Secure Git Server – Preventing Git User Logging in via SSH

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This post was originally published in 2011
It may contain stale & outdated information. Or it may have grown more awesome with age, like the author.

A short tutorial detailing the steps required to quickly setup a secure git server that doesn’t allow the git user access via ssh – in other words, git commands work & one may use keys for password-less access, but you may prevent any / all ssh keys from being able to log into your server as the `git` user.

On your workstation:

Each user needs to generate an RSA key. This can be done like so (*nix)

$~ ssh-keygen -t rsa

Copy your public key (not your private key – that should never leave your machine!)

$~ scp ~/.ssh/id_rsa.pub <username>@<server>/tmp/

On your server

Install git

$~ yum install git

Create git user

$~ useradd git

Create the git user’s `.ssh` directory

$~ mkdir /home/git/.ssh

Add your workstation’s public key to the git user’s authorized_keys file

$~ cat /tmp/id_rsa.pub /home/git/.ssh/authorized_keys

Test what you’ve done so far by attempting to ssh to your server from your workstation with

$~ ssh -v git@<server>

Assuming that worked fine, create a git repository on your server

$~ mkdir /home/git/new-repo.git
$~ cd /home/git/new-repo.git
$~ git --bare init

Now on your workstation, add this repository, add the remote, create a file, add & commit it, then push it to the server

$~ mkdir ~/new-repo
$~ cd ~/new-repo
$~ git init
$~ git remote add origin git@<server>:new-repo.git
$~ touch README
$~ git add README
$~ git commit -m 'Added README file, first commit'
$~ git push origin master

Assuming that went well, you’re nearly done. Now all we have to do is prevent anyone from being able to ssh into your server with the git user. What we need to do is to lock down the relevant ssh keys. This is accomplished on your server by prepending the following string to the git user’s authorized_keys entry for each key we don’t want to have ssh access

command="perl -e 'exec qw(git-shell -c), $ENV{SSH_ORIGINAL_COMMAND}'"

For example, change the current authorized_keys file from

ssh-rsa <rsa-key> <username>@<hostname>

To the ‘locked down’ version

command="perl -e 'exec qw(git-shell -c), $ENV{SSH_ORIGINAL_COMMAND}'" ssh-rsa <rsa-key> <username>@<hostname>

Any attempt to login to your server from your workstation should now fail. You may now collect authorized keys from your developers and add them (not forgetting to prepend the ‘lock down’ line!) to the git users’s authorized_keys file.

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