Re: Question: What's the best way to implement directory permission control in git?

From: Thomas Guyot <tguyot@gmail.com>
Date: Jul 27, 2022, 09:24 UTC
Message-ID: <80dd46c5-f9ff-d2b3-2d7f-4b80e00494b8@gmail.com>
In-Reply-To: <CAOLTT8QusNzdO1mHqQFPz84pznYSpFWJunroRGXQ7qk6sJjeYg@mail.gmail.com>

On 2022-07-27 04:56, ZheNing Hu wrote:

Show 27 quoted lines

> if there is a monorepo such as
> git@github.com:derrickstolee/sparse-checkout-example.git
>
> There are many files and directories:
>
> client/
>      android/
>      electron/
>      iOS/
> service/
>      common/
>      identity/
>      list/
>      photos/
> web/
>      browser/
>      editor/
>      friends/
> boostrap.sh
> LICENSE.md
> README.md
>
> Now we can use partial-clone + sparse-checkout to reduce
> the network overhead, and reduce disk storage space size, that's good.
>
> But I also need a ACL to control what directory or file people can fetch/push.
> e.g. I don't want a client fetch the code in "service" or "web".

Pushes can easily be blocked with a pre-receive or update hook on the server side. That covers the case where you want to prevenr users to update certain paths in the repo.

Show 7 quoted lines

> Now if the user client use "git log -p" or "git sparse-checkout add service"...
> or other git command, git which will  download them by
> "git fetch --filter=blob:none --stdin <oid>" automatically.
>
> This means that the git client and server interact with git objects
> (and don't care about path) we cannot simply ban someone download
> a "path" on the server side.

Indeed - core devs can correct me if I'm wrong but afaik even in the case of sparse checkouts and partial clones the packs may include other objects. I have no ideas how git selects objects and packs on sent and when it decides to repack objects... What I know is it can pack entire repos in just a few files using delta compression and it would probably make sense to sent these pack if there is no real benefit in repacking just the requested objects.

> What should I do? You may recommend me to use submodule,
> but due to its complexity, I don't really want to use it :-(

Submodules is definitively an option for read ACLs, and considering git was not originally designed to hide information from a single store it's probably your only option. Moreover, if the git client is able to fetch directly blobs and trees (the later includes partial trees as a tree object is a single "directory" that can contain other blobs and trees), then even the server has no knowledge of where a tree hook into, or even how it's named. All that information would have to be mapped elsewhere.

To take your example above, the "common" subtree of "service/" could be in multiple top level directories (i,e, the same tree with same contents), and each top level dirs could have a different "common" subtree. So git would have to find where each tree object (one per directory) is accessible from for *each revision* before deciding if a client should be authorized to fetch an object, and the same would be required for blobs (and tree objects don't even know their own name, that comes from the reference in the parent tree or commit object for the top-level tree).

So even before solving the client/server protocol issue you mentioned, you can't just hide part of a repo in git right now and changing that is definitively not trivial.

-- Thomas