Capabilities on executables

Note on Linux Kernel capabilities

Suraj Deshmukh

1 minute read

File capabilities allow users to execute programs with higher privileges. Best example is network utility ping. A ping binary has capabilities CAP_NET_ADMIN and CAP_NET_RAW. A normal user doesn’t have CAP_NET_ADMIN privilege, since the executable file ping has that capability you can run it. $ getcap which ping /usr/bin/ping = cap_net_admin,cap_net_raw+p Which normally works as follows: $ ping -c 1 PING ( 56(84) bytes of data. 64 bytes from 1.

Root user inside container is root on the host

The easiest way to prove that root inside the container is also root on the host

Suraj Deshmukh

4 minute read

Here are simple steps that you can follow to prove that the root user inside container is also root on the host. And how to mitigate this. Root in container, root on host I have a host with docker daemon running on it. I start a normal container on it with sleep process as PID1. See in the following output that the container clever_lalande started with sleep process. $ docker run -d –rm alpine sleep 9999 6c541cf8f7b315783d2315eebc2f7dddd1f7b26f427e182f8597b10f2746ab0b $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 6c541cf8f7b3 alpine "sleep 9999" 12 seconds ago Up 11 seconds clever_lalande Now let’s find out the process sleep on the host.

Project specific scripts

Instead of polluting your PATH the easier way to put project specific scripts

Suraj Deshmukh

2 minute read

There are always scripts that you write to automate some mundane tasks. And then you put that script in a directory that is in your PATH. But what this does is that it pollutes your system global PATH and shows up in places you wouldn’t want it to be in. I was struggling with this issue for a while and struggling to get a proper solution. But there is a very simple and clever trick to solve this problem.

Copying files to container the generic way

No docker cp needed to copy files from host to your container

Suraj Deshmukh

2 minute read

This blog shows you how you can copy stuff from your host machine to the running container without the docker cp command that we usually use. Steps in text Here I have a script on the host, which looks following: #!/bin/bash tput bold echo "OS Information:" tput sgr0 echo cat /etc/os-release After running which looks like following: $ ls $ ./ OS Information: NAME="Flatcar Linux by Kinvolk" ID=flatcar ID_LIKE=coreos VERSION=2079.