Seccomp and Process Isolation

Oct 13, 2025 by wbrum.org 38 views

Introduction

In a Linux-based system, processes can be executed with various privileges, and some of these processes may have the ability to run subcommands. This can be a security risk if not properly managed, as it allows malicious users to execute unauthorized commands. In this article, we will discuss how to prevent a process from running a subcommand, particularly in the context of a web application that allows users to execute shell commands.

Background

In a typical Linux system, a process can execute a subcommand by using the fork() system call to create a new process, and then executing the subcommand in the new process. This allows the original process to continue running while the subcommand is executed in the new process. However, this also means that the original process can potentially be compromised if the subcommand is executed with elevated privileges.

Seccomp and Process Isolation

One way to prevent a process from running a subcommand is to use the Seccomp (Secure Computing) mechanism, which is a Linux kernel feature that allows processes to restrict the system calls that can be made by a process. By using Seccomp, a process can be configured to only allow certain system calls, and to block others. This can be used to prevent a process from executing a subcommand.

Another way to prevent a process from running a subcommand is to use process isolation, which involves running the process in a separate namespace or container. This can be achieved using Linux containers, such as Docker, or by using the unshare command to create a new namespace for the process.

Using Seccomp to Prevent Subcommand Execution

To use Seccomp to prevent a process from running a subcommand, you can use the seccomp command to configure the process to only allow certain system calls. For example, you can use the following command to configure a process to only allow the execve system call:

seccomp -f seccomp_filter.json

The seccomp_filter.json file would contain the following configuration:

{
  "default_action": "SCMP_ACT_ALLOW",
  "actions": [
    {
      "type": "SCMP_ACT_ALLOW",
      "args": [
        {
          "op": "SCMP_OP_EXECVE",
          "arg": 0
        }
      ]
    }
  ]
}

This configuration allows the execve system call, but blocks all other system calls.

Using Process Isolation to Prevent Subcommand Execution

To use process isolation to prevent a process from running a subcommand, you can use Linux containers, such as Docker, to run the process in a separate namespace. For example, you can use the following command to run a process in a Docker container:

docker run -it --rm --name my_container my_image /bin/bash

This command runs a new container from the my_image image, and executes the /bin/bash command in the container.

Example Use Case

Suppose we have a web application that allows users to execute shell commands. We want to prevent the application from executing a subcommand that could potentially compromise the system. We can use Seccomp to configure the application to only allow certain system calls, and to block others.

For example, we can use the following configuration to allow the execve system call, but block all other system calls:

{
  "default_action": "SCMP_ACT_ALLOW",
  "actions": [
    {
      "type": "SCMP_ACT_ALLOW",
      "args": [
        {
          "op": "SCMP_OP_EXECVE",
          "arg": 0
        }
      ]
    }
  ]
}

We can then use the seccomp command to configure the application to use this configuration:

seccomp -f seccomp_filter.json

This will prevent the application from executing any system calls other than execve.

Conclusion

In this article, we discussed how to prevent a process from running a subcommand, particularly in the context of a web application that allows users to execute shell commands. We used Seccomp and process isolation to configure the application to only allow certain system calls, and to block others. This can be used to prevent a process from executing a subcommand that could potentially compromise the system.

References

Future Work

Introduction

In our previous article, we discussed how to prevent a process from running a subcommand, particularly in the context of a web application that allows users to execute shell commands. We used Seccomp and process isolation to configure the application to only allow certain system calls, and to block others. In this article, we will answer some frequently asked questions about preventing a process from running a subcommand.

Q: What is Seccomp, and how does it work?

A: Seccomp is a Linux kernel feature that allows processes to restrict the system calls that can be made by a process. By using Seccomp, a process can be configured to only allow certain system calls, and to block others. This can be used to prevent a process from executing a subcommand.

Q: How do I configure Seccomp to prevent a process from running a subcommand?

A: To configure Seccomp to prevent a process from running a subcommand, you can use the seccomp command to configure the process to only allow certain system calls. For example, you can use the following command to configure a process to only allow the execve system call:

seccomp -f seccomp_filter.json

The seccomp_filter.json file would contain the following configuration:

{
  "default_action": "SCMP_ACT_ALLOW",
  "actions": [
    {
      "type": "SCMP_ACT_ALLOW",
      "args": [
        {
          "op": "SCMP_OP_EXECVE",
          "arg": 0
        }
      ]
    }
  ]
}

This configuration allows the execve system call, but blocks all other system calls.

Q: What is process isolation, and how does it work?

A: Process isolation is a technique that involves running a process in a separate namespace or container. This can be achieved using Linux containers, such as Docker, or by using the unshare command to create a new namespace for the process.

Q: How do I use process isolation to prevent a process from running a subcommand?

A: To use process isolation to prevent a process from running a subcommand, you can use Linux containers, such as Docker, to run the process in a separate namespace. For example, you can use the following command to run a process in a Docker container:

docker run -it --rm --name my_container my_image /bin/bash

This command runs a new container from the my_image image, and executes the /bin/bash command in the container.

Q: What are the benefits of using Seccomp and process isolation to prevent a process from running a subcommand?

A: The benefits of using Seccomp and process isolation to prevent a process from running a subcommand include:

Improved security: By restricting the system calls that can be made by a process, Seccomp and process isolation can help prevent a process from executing a subcommand that could potentially compromise the system.
Reduced risk: By running a process in a separate namespace or container, process isolation can help reduce the risk of a process executing a subcommand that could potentially compromise the system.
Improved flexibility: Seccomp and process isolation can be used to configure a process to only allow certain system calls, and to block others. This can be useful in a variety of scenarios, such as in cloud computing and container orchestration.

Q: What are some common use cases for preventing a process from running a subcommand?

A: Some common use cases for preventing a process from running a subcommand include:

Web applications that allow users to execute shell commands
Cloud computing and container orchestration
Linux containers and Docker
Security and compliance

Conclusion

In this article, we answered some frequently asked questions about preventing a process from running a subcommand. We discussed the benefits of using Seccomp and process isolation to prevent a process from running a subcommand, and provided examples of how to use these techniques in a variety of scenarios.

References

Future Work

In the future, we plan to explore other ways to prevent a process from running a subcommand, such as using Linux namespaces and cgroups. We also plan to investigate the use of Seccomp and process isolation in other contexts, such as in cloud computing and container orchestration.