Subject: Re: Git clone reads safe.directory differently?

From: "W. Michael Petullo" <[email-masked]>
Date: Sun, 28 Jul 2024 10:27:00 -0500

>> Glen Choo's commit 6061601d modified Git so that safe.directory could
>> be set on the command line using "-c". It seems most sub-commands work
>> this way, but not "clone". Here is an example:
> 
> This is because upload-pack, the server half of a fetch/clone, is run as
> a separate process which does not accept the client-side "-c" options.
> See this email for more details and a workaround:
> 
>   https://lore.kernel.org/git/[email-masked]/

Thank you, Jeff! This works and makes sense, although I can see how users
would be confused by the edge case.

For completeness, I investigated how to do the same over SSH. Imagine a
repository user-owned by Bob, but group-owned with r/w/x permissions by
a group containing Alice. It seems the same trick fails because git-shell
rejects the custom upload-pack command:

	git -c safe.directory="*" clone -u 'git -c safe.directory="*" upload-pack' [email-masked]:/shared/repository
	Cloning into 'git'...
	fatal: unrecognized command 'git -c safe.directory="*" upload-pack '/shared/repository''
	fatal: Could not read from remote repository.

	Please make sure you have the correct access rights
	and the repository exists.

I was able to overcome this by creating /home/alice/git-shell-commands/upload-pack-safe,
placing the following there

	#!/bin/sh

	git -c safe.directory="$1" upload-pack $1

and running:

	git -c safe.directory="*" clone -u upload-pack-safe [email-masked]:/shared/repository

This seems to be another interface edge case. Is my solution reasonable,
or is there something else that would be more consistent?

Related: Would anyone be interested in working on an academic paper
about safe.directory? It seems like people who write Git forge-type
software or other collaborative systems based on Git would benefit from
a rigorous description of the conditions and operations under which the
use of safe.directory is indeed safe. I am not sure I have this worked
out in my own mind yet. Something like "Setuid Demystified" from USENIX
2002 might help.

-- 
Mike

:wq