying the API name and exact Win32 code. Sessions share the intentionally standing workspace capability but not their revocable temp capabilities; restart residue cannot block or authorize a resumed session. Cost: enforcement is structurally partial because Everyone-granted writes and NTFS hard-link aliases cannot be path-confined by this token shape; no read-side or network isolation; console isolation unavailable (hidden-console children die with STATUS_DLL_INIT_FAILED; children share the host console); standing workspace ACE mutations (the reuse cache, plus inert residue when a workspace is renamed) and random temp litter after an unclean shutdown until OS hygiene reclaims it; EAGER full-tree workspace propagation (SetNamedSecurityInfoW walks every descendant immediately — tens of seconds on large workspaces), paid once per workspace per machine; CIM unavailable in both confined modes (Authenticated Users is absent, closing the C:-root tree-creation escape); FAT-class non-ACL targets still writable; NULL-DACL directories not identity-preserving under a grant/revoke round trip; whoami and token-inspection cmdlets failing under the restricted token; read-only pwsh entering ConstrainedLanguage while workspace-write remains FullLanguage absent host policy; and named-pipe opens remaining denied, so libuv piped-stdio grandchildren fail with EPERM while inherited/ignored stdio and anonymous pipes work. The package README owns these operational limits.
Testing
The product-visible Windows roster flip is win32-only, so keyless snapshots that must replay on macOS/Linux cannot cover it; bundle composition specs plus the win32 real-runner suites are the substitute evidence, and the CI Windows lane owns the assembled signal. sandbox-local/tests/acl-grants.spec.ts pins random temp allocation, per-session/workspace reuse, fork/workspace separation, crash-resume non-collision, paired argv SIDs, failure cleanup, and standing-versus-revocable lifecycle with Win32 mocked. On Windows, workspace-sid.spec.ts pins workspace/temp derivation and domain separation; acl.spec.ts pins real DACL lifecycle; and runner.spec.ts pins paired-SID validation, sibling temp denial under a shared workspace SID, per-call agentless temp creation/removal, TMP/TEMP rewriting, mode downgrade, Public denial, Everyone/hard-link partial boundaries, mode-specific PowerShell language behavior, and grandchild stdio. ARM64 and emulated x64 native runs own the architecture-specific acceptance evidence.
Related
The pwsh executor decision owns the pwsh-sandbox/tool-pwsh dialect split this rung consumes.
中文
问题
最初的沙箱决策将 PLATFORM_CHAINS.win32 留空，因此交付的 Windows profile 因不存在隔离执行器而退化为 danger-full-access。win32 档必须约束沙箱词汇表中的两种文件效果模式——read-only（不显式授予任何可写根目录）与 workspace-write（允许写入工作区根目录及后端定义的临时区域）——并报告其机制无法约束的任何效果；读取、网络与进程可见性仍在这套词汇之外。
决策
直接基于原始 ACL 机制实现该档：把调用者令牌复制为 WRITE_RESTRICTED 受限令牌（CreateRestrictedToken，WRITE_RESTRICTED + DISABLE_MAX_PRIVILEGE + LUA_TOKEN），其 restricting SIDs 携带彼此独立的工作区能力与私有临时目录能力。WRITE_RESTRICTED 只对写访问做交集检查，因此读取保留调用者的环境访问，而写入还必须匹配这些能力 ACE 之一。该机制来自 huoyaoyuan/windows-acl-restrict-poc（10e4dfb）的演示；本移植检查每个 API 调用并 fail-closed（POC 因忽略失败而 fail-open）。工作区 SID 由规范工作区路径确定性派生（workspaceWriteSid——sha256 → S-1-4-x-y）；其常驻工作区 ACE 是跨会话复用缓存，精确 ACE 跳过可避免重复的急切全树传播。每个活跃的会话/工作区对则获得一个随机私有临时目录，以及一个从该路径派生的、经过域分离的 SID（tempWriteSid）；其 ACE 可回收，TMP/TEMP 指向该目录，令牌默认 DACL 列入该临时 SID，因此新建的临时对象不会获得共享的工作区能力。fork 因此无法写入同级会话的临时目录树。即使恢复的是同一会话，新的提供方也会选择新的路径和 SID，因此崩溃残留只是失效垃圾，而非冲突或继承的能力；无 agent（智能体）的调用会逐调用创建并移除同样的形态。环境临时根目录绝不会被隐式授权。如果工作区等于或包含临时根目录，调用会在任何 ACL 改动发生前失败，因为否则其可继承的常驻 ACE 会向每个私有子目录授权；直接 API 会拒绝可写根目录与实际私有临时目录在任一方向上的重叠。PowerShell 可借助这项私有临时目录能力完成启动时的 AppLocker 探针，因此在没有主机范围策略时，workspace-write 会保持 FullLanguage；read-only 无法创建探针文件，会保守地进入 ConstrainedLanguage。这一区别属于 PowerShell 启动行为，不是 ACL 边界的一部分。令牌列表为 read-only = [登录 SID、Everyone]，workspace-write = [登录 SID、Everyone、工作区 SID、可选临时 SID]。登录 SID + Everyone 是保活不变式（没有它们，早期 DLL 初始化会以 0xC0000142 死亡，CNG 会让 pwsh 以 0xE0434352 崩溃）。由于 Everyone 仍在列表中，向 Everyone 授予写访问的外部对象会通过两次检查；由于 NTFS ACL 属于文件对象，工作区内获授权的硬链接也会使同一对象的外部别名获得授权。拒绝所有硬链接会让普通 pnpm 工作区不可用，因此提供方报告 enforcement: 'partial'，原生套件则钉住这两个缺口。Read-only 不含任何能力 SID，因此常驻工作区 ACE 在模式降级后保持失效。Authenticated Users 在两种列表中都不存在——CIM 不可用，从而关闭 C:-root 建树逃逸——INTERACTIVE/LOCAL 也不存在，因此 Public 树写入被拒绝。新建匿名管道和同步对象通过 SetTokenInformation(TokenDefaultDacl) 继承临时 SID（禁用临时目录时继承工作区 SID，read-only 下继承 Everyone）；named pipe 保持 Win32 层 owner/SYSTEM/Admins 全权、Everyone/ANONYMOUS 只读的模板，因此受限孙进程的管道 stdio 仍被拒绝。它以 @deepseek-ai/dsh-sandbox-windows-acl、dsh-sandbox-local 的 win32 档，以及作为隔离执行器的 @deepseek-ai/dsh-pwsh-sandbox 交付。
How the restriction works (why no new identity)
身份路线靠"谁在跑子进程"来限制，本档靠"令牌派生"来限制。身份路线（landstrip 的 restricted-user、AppContainer）用全新账户或容器 SID 运行子进程，该身份在宿主的文件上从零条 ACE 开始——一切访问（包括读）默认拒绝，子进程要碰的每条路径都必须事后为那个身份补写 ACE 才能放行：这正是让两个备选方案出局的全盘 DACL 改造。受限令牌保留调用者自己的 SID 与 logon session：CreateRestrictedToken 派生一个加入 restricting SIDs 与 WRITE_RESTRICTED 标志的令牌，于是 Windows 做两次访问检查——一次按正常 SID，一次按 restricting SIDs——只有两次都放行，写类访问才被授予。读只凭正常检查即可通过（调用者的 SID 在其可读范围内本来就携带读权限），所以本档不需要任何读授权、也不需要新账户；写还必须额外通过能力 SID 检查，而只有工作区与临时目录的 ACE 能满足它。DISABLE_MAX_PRIVILEGE | LUA_TOKEN 在令牌侧合成了新账户的受限用户效果，即使提升过的调用者派生的也是过滤令牌。同一原语其实也能限制读（SidsToDisable 把 SID 变为 deny-only），但受限读的令牌需要逐路径的读授权——恰好重新引入身份路线付出的代价——而沙盒词汇表从不要求读隔离。
考虑过的替代方案
为什么不选 mxc（Microsoft xContainer）？
两个否决理由。其一，OS 版本要求太新：mxc 的 OS 版本支持文档把产品下限设在 Windows 11 24H2（build 26100），而 BaseContainer 档（T1，Experimental_CreateProcessInSandbox）只在 25H2+（build 26600+）且启用 OS feature 时存在——在 25H2 及以下的所有受支持版本上，文件系统策略都会回退到 T3，即 AppContainer 加宿主侧 DACL ACE 改造。其二，在任一档下支持任意路径读都意味着要为子进程可读的每个路径写 ACL 授予读权限：模型要读整个工作区和任意文件，就需要全盘改写宿主 DACL——对只做写限制的需求而言，这是不必要的驻留副作用与代价。
为什么不选 AppContainer？
AppContainer 令牌没有环境读访问：每个可读路径都必须预先通过 capability 或显式 ACE 授予，因此任意路径读——harness 的读模型——在不做同样的全盘授予时无法支持。受限令牌完全不需要读授予：它只对写访问做交集。
为什么不选 landstrip？
landstrip 评估在实现前已被否决（未经实战检验；自建 launcher 方案胜出），且其 Windows 后端是 AppContainer 形态，继承同样的任意路径读问题。
后果
所得：仅写隔离、不引入新的 OS 版本下限（CreateRestrictedToken 比 mxc 的版本早二十年）、读/网络/进程可见性完全不受影响（与模式词汇表一致），且 fail-closed 错误携带 API 名与精确 Win32 错误码。会话共享有意常驻的工作区能力，但不共享各自可回收的临时能力；重启残留既不能阻塞恢复的会话，也不能向其授权。所失：强制执行在结构上只能是部分的，因为此令牌形态无法把 Everyone 授予的写入与 NTFS 硬链接别名限制在路径边界内；无读侧或网络隔离；控制台隔离不可用（隐藏控制台子进程以 STATUS_DLL_INIT_FAILED 死亡；子进程共享宿主控制台）；工作区常驻 ACE 改动（复用缓存，以及工作区改名后的失效残留）与异常关闭后遗留的随机临时目录垃圾，直到 OS 卫生机制将其回收；工作区授权采用急切的全树传播（SetNamedSecurityInfoW 立即遍历每个后代——大型工作区上耗时数十秒），每台机器每个工作区只付一次；CIM 在两种受限模式下均不可用（Authenticated Users 不存在，从而关闭 C:-root 建树逃逸）；FAT 类无 ACL 目标仍可写；NULL-DACL 目录在 grant/revoke 往返下不保持身份；whoami 与令牌检查 cmdlet 在受限令牌下失败；read-only pwsh 会进入 ConstrainedLanguage，而在没有主机策略时 workspace-write 保持 FullLanguage；named pipe 打开仍被拒绝，因此 libuv 管道 stdio 的孙进程以 EPERM 失败，而继承/忽略的 stdio 与匿名管道可用。包 README 负责记录这些运行限制。
测试
产品可见的 Windows 阵容切换仅存在于 win32，而必须在 macOS/Linux 上可重放的 keyless 快照无法覆盖它；替代证据是 bundle 组合 spec 加上 win32 真实 runner 套件，组装态信号由 CI 的 Windows lane 负责。sandbox-local/tests/acl-grants.spec.ts 在 mock Win32 的情况下钉住随机临时目录分配、按会话/工作区复用、fork/工作区分离、崩溃后恢复不冲突、成对 argv SID、失败清理，以及常驻/可回收生命周期。在 Windows 上，workspace-sid.spec.ts 钉住工作区/临时目录派生与域分离；acl.spec.ts 钉住真实 DACL 生命周期；runner.spec.ts 钉住成对 SID 验证、共享工作区 SID 时对同级会话临时目录的拒绝、无 agent 调用的逐调用临时目录创建/移除、TMP/TEMP 重写、模式降级、Public 拒绝、Everyone/硬链接部分边界、按模式区分的 PowerShell 语言行为与孙进程 stdio。ARM64 与模拟 x64 原生运行负责提供架构特定的验收证据。
Related
pwsh 执行器决策拥有本档所消费的 pwsh-sandbox/tool-pwsh 方言划分。