126 lines
7.2 KiB
Markdown
126 lines
7.2 KiB
Markdown
# Process Sandbox
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The process-sandbox seam of [dsh-sandbox](../../packages/sandbox/sandbox) wraps a same-world subprocess argv in a file-effect policy without coupling consumers to a platform runner. [dsh-sandbox-local](../../packages/sandbox/sandbox-local) supplies the Linux bwrap/Landlock and macOS Seatbelt backends; [dsh-bash-sandbox](../../packages/bash/bash-sandbox) is the first consumer. Containers, microVMs, and remote execution are sibling implementations of whole capability seams, not providers of `ctx.sandbox`.
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Source: [`packages/sandbox/sandbox/src/index.ts`](../../packages/sandbox/sandbox/src/index.ts)
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## Modes and enforcement
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`SandboxMode` governs filesystem effects only. `read-only` denies writes except the required `/dev/null` sink; `workspace-write` permits writes under the workspace root and the backend's promised temp area; `danger-full-access` bypasses confinement. Network and process visibility are outside this vocabulary.
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```ts type-equiv
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/**
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* File-effect policy for confined processes. `read-only` permits only required
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* sinks such as `/dev/null`; `workspace-write` also permits the workspace and a
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* backend-defined temp area; `danger-full-access` bypasses confinement. Network
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* and process visibility are outside this vocabulary.
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*/
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type SandboxMode = 'read-only' | 'workspace-write' | 'danger-full-access'
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```
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Only the first two modes can be sent to a provider. A `danger-full-access` consumer spawns its original argv and does not call `ctx.sandbox`.
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```ts type-equiv
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/** A confining (non-`danger-full-access`) mode — the modes a {@link SandboxPolicy} can carry. */
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type ConfinedSandboxMode = Exclude<SandboxMode, 'danger-full-access'>
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```
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Enforcement is a reported fact. `full` means the backend governs every file effect promised by the mode; `partial` means an active backend or older kernel ABI governs only a subset, so consumers that require the absolute promise must reject or surface that distinction.
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```ts type-equiv
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/**
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* Enforcement completeness for this host. `partial` means an active backend or
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* older kernel ABI cannot govern every promised file effect; callers requiring
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* an absolute boundary must not treat it as `full`.
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*/
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type SandboxEnforcement = 'full' | 'partial'
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```
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## Per-call policy
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The complete execution policy is resolved and carried per capability call. It includes `danger-full-access` so a consumer can resolve policy once before deciding whether to bypass confinement. Normal tool calls derive `workspaceRoot` from the calling session's immutable cwd; deployment configuration is the agentless fallback. The root is canonicalized with filesystem semantics before lexical normalization, so a cwd containing `symlink/..` identifies the directory where a spawned process actually runs.
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```ts type-equiv
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/**
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* The complete file-effect policy resolved for one capability call. The root
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* is carried even under modes that do not consume it so callers can resolve
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* policy once before choosing the enforcement path.
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*/
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interface SandboxExecutionPolicy {
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/** The file-effect mode this execution runs under. */
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mode: SandboxMode
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/** Absolute root directory `workspace-write` may write under. */
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workspaceRoot: string
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}
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```
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`ctx.sandboxPolicy.resolve()` accepts the active session and, for an approved retry, an explicit mode. The service owns precedence and root fallback so bash and fs do not repeat it.
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```ts type-equiv
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/** Inputs that select the sandbox policy for one capability call. */
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interface SandboxPolicyRequest {
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/** Calling session; its immutable cwd becomes the workspace boundary. */
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session?: Session
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/** Explicit approved mode override, which outranks session policy. */
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mode?: SandboxMode
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}
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```
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Only a confined execution reaches `ctx.sandbox`; its provider policy narrows the mode while retaining the same root. This permits concurrent sessions, consumers, and one-shot escalated retries to ask the same provider for different boundaries without mutating provider state.
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```ts type-equiv
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/**
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* What one confined execution is allowed to touch — carried PER CALL, not
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* fixed on the provider: two consumers may confine under different policies
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* at the same instant (bash under `read-only` while a confined child agent
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* needs its state directory writable), and an approved escalated retry is a
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* new call with a wider policy. Defaulting/resolution is an explicit step at
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* the consumer boundary; the provider treats the policy as fully specified.
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*/
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interface SandboxPolicy extends SandboxExecutionPolicy {
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/** The file-effect mode this execution runs under. */
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mode: ConfinedSandboxMode
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}
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```
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## Wrapped argv and classification dialects
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`ConfinedArgv` is what the consumer spawns. Besides the replacement argv, it carries the backend's enforcement fact and two orthogonal stderr dialects. `denialSignatures` identify the confined command being blocked while the sandbox works correctly. `runnerFailureSignatures` identify the sandbox runner refusing or failing before it executes the command; consumers check these first and surface a sandbox infrastructure failure, never an ordinary task failure.
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```ts type-equiv
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/**
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* A {@link SandboxProvider.confine} result: the argv to spawn in place of
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* the caller's own, plus the enforcement completeness the selected backend
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* achieves for it.
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*/
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interface ConfinedArgv {
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/** The wrapped argv (runner, profile, separator, then the caller's argv). */
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argv: string[]
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/** How completely the selected backend enforces the policy's file effects. */
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enforcement: SandboxEnforcement
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/**
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* The selected backend's denial DIALECT: the case-insensitive stderr
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* substrings a file effect denied by THIS backend produces (EROFS text
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* under bwrap's read-only binds, EACCES under Landlock, EPERM under
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* Seatbelt). A consumer that infers denials from a failed run's stderr
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* matches against exactly these rather than a cross-backend union — the
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* union claims denials a given backend never produces.
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*/
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denialSignatures: readonly string[]
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/**
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* Case-insensitive signatures for runner failure before command execution.
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* Consumers check these before denial signatures: runner failure means the
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* command never ran, while denial means confinement worked and blocked it.
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*/
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runnerFailureSignatures: readonly string[]
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}
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```
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An operator-configured local runner must supply at least one `runnerFailureSignatures` entry for its own pre-exec refusal dialect; the provider adds outer-shell missing and unexecutable forms automatically. This makes an executable custom runner rejecting its profile distinguishable from the wrapped command exiting with the same status.
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## Provider and fail-closed errors
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`ctx.sandbox.confine(argv, policy)` returns a `ConfinedArgv` or throws `SandboxUnavailableError` with code `SANDBOX_UNAVAILABLE` when no usable backend exists. A selected runner can also fail closed at execution time, in which case its failure signature carries the same infrastructure meaning. Silent unconfined passthrough is never legal for a confined policy.
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Provider probing arbitrates between multiple candidates and is cached for the provider lifetime. A platform with one candidate may select it directly; execution-time refusal retains the safety property. The local provider reports bwrap and Seatbelt as full and preserves the Landlock launcher's full/partial kernel verdict.
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