Function checkReadPermissionForTool

src/utils/permissions/filesystem.ts:1030–1194

(
  tool: Tool,
  input: { [key: string]: unknown },
  toolPermissionContext: ToolPermissionContext,
)

 * Permission result for read permission for the specified tool & tool input
 */
export function checkReadPermissionForTool(
  tool: Tool,
  input: { [key: string]: unknown },
  toolPermissionContext: ToolPermissionContext,
): PermissionDecision {
  if (typeof tool.getPath !== 'function') {
    return {
      behavior: 'ask',
      message: `Claude requested permissions to use ${tool.name}, but you haven't granted it yet.`,
    }
  }
  const path = tool.getPath(input)

  // Get paths to check (includes both original and resolved symlinks).
  // Computed once here and threaded through checkWritePermissionForTool →
  // checkPathSafetyForAutoEdit → pathInAllowedWorkingPath to avoid redundant
  // existsSync/lstatSync/realpathSync syscalls on the same path (previously
  // 6× = 30 syscalls per Read permission check).
  const pathsToCheck = getPathsForPermissionCheck(path)

  // 1. Defense-in-depth: Block UNC paths early (before other checks)
  // This catches paths starting with \\ or // that could access network resources
  // This may catch some UNC patterns not detected by containsVulnerableUncPath
  for (const pathToCheck of pathsToCheck) {
    if (pathToCheck.startsWith('\\\\') || pathToCheck.startsWith('//')) {
      return {
        behavior: 'ask',
        message: `Claude requested permissions to read from ${path}, which appears to be a UNC path that could access network resources.`,
        decisionReason: {
          type: 'other',
          reason: 'UNC path detected (defense-in-depth check)',
        },
      }
    }
  }

  // 2. Check for suspicious Windows path patterns (defense in depth)
  for (const pathToCheck of pathsToCheck) {
    if (hasSuspiciousWindowsPathPattern(pathToCheck)) {
      return {
        behavior: 'ask',
        message: `Claude requested permissions to read from ${path}, which contains a suspicious Windows path pattern that requires manual approval.`,
        decisionReason: {
          type: 'other',
          reason:
            'Path contains suspicious Windows-specific patterns (alternate data streams, short names, long path prefixes, or three or more consecutive dots) that require manual verification',
        },
      }
    }
  }

  // 3. Check for READ-SPECIFIC deny rules first - check both the original path and resolved symlink path
  // SECURITY: This must come before any allow checks (including "edit access implies read access")
  // to prevent bypassing explicit read deny rules
  for (const pathToCheck of pathsToCheck) {
    const denyRule = matchingRuleForInput(
      pathToCheck,
      toolPermissionContext,