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Understand permission requirements for Windows

This page contains information about the permission requirements for running and installing Docker Desktop on Windows, the functionality of the privileged helper process com.docker.service and the reasoning behind this approach.

It also provides clarity on running containers as root as opposed to having Administrator access on the host and the privileges of the Windows Docker engine and Windows containers.

Permission requirements

While Docker Desktop on Windows can be run without having Administrator privileges, it does require them during installation. On installation you recieve a UAC prompt which allows a privileged helper service to be installed. After that, Docker Desktop can be run without administrator privileges, provided you are members of the docker-users group. If you performed the installation, you are automatically added to this group, but other users must be added manually. This allows the administrator to control who has access to Docker Desktop.

The reason for this approach is that Docker Desktop needs to perform a limited set of privileged operations which are conducted by the privileged helper process com.docker.service. This approach allows, following the principle of least privilege, Administrator access to be used only for the operations for which it is absolutely necessary, while still being able to use Docker Desktop as an unprivileged user.

Privileged helper

The privileged helper com.docker.service is a Windows service which runs in the background with SYSTEM privileges. It listens on the named pipe //./pipe/dockerBackendV2. The developer runs the Docker Desktop application, which connects to the named pipe and sends commands to the service. This named pipe is protected, and only users that are part of the docker-users group can have access to it.

The service performs the following functionalities:

  • Ensuring that kubernetes.docker.internal is defined in the Win32 hosts file. Defining the DNS name kubernetes.docker.internal allows Docker to share Kubernetes contexts with containers.
  • Ensuring that host.docker.internal and gateway.docker.internal are defined in the Win32 hosts file. They point to the host local IP address and allow an application to resolve the host IP using the same name from either the host itself or a container.
  • Securely caching the Registry Access Management policy which is read-only for the developer.
  • Creating the Hyper-V VM "DockerDesktopVM" and managing its lifecycle - starting, stopping and destroying it. The VM name is hard coded in the service code so the service cannot be used for creating or manipulating any other VMs.
  • Moving the VHDX file or folder.
  • Starting and stopping the Windows Docker engine and querying whether it's running.
  • Deleting all Windows containers data files.
  • Checking if Hyper-V is enabled.
  • Checking if the bootloader activates Hyper-V.
  • Checking if required Windows features are both installed and enabled.
  • Conducting healthchecks and retrieving the version of the service itself.

The service start mode depends on which container engine is selected, and, for WSL, on whether it is needed to maintain host.docker.internal and gateway.docker.internal in the Win32 hosts file. This is controlled by a setting under Use the WSL 2 based engine in the settings page. When this is set, WSL engine behaves the same as Hyper-V. So:

  • With Windows containers, or Hyper-v Linux containers, the service is started when the system boots and runs all the time, even when Docker Desktop isn't running. This is required so you can launch Docker Desktop without admin privileges.
  • With WSL2 Linux containers, the service isn't necessary and therefore doesn't run automatically when the system boots. When you switche to Windows containers or Hyper-v Linux containers, or chooses to maintain host.docker.internal and gateway.docker.internal in the Win32 hosts file, a UAC prompt is displayed which asks you to accept the privileged operation to start the service. If accepted, the service is started and set to start automatically upon the next Windows boot.

Containers running as root within the Linux VM

The Linux Docker daemon and containers run in a minimal, special-purpose Linux VM managed by Docker. It is immutable so you can’t extend it or change the installed software. This means that although containers run by default as root, this doesn't allow altering the VM and doesn't grant Administrator access to the Windows host machine. The Linux VM serves as a security boundary and limits what resources from the host can be accessed. File sharing uses a user-space crafted file server and any directories from the host bind mounted into Docker containers still retain their original permissions. It doesn't give you access to any files that it doesn’t already have access to.

Windows Containers

Unlike the Linux Docker engine and containers which run in a VM, Windows containers are an operating system feature, and run directly on the Windows host with Administrator privileges. For organizations who don't want their developers to run Windows containers, a –no-windows-containers installer flag is available from version 4.11 to disable their use.

Networking

For network connectivity, Docker Desktop uses a user-space process (vpnkit), which inherits constraints like firewall rules, VPN, HTTP proxy properties etc. from the user that launched it.