ikiwiki/doc/tips/untrusted_git_push.mdwn

This tip will describe how to allow anyone on the planet to `git push`
changes into your wiki, without needing a special account. All a user needs
to know is:

	git clone git://your.wiki/path
	# now modify any of the files the wiki would let you modify on the web
	git push

This is a wonderful thing to set up for users, because then they can work
on the wiki while offline, and they don't need to mess around with web
browsers.

## security

But, you might be wondering, how can this possibly be secure. Won't users
upload all sorts of garbage, change pages you don't want them to edit, and so
on.

The key to making it secure is configuring ikiwiki to run as your git
repository's `pre-receive` hook. There it will examine every change that
untrusted users push into the wiki, and reject pushes that contain changes
that cannot be made using the web interface.

So, unless you have the [[plugins/attachment]] plugin turned on,
non-page files cannot be added. And if it's turned on, whatever
`allowed_attachments` checks you have configured will also check files
pushed into git.

And, unless you have the [[plugins/remove]] plugin turned on, no
files can be deleted.

And if you have `locked_pages` configured, then it will also affect what's
pushed into git.

Untrusted committers will also not be able to upload files with strange
modes, or push to any branch except for the configured `gitorigin_branch`,
or manipulate tags.

One thing to keep an eye on is uploading large files. It may be easier to
do this via git push than using the web, and that could be abused.

Also, no checking is done that the authors of commits are right, so people
can make a commit that pretends to be done by someone else.

## user setup

Add a dedicated user who will push in untrusted commits. This user should have
a locked password, and `git-shell` as its shell.

	root@bluebird:/home/joey>adduser --shell=/usr/bin/git-shell --disabled-password anon
	Adding user `anon' ...

## ikiwiki setup

You should set up ikiwiki before turning on anonymous push in git. 

Edit your wiki's setup file, and uncomment the lines for
`git_test_receive_wrapper` and `untrusted_committers`.

	# git pre-receive hook to generate
	git_test_receive_wrapper => '/srv/git/ikiwiki.info/.git/hooks/pre-receive',
	# unix users whose commits should be checked by the pre-receive hook
	untrusted_committers => ['anon'],

The `git_test_receive_wrapper` will become the git `pre-receive` hook. The
`untrusted_committers` list is the list of unix users who will be pushing in
untrusted changes. It should *not* include the user that ikiwiki normally runs
as.

Once you're done modifying the setup file, don't forget to run
`ikiwiki -setup --refresh --wrappers` on it.

## git setup

You'll need to arrange the permissions on your bare git repository so that
user anon can write to it. One way to do it is to create a group, and put
both anon and your regular user in that group. Then make make the bare git
repository owned and writable by the group. See [[rcs/git]] for some more
tips on setting up a git repository with multiple committers.

Note that anon should *not* be able to write to the `srcdir`, *only* to the bare git
repository for your wiki.

If you want to allow git over `ssh`, generate a ssh key for anon, and
publish the *private* key for other people to use. This is optional; you
can use `git-daemon` instead and not worry about keys.

Now set up `git-daemon`. It will need to run as user `anon`, and be
configured to export your wiki's bare git repository. I set it up as
follows in `/etc/inetd.conf`, and ran `/etc/init.d/openbsd-inetd restart`.

	git     stream  tcp     nowait  anon          /usr/bin/git-daemon git-daemon --inetd --export-all --interpolated-path=/srv/git/%H%D /srv/git

At this point you should be able to `git clone git://your.wiki/path` from
anywhere, and check out the source to your wiki. But you won't be able to
push to it yet, one more change is needed to turn that on. Edit the
`config` file of your bare git repository, and allow `git-daemon` to
receive pushes:

	[daemon]
		receivepack = true

Now pushes should be accepted, and your wiki immediatly be updated. If it
doesn't, check your git repo's permissions, and make sure that the
`post-update` and `pre-receive` hooks are suid so they run as the user who
owns the `srcdir`.

## infelicities

If a user tries to push a changeset that ikiwiki doesn't like, it will
abort the push before refs are updated. However, the changeset will still
be present in your repository, wasting space. Since nothing refers to it,
it will be expired eventually. You can speed up the expiry by running `git
prune`.

When aborting a push, ikiwiki displays an error message about why it didn't
accept it. If using git over ssh, the user will see this error message,
which is probably useful to them. But `git-daemon` is buggy, and hides this
message from the user. This can make it hard for users to figure out why
their push was rejected. (If this happens to you, look at "'git log --stat
origin/master..`" and think about whether your changes would be accepted
over the web interface.)