Re: [PATCH 1/1] upload-pack.c: fix filter spec quoting bug

>
> On Fri, Jan 22, 2021 at 03:21:37PM +0100, Jacob Vosmaer wrote:
>
> > This fixes a bug that occurs when you combine partial clone and
> > uploadpack.packobjectshook. You can reproduce it as follows:
> >
> > git clone -u 'git -c uploadpack.allowfilter '\
> > '-c uploadpack.packobjectshook=" exec" '\
> > 'upload-pack' --filter=blob:none --no-local \
> > src.git dst.git
> >
> > Be careful with the line endings because this has a long quoted string
> > as the -u argument. Note that there is an intentional space before
> > 'exec'. Without that space, run-command.c tries to be smart and the
> > command fails for the wrong reason.
>
> The "-u" command is run with a shell, so:
>
>   git clone \
>     -u 'git -c uploadpack.allowfilter \
>             -c uploadpack.packobjectshook=env \
>             upload-pack' \
>   --filter=blob:none --no-local src.git dst.git
>
> may be a more readable version. I also found the use of " exec" clever,
> but rather subtle; you need the extra space so that our "don't bother
> using a shell" run-command optimization does not kick in. I replaced it
> with "env" here, which is a slightly more canonical way of running a
> sub-program that does not rely on shell builtins.
>
> But all of this should be added as a new test, probably in t5544 with
> the other pack-objects hook tests.
>
> > The problem is an unnecessary and harmful layer of quoting. I tried
> > digging through the history of this function and I think this quoting
> > was there from the start. My best guess is that it stems from a
> > misunderstanding of what use_shell=1 means. The code seems to assume
> > it means "arguments get joined into one big string, then fed to
> > /bin/sh". But that is not what it means: use_shell=1 means that the
> > first argument in the arguments array may be a shell script and if so
> > should be passed to /bin/sh. All other arguments are passed as normal
> > arguments.
>
> Yeah, that is exactly right. "use_shell" just means that the command is
> (possibly) run with a shell. Quoting for any extra arguments is handled
> automatically.
>
> I think you're correct that this was broken from the start in 10ac85c785
> (upload-pack: add object filtering for partial clone, 2017-12-08).
> That's even before the use_shell was added, and then later it was pushed
> into that conditional by 0b6069fe0a (fetch-pack: test support excluding
> large blobs, 2017-12-08). Presumably because the non-hook path would not
> have worked at all, and that was the first time any of it was actually
> tested. ;)
>
> (I've cc'd authors of those commits as an FYI; I think both were
> relatively new to the project at the time so misunderstanding this
> subtlety of run-command is not too surprising).
>
> I'm somewhat embarrassed to say that despite being the one who added the
> pack-objects hook 4 years ago, we still have not switched over to it at
> GitHub from our custom patch (the reason is just mundane; there's some
> other adjustments that would have to happen and nobody has ever quite
> gotten around to it). Presumably you are looking to use it at GitLab.
> Just beware that you are probably treading new-ish ground, so there may
> be other bugs like this lurking.
>
> > diff --git a/upload-pack.c b/upload-pack.c
> > index 3b66bf92ba..eae1fdbc55 100644
> > --- a/upload-pack.c
> > +++ b/upload-pack.c
> > @@ -305,14 +305,7 @@ static void create_pack_file(struct upload_pack_data *pack_data,
> >       if (pack_data->filter_options.choice) {
> >               const char *spec =
> >                       expand_list_objects_filter_spec(&pack_data->filter_options);
> > -             if (pack_objects.use_shell) {
> > -                     struct strbuf buf = STRBUF_INIT;
> > -                     sq_quote_buf(&buf, spec);
> > -                     strvec_pushf(&pack_objects.args, "--filter=%s", buf.buf);
> > -                     strbuf_release(&buf);
> > -             } else {
> > -                     strvec_pushf(&pack_objects.args, "--filter=%s", spec);
> > -             }
> > +             strvec_pushf(&pack_objects.args, "--filter=%s", spec);
>
> Yep, this looks like the right fix. I think with an addition to the test
> suite, this will be good to go.
>
> -Peff