Re: Segmentation fault found while fuzzing .pack file under 2.7.0.rc3

From: Jeff King <peff@peff.net>
Date: Jan 6, 2016, 07:23 UTC
Message-ID: <20160106072321.GA18477@sigill.intra.peff.net>
In-Reply-To: <20160106002333.GA16090@google.com>

On Tue, Jan 05, 2016 at 04:23:33PM -0800, Jonathan Nieder wrote:

Show 15 quoted lines

> > Git packfiles come from two places:
> >
> >   1. Local maintenance repacks loose and already-packed objects into a
> >      new packfile. We trust the local repack process to generate a valid
> >      packfile (though the contents of individual objects may be
> >      untrusted, of course).
> 
> I think we should reconsider such trust.  If one user creates a
> malicious pack, if another user uses read-only git commands to access
> the repository (after inspecting .git/config to make sure it doesn't
> contain anything scary) the result should not be arbitrary code
> execution.
> 
> Producing bogus output or aborting is okay; arbitrary code execution
> less so.

I agree it is better if we can meet this standard, and I didn't mean to discourage fixes in the area. But I do think it is worth classifying them differently than bugs that can be triggered via the network. The attack surface for on-disk attacks is much larger, and the number of people affected is much smaller.

Regarding your example, I'm not sure it's the best motivating example, as I imagine hardly anyone examines .git/config. :) A simplified one might be that:

  git fetch me@shared-server:/home/you/foo.git

is running git-upload-pack as me on packfiles created by you (on the server). We normally expect that to be a "safe" operation (and it is if done over git:// or similar).

-Peff