X-Git-Url: https://git.ralfj.de/schsh.git/blobdiff_plain/ee2713792d210cf285ca0e82fb1a00ab3e5da213..99d40029c416c5f3a677961e148fa371103413fe:/README.rst diff --git a/README.rst b/README.rst new file mode 100644 index 0000000..991ed6a --- /dev/null +++ b/README.rst @@ -0,0 +1,102 @@ +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 `_. +