Looking Glass: BIRD configuration and tips.
Only BIRD on Debian GNU/Linux and how to (merely) secure an restricted ssh user will be detailed. Other OSes were not tested.
Security will be mainly based on shell, path and ssh access restriction. Password authentication will not even be presented here, only key based authentication.
apt-get install traceroute bash iputils-ping
- BIRD: a functionnal installation of BIRD, assuming group bird exists (requires at least the Debian package from wheezy-backports)
Security and user access
Looking Glass directly calls
birdc "bird command" and
birdc6 "bird command". Thus, the
lg user only needs to run
traceroute. To achieve this, we recommend the use of
rbash (restricted bash, see ), ssh key based authentication and a bit of
Rough steps ahead (maybe more doc later):
# create the "lg" unix user and add it to "bird" group root@bird-router ~# adduser lg (boring questions) root@bird-router ~# adduser lg bird # log in as lg user root@bird-router ~# su -l lg # create ssh userdir and authorized the looking glass RSA pubkey with limited access and features lg@bird-router ~# mkdir ~/.ssh/ lg@bird-router ~# echo 'from="lg.example.com,$IP4-OF-YOUR-LG",no-port-forwarding,no-x11-forwarding,no-agent-forwarding ssh-rsa $RSA-PUBKEY-HERE lg@looking-glass' >| ~/.ssh/authorized_keys # truncate the profile dotfile (Debian-based distributions) # for CentOS/RHEL, apply the below steps to ~/.bashrc instead lg@bird-router ~# echo >| ~/.profile # set up a limited PATH lg@bird-router ~# echo "export PATH=/opt/lg-bin" >| ~/.profile lg@bird-router ~# exit # render the profile dotfile immutable, the lg user will not be able to truncate/edit it root@bird-router ~# chattr +i ~lg/.profile # change lg user shell to restricted bash root@bird-router ~# chsh -s /bin/rbash lg # set up the restricted PATH with the only necessary binaries simlinks root@bird-router ~# mkdir -p /opt/lg-bin root@bird-router ~# for cmd in birdc birdc6 ping ping6 traceroute traceroute6; do ln -s $(which $cmd) /opt/lg-bin/; done root@bird-router ~#
You can disable password authentication for the lg user in the sshd config:
Match user lg PasswordAuthentication no
and reload sshd:
service ssh reload
Test the SSH connection from the server where the looking glass is installed:
ssh -i lg-user-id_rsa.key email@example.com
After successful login, verify that only built-in functions and
traceroute are available and functionnal.
-  http://en.wikipedia.org/wiki/Restricted_shell