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@@ -1,105 +1,3 @@ - _ _ - _____ ___ __ ___ __ _ ___| |__ (_)_ __ __ _ - / _ \ \/ / '_ ` _ \ / _` |/ __| '_ \| | '_ \ / _` | - | __/> <| | | | | | (_| | (__| | | | | | | | (_| | - \___/_/\_\_| |_| |_|\__,_|\___|_| |_|_|_| |_|\__,_| - +THIS IS DISOWNED. DO NOT USE. -### DISCLAIMER - - ----- ACHTUNG! WARNING! DANGER! ---- - -This code is hackish and not "production quality. It represents a potential -approach to a specific problem (privilege separation for system configuration). -It has not been extensively reviewed or tested and does not represent a known -best practice. - -### What is this? - -exmachina is a small system configuration system which runs as separate but -coupled client/server UNIX processes for the purpose of privilege separation: -the "server" process runs with root privileges and a python program using the -"client" library runs as any unprivileged user. The commands and parameters -that the client can send to the server are limited, though in this particular -case can of course be used to deny service (reboot or shutdown the machine) or -probably escalate privileges one way or another (install arbitrary packages, -reconfigure networks, enable callback scripts, edit system configuration -files). - -The server and client processes should be one-to-one: only one client should -ever connect to the server. The init_test.sh script shows how this could be -achieved in a SysV-style /etc/init.d script. - -The intended use case is writing a user-friendly web control panel for a Debian -server or router: the web designer creating the user interface should not be -overly concerned with writing secure code, and the web application itself -(possibly including lots of third party framework code, javascript libraries, -etc) should not run with strong system permissions, but core components of the -system (such as hostname, wireless access point configuration, network -settings, package installation, locale, timezone, etc) need to be modified. - -See the comments in exmachina.py for more information. - -### Alternatives - -The most simple alternative to exmachina that has been recommended to me is to -create simple setuid/setgid programs or scripts to execute privileged system -changes, and to only allow execute permissions to those programs for the -user/group of the less-trusted user interface program. This seems to be the -current best practice. For the more complicated case of generalized system -configuration, the setuid/setgid program becomes complicated, or you need to -write and install many of them, but this is no worse that the situation with -exmachina. - -Another approach is the Assuan protocol used by GPG, which has been generalized -as libassuan: - - "Assuan permits the servers, which do the actual work, e.g. encryption and - decryption of data using a secret key, to be developed independently of the - user interfaces, e.g. mail clients and other encryption front ends." - - http://www.gnupg.org/related_software/libassuan/index.en.html - -### Status - -Basic server and client functionality implemented. Crude, and far more simple -than it may appear or the length of code would imply. - -This was code was written in a weekend "sprint" for the FreedomBox project and -their Plinth web user interface in 2012. - -I may or may not maintain this code. I have hesitation even publishing it -because i'm almost certain there are implementation bugs and that the entire -concept is problematic. - -Features: -* shared secret key process/privilege separation -* call augeas API: match, set, setm, get, save, move, insert, remove -* call init.d service scripts: status, start, stop, restart - -In late 2012 Nick Daly (of the FreedomBox project) wrote up a brief audit of -this code and concept on his blog (https://www.betweennowhere.net/). Link is -frequantly broken. - -### Dependencies (server) - -* augeas configuration editing library -* python-augeas wrapper for augeas -* bjsonrpc python library - -On debian (wheezy) try: - - $ sudo apt-get install augeas-tools python-bjsonrpc python-augeas - -### Dependencies (client) - -* bjsonrpc - -On debian (wheezy) try: - - $ sudo apt-get install bjsonrpc - -### License - -exmachina.py is GPLv3 or later |