zc/git-remote-only

#!/usr/bin/env python3
#
# Restrict an ssh authorized_keys entry to be used only for git push
# and git fetch.  Use thusly:
#
#  command="git-remote-only /path/to/repository.git alice@example.org" ssh-rsa ABCDEF....== alice@example.org dedicated git key
#
# You might also want options like no-port-forwarding,no-X11-forwarding,no-agent-forwarding.
#
# Copyright (c) 2017, Grunchweather Associates
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
# OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

import os, sys, shlex

os.environ.update(GIT_REMOTE_ONLY_COMMAND = " ".join(sys.argv))

cmd = shlex.split(os.getenv("SSH_ORIGINAL_COMMAND", ""))

if len(cmd) == 2 and cmd[0] in ("git-upload-pack", "git-receive-pack") and cmd[1] == sys.argv[1]:
    os.execv("/usr/bin/" + cmd[0], cmd)

sys.exit("Not authorized: {}".format(" ".join(cmd)))