110 lines
3.0 KiB
Go
110 lines
3.0 KiB
Go
package main
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/*
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The purpose of this command is to be run as a new user. It initializes their ssh authorized_keys2 file, which allows them to ssh in for the first time.
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This is an isolated command because creating a file and chowning it normally requires root permissions. We don't want to run the welcome command as root, so we give it `sudo` permission to run this one command as any user. The keyfile path is hardcoded, so if someone were to assume `welcome`'s identity, it could of course cause havoc but not delete
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This is a port of the old createkeyfile.py script from the former admin system.
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There are two functional changes:
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1. It also creates `.ssh`. I can't remember if there was a reason the old script didn't do that as there is no record one way or the other. But having this command make `.ssh` means one fewer thing in the sudoers file.
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2. It guards against overwriting of both .ssh and authorized_keys2. This is solely to limit the effect of a security breach. In the old admin system keys were managed via the django admin, meaning this script was used to add keys to authorized_keys2. these days we just edit authorized_keys2 directly, so this new command should only ever be used to initialize .ssh for a new user.
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*/
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import (
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"fmt"
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"os"
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"os/user"
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"path"
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"strings"
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)
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const keyfileName = "authorized_keys2"
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func quit(msg string, code int) {
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fmt.Println(msg)
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os.Exit(code)
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}
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func main() {
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username := os.Args[1]
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if username == "" {
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quit("expected username as argument", 1)
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}
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u, err := user.Current()
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if err != nil {
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quit(err.Error(), 2)
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}
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if u.Username != username {
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quit("that's my purse; I don't know you", 3)
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}
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sshPath := path.Join("/home", u.Username, ".ssh")
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keyfilePath := path.Join(sshPath, keyfileName)
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if err = os.Mkdir(sshPath, os.FileMode(0700)); err != nil {
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quit(err.Error(), 4)
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}
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f, err := os.OpenFile(keyfilePath, os.O_CREATE|os.O_EXCL|os.O_RDWR, 0600)
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if err != nil {
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quit(fmt.Sprintf("failed to open %s: %s", keyfilePath, err.Error()), 5)
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}
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defer f.Close()
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stdin := make([]byte, 90000) // arbitrary limit
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n, err := os.Stdin.Read(stdin)
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if err != nil {
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quit(err.Error(), 6)
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} else if n == 0 {
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quit("nothing passed on STDIN", 7)
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}
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stdin = stdin[0:n]
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if !strings.HasPrefix(string(stdin), "########## GREETINGS! ##########") {
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// TODO further validation?
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quit(fmt.Sprintf("file contents look wrong: %s", string(stdin)), 8)
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}
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n, err = f.Write(stdin)
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if err != nil {
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quit(err.Error(), 9)
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} else if n == 0 {
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quit("wrote nothing to keyfile", 10)
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}
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}
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/*
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The old script, in full:
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#!/usr/bin/env python3
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"""this script allows django to add public keys for a user. it's in its own
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script so that a specific command can be added to the ttadmin user's sudoers
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file."""
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import sys
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KEYFILE_PATH = '/home/{}/.ssh/authorized_keys2'
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def main(argv):
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username = argv[1]
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with open(KEYFILE_PATH.format(username), 'w') as f:
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f.write(sys.stdin.read())
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if __name__ == '__main__':
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exit(main(sys.argv))
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*/
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