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Chrooted Drop Bear :: HowTo
This tutorial is being written to help you install Drop Bear to a chroot environment.
It covers the below sections:
* Installation of Drop Bear
* Setup Drop Bear
* Setup Chroot Enviroment
* Debug Chrooted Drop Bear
Drop Bear
Dropbear is a relatively small SSH 2 server and client.
It is an alternative lightweight program of 
openssh and it is designed for environments with low memory and processor resources, such as embedded systems.
http://matt.ucc.asn.au/dropbear/dropbear.html
Installation
Download
Extract
Configuration
In our installation we choose: /chroot/dropbear as the root path of our chroot environment
And for educational purpose only, we change the default TCP port of ssh to 2222:
Compilation
Simple as that:
Installation
The default installation process:
Keys
The next step is to create dss & rsa keys for dropbear ssh server.
We must create the dropbear's key folder first:
and then:
As you can see, we used the chroot environment path without the need of our distribution path hierarchy.
The Drop Bear's? keys are already installed to our chroot environment at once.
Shared Libraries
We now have to check all the necessaries shared libraries that dropbear needs to run inside a chroot environment
Chroot Environment
Structure
Libraries
Extra Libraries
This libraries are mostly for the authentication process.
Files
Copy necessaries files from root to chroot
Devices
We now must be very careful with the next step of our process.
We have to create all the necessaries devices for dropbear to run
(Remember, we are always on the chroot path – eg. /chroot/dropbear)
Users
Of course we need to add users to our chroot dropbear setup.
You can choose to add an existence user or you can create a new one.
I prefer to add an existence user (eg. ebal):
Shell
Every user needs a shell!
But we dont need to install bash, we can simple use busybox.
Busybox is a lightweight shell and combines a lot of common unix utils into a small executable binary file.
Mount Points
This is the most important thing that we (you) have to do properly.
The new environment needs access to terminals (this is necessary for a user to login) and to proc filesystem.
Run
Finally we are ready to run Drop Bear from a chroot enviroment:
Debug
But if something goes wrong, we can always debug the running process with strace: