Files
2026-07-13 11:59:58 +08:00

573 lines
26 KiB
Markdown

# Guardrails: Pre-Tool-Call Authorization
> **Context:** [Issue #1213](https://github.com/bytedance/deer-flow/issues/1213) — DeerFlow has Docker sandboxing and human approval via `ask_clarification`, but no deterministic, policy-driven authorization layer for tool calls. An agent running autonomous multi-step tasks can execute any loaded tool with any arguments. Guardrails add a middleware that evaluates every tool call against a policy **before** execution.
## Why Guardrails
```
Without guardrails: With guardrails:
Agent Agent
│ │
▼ ▼
┌──────────┐ ┌──────────┐
│ bash │──▶ executes immediately │ bash │──▶ GuardrailMiddleware
│ rm -rf / │ │ rm -rf / │ │
└──────────┘ └──────────┘ ▼
┌──────────────┐
│ Provider │
│ evaluates │
│ against │
│ policy │
└──────┬───────┘
┌─────┴─────┐
│ │
ALLOW DENY
│ │
▼ ▼
Tool runs Agent sees:
normally "Guardrail denied:
rm -rf blocked"
```
- **Sandboxing** provides process isolation but not semantic authorization. A sandboxed `bash` can still `curl` data out.
- **Human approval** (`ask_clarification`) requires a human in the loop for every action. Not viable for autonomous workflows.
- **Guardrails** provide deterministic, policy-driven authorization that works without human intervention.
## Architecture
```
┌─────────────────────────────────────────────────────────────────────┐
│ Middleware Chain │
│ │
│ 1. ThreadDataMiddleware ─── per-thread dirs │
│ 2. UploadsMiddleware ─── file upload tracking │
│ 3. SandboxMiddleware ─── sandbox acquisition │
│ 4. DanglingToolCallMiddleware ── fix incomplete tool calls │
│ 5. GuardrailMiddleware ◄──── EVALUATES EVERY TOOL CALL │
│ 6. ToolErrorHandlingMiddleware ── convert exceptions to messages │
│ 7-12. (Summarization, Title, Memory, Vision, Subagent, Clarify) │
│ │
└─────────────────────────────────────────────────────────────────────┘
┌──────────────────────────┐
│ GuardrailProvider │ ◄── pluggable: any class
│ (configured in YAML) │ with evaluate/aevaluate
└────────────┬─────────────┘
┌─────────┼──────────────┐
│ │ │
▼ ▼ ▼
Built-in OAP Passport Custom
Allowlist Provider Provider
(zero dep) (open standard) (your code)
Any implementation
(e.g. APort, or
your own evaluator)
```
The `GuardrailMiddleware` implements `wrap_tool_call` / `awrap_tool_call` (the same `AgentMiddleware` pattern used by `ToolErrorHandlingMiddleware`). It:
1. Builds a `GuardrailRequest` with tool name, arguments, and passport reference
2. Calls `provider.evaluate(request)` on whatever provider is configured
3. If **deny**: returns `ToolMessage(status="error")` with the reason -- agent sees the denial and adapts
4. If **allow**: passes through to the actual tool handler
5. If **provider error** and `fail_closed=true` (default): blocks the call
6. `GraphBubbleUp` exceptions (LangGraph control signals) are always propagated, never caught
## Three Provider Options
### Option 1: Built-in AllowlistProvider (Zero Dependencies)
The simplest option. Ships with DeerFlow. Block or allow tools by name. No external packages, no passport, no network.
**config.yaml:**
```yaml
guardrails:
enabled: true
provider:
use: deerflow.guardrails.builtin:AllowlistProvider
config:
denied_tools: ["bash", "write_file"]
```
This blocks `bash` and `write_file` for all requests. All other tools pass through.
You can also use an allowlist (only these tools are permitted):
```yaml
guardrails:
enabled: true
provider:
use: deerflow.guardrails.builtin:AllowlistProvider
config:
allowed_tools: ["web_search", "read_file", "ls"]
```
**Try it:**
1. Add the config above to your `config.yaml`
2. Start DeerFlow: `make dev`
3. Ask the agent: "Use bash to run echo hello"
4. The agent sees: `Guardrail denied: tool 'bash' was blocked (oap.tool_not_allowed)`
### Option 2: OAP Passport Provider (Policy-Based)
For policy enforcement based on the [Open Agent Passport (OAP)](https://github.com/aporthq/aport-spec) open standard. An OAP passport is a JSON document that declares an agent's identity, capabilities, and operational limits. Any provider that reads an OAP passport and returns OAP-compliant decisions works with DeerFlow.
```
┌─────────────────────────────────────────────────────────────┐
│ OAP Passport (JSON) │
│ (open standard, any provider) │
│ { │
│ "spec_version": "oap/1.0", │
│ "status": "active", │
│ "capabilities": [ │
│ {"id": "system.command.execute"}, │
│ {"id": "data.file.read"}, │
│ {"id": "data.file.write"}, │
│ {"id": "web.fetch"}, │
│ {"id": "mcp.tool.execute"} │
│ ], │
│ "limits": { │
│ "system.command.execute": { │
│ "allowed_commands": ["git", "npm", "node", "ls"], │
│ "blocked_patterns": ["rm -rf", "sudo", "chmod 777"] │
│ } │
│ } │
│ } │
└──────────────────────────┬──────────────────────────────────┘
Any OAP-compliant provider
┌────────────────┼────────────────┐
│ │ │
Your own APort (ref. Other future
evaluator implementation) implementations
```
**Creating a passport manually:**
An OAP passport is just a JSON file. You can create one by hand following the [OAP specification](https://github.com/aporthq/aport-spec/blob/main/oap/oap-spec.md) and validate it against the [JSON schema](https://github.com/aporthq/aport-spec/blob/main/oap/passport-schema.json). See the [examples](https://github.com/aporthq/aport-spec/tree/main/oap/examples) directory for templates.
**Using APort as a reference implementation:**
[APort Agent Guardrails](https://github.com/aporthq/aport-agent-guardrails) is one open-source (Apache 2.0) implementation of an OAP provider. It handles passport creation, local evaluation, and optional hosted API evaluation.
```bash
pip install aport-agent-guardrails
aport setup --framework deerflow
```
This creates:
- `~/.aport/deerflow/config.yaml` -- evaluator config (local or API mode)
- `~/.aport/deerflow/aport/passport.json` -- OAP passport with capabilities and limits
**config.yaml (using APort as the provider):**
```yaml
guardrails:
enabled: true
provider:
use: aport_guardrails.providers.generic:OAPGuardrailProvider
```
**config.yaml (using your own OAP provider):**
```yaml
guardrails:
enabled: true
provider:
use: my_oap_provider:MyOAPProvider
config:
passport_path: ./my-passport.json
```
Any provider that accepts `framework` as a kwarg and implements `evaluate`/`aevaluate` works. The OAP standard defines the passport format and decision codes; DeerFlow doesn't care which provider reads them.
**What the passport controls:**
| Passport field | What it does | Example |
|---|---|---|
| `capabilities[].id` | Which tool categories the agent can use | `system.command.execute`, `data.file.write` |
| `limits.*.allowed_commands` | Which commands are allowed | `["git", "npm", "node"]` or `["*"]` for all |
| `limits.*.blocked_patterns` | Patterns always denied | `["rm -rf", "sudo", "chmod 777"]` |
| `status` | Kill switch | `active`, `suspended`, `revoked` |
**Evaluation modes (provider-dependent):**
OAP providers may support different evaluation modes. For example, the APort reference implementation supports:
| Mode | How it works | Network | Latency |
|---|---|---|---|
| **Local** | Evaluates passport locally (bash script). | None | ~300ms |
| **API** | Sends passport + context to a hosted evaluator. Signed decisions. | Yes | ~65ms |
A custom OAP provider can implement any evaluation strategy -- the DeerFlow middleware doesn't care how the provider reaches its decision.
**Try it:**
1. Install and set up as above
2. Start DeerFlow and ask: "Create a file called test.txt with content hello"
3. Then ask: "Now delete it using bash rm -rf"
4. Guardrail blocks it: `oap.blocked_pattern: Command contains blocked pattern: rm -rf`
### Option 3: Custom Provider (Bring Your Own)
Any Python class with `evaluate(request)` and `aevaluate(request)` methods works. No base class or inheritance needed -- it's a structural protocol.
```python
# my_guardrail.py
class MyGuardrailProvider:
name = "my-company"
def evaluate(self, request):
from deerflow.guardrails.provider import GuardrailDecision, GuardrailReason
# Example: block any bash command containing "delete"
if request.tool_name == "bash" and "delete" in str(request.tool_input):
return GuardrailDecision(
allow=False,
reasons=[GuardrailReason(code="custom.blocked", message="delete not allowed")],
policy_id="custom.v1",
)
return GuardrailDecision(allow=True, reasons=[GuardrailReason(code="oap.allowed")])
async def aevaluate(self, request):
# This skeleton reuses the sync path. If policy evaluation performs
# async I/O, call and await the async evaluator here instead.
return self.evaluate(request)
```
**config.yaml:**
```yaml
guardrails:
enabled: true
provider:
use: my_guardrail:MyGuardrailProvider
```
Make sure `my_guardrail.py` is on the Python path (e.g. in the backend directory or installed as a package).
**Try it:**
1. Create `my_guardrail.py` in the backend directory
2. Add the config
3. Start DeerFlow and ask: "Use bash to delete test.txt"
4. Your provider blocks it
#### Optional: Runtime Attribution
Runtime attribution fields are optional. Providers that need richer policy context or audit records can read them, while simple tool allow/deny providers can ignore them:
| Field | Example use |
|---|---|
| `user_id` | Attach the authenticated DeerFlow user to a provider-side policy or audit record |
| `user_role` | Apply simple role-based policy, such as allowing an admin-only tool. Sourced from the authenticated user's `system_role` (renamed for the guardrail-facing surface, not a separate field) |
| `oauth_provider` | Link a decision to an external identity provider, when present |
| `oauth_id` | Link a decision to the external provider's subject/user id, when present |
| `thread_id` | Link a decision back to the conversation thread |
| `run_id` | Link a decision back to one execution run |
| `tool_call_id` | Identify the exact tool call that was allowed or denied |
These fields are populated by the Gateway from server-side auth state (the run worker always sets `thread_id`/`run_id`). For web-authenticated runs, `inject_authenticated_user_context` writes `user_id`/`user_role`/`oauth_provider`/`oauth_id` from `request.state.user`. For trusted IM / internal-auth runs (Slack, Discord, Telegram, Feishu, DingTalk, and other internal callers that provide a trusted owner header), the Gateway resolves the owner user server-side and writes the same attribution fields from that owner. Client-supplied values cannot override them — the server-side assignment wins.
If a trusted internal caller does not resolve to an owner user, the Gateway strips client-supplied `user_role`/`oauth_provider`/`oauth_id` from the run context instead of treating them as authoritative. Any `user_id` already present is left in place for legacy channel storage behavior, but role/oauth-based policy is only applied when the owner user was resolved server-side.
For example, if your deployment has user-scoped policy requirements, you can opt into a context-aware provider that passes the runtime fields into an external policy file. This keeps business policy out of Python code and `config.yaml`; the provider only normalizes context, evaluates a configured policy, and maps the result back to `GuardrailDecision`.
```python
import asyncio
import json
from pathlib import Path
from deerflow.guardrails.provider import GuardrailDecision, GuardrailReason
class ContextAwareGuardrailProvider:
"""Illustrative provider skeleton; policy loading/evaluation is provider-defined."""
name = "context-aware-example"
def __init__(self, *, policy_path, audit_path="./logs/guardrail-audit.jsonl", **kwargs):
self.policy_path = Path(policy_path)
self.audit_path = Path(audit_path)
# Load policy rules here. In a real deployment this could call an
# internal policy service, OPA/Cedar, AGT, or another rule engine.
self.policy = self._load_policy(self.policy_path)
def evaluate(self, request):
decision = self._decide(request)
self._write_audit(request, decision)
return decision
async def aevaluate(self, request):
# ``_decide`` is in-memory policy work; the audit write is blocking
# file I/O, so offload it off the event loop with ``asyncio.to_thread``
# (DeerFlow enforces a blocking-IO gate in CI). If your policy
# evaluation itself does blocking I/O — external policy service, file
# read per call — move that behind ``asyncio.to_thread`` too, or
# implement a native async evaluator and await it here.
decision = self._decide(request)
await asyncio.to_thread(self._write_audit, request, decision)
return decision
def _decide(self, request):
# 1. Normalize DeerFlow request data into policy context.
context = {
"tool_name": request.tool_name,
"tool_input": request.tool_input,
"user_id": request.user_id,
"user_role": request.user_role,
"oauth_provider": request.oauth_provider,
"oauth_id": request.oauth_id,
"thread_id": request.thread_id,
"run_id": request.run_id,
"tool_call_id": request.tool_call_id,
"agent_id": request.agent_id,
"timestamp": request.timestamp,
# Derived fields make simple rule engines handle multi-field checks.
# Example policy: allow bash only for admin users.
"role_tool_key": f"{request.user_role or ''}:{request.tool_name}",
"command": request.tool_input.get("command", ""),
"message": json.dumps(request.tool_input, ensure_ascii=False, default=str),
}
# 2. Evaluate the provider-defined policy schema.
result = self._evaluate_policy(self.policy, context)
# 3. Convert the policy result back to DeerFlow's decision object.
return GuardrailDecision(
allow=result["allow"],
reasons=[
GuardrailReason(
code=result["code"],
message=result["message"],
)
],
policy_id=result.get("policy_id"),
metadata={
"user_id": request.user_id,
"user_role": request.user_role,
"oauth_provider": request.oauth_provider,
"oauth_id": request.oauth_id,
"thread_id": request.thread_id,
"run_id": request.run_id,
"tool_call_id": request.tool_call_id,
},
)
def _write_audit(self, request, decision):
event = {
"decision": "allow" if decision.allow else "deny",
"reason": decision.reasons[0].message if decision.reasons else "",
"policy_id": decision.policy_id,
"tool_name": request.tool_name,
"user_id": request.user_id,
"user_role": request.user_role,
"oauth_provider": request.oauth_provider,
"oauth_id": request.oauth_id,
"thread_id": request.thread_id,
"run_id": request.run_id,
"tool_call_id": request.tool_call_id,
"agent_id": request.agent_id,
"timestamp": request.timestamp,
}
self.audit_path.parent.mkdir(parents=True, exist_ok=True)
with self.audit_path.open("a", encoding="utf-8") as f:
f.write(json.dumps(event, ensure_ascii=False) + "\n")
def _load_policy(self, path):
# Load your provider-defined policy file.
raise NotImplementedError
def _evaluate_policy(self, policy, context):
# Evaluate ordered rules and return:
# {"allow": bool, "code": str, "message": str, "policy_id": str | None}
raise NotImplementedError
```
**config.yaml:**
```yaml
guardrails:
enabled: true
provider:
use: my_guardrail:ContextAwareGuardrailProvider
config:
policy_path: ./policies/guardrail-policy.yml
audit_path: ./logs/guardrail-audit.jsonl
```
Many policy engines use a similar shape: normalize request context, evaluate ordered rules, and return an allow/deny decision. The exact schema is provider-defined; the YAML below is illustrative:
```yaml
# policies/guardrail-policy.yml
version: "1.0"
rules:
- name: allow-admin-bash
condition:
field: role_tool_key
operator: eq
value: admin:bash
action: allow
priority: 300
message: Admin users may execute bash
- name: deny-bash-for-other-roles
condition:
field: tool_name
operator: eq
value: bash
action: deny
priority: 200
message: bash is restricted to admin users
- name: deny-dangerous-command
condition:
field: message
operator: matches
value: "\\brm\\s+-rf\\b"
action: deny
priority: 100
message: Dangerous shell command detected
defaults:
action: allow
```
## Implementing a Provider
### Required Interface
```
┌──────────────────────────────────────────────────┐
│ GuardrailProvider Protocol │
│ │
│ name: str │
│ │
│ evaluate(request: GuardrailRequest) │
│ -> GuardrailDecision │
│ │
│ aevaluate(request: GuardrailRequest) (async) │
│ -> GuardrailDecision │
└──────────────────────────────────────────────────┘
┌──────────────────────────┐ ┌──────────────────────────┐
│ GuardrailRequest │ │ GuardrailDecision │
│ │ │ │
│ tool_name: str │ │ allow: bool │
│ tool_input: dict │ │ reasons: [GuardrailReason]│
│ agent_id: str | None │ │ policy_id: str | None │
│ thread_id: str | None │ │ metadata: dict │
│ is_subagent: bool │ │ │
│ timestamp: str │ │ GuardrailReason: │
│ user_id: str | None │ │ code: str │
│ user_role: str | None │ │ message: str │
│ oauth_provider: str | None│ │ │
│ oauth_id: str | None │ │ │
│ run_id: str | None │ │ │
│ tool_call_id: str | None │ │ │
│ │ │ │
└──────────────────────────┘ │ │
└──────────────────────────┘
```
### DeerFlow Tool Names
These are the tool names your provider will see in `request.tool_name`:
| Tool | What it does |
|---|---|
| `bash` | Shell command execution |
| `write_file` | Create/overwrite a file |
| `str_replace` | Edit a file (find and replace) |
| `read_file` | Read file content |
| `ls` | List directory |
| `web_search` | Web search query |
| `web_fetch` | Fetch URL content |
| `image_search` | Image search |
| `present_files` | Present file to user |
| `view_image` | Display image |
| `ask_clarification` | Ask user a question |
| `task` | Delegate to subagent |
| `mcp__*` | MCP tools (dynamic) |
### OAP Reason Codes
Standard codes used by the [OAP specification](https://github.com/aporthq/aport-spec):
| Code | Meaning |
|---|---|
| `oap.allowed` | Tool call authorized |
| `oap.tool_not_allowed` | Tool not in allowlist |
| `oap.command_not_allowed` | Command not in allowed_commands |
| `oap.blocked_pattern` | Command matches a blocked pattern |
| `oap.limit_exceeded` | Operation exceeds a limit |
| `oap.passport_suspended` | Passport status is suspended/revoked |
| `oap.evaluator_error` | Provider crashed (fail-closed) |
### Provider Loading
DeerFlow loads providers via `resolve_variable()` -- the same mechanism used for models, tools, and sandbox providers. The `use:` field is a Python class path: `package.module:ClassName`.
The provider is instantiated with `**config` kwargs if `config:` is set, plus `framework="deerflow"` is always injected. Accept `**kwargs` to stay forward-compatible:
```python
class YourProvider:
def __init__(self, framework: str = "generic", **kwargs):
# framework="deerflow" tells you which config dir to use
...
```
## Configuration Reference
```yaml
guardrails:
# Enable/disable guardrail middleware (default: false)
enabled: true
# Block tool calls if provider raises an exception (default: true)
fail_closed: true
# Passport reference -- passed as request.agent_id to the provider.
# File path, hosted agent ID, or null (provider resolves from its config).
passport: null
# Provider: loaded by class path via resolve_variable
provider:
use: deerflow.guardrails.builtin:AllowlistProvider
config: # optional kwargs passed to provider.__init__
denied_tools: ["bash"]
```
## Testing
```bash
cd backend
uv run python -m pytest tests/test_guardrail_middleware.py -v
```
25 tests covering:
- AllowlistProvider: allow, deny, both allowlist+denylist, async
- GuardrailMiddleware: allow passthrough, deny with OAP codes, fail-closed, fail-open, passport forwarding, empty reasons fallback, empty tool name, protocol isinstance check
- Async paths: awrap_tool_call for allow, deny, fail-closed, fail-open
- GraphBubbleUp: LangGraph control signals propagate through (not caught)
- Config: defaults, from_dict, singleton load/reset
## Files
```
packages/harness/deerflow/guardrails/
__init__.py # Public exports
provider.py # GuardrailProvider protocol, GuardrailRequest, GuardrailDecision
middleware.py # GuardrailMiddleware (AgentMiddleware subclass)
builtin.py # AllowlistProvider (zero deps)
packages/harness/deerflow/config/
guardrails_config.py # GuardrailsConfig Pydantic model + singleton
packages/harness/deerflow/agents/middlewares/
tool_error_handling_middleware.py # Registers GuardrailMiddleware in chain
config.example.yaml # Three provider options documented
tests/test_guardrail_middleware.py # 25 tests
docs/GUARDRAILS.md # This file
```