Linux Kernel Notes - Namespaces

 Namespaces

In Linux, namespaces are a feature of the kernel that allow for process isolation and resource control. Namespaces provide a way to create a separate context for a group of processes, so that they can have their own isolated view of system resources like process IDs, network interfaces, mount points, and more.

The concept of namespaces can be a bit abstract, so let's take a look at a few examples to see how they work in practice.

1. PID namespace: Each process on a Linux system has a unique process ID (PID) assigned to it. The PID namespace provides a way to create a separate view of the PID space for a group of processes. This can be useful for process isolation, containerization, and resource control.

For example, if you start a new process in a new PID namespace, it will have its own set of PIDs that are separate from the PIDs in the parent namespace. This means that the process will see only its own child processes, and not the child processes of other processes in the system.

2. Network namespace: The network namespace provides a way to create a separate network stack for a group of processes. This can be useful for network isolation and virtualization.

For example, if you start a new process in a new network namespace, it will have its own network interfaces, routing tables, and firewall rules that are separate from those in the parent namespace. This means that the process can communicate with other processes in the same namespace, but not with processes in other namespaces.

3. Mount namespace: The mount namespace provides a way to create a separate view of the file system for a group of processes. This can be useful for file system isolation and virtualization.

For example, if you start a new process in a new mount namespace, it will have its own set of mount points and file system access that are separate from those in the parent namespace. This means that the process can access only the files and directories that are available in its own namespace, and not those in other namespaces.

Overall, namespaces provide a powerful tool for process isolation and resource control in Linux. By using namespaces, you can create a secure and isolated environment for running processes, without affecting other processes running on the same system.

 Useful Commands

Here are some useful commands for working with Linux namespaces:

1. unshare: This command allows you to create a new namespace and run a command in that namespace. For example, the command unshare --pid bash will create a new PID namespace and start a new bash shell in that namespace.

2. ip netns: This command is used to manage network namespaces. You can create a new network namespace with the command ip netns add <name>, and then run commands in that namespace with the command ip netns exec <name> <command>. For example, the command ip netns add myns; ip netns exec myns ping 8.8.8.8 will create a new network namespace called "myns" and then run the ping command in that namespace.

3. mount --make-private: This command is used to create a new mount namespace. You can use the mount --make-private command to make the current mount namespace private, so that changes to the file system in one namespace do not affect other namespaces.

4. nsenter: This command allows you to enter an existing namespace and run a command in that namespace. For example, the command nsenter --pid=/proc/1234/ns/pid bash will enter the PID namespace of process 1234 and start a new bash shell in that namespace.

5. ip link set: This command is used to manage network interfaces. You can use the ip link set <interface> netns <name> command to move a network interface to a different network namespace. For example, the command ip link set eth0 netns myns will move the eth0 interface to the network namespace called "myns".

These are just a few of the many commands available for working with Linux namespaces. The exact commands and syntax may vary depending on your distribution and version of Linux, so it's always a good idea to consult the documentation for your specific system.

Security

The security of a namespace depends on the specific use case and configuration. Here are a few things to consider when evaluating the security of a namespace:

1. Isolation: The primary purpose of namespaces is to provide isolation between processes and system resources. A vulnerable namespace is one where processes in the namespace can access resources that they should not be able to access, or where resources outside the namespace can be accessed by processes inside the namespace.

2. Escalation: In some cases, a process running in a namespace may be able to escape the namespace and gain access to resources outside the namespace. This can happen if there are bugs or vulnerabilities in the kernel or in the tools used to manage namespaces.

3. Privileges: Some namespaces require special privileges to create or modify. For example, creating a new network namespace requires the CAP_NET_ADMIN capability. A vulnerable namespace is one where untrusted users or processes are able to create or modify namespaces, or where namespaces are created with more privileges than necessary.

4. Configuration: The security of a namespace also depends on how it is configured. For example, a network namespace with no firewall rules may be more vulnerable to attacks than one with strict firewall rules. Similarly, a mount namespace with read-write access to the host file system may be more vulnerable than one with read-only access.

To determine if a namespace is vulnerable, you should evaluate the above factors for your specific use case and configuration. You can also perform security assessments or penetration testing to identify vulnerabilities and potential attack vectors. It is important to regularly monitor and update your system and namespaces to ensure that they remain secure.