Re: [PATCH v3 1/4] environment.c: fix potential segfault by get_git_common_dir()

[Duy Nguyen <pclouds@gmail.com>]

On Sun, Mar 19, 2017 at 12:54 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> setup_git_env() must be called before this function to initialize
>> git_common_dir so that it returns a non NULL string. And it must return
>> a non NULL string or segfault can happen because all callers expect so.
>>
>> Normally if somebody has called get_git_dir(), or set_git_dir() then
>> setup_git_env() is already called. But if you do setup_git_directory()
>> at top dir (which skips set_git_dir) and never call get_git_dir, you'll
>> get NULL here.
>
> Hmph, and the solution for the problem not being "so let's make sure
> get_git_dir() is called even when the command is started at the top
> directory" is because...?

-EHARDTOPARSE. There's a hidden dependency between get_git_dir() and
get_git_common_dir() which is not good. If we lazily call
set_git_env(), make sure we do it lazily but consistently at all
relevant function calls (i.e. including get_git_common_dir).

Alternatively (I was thinking of this but didn't really follow up
because this was side issue) we should make sure setup_git_env() is
always called at the end of setup_git_dir...() and remove the laziness
in get_git_dir(). This may be more in line of recent attempts to catch
repo access without calling setup_git_directory..() first. But sadly I
haven't read Jeff's series, so I can't say whether it's true.
-- 
Duy