Re: Git and SHA-1 security (again)

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 19, 2016, 17:06 UTC
Message-ID: <xmqqk2ghh80x.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CACsJy8CR_fkYL5UYbV1MqiTSe3gTqWfOrA1NOHTw09vZn7Y-Aw@mail.gmail.com>

Duy Nguyen <pclouds@gmail.com> writes:

Show 8 quoted lines

> Post-shower thoughts. In a tree object, a submodule entry consists of
> perm (S_IFGITLINK), hash (which is the external hash) and path. We
> could fill the "hash" part with all zero (invalid, signature of new
> submodule hash format), then append "/<hashtype>:<external hash>" to
> the "path" part. This way we don't have to update tree object or index
> format. And I suspect the "path" part is available everywhere we need
> to handle submodules already, so extracting the external hash should
> be possible...

Even though that single operation might be possible, do not go there. A "pathname" identifies a "path", not its contents, and "appending crap after path" breaks the data model badly. Also other things like merge, checkout and diff would break by butchering ordering the entries in tree objects.