Re: [PATCH v2] upload-pack.c: fix filter spec quoting bug

Jacob Vosmaer [off-list ref] writes:

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=env '\
'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.

The error I get when I run this is:

Cloning into '/tmp/broken'...
remote: fatal: invalid filter-spec ''blob:none''
error: git upload-pack: git-pack-objects died with error.
fatal: git upload-pack: aborting due to possible repository corruption on the remote side.
remote: aborting due to possible repository corruption on the remote side.
fatal: early EOF
fatal: index-pack failed

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.

Meaning that 10ac85c7 (upload-pack: add object filtering for partial
clone, 2017-12-08) that added:

        if (filter_options.filter_spec) {
                struct strbuf buf = STRBUF_INIT;
                sq_quote_buf(&buf, filter_options.filter_spec);
                argv_array_pushf(&pack_objects.args, "--filter=%s", buf.buf);
                strbuf_release(&buf);
        }

My best guess is that it stems from a
misunderstanding 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.

I noticed another thing that hasn't changed since that commit, which
is that the setting of .use_shell is conditional.  In today's code,
at the beginning of create_pack_file(), we have

        if (!pack_data->pack_objects_hook)
                pack_objects.git_cmd = 1;
        else {
                strvec_push(&pack_objects.args, pack_data->pack_objects_hook);
                strvec_push(&pack_objects.args, "git");
                pack_objects.use_shell = 1;
        }

I suspect that 0b6069fe (fetch-pack: test support excluding large
blobs, 2017-12-08) sort-of fixed half of the problem (i.e. the half
when there is no hook used) while leaving the other half still
broken as before.

But because .use_shell does not affect if we should or should not
quote, we can unconditionally drop the use of sq_quote_buf().

The solution is simple: never quote the filter spec.

Which makes sense.

This commit removes the conditional quoting and adds a test for
partial clone in t5544.
---

Thanks.  Missing sign-off.