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fix(sandbox): isolate Windows temp capabilities

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Tianyi Cui
2026-08-10 15:31:38 +08:00
parent 9a3c89d04a
commit fd650af340
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.agents/notes/implemented/feature/2026-08-08-windows-acl-restricted-token-sandbox.md
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@@ -10,7 +10,7 @@ The [sandbox decision](2026-07-06-sandbox.md) leaves `PLATFORM_CHAINS.win32` emp
## 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 include a write SID (`S-1-4-x-y`); the write SID's Write ACEs on the workspace and temp roots are the primary write allowlist, because `WRITE_RESTRICTED` intersects write accesses only and reads keep the caller's full ambient access. 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 every ignored return value). The write SID is the PER-WORKSPACE identity, derived deterministically from the canonical workspace path (`workspaceWriteSid` — sha256 → `S-1-4-x-y`) and stored NOWHERE: the workspace-root ACE therefore materializes once per workspace per machine — the standing ACE is the cross-session reuse cache, and every later provision hits the exact-ACE skip (idempotent re-grant skips the eager full-tree re-propagation — no garbage collection) — instead of once per session, which is what the earlier per-session random SID paid a full tree propagation per session for. The seam derives the session's PRIVATE temp subdirectory from the session id + workspace (sha256, 16 hex — stored nowhere, so no tamper surface exists) and creates it exclusively; it is removed on provider dispose, and a crash leaves it as `%TEMP%` litter whose next resume fails loudly at the exclusive creation until temp hygiene reclaims it. The seam materializes the workspace ACE STANDING (never revoked — the cache) and the temp ACE REVOCABLY (revoked on provider dispose, so an inheritable ACE never outlives its session's temp directory on the ambient temp root). The token's restricting list is the keep-alive group plus the write SID only under workspace-write: read-only = [logon SID, Everyone] and workspace-write = [logon SID, Everyone, write SID]. The keep-alive invariants are logon SID + Everyone (early DLL init dies with 0xC0000142 and CNG crashes pwsh with 0xE0434352 without them). Because Everyone remains a restricting SID, an external object that grants 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 runner suite pins both gaps. Read-only carries no workspace write SID: a standing grant ACE from an earlier workspace-write period stays INERT (the pass-2 check grants only what the restricting list carries, so read-only adds no writable root across a `/permission` downgrade or a crash-resumed session, while the standing ACE keeps the re-upgrade free). Authenticated Users is absent from BOTH lists — the WMI namespace security check fails (0x80041003), so CIM is 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; INTERACTIVE/LOCAL are likewise absent from both (the Public tree writes are denied — pinned by the runner's Public-probe regression). Workspace-write children see a PRIVATE per-session temp subdirectory (`<temp>\dsh-<16 hex>` derived from the session id + workspace — created exclusively, reparse points rejected, removed on provider dispose — TMP/TEMP rewritten by the runner — bwrap `--tmpfs /tmp` semantics). The restricted token's DEFAULT DACL is extended with a full-access write-SID ACE (`SetTokenInformation(TokenDefaultDacl)`): new objects created without an explicit security descriptor (anonymous pipes — CreatePipe, sync objects) then carry a restricting-SID ACE and pass the write pass-2 check at creation; NAMED pipes are exempt — their default security descriptor is the Win32 layer's user-mode default SD template (built by KernelBase — owner/SYSTEM/Admins full, Everyone/ANONYMOUS read-only), which the token cannot influence, so piped stdio capture stays denied for confined grandchildren (the POC-documented boundary, pinned by the runner suite). It ships as [`@deepseek-ai/dsh-sandbox-windows-acl`](../../../../packages/sandbox/sandbox-windows-acl/README.md) (backend plus the `./runner` argv-prefix entry), the `win32` chain rung of [`dsh-sandbox-local`](../../../../packages/sandbox/sandbox-local/README.md), and [`@deepseek-ai/dsh-pwsh-sandbox`](../../../../packages/bash/pwsh-sandbox/README.md) as the confining executor; the Windows platform layer re-enables the full permission surface (sandbox/sandbox-policy/permission/approval/fs-sandbox) over the confined pwsh stack.
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. 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`](../../../../packages/sandbox/sandbox-windows-acl/README.md), the `win32` rung of [`dsh-sandbox-local`](../../../../packages/sandbox/sandbox-local/README.md), and [`@deepseek-ai/dsh-pwsh-sandbox`](../../../../packages/bash/pwsh-sandbox/README.md) as the confining executor.
## How the restriction works (why no new identity)
@@ -32,11 +32,11 @@ The [landstrip evaluation](../../rejected/feature/2026-07-26-evaluate-landstrip-
## 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 the exact Win32 code. Cost: enforcement is structurally partial because Everyone-granted writes and NTFS hard-link aliases cannot be made 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 ACE mutations on the granted roots (caller-owned directories; workspace ACEs stand forever by design — the reuse cache, invisible residue when a workspace is renamed — temp ACEs revoked by provider dispose together with the derived private temp directory — a crash leaves both behind and the next resume fails loudly at the exclusive creation until temp hygiene reclaims the directory); grant materialization is an EAGER full-tree propagation (`SetNamedSecurityInfoW` walks every descendant immediately — tens of seconds on large workspaces), paid once per workspace per machine by the per-workspace identity; CIM is unavailable in BOTH confined modes (AuthUsers dropped from both lists — the WMI namespace security check fails, and `Get-ComputerInfo` silently returns incomplete results) as the price of closing the C:\-root tree-creation escape in both; FAT-class (non-ACL) targets outside the granted roots remain writable under both modes (no security descriptors to intersect — a legacy residue treated as unsupported, warn-only, documented in the README); NULL-DACL directories are not identity-preserving under a grant+revoke round-trip (documented edge, the POC shares it); `whoami` and token-inspection cmdlets fail under the restricted token (diagnostic noise, documented); and BOTH confined modes run `pwsh` in ConstrainedLanguage mode — the restricted token trips PowerShell's lockdown detection, so `Add-Type`, non-core .NET statics (`[System.IO.*]::`, `[math]::`), COM objects, and reflection fail with "only core types" errors while `-f` formatting, property access, and core cmdlets/types keep working, and the language mode cannot be lifted back to FullLanguage from inside — taught to the model in the pwsh tool description and documented in the package README's Known Limitations; BOTH confined modes also deny named-pipe opens — libuv's piped-stdio spawns fail with EPERM (the POC-documented "no output redirection" boundary; inherited/ignored stdio and anonymous pipes work) — documented in the package README's Known Limitations and taught to the model in the pwsh tool description.
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 the keyless snapshot fixtures — which must replay on macOS/Linux — cannot cover it; the bundle composition specs ([`base.spec.ts`](../../../../packages/bundle/base/tests/base.spec.ts), [`windows-shell.spec.ts`](../../../../apps/cli/tests/windows-shell.spec.ts)) plus the win32 real-runner suites (`packages/sandbox/sandbox-windows-acl/tests/`, `packages/bash/pwsh-sandbox/tests/`) are the substitute evidence, and the CI Windows lane owns the assembled signal. The grant machinery is pinned cross-platform by `packages/sandbox/sandbox-local/tests/acl-grants.spec.ts` (the derived private-temp identity — deterministic per session + workspace, distinct across sessions — one-shot materialization, exclusive temp creation with reparse-point rejection and self-cleanup on failure, clean-restart re-grant of the same derived directory, the standing-vs-revocable lifecycle across dispose and the mode-switch cycle, and the derived-SID argv contract — with the Win32 surface mocked) and on win32 by `workspace-sid.spec.ts` (derivation determinism/shape/distinctness), `grant.spec.ts` (real-DACL materialization: revocable paths revoke on dispose, standing paths survive it), the `acl.spec.ts` idempotent-grant fast-path and standing-ACE-after-dispose contract, the `failure-paths.spec.ts` suspension-orphan regression (AssignProcessToJobObject failure terminates the child), and the `runner.spec.ts` `--write-sid` contract (caller-owned grants, private temp subdir through TMP/TEMP, both-mode CIM-denial probes, the mode-downgrade regression — a standing grant ACE is inert under read-only and effective again on re-upgrade — the ambient-writable Public-probe regression (a C:\Users\Public subdirectory write is denied under both modes), the partial-boundary regressions (external `Everyone:Modify` writes in both modes and a workspace hard link mutating its external file object), and the ConstrainedLanguage pins in both modes, plus the grandchild-stdio matrix pins — inherited/ignored stdio spawns succeed while piped capture is DENIED in both modes). The runner-failure classification is exit-gated on 127 (a confined command that merely prints the `windows-acl-run:` signature on a non-127 exit is never misclassified as "the command did not run" — pinned in the pwsh-sandbox helper suite).
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