Re: [PATCH 1/7] sha1_file: keep track of where an SHA-1 object comes from

On Fri, Jan 25, 2013 at 12:45 AM, Junio C Hamano [off-list ref] wrote:

quoted

 How about this way instead: we keep track of where objects come from
 so we can verify object source when we create or update something
 that contains SHA-1.

The overall approach taken by this series may be worth considering, but
I do not think the check implemented here is correct.

An object may be found in an alternate odb but we may also have our
own copy of the same object.  You need to prove that a suspicious
object is visible to us *ONLY* through add_submodule_odb().

The way alt odbs are linked (new odbs area always at the end), if we
have the same copy, their copy will never be read (we check out alt
odbs from head to tail). So those duplicate suspicious objects are
actually invisible to us.

Once you do add_submodule_odb() to contaminate our object pool, you
make everything a suspicious object that needs to be checked; that
is the worst part of the story.

And because we never really touch their alt copy, the returned alt
source is "ours", trusted and not checked. The check should only occur
on objects that we do not have.
-- 
Duy