Re: merge: fix NULL pointer dereference when merging nothing into void

From: Eric Sunshine <sunshine@sunshineco.com>
Date: Mar 21, 2016, 19:36 UTC
Message-ID: <CAPig+cQjt==AKTWfCk6kzgVciGVb9XtKNiwPK14nPM7=4yhmjQ@mail.gmail.com>
In-Reply-To: <xmqq7fgvmz8o.fsf_-_@gitster.mtv.corp.google.com>

On Mon, Mar 21, 2016 at 3:01 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 22 quoted lines

> When we are on an unborn branch and merging only one foreign parent,
> we allow "git merge" to fast-forward to that foreign parent commit.
>
> This codepath incorrectly attempted to dereference the list of
> parents that the merge is going to record even when the list is
> empty.  It must refuse to operate instead when there is no parent.
>
> All other codepaths make sure the list is not empty before they
> dereference it, and are safe.
>
> Reported by Jose Ivan B. Vilarouca Filho
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
> @@ -725,4 +725,14 @@ test_expect_success 'merge detects mod-256 conflicts (resolve)' '
> +test_expect_success 'merge nothing into void' '
> +       git init void &&
> +       (
> +               cd void &&
> +               git remote add up .. &&
> +               git fetch up &&
> +               test_must_fail git merge FETCH_HEAD

Ah, nice. I either didn't know or had forgotten that test_must_fail is smart enough to detect unexpected failures (such as segfault), so my advice to Jose about capturing stderr[1] was misdirected. Thanks.

[1]: http://article.gmane.org/gmane.comp.version-control.git/289405

> +       )
> +'
> +
>  test_done