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# Debian conference Pinpoint talk about Gitano

[backing.png]
[center]
[font=Sans 50px]
[stretch]

-- [backing-cat-flop.png]

-- [backing-cat-flop.png] [no-markup]

Gitano - A Git service configured in Git

Daniel Silverstone <dsilvers@debian.org>

# Burble like a tard about who you are

-- [backing-cat-flop.png]

What is it?

# Git Server
# Written in Lua
# Configured in Git where plausible

-- [backing-cat-flop.png]

Why do it?

# Looked at gitolite and decided I could do
# better or nicer or whatever

-- [backing-cat-flop.png]

Who is it for?

# People who would like to run their own git server
# Github is a more effective centralised version control
# system than Subversion could ever hope to be.
# P.S. Alioth.
# Gitorious is a large unwieldy pile of crap
# Both of them rely on data stores which are not Git

-- [backing-cat-sunbathing.png]

-- [backing-cat-sunbathing.png]

Technology choices

# Git - odd to list, but I mean configuration is in git
# Lua - I like Lua, it's easy to prototype and write stuff
# libgit2/luagit2 - Way faster than invoking git commands
# although Gitano *can* operate without them
# cgit rather than gitweb - much faster, caches, prettier

-- [backing-cat-sunbathing.png]

Lace - Lua Access Control Engine

# ACL engine for rulesets.  Most people who are at least technically
# minded understand ACLs.  Non-turing-complete means output more easily cached
# Not using Lua means I *could* switch implementation language if I wanted.

-- [font=Monospace 50px]

define ref_has_user_prefix ref prefix refs/heads/${user}/
allow "User branches are okay" op_is_reffy ref_has_user_prefix

# Simple example showing definitions, prefix-matches, expansions (gitano
# specific) and permission statements.
# list of defined predicates on the allow line must all pass

-- [backing-cat-sunbathing.png]

Clod - Configuration Language Organised (by) Dots

# Designed to keep track of ordering of entries (and spaces)
# Currently doesn't track comments (because that's super hard)
# Humans and the library tend to edit files in similar ways meaning
# diffs are sane

-- [font=Monospace 50px]

project.head "refs/heads/master"
project.description "Black box testing of Unix programs"
project.owner "liw"

# Three simple string entries as might be found in a repository configuration
# in Gitano.

-- [font=Monospace 50px]

description "Gitano Instance Administrators"

members["*"] "dsilvers"

# Clod also supports lists which remain ordered.  This is an example group
# file in a Gitano repository

-- [backing-cat-sunbathing.png]

Supple - Sandbox [(for) Untrusted Procedure Partitioning (in) Lua] Engine

# Supple allows me to run hooks provided by project owners safely without
# risking them gaining access to the server in any unusual way.

# Hooks are run as Lua code with a limited set of functions and only the data
# relevant to the event they're hooking (along with a read-only repository
# object they can use to interrogate other things a bit)

-- [backing-cat-sunbathing.png]

To limit the attack surface...

The "untrusted" code runs in a (limited) Lua sandbox.

That sandbox is soft-limited in terms of VM opcodes and memory.

The sandbox is monitored and IO marshalled externally.

# Your "untrusted" code is run inside a Lua sandbox which has only a limited
# set of Lua's functionality exposed to it.

# That sandbox is soft-limited (optionally) in terms of VM opcodes and memory
# allocated by Lua

# The sandbox is run inside a monitoring Lua VM instance which is responsible
# for carefully marshalling calls etc into and out of the sandbox. All your
# comms go via this monitor.

-- [backing-cat-sunbathing.png]

Just in case...

The monitor is a Lua VM anyway, and it's all inside a separate process.

The sandbox process is in an ephemeral chroot.

# The monitor is, itself, a Lua VM anyway, inside a process which is separate
# from the process you're doing untrusted work on behalf of.

# The sandbox process is created using a rootly helper so that it's put into an
# isolation state consisting of a directory which is owned by root which is set
# as your root via the chroot call, but which is also rmdir'd so it's
# ephemeral. Your process drops privileges back to the calling UID so it cannot
# do anything inside its CWD anyway.

-- [backing-cat-sunbathing.png]

And if that's not enough...

Solid rlimits in terms of memory and open FDs

And on Linux, memory is pre-allocated and we enter seccomp mode 1.

# On top of that, the sandbox has some pretty solid rlimits set in terms of max
# CPU usage, max VM size, max FDs open, and max size of any file it writes. As
# such, it can't create > 0 byte files in the directory it doesn't have access
# to, and could only do that if it closed the FD to the host process which is
# its only communications avenue.

# Then, if you're on Linux, we go one step further and pre-allocate enough
# memory for the interpreter to not hit the rlimit and then enter seccomp mode
# 1 which limits the syscalls permissible to read, write, _exit and sigreturn
# so even if you could have circumvented any/all of the limits above, you now
# can't make syscalls to take advantage of them.

# If that's not sandbox enough, please tell me how to improve matters further.

-- [backing-cat-sunbathing.png]

Gall - Git Abstraction Layer (in) Lua

# Abstraction layer for accessing Git repositories from Lua.  Focusses on
# bare repositories and can operate using the git commandline or the libgit2
# library (via the luagit2 binding).

# Next comes inelegance, so "phew" goes here.

-- [backing-cat-inelegant.png]

-- [backing-cat-inelegant.png]

Putting it all together.

Gitano uses all of these libraries and adds utility commands
for managing repositories, users, rules, etc.

# Using these libraries and with a small amount of code of its own
# Gitano then provides a git service with important additional
# commands such as creating and destroying repositories

-- [font=Monospace 50px] [no-markup]

ssh git@server create fooproject/barrepo
[example] Creating repository: fooproject/barrepo
[example] Setting repository owner to dsilvers
[example] <fooproject/barrepo> Set owner to <dsilvers>
[example] Running checks to ensure hooks etc are configured
[example] Repository fooproject/barrepo created ok.  Remember to configure rules etc.

ssh git@server help config
[example] config ---- View and change configuration for a repository (Takes a repo)
[example] 
[example] => usage: config <reponame> <cmd> [args...]
[example] => 
[example] => View and manipulate the configuration of a repository.
...


# Create a repository, ask for help about configuration
# Gitano has help built in for all its commands too

# And now for something shocking

-- [backing-cat-shocked.png]

-- [backing-cat-shocked.png]

Integrating with external apps and services

OpenSSH server, Cgit (gitweb at a pinch), git-daemon

Outgoing HTTP calls from hooks

# Horrifyingly shocking idea, but integrating with external services
# is a good idea.  As such, Gitano uses OpenSSH (nominally any other SSH too)
# for authentication and secure connections.
# Primarily focussed on cgit, we do generate the bits needed for gitweb
# to operate too.  And we produce the git-daemon-export-ok file for the
# git daemon to be able to work.

-- [backing-cat-shocked.png]

Real users of Gitano

 - git.gitano.org.uk, git.liw.fi
 - git.netsurf-browser.org, richard.maw.name/git
 - Codethink and Baserock

# Equally horrifyingly, people use this crap what I wrote.

# But, it's not enough (sound stern)

-- [backing-cat-stern.png]

-- [command=google-chrome --app=https://trello.com/b/l4Id6iiC/gitano] [backing-cat-stern.png]

Future plans

Lots of ideas for future content, see the Trello

 - https://trello.com/b/l4Id6iiC/gitanow
 - (Link is on www.gitano.org.uk)

# I would welcome contributions to Gitano or the libraries behind it.
# I would especially welcome contributions which increase the scenario test
# suite coverage.

-- [backing-cat-eat-you.png]

-- [command=gnome-terminal -e 'mutt'] [backing-cat-eat-you.png]

Live demo and walkthrough

"Stand by for action!
 We are about to launch Stingray!
 Marineville - I am calling 'Battle Stations'!
 Anything can happen in the next half-hour!"

 - Commander Shore

# I make no promises, but here goes a demo which might eat my face.

-- [backing-cat-flop.png]

Mailing list: <span font="Monospace 50px">gitano-dev@gitano.org.uk</span>
IRC Channel: <span font="Monospace 50px">#gitano</span> on Freenode
Website: <span font="Monospace 50px">http://www.gitano.org.uk/</span>

Any questions?

-- [backing-cat-sat.png]

# Intrusive cat says "Enough with the talkings"

-- [backing-cat-sat.png]

Thank you for listening

This talk is available from:
<span font="Monospace 50px">git://git.gitano.org.uk/personal/dsilvers/gitano-talk.git</span>

Current (at time of talk) gitano-all deb (4-1) at:
<span font="Monospace 50px">http://users.pepperfish.net/dsilvers/gitano-deb/</span>