From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5246BC433FE for ; Thu, 7 Apr 2022 22:40:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232288AbiDGWmn convert rfc822-to-8bit (ORCPT ); Thu, 7 Apr 2022 18:42:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54914 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232331AbiDGWmi (ORCPT ); Thu, 7 Apr 2022 18:42:38 -0400 Received: from elephants.elehost.com (elephants.elehost.com [216.66.27.132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D49E1104 for ; Thu, 7 Apr 2022 15:40:33 -0700 (PDT) Received: from Mazikeen (cpe00fc8d49d843-cm00fc8d49d840.cpe.net.cable.rogers.com [174.119.251.39] (may be forged)) (authenticated bits=0) by elephants.elehost.com (8.16.1/8.16.1) with ESMTPSA id 237MeNTP036236 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 7 Apr 2022 18:40:23 -0400 (EDT) (envelope-from rsbecker@nexbridge.com) Reply-To: From: To: "'brian m. carlson'" , "'Justin Steven'" Cc: "'Glen Choo'" , , "'Emily Shaffer'" , "'Taylor Blau'" References: In-Reply-To: Subject: RE: Bare repositories in the working tree are a security risk Date: Thu, 7 Apr 2022 18:40:18 -0400 Organization: Nexbridge Inc. Message-ID: <005d01d84ad0$782e8fc0$688baf40$@nexbridge.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQG01znzod2GH02gC8Rr2yDfyYoUKAGz53C7AbAKRRUCK/yt0Kz/cVpQ Content-Language: en-ca Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On April 7, 2022 6:10 PM, brian m. carlson wrote: >On 2022-04-07 at 21:53:26, Justin Steven wrote: >> Hi all, >> >> I'm the author of one of the articles linked in Glen's mail. Thank you >> Glen for summarising the problem beautifully and pushing this forward. >> >> Brian said: >> > As mentioned elsewhere, git status doesn't work without a working tree. >> >> This is correct. However, it is possible to embed a bare repo that has >> its own core.worktree which points to a directory within the >> containing repo, satisfying the requirement of having a working tree. >> This is covered in the article [1] and looks to be accounted for in >> Taylor's reproducer script which admittedly I haven't run. >> >> > Instead, I'd rather see us avoid executing any program from the >> > config or any hooks in a bare repository without a working tree >> > (except for pushes). I think that would avoid breaking things while >> > still improving security. >> >> Due to the fact that the embedded bare repo can be made to have a >> working tree, this won't be an effective fix. > >Then we'd probably be better off just walking up the entire hierarchy and >excluding worktrees from embedded bare repositories, or otherwise restricting >the config we read. That will probably mean we'll need to walk the entire >directory hierarchy to see if it's embedded (or at least to the root of the device) in >such a case, but that should be relatively uncommon. > >I'd definitely like to see us make a security improvement here, but I also would like >to avoid us breaking a lot of repositories, especially since we lack alternatives. > >If git fast-import could 100% correctly round-trip all commits and repositories, I >would be much more open to blocking this in fsck after a deprecation period, but >as it stands that's not possible. Perhaps improving that would be a suitable way >forward. One option relating to enable/disable this is to set up a config option that, by default is false, to allow embedded bare repositories. At least with enough warning that this option is required, it might be acceptable. I would prefer never to receive a bare repo through any means (including through a more worrying submodule). From an attack vector standpoint, I would be more concerned about this in an automation setting, say GitHub workflows or Jenkins GitSCM. At least with GitHub workflows, this is "somewhat" contained within VMs under GitHub's control - although not entirely. Jenkins is probably more vulnerable as the clones done through that path do not get the same scrutiny, although in my world, I use a dedicated non-root UID and sandbox the whole thing. This topic makes me nervous and wonder whether we should be self-reporting a CVE. Shuddering, Randall