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
