kobopatch-ssh

This repository contains the tools needed to compile dropbear for the arm-kobo-linux-gnueabihf system (all recent Kobo products). This binary is used for root shell access on Kobo devices which, in my case, is used to deploy and debug software on e-readers. As of now, this dynamically compiled dropbear has been tested on a Kobo Libra 2.

Cloning

This repository uses submodules, and must be cloned with the following command

git clone --recursive git@github.com:obynio/kobopatch-ssh.git

Compiling locally

This project piggy-backs off the toolchain I use for kolib, so everything is done inside a docker container. You must have docker installed on your system to compile dropbear. With docker installed, simply pull the image or grab a book and compile the dockerfile yourself.

docker pull obynio/kobo-toolchain:crosstools
./compile.sh

Kobo setup

Important

This assumes you already have telnet access to the device

Dropbear needs somewhere to go on the system. Since the non-static binary is very light I chose /usr/local/bin. The host keys must also be generated with dropbearkey that needs to be compiled separately.

dropbearkey -t dss -f /etc/dropbear/dropbear_dss_host_key
dropbearkey -t rsa -f /etc/dropbear/dropbear_rsa_host_key
dropbearkey -t ecdsa -f /etc/dropbear/dropbear_ecdsa_host_key
dropbearkey -t ed25119 -f /etc/dropbear/dropbear_ed25519_host_key

To start dropbear on boot you need to add the startup script and the corresponding udev rule.

mkdir /usr/local/dropbear

cp scripts/boot.sh /usr/local/dropbear
chmod +x /usr/local/dropbear/boot.sh

cp script/on-boot.sh /usr/local/dropbear
chmod +x /usr/local/dropbear/on-boot.sh

cp rules/96-dropbear.rules /etc/udev/rules.d
chmod 777 /etc/udev/rules.d/96-dropbear.rules

Improvement ideas

• Add toolchain for dropbearkey
• Add a way to trigger dropbear when wifi is enabled or disabled using udev
• Add continuous integration
• Look into @pgaskin kobo's toolchain
• Look into koxtoolchain which is better suited than the toolchain above

Credits

Many thanks to ewpratten for its original work on the matter.