Quoting Junio C Hamano (2017-03-17 08:26:39)
> Michael Haggerty <mhagger@alum.mit.edu> writes:
> I _think_ the real bug is that somehow a user got a wrong impression
> that directly underneath $GIT_DIR/ is somehow different from its
> subdirectory and it is OK to make the directory unwritable.  I do
> not think we never intended to give such a promise, but there may be
> a documentation bug that gives the wrong impression, which we may
> have to fix.

Actually, yeah, that's a useful outcome I can steelman out of this
email: given that git init --shared has always introduced trivially
exploitable security escalations, it should probably either be changed
to use sane permissions or have its documentation changed to mention
that, at least on base POSIX, using --shared to share a repository
between multiple UIDs literally eliminates the purpose of having
multiple UIDs.