It's actually pretty simple to get exactly what you describe; the key is ssh's "forced command" option. Essentially you tell ssh that, no matter what command the client tries to execute it always executes the forced command. You set the forced command to point to a simple wrapper script that verifies the command is
svnserve -t. If it is, it executes as requested. Otherwise it exits. This is the script I use:
# Verify that the requested command is an svnserve call.
# Note that sshd stores the command requested by the client in
# the variable "SSH_ORIGINAL_COMMAND".
if [[ $SSH_ORIGINAL_COMMAND = "svnserve -t" ]]
echo "You are only allowed svn access to this server."
There are two ways to set this forced command:
- If your users are logging in using key-based authentication (and they should) you can add ``command="/usr/local/sbin/validate_svn'' as the first field in their public key in
~/.ssh/authorized_keys. In order for this to be safe, though, you'll have to disable password auth. Otherwise they can log in with a password (bypassing the forced command) and edit
~/.ssh/authorized_keys to remove the restriction.
- Add a "Match" stanza to the end of
/etc/ssh/sshd_config for the user(s) that should only be able to use svn. It should look something like this:
Match user svn