~azzar1/unity/add-show-desktop-key : revision 1336

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.. _Genshi: http://genshi.edgewall.org/

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.. _ref-jail:

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Jail System

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===========

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To each user, it appears that they have their own private Unix filesystem

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containing software, libraries and a home directory to do with what they

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please. This is mainly done by the setuid root program ``trampoline`` (See

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:file:`bin/trampoline/trampoline.c`) which mounts the users home directory,

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sets up the users environment, jumps into the user's jail using the

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:manpage:`chroot(2)` system call and finally drops privileges to the desired

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user and group.

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please. This is mainly done by the setuid root program ``trampoline`` which

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mounts the users home directory, sets up the users environment, jumps into the

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user's jail using the :manpage:`chroot(2)` system call and finally drops

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privileges to the desired user and group.

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To prevent abuse, ``trampoline`` can only be used by root or one of the uids

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specified when trampoline is built by ``setup.py build`` (defaults to UID 33,

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www-data on Debian systems). Since it's one of two C programs involved in IVLE

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and runs setuid root it is rather secuity sensative.

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and runs setuid root it is rather security sensitive.

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.. seealso:: Source code :file:`bin/trampoline/trampoline.c`

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Base Image Generation

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---------------------

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directories to be accessible from another location in the file system. By

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carefully bind-mounting the jail image as read-only and then bind-mounting the

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user's :file:`/home` and :file:`/tmp` directory data over the top, we create a

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jail with only three bind mounts and at virtually no filesystem overhead.

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jail with only three bind mounts and at virtually no file system overhead.

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.. note::

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IVLE has historically used numerous solutions to this problem, which are

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than the real memory used. For this reason :const:`RLIMIT_AS` is currently set

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very large.

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.. ref-python-console

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Python Console

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==============

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.. _JSON: http://json.org

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.. _ref-usermgt-server:

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User Management Server

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======================

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* Creating group Subversion repositories.

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* Rebuilding Subversion authorization files.

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Communication with the Server is done using the `Chat Protocol`_. To prevent

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unauthorized use, communication with the User Management Server requires that

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a *shared secret* be used to communicate with the server. This secret is

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stored in the `magic` variable in the `[usrmgt]` section of

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Communication with the Server is done using the `Chat Protocol <ref-chat>`_.

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To prevent unauthorized use, communication with the User Management Server

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requires that a *shared secret* be used to communicate with the server. This

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secret is stored in the `magic` variable in the `[usrmgt]` section of

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:file:`/etc/ivle/ivle.conf`.

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The User Management Server is called almost exclusively from the

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:mod:`ivle.webapp.userservice` module.

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See :file:`services/usrmgt-server` for details.

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.. seealso:: Source code :file:`services/usrmgt-server`

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.. _ref-chat:

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Chat Protocol

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=============

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**Chat** is our JSON_-based client/server communication protocol used in

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communicating to `Python Console`_ processes and `User Management Server`_.

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Since it is JSON-based it can be called from either Python or JavaScript.

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communicating to `Python Console <ref-python-console>`_ processes and `User

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Management Server <ref-usrmgt-server>`_. Since it is JSON-based it can be

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called from either Python or JavaScript.

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Protocol

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--------

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exception and :const:`TRACEBACK` is a string of the traceback generated by the

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server's exception handler.

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See :file:`ivle/chat.py` for details.

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.. seealso:: Source code :file:`ivle/chat.py`

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Version Control

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===============

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Along with traditional file system access, IVLE allows users to version their

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files using Subversion_. Much like how Subversion workspaces are used on a

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standard desktop, workspaces are checked out into users home directories where

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they can be manipulated through a series of AJAX requests to the

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``fileservice`` app.

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Like all other user file system actions, version control actions need to be

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executed inside the user's :ref:`jail <ref-jail>`. Requests are made to the

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``fileservice`` app in :mod:`ivle.webapp.fileservice` which then calls the

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``fileservice`` CGI script using ``trampoline``. This script is simply a

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wrapper around :mod:`ivle.fileservice_lib` which actually contains the code to

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handle each of the actions.

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Manipulation of the Subversion workspaces is done using the pysvn_ library.

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.. _Subversion: http://subversion.tigris.org/

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.. _pysvn: http://pysvn.tigris.org/

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Repositories

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------------

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Each user is allocated a Subversion repository when their :ref:`Jail

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<ref-jail>` is created by the :ref:`User Management Server

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<ref-usermgt-server>`. Repository are stored in the location specified by

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``[paths] [[svn]] repo_path`` in :file:`/etc/ivle/ivle.conf` (by default

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:file:`/var/lib/ivle/svn/repositories/`). User repositories are stored in the

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:samp:`users/{USERNAME}/` subdirectory and group repositories in

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:samp:`groups/{SUBJECT}_{YEAR}_{SEMESTER}_{GROUP}`.

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.. warning::

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While it would be possible to give users direct access to their repository

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using Subversion's file backend, this would allow users to potentially

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modify the history of any repository that they had access to. To ensure

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repository integrity, all Subversion interaction must be done remotely.

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Subversion WebDAV

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-----------------

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These repositories are served by Apache using ``mod_dav_svn`` allowing access

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over Subversion's WebDAV HTTP or HTTPS backends. Users are authenticated using

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a randomly generated key which is stored in the database and is made available

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to each user inside their Jail (``svn_pass`` property inside

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:file:`/home/.ivle.conf`). This key is automatically provided when doing

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Subversion actions, but can be manually entered when accessing a users

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repository from an external Subversion client such as with :samp:`svn checkout

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{svn_addr}/users/{USERNAME}/ workspace`.

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Repository permissions for ``AuthzSVNAccessFILE`` are automatically generated

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and placed in the file located at ``[paths] [[svn]] conf`` for user

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repositories and ``[paths] [[svn]] group_conf`` for group repositories. User

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authentication keys for ``AuthUserFile`` are stored in the file located at

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``[path] [[svn]] auth_ivle``. These will be regenerated each time user or

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group repository settings change.

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Worksheets

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==========

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