--- /dev/null
+schsh: Restricted file access via SSH
+=====================================
+
+Introduction
+------------
+
+Welcome to schsh_, a schroot-based shell.
+
+Its purpose is simple: I want to provide users with scp, sftp and rsync access
+to my server, such that they can only operate in a certain subdirectory.
+There are plenty of solutions for this problem out there, and all have one
+drawback in common:
+You need to manually set up a bunch of chroots, and copy the files needed for
+scp, sftp and rsync into them.
+
+I didn't like that, so here is my alternative solution: Use schroot for the
+chroots. This gets OpenSSH out of the loop when it comes to chroots, instead
+the relevant users get a special shell (schsh, the schroot shell). That shell
+essentially calls schroot and runs the desired command inside the chroot. It
+also provides some very basic command restriction (so that you can allow scp,
+sftp and rsync and nothing else).
+
+Unfortunately, this still needs a (s)chroot to be set up for each user, but at
+least no files have to be copied: Instead, schroot is configured to bind-mount
+the relevant system folders into the user-chroot. Hence no files are
+duplicated, and system updates to the relevant tools are applied inside the
+chroots automatically. For additional hardening, these bind-mounts are
+configured to be read-only and no-setuid, while the only user-writeable folder
+is no-exec.
+
+.. _schsh: http://www.ralfj.de/projects/schsh/
+
+Setup
+-----
+
+Before you start, make sure you have the dependencies installed:
+schsh needs `Python 3`_ (I tested it with version 3.2) and
+schroot_ (version 1.6 or newer).
+
+Installation is simple: Just run ``make install``. That will copy some files
+to ``/usr/local/bin``, and some configuration to ``/etc/schroot/``.
+Before you create any users, make sure the directory ``/var/lib/schsh`` and a
+group called ``schsh`` exist.
+
+You should also set up SSH to disallow port forwarding for users controlled by
+schsh. See ``sshd_config`` in the source folder for an appropriate snippet
+of OpenSSH configuration.
+
+Before you can set up schsh for a user, you need to create it first::
+
+ adduser sandboxed --disabled-password
+
+Any existing user can be "sandboxed" by running::
+
+ makeschsh sandboxed
+
+This does the following:
+
+* Change the user's shell to ``/usr/local/bin/schsh``
+* Create a chroot base in ``/var/lib/schsh/sandboxed`` with some empty
+ subfolders as well as ``/etc/passwd`` and ``/etc/group`` containing
+ only root, this user and the ``schsh`` group
+* Add the user to the ``schsh`` group
+* Set up a schroot called ``schsh-sandboxed`` for the given folder, and an
+ fstab file in ``/etc/schroot/schsh`` used by this schroot
+
+Now if the user logs in via SSH, ``/usr/local/bin/schsh`` will be executed,
+and it will lock the user into the schroot ``schsh-sandboxed``. It will
+only see some system folders and a folder called ``/data`` mapped to
+``/home/sandboxed/data``. If you want to give the user access to more
+folders, or another folder, simply edit ``/etc/schroot/schsh/sandboxed.fstab``.
+The only part of schsh writing any files is ``makeschsh``, so you can change
+the users' schroot configurations at your will.
+
+.. _Python 3: http://www.python.org
+.. _schroot: https://wiki.debian.org/Schroot
+
+Configuration
+-------------
+
+There is not much to configure at the moment. However, there are some
+global variables at the top of both ``schsh`` and ``makeschsh`` to
+change the base paths, and to tell which commands are allowed.
+
+Source, License
+---------------
+
+You can find the sources in the `git repository`_. They are provided under
+the GPLv3_. In addition, all files except for ``schsh-rrsync`` are
+provided under the GPLv2_ or (at your option) any later version of the
+GPL.
+
+.. _git repository: http://www.ralfj.de/git/schsh.git
+.. _GPLv2: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+.. _GPLv3: https://www.gnu.org/licenses/gpl.html
+
+Contact
+-------
+
+If you found a bug, or want to leave a comment, please
+`send me a mail <post AT ralfj DOT de>`_.
+
projects / schsh.git / blobdiff