gemini-cli/packages/core/src/policy/config.ts

/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import * as fs from 'node:fs/promises';
import * as path from 'node:path';
import { fileURLToPath } from 'node:url';
import { Storage } from '../config/storage.js';
import {
  type PolicyEngineConfig,
  PolicyDecision,
  type PolicyRule,
  type ApprovalMode,
  type PolicySettings,
} from './types.js';
import type { PolicyEngine } from './policy-engine.js';
import { loadPoliciesFromToml, type PolicyFileError } from './toml-loader.js';
import { buildArgsPatterns } from './utils.js';
import toml from '@iarna/toml';
import {
  MessageBusType,
  type UpdatePolicy,
} from '../confirmation-bus/types.js';
import { type MessageBus } from '../confirmation-bus/message-bus.js';
import { coreEvents } from '../utils/events.js';
import { debugLogger } from '../utils/debugLogger.js';
import { SHELL_TOOL_NAMES } from '../utils/shell-utils.js';
import { SHELL_TOOL_NAME } from '../tools/tool-names.js';

import { isDirectorySecure } from '../utils/security.js';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
export const DEFAULT_CORE_POLICIES_DIR = path.join(__dirname, 'policies');

// Policy tier constants for priority calculation
export const DEFAULT_POLICY_TIER = 1;
export const USER_POLICY_TIER = 2;
export const ADMIN_POLICY_TIER = 3;

/**
 * Gets the list of directories to search for policy files, in order of increasing priority
 * (Default -> User -> Admin).
 *
 * @param defaultPoliciesDir Optional path to a directory containing default policies.
 */
export function getPolicyDirectories(defaultPoliciesDir?: string): string[] {
  const dirs = [];

  if (defaultPoliciesDir) {
    dirs.push(defaultPoliciesDir);
  } else {
    dirs.push(DEFAULT_CORE_POLICIES_DIR);
  }

  dirs.push(Storage.getUserPoliciesDir());
  dirs.push(Storage.getSystemPoliciesDir());

  // Reverse so highest priority (Admin) is first for loading order if needed,
  // though loadPoliciesFromToml might want them in a specific order.
  // CLI implementation reversed them: [DEFAULT, USER, ADMIN].reverse() -> [ADMIN, USER, DEFAULT]
  return dirs.reverse();
}

/**
 * Determines the policy tier (1=default, 2=user, 3=admin) for a given directory.
 * This is used by the TOML loader to assign priority bands.
 */
export function getPolicyTier(
  dir: string,
  defaultPoliciesDir?: string,
): number {
  const USER_POLICIES_DIR = Storage.getUserPoliciesDir();
  const ADMIN_POLICIES_DIR = Storage.getSystemPoliciesDir();

  const normalizedDir = path.resolve(dir);
  const normalizedUser = path.resolve(USER_POLICIES_DIR);
  const normalizedAdmin = path.resolve(ADMIN_POLICIES_DIR);

  if (
    defaultPoliciesDir &&
    normalizedDir === path.resolve(defaultPoliciesDir)
  ) {
    return DEFAULT_POLICY_TIER;
  }
  if (normalizedDir === path.resolve(DEFAULT_CORE_POLICIES_DIR)) {
    return DEFAULT_POLICY_TIER;
  }
  if (normalizedDir === normalizedUser) {
    return USER_POLICY_TIER;
  }
  if (normalizedDir === normalizedAdmin) {
    return ADMIN_POLICY_TIER;
  }

  return DEFAULT_POLICY_TIER;
}

/**
 * Formats a policy file error for console logging.
 */
export function formatPolicyError(error: PolicyFileError): string {
  const tierLabel = error.tier.toUpperCase();
  let message = `[${tierLabel}] Policy file error in ${error.fileName}:\n`;
  message += `  ${error.message}`;
  if (error.details) {
    message += `\n${error.details}`;
  }
  if (error.suggestion) {
    message += `\n  Suggestion: ${error.suggestion}`;
  }
  return message;
}

/**
 * Filters out insecure policy directories (specifically the system policy directory).
 * Emits warnings if insecure directories are found.
 */
async function filterSecurePolicyDirectories(
  dirs: string[],
): Promise<string[]> {
  const systemPoliciesDir = path.resolve(Storage.getSystemPoliciesDir());

  const results = await Promise.all(
    dirs.map(async (dir) => {
      // Only check security for system policies
      if (path.resolve(dir) === systemPoliciesDir) {
        const { secure, reason } = await isDirectorySecure(dir);
        if (!secure) {
          const msg = `Security Warning: Skipping system policies from ${dir}: ${reason}`;
          coreEvents.emitFeedback('warning', msg);
          return null;
        }
      }
      return dir;
    }),
  );

  return results.filter((dir): dir is string => dir !== null);
}

export async function createPolicyEngineConfig(
  settings: PolicySettings,
  approvalMode: ApprovalMode,
  defaultPoliciesDir?: string,
): Promise<PolicyEngineConfig> {
  const policyDirs = getPolicyDirectories(defaultPoliciesDir);
  const securePolicyDirs = await filterSecurePolicyDirectories(policyDirs);

  // Load policies from TOML files
  const {
    rules: tomlRules,
    checkers: tomlCheckers,
    errors,
  } = await loadPoliciesFromToml(securePolicyDirs, (dir) =>
    getPolicyTier(dir, defaultPoliciesDir),
  );

  // Emit any errors encountered during TOML loading to the UI
  // coreEvents has a buffer that will display these once the UI is ready
  if (errors.length > 0) {
    for (const error of errors) {
      coreEvents.emitFeedback('error', formatPolicyError(error));
    }
  }

  const rules: PolicyRule[] = [...tomlRules];
  const checkers = [...tomlCheckers];

  // Priority system for policy rules:
  // - Higher priority numbers win over lower priority numbers
  // - When multiple rules match, the highest priority rule is applied
  // - Rules are evaluated in order of priority (highest first)
  //
  // Priority bands (tiers):
  // - Default policies (TOML): 1 + priority/1000 (e.g., priority 100 → 1.100)
  // - User policies (TOML): 2 + priority/1000 (e.g., priority 100 → 2.100)
  // - Admin policies (TOML): 3 + priority/1000 (e.g., priority 100 → 3.100)
  //
  // This ensures Admin > User > Default hierarchy is always preserved,
  // while allowing user-specified priorities to work within each tier.
  //
  // Settings-based and dynamic rules (all in user tier 2.x):
  //   2.95: Tools that the user has selected as "Always Allow" in the interactive UI
  //   2.9:  MCP servers excluded list (security: persistent server blocks)
  //   2.4:  Command line flag --exclude-tools (explicit temporary blocks)
  //   2.3:  Command line flag --allowed-tools (explicit temporary allows)
  //   2.2:  MCP servers with trust=true (persistent trusted servers)
  //   2.1:  MCP servers allowed list (persistent general server allows)
  //
  // TOML policy priorities (before transformation):
  //   10: Write tools default to ASK_USER (becomes 1.010 in default tier)
  //   15: Auto-edit tool override (becomes 1.015 in default tier)
  //   50: Read-only tools (becomes 1.050 in default tier)
  //   999: YOLO mode allow-all (becomes 1.999 in default tier)

  // MCP servers that are explicitly excluded in settings.mcp.excluded
  // Priority: 2.9 (highest in user tier for security - persistent server blocks)
  if (settings.mcp?.excluded) {
    for (const serverName of settings.mcp.excluded) {
      rules.push({
        toolName: `${serverName}__*`,
        decision: PolicyDecision.DENY,
        priority: 2.9,
        source: 'Settings (MCP Excluded)',
      });
    }
  }

  // Tools that are explicitly excluded in the settings.
  // Priority: 2.4 (user tier - explicit temporary blocks)
  if (settings.tools?.exclude) {
    for (const tool of settings.tools.exclude) {
      rules.push({
        toolName: tool,
        decision: PolicyDecision.DENY,
        priority: 2.4,
        source: 'Settings (Tools Excluded)',
      });
    }
  }

  // Tools that are explicitly allowed in the settings.
  // Priority: 2.3 (user tier - explicit temporary allows)
  if (settings.tools?.allowed) {
    for (const tool of settings.tools.allowed) {
      // Check for legacy format: toolName(args)
      const match = tool.match(/^([a-zA-Z0-9_-]+)\((.*)\)$/);
      if (match) {
        const [, rawToolName, args] = match;
        // Normalize shell tool aliases
        const toolName = SHELL_TOOL_NAMES.includes(rawToolName)
          ? SHELL_TOOL_NAME
          : rawToolName;

        // Treat args as a command prefix for shell tool
        if (toolName === SHELL_TOOL_NAME) {
          const patterns = buildArgsPatterns(undefined, args);
          for (const pattern of patterns) {
            if (pattern) {
              rules.push({
                toolName,
                decision: PolicyDecision.ALLOW,
                priority: 2.3,
                argsPattern: new RegExp(pattern),
                source: 'Settings (Tools Allowed)',
              });
            }
          }
        } else {
          // For non-shell tools, we allow the tool itself but ignore args
          // as args matching was only supported for shell tools historically.
          rules.push({
            toolName,
            decision: PolicyDecision.ALLOW,
            priority: 2.3,
            source: 'Settings (Tools Allowed)',
          });
        }
      } else {
        // Standard tool name
        const toolName = SHELL_TOOL_NAMES.includes(tool)
          ? SHELL_TOOL_NAME
          : tool;
        rules.push({
          toolName,
          decision: PolicyDecision.ALLOW,
          priority: 2.3,
          source: 'Settings (Tools Allowed)',
        });
      }
    }
  }

  // MCP servers that are trusted in the settings.
  // Priority: 2.2 (user tier - persistent trusted servers)
  if (settings.mcpServers) {
    for (const [serverName, serverConfig] of Object.entries(
      settings.mcpServers,
    )) {
      if (serverConfig.trust) {
        // Trust all tools from this MCP server
        // Using pattern matching for MCP tool names which are formatted as "serverName__toolName"
        rules.push({
          toolName: `${serverName}__*`,
          decision: PolicyDecision.ALLOW,
          priority: 2.2,
          source: 'Settings (MCP Trusted)',
        });
      }
    }
  }

  // MCP servers that are explicitly allowed in settings.mcp.allowed
  // Priority: 2.1 (user tier - persistent general server allows)
  if (settings.mcp?.allowed) {
    for (const serverName of settings.mcp.allowed) {
      rules.push({
        toolName: `${serverName}__*`,
        decision: PolicyDecision.ALLOW,
        priority: 2.1,
        source: 'Settings (MCP Allowed)',
      });
    }
  }

  return {
    rules,
    checkers,
    defaultDecision: PolicyDecision.ASK_USER,
    approvalMode,
  };
}

interface TomlRule {
  toolName?: string;
  mcpName?: string;
  decision?: string;
  priority?: number;
  commandPrefix?: string | string[];
  argsPattern?: string;
  // Index signature to satisfy Record type if needed for toml.stringify
  [key: string]: unknown;
}

export function createPolicyUpdater(
  policyEngine: PolicyEngine,
  messageBus: MessageBus,
) {
  messageBus.subscribe(
    MessageBusType.UPDATE_POLICY,
    async (message: UpdatePolicy) => {
      const toolName = message.toolName;

      if (message.commandPrefix) {
        // Convert commandPrefix(es) to argsPatterns for in-memory rules
        const patterns = buildArgsPatterns(undefined, message.commandPrefix);
        for (const pattern of patterns) {
          if (pattern) {
            policyEngine.addRule({
              toolName,
              decision: PolicyDecision.ALLOW,
              // User tier (2) + high priority (950/1000) = 2.95
              // This ensures user "always allow" selections are high priority
              // but still lose to admin policies (3.xxx) and settings excludes (200)
              priority: 2.95,
              argsPattern: new RegExp(pattern),
              source: 'Dynamic (Confirmed)',
            });
          }
        }
      } else {
        const argsPattern = message.argsPattern
          ? new RegExp(message.argsPattern)
          : undefined;

        policyEngine.addRule({
          toolName,
          decision: PolicyDecision.ALLOW,
          // User tier (2) + high priority (950/1000) = 2.95
          // This ensures user "always allow" selections are high priority
          // but still lose to admin policies (3.xxx) and settings excludes (200)
          priority: 2.95,
          argsPattern,
          source: 'Dynamic (Confirmed)',
        });
      }

      if (message.persist) {
        try {
          const userPoliciesDir = Storage.getUserPoliciesDir();
          await fs.mkdir(userPoliciesDir, { recursive: true });
          const policyFile = path.join(userPoliciesDir, 'auto-saved.toml');

          // Read existing file
          let existingData: { rule?: TomlRule[] } = {};
          try {
            const fileContent = await fs.readFile(policyFile, 'utf-8');
            existingData = toml.parse(fileContent) as { rule?: TomlRule[] };
          } catch (error) {
            if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
              debugLogger.warn(
                `Failed to parse ${policyFile}, overwriting with new policy.`,
                error,
              );
            }
          }

          // Initialize rule array if needed
          if (!existingData.rule) {
            existingData.rule = [];
          }

          // Create new rule object
          const newRule: TomlRule = {};

          if (message.mcpName) {
            newRule.mcpName = message.mcpName;
            // Extract simple tool name
            const simpleToolName = toolName.startsWith(`${message.mcpName}__`)
              ? toolName.slice(message.mcpName.length + 2)
              : toolName;
            newRule.toolName = simpleToolName;
            newRule.decision = 'allow';
            newRule.priority = 200;
          } else {
            newRule.toolName = toolName;
            newRule.decision = 'allow';
            newRule.priority = 100;
          }

          if (message.commandPrefix) {
            newRule.commandPrefix = message.commandPrefix;
          } else if (message.argsPattern) {
            newRule.argsPattern = message.argsPattern;
          }

          // Add to rules
          existingData.rule.push(newRule);

          // Serialize back to TOML
          // @iarna/toml stringify might not produce beautiful output but it handles escaping correctly
          const newContent = toml.stringify(existingData as toml.JsonMap);

          // Atomic write: write to tmp then rename
          const tmpFile = `${policyFile}.tmp`;
          await fs.writeFile(tmpFile, newContent, 'utf-8');
          await fs.rename(tmpFile, policyFile);
        } catch (error) {
          coreEvents.emitFeedback(
            'error',
            `Failed to persist policy for ${toolName}`,
            error,
          );
        }
      }
    },
  );
}