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

[Christian Couder <christian.couder@gmail.com>]

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 <chriscool@tuxfamily.org>
---
 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);
+	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) {
-- 
2.13.1.519.g0a0746bea4