Docker --privileged

👉 Overview

👀 What ?

Docker --privileged is a flag option that can be used when running a Docker container. This option gives the container almost the same privileges as the host machine. It allows the container to access all devices, it can allow the container to modify the host's system kernel and it can also enable the container to mount (and unmount) filesystems anywhere.

🧐 Why ?

Understanding the Docker --privileged option is important because it has significant implications for the security of your Docker environment. If a container running with the --privileged flag is compromised, the attacker may gain access to the entire host system, leading to a breach of the system's security. Therefore, it's important to use this flag sparingly and only when necessary.

⛏️ How ?

To use the --privileged flag with Docker, you simply append it to your Docker run command like so: docker run --privileged -d my_container. This will start a new container called 'my_container' with privileged status. However, it's recommended to consider safer alternatives whenever possible, such as using Linux capabilities, or using the --device flag to allow specific device access, instead of giving all-encompassing access with the --privileged flag.

⏳ When ?

The --privileged flag has been available in Docker since its early versions. However, its use is generally discouraged unless absolutely necessary due to the security risks it presents.

⚙️ Technical Explanations

The Docker --privileged flag is a powerful tool that can significantly enhance a Docker container's capabilities, but it also comes with high security risks. When the --privileged flag is used, it enables all capabilities for the container, effectively giving it the same privileges as the host machine. This includes unrestricted access to all the host's resources, such as its devices, file systems, and system kernel.

Technically, the --privileged flag lifts all the limitations enforced by the device cgroup controller in Linux, which is responsible for limiting the resources a process (or in this case, a container) can use. This means that a Docker container run with the --privileged flag can potentially modify the system kernel, mount and unmount file systems anywhere, and access all devices.

However, this level of access could be a severe security risk. If a container running with the --privileged flag is compromised, the attacker could have the potential to access, modify, or even delete any files on the host system, or change the system's configurations, leading to a system-wide breach.

Because of these risks, it's highly recommended to use the --privileged flag sparingly and only when absolutely necessary. Alternatives, such as using Linux capabilities or the --device flag to allow specific device access, should be considered whenever possible. These methods can provide a container with the necessary access it needs to function, without exposing the entire system to potential risks.

Consider a situation where a Docker container needs specific access to a device on the host system, such as a USB device. Instead of using the --privileged flag, which would give the container full access to all devices and pose a significant security risk, you can use the --device flag to grant access only to the specific device needed.

Here is an example of how to do this:

1. Identify the device you want the container to access. In this case, let's say it's a USB device located at /dev/ttyUSB0.

2. Run the Docker container with the -device flag, specifying the device you want the container to access. The command would look like this:

   docker run --device=/dev/ttyUSB0 -d my_container
   
   

   This command tells Docker to run a new container named 'my_container' and allows it access to the device at /dev/ttyUSB0.

3. Now, 'my_container' can interact with the USB device as if it was directly connected to it, while other devices remain secure and inaccessible.

This method is more secure than using the --privileged flag because it limits the container's access to only what it needs, thus reducing the potential for a security breach. Remember, always aim to give the least privileges necessary for a container to function.