Re: [PATCH] Fix potential segfault on cloning invalid tag

From: Jeff King <peff@peff.net>
Date: Oct 30, 2020, 15:09 UTC
Message-ID: <20201030150942.GB3282152@coredump.intra.peff.net>
In-Reply-To: <pull.906.git.git.1604058401991.gitgitgadget@gmail.com>

On Fri, Oct 30, 2020 at 11:46:41AM +0000, Sohom Datta via GitGitGadget wrote:

Show 10 quoted lines

> From: Sohom Datta <sohom.datta@learner.manipal.edu>
> 
> Git allows users to create tags pointing to object hashes
> that may or may not be commits. When a tag that doesn't
> point to a commit is used with the -b (--branch) parameter
> of git clone, git segfaults as it assumes that the tag will
> always reference a commit.
> 
> Add a check to make sure that lookup_commit_reference returns a commit
> before detaching HEAD.

This seemed eerily familiar, so I dug up these threads:

  - https://lore.kernel.org/git/20191029092735.GA84120@carpenter.lan/

  - https://lore.kernel.org/git/20191101002432.GA49846@carpenter.lan/

The interesting things are:

  - there are some other cases where we might see a non-commit, which
    are also worth covering

  - it would be friendlier to the user to put in a fallback value for
    HEAD. We already transferred the whole history, so deleting it is a
    bit less friendly than leaving it in a state the user can recover
    from locally

I think the patches there were moving in a good direction, but it looks like they just got stalled.

-Peff