Subject: Re: [PATCH v2 1/3] read-cache: use shared perms when writing shared index

From: Junio C Hamano <[email-masked]>
Date: Fri, 23 Jun 2017 14:55:08 -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.
>
> Because of 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.
>
> We could use create_tempfile() that calls adjust_shared_perm(), but
> unfortunately create_tempfile() doesn't replace the XXXXXX at the end
> of the path it is passed. So let's just call adjust_shared_perm() by
> ourselves.
>
> Signed-off-by: Christian Couder <[email-masked]>
> ---
>  read-cache.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/read-cache.c b/read-cache.c
> index bc156a133e..66f85f8d58 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -2425,6 +2425,14 @@ static int write_shared_index(struct index_state *istate,
>  		delete_tempfile(&temporary_sharedindex);
>  		return ret;
>  	}
> +	ret = adjust_shared_perm(temporary_sharedindex.filename.buf);

Shouldn't we be using the API function get_tempfile_path() for this
instead of reaching into its implementation detail?

> +	if (ret) {
> +		int save_errno = errno;
> +		error("cannot fix permission bits on %s", temporary_sharedindex.filename.buf);
> +		delete_tempfile(&temporary_sharedindex);
> +		errno = save_errno;
> +		return ret;
> +	}
>  	ret = rename_tempfile(&temporary_sharedindex,
>  			      git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
>  	if (!ret) {