Subject: Re: [PATCH 1/3] read-cache: use shared perms when writing shared index

From: Junio C Hamano <[email-masked]>
Date: Thu, 22 Jun 2017 12:51:54 -0700

Christian Couder <[email-masked]> writes:

> Since f6ecc62dbf (write_shared_index(): use tempfile module, 2015-08-10)
> write_shared_index() has been using mks_tempfile() to create the
> temporary file that will become the shared index.
>
> But even before that, it looks like the functions used to create this
> file didn't call adjust_shared_perm(), which means that the shared
> index file has always been created with 600 permissions regardless
> of the shared permission settings.
>
> This means that on repositories created with `git init --shared=all`
> and using the split index feature one gets an error like:
>
> fatal: .git/sharedindex.a52f910b489bc462f187ab572ba0086f7b5157de: index file open failed: Permission denied
>
> when another user performs any operation that reads the shared index.

Assuming that a "shared" repository setting should allow uses by
different users, the above analysis makes sense to me.

But the conclusion does not.

> Let's fix that by using create_tempfile() instead of mks_tempfile()
> to create the shared index file.
>
> ...
> -	fd = mks_tempfile(&temporary_sharedindex, git_path("sharedindex_XXXXXX"));
> +	fd = create_tempfile(&temporary_sharedindex, git_path("sharedindex_XXXXXX"));

So we used to create a temporary file that made sure its name is
unique but now we create sharedindex_XXXXXX with 6 X's literally 
at the end?

Doesn't mks_tempfile() family include a variant where you can give
custom mode?  Better yet, perhaps you can call adjust_shared_perm()
on the path _after_ seeing that mks_tempfile() succeeds (you can ask
get_tempfile_path() which path to adjust, I presume)?

>  	if (fd < 0) {
>  		hashclr(si->base_sha1);
>  		return do_write_locked_index(istate, lock, flags);