DESCRIPTION

Utility to create restricted shell, to jail, account using Bash in rbash mode.

GNU project's Bash running in rbash mode is a viable choice if you are trying to somewhat contain semi-trusted users. This project includes basic files and utility to create a dummy user that only can run commands of your choice. Useful for setting up tightly confined secure accounts that allow minimum access to restricted set of commands.

How does it work?

Bash installation contains rbash binary which can restrict access. See <http://www.gnu.org/s/bash/manual/html_node/The-Restricted-Shell.html>. What is left to do is to provide a small set of configuration files to go with the account. The concept is pretty straight forward but it is tedious to type all the commands. This project automates the steps to:

1. Create a user account, provided it does not exist. Set login shell to rbash
2. Copy minimal startup files (Bash, SSH).

2. Symlink allowed commands to user's bin/ directory and point PATH there.
3. Set tight permissions for the account directory and its files.

After these steps, the account is hopefully sufficiently locked down. User cannot edit configuration files, change PATH, run commands starting with slash, or cd anywhere, so the only commands available to him are those in bin/.

REQUIREMENTS

1. Environment: Linux only
2. Build: Perl and standard GNU make
3. Run: Bash for /bin/rbash, POSIX /bin/sh and GNU command line programs, e2fsprogs package for /usr/bin/chattr and optionally util-linux package for /usr/bin/getopt

USAGE

Login to the server that distributes /home directories, switch to administrator root, select a login name (or supply existing login), which will be locked. Use Option --test to see what would happen

./makefile.sh -v --init --force --test dummy date ls ssh
                                       |     |
                                       |     List of allowed commands
                                    User's login name

-f, --force
    Allow destructive changes, like overwriting files in user's account.
    Used prmarily when command is repeated so that new set of commands
    can be defined freely.

-i, --init
    Clean initialization. Delete all previous commands from user's
    bin/ directory before creating symlinks to the allowed
    commands.

-v, --verbose
    Display verbose messages.

After the initialization, you might want to check how the account works:

# set password
passwd dummy
  Enter new UNIX password: xxx
  Retype new UNIX password: xxx

# Test restricted shell by logging to an account. It's not possible
# to use su(1) here. See manual page of restricted-shell-create(5)
# why su(1) does not work.
login dummy
  password: xxxxxx

# See what you can do as user dummy?
$ ls
$ date
$ perl -V
-rbash: perl: command not found

MENU BASED SHELL

The implementation presented here does not require Perl and additional modules, just plain POSIX shell /bin/sh.

Directory bin/ contains a very simple menu script that allows running only defined set of commands. You could use it instead of previous rbash approach by setting user's shell to the script. This script is experimental and provided "as is". Use your judgement if you want to use this approach

# Create user "dummy"
./makefile.sh dummy

# Install command menu based "restricted shell"
install -D -m 700 bin/rshell.sh ~dummy/bin/rshell

# Edit commands in case-statement of Main() function
$EDITOR ~dummy/bin/rshell

Note: See also a Perl based menu shell at <http://freecode.com/projects/pshell> and <https://sourceforge.net/projects/psydev/>.

COPYRIGHT AND LICENSE

Copyright (C) 2011-2024 Jari Aalto <jari.aalto@cante.net>

This project is free; you can redistribute and/or modify it under the terms of GNU General Public license either version 2 of the License, or (at your option) any later version.

Project homepage (bugs and source) is at https://github.com/jaalto/project--restricted-shell-rbash