Re: [PATCH 0/3] refs-advertise: add hook to filter advertised refs

From

孙超 <16657101987@163.com>

Date

Aug 4, 2022, 08:27 UTC

Message-ID

<FEAF81E9-61C7-4A41-9882-D05895340003@163.com>

In-Reply-To

<xmqq35ed9iof.fsf@gitster.g>

> On Aug 4, 2022, at 04:27, Junio C Hamano <gitster@pobox.com> wrote:
> 
> "Sun Chao via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> Gerrit is implemented by JGit and is known as a centralized workflow system
>> which supports reference-level access control for repository. If we choose
>> to work in centralized workflow like what Gerrit provided, reference-level
>> access control is needed and is possible if we add a reference advertise
>> filter hook just like what Gerrit did.
> 
> It may be one starting point, but is it sufficient to call it
> "possible"?  The server side needs to tighten "fetch by object name"
> to refuse to serve objects that are not reachable from any of the
> refs advertised to the client requesting them.  IIRC, fetch protocol
> v2 is wide open and does not limit the requests to those that are
> only reachable from the advertised refs.
> 
> 

Hi Junio, thanks for you reply.

```diff

@@ -1118,7 +1119,7 @@ static void receive_needs(struct upload_pack_data *data,
               }

               o = parse_object(the_repository, &oid_buf);
-               if (!o) {
+               if ((!o) || (filter_advertise_object(&oid_buf))) {
                       packet_writer_error(&data->writer,
                                           "upload-pack: not our ref %s",
                                           oid_to_hex(&oid_buf));

...

@@ -1421,7 +1445,7 @@ static int parse_want(struct packet_writer *writer, const char *line,
               else
                       o = parse_object(the_repository, &oid);

-               if (!o) {
+               if ((!o) || (filter_advertise_object(&oid))) {
                       packet_writer_error(writer,
                                           "upload-pack: not our ref %s",
                                           oid_to_hex(&oid));
```

The `filter_advertise_object` will exchange messages with the hook by pkt-line
messages, eg:

       # Send commit filter request to hook
       G: PKT-LINE(obj <oid>)
       G: flush-pkt

       # Receive result from the hook.
       # Case 1: this object is valid
       H: PKT-LINE(ok obj <oid>)
       H: flush-pkt
       # Case 2: this object is filtered out
       H: PKT-LINE(ng obj <oid>)
       H: flush-pkt

the hook can check if the `oid` is valid for the client and returns `ng` message if not,
so git server will hide the objects to the client. And I added some test cases for
upload-pack V1 and V2 and looks like it works, but maybe I lost some important points and
I'm still trying to understand other codes for upload-pack and receive-pack because
currently I only implements the filter process for upload-pack and receive-pack.

Thanks for your reply again.