From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: Gustavo Grieco <gustavo.grieco@imag.fr>, git@vger.kernel.org
Subject: Re: Stack read out-of-bounds in parse_sha1_header_extended using git 2.10.0
Date: Tue, 27 Sep 2016 03:19:36 -0400 [thread overview]
Message-ID: <20160927071936.5hneqhv22zw73asy@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqqtwd2sf9t.fsf@gitster.mtv.corp.google.com>
On Mon, Sep 26, 2016 at 11:10:54AM -0700, Junio C Hamano wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
> > I am inclined to say that it has no security implications. You have
> > to be able to write a bogus loose object in an object store you
> > already have write access to in the first place, in order to cause
> > this ...
>
> Note that you could social-engineer others to fetch from you and
> feed a small enough update that results in loose objects created in
> their repositories, without you having a direct write access to the
> repository.
>
> The codepath under discussion in this thread however cannot be used
> as an attack vector via that route, because the "fetch from
> elsewhere" codepath runs verification of the incoming data stream
> before storing the results (either in loose object files, or in a
> packfile) on disk.
I don't think it could be used at all for anything that speaks the git
protocol, because the object header is not present at all in a packfile.
So even if you hit unpack-objects, it would be writing the (correct)
loose object header itself.
But when we grab loose objects _directly_ from a remote, as in dumb-http
fetch, I'd suspect that the code doing the verification calls
unpack_sha1_header() as part of it. So I didn't test, but I'd strongly
suspect that's a viable attack vector.
I'm not sure what the actual attack would look like, though, aside from
locally accessing memory in a read-only way.
-Peff
next prev parent reply other threads:[~2016-09-27 7:20 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1399913289.8224468.1474810664933.JavaMail.zimbra@imag.fr>
2016-09-25 14:12 ` Stack read out-of-bounds in parse_sha1_header_extended using git 2.10.0 Gustavo Grieco
2016-09-26 0:10 ` Junio C Hamano
2016-09-26 4:29 ` [PATCH] unpack_sha1_header(): detect malformed object header Junio C Hamano
2016-09-26 14:03 ` Jeff King
2016-09-26 16:15 ` Junio C Hamano
2016-09-26 17:33 ` Junio C Hamano
2016-09-26 17:35 ` Jeff King
2016-09-26 17:39 ` Junio C Hamano
2016-09-26 17:34 ` Junio C Hamano
2016-09-26 17:38 ` Jeff King
2016-09-26 13:50 ` Stack read out-of-bounds in parse_sha1_header_extended using git 2.10.0 Jeff King
2016-09-26 17:48 ` Gustavo Grieco
2016-09-26 17:55 ` Junio C Hamano
2016-09-26 18:01 ` Gustavo Grieco
2016-09-26 18:06 ` Junio C Hamano
2016-09-26 18:10 ` Junio C Hamano
2016-09-27 2:13 ` Gustavo Grieco
2016-09-27 7:19 ` Jeff King [this message]
2016-09-27 2:30 ` Possible integer overflow parsing malformed objects in " Gustavo Grieco
2016-09-27 8:07 ` Jeff King
2016-09-27 15:57 ` Junio C Hamano
2016-09-27 19:14 ` Gustavo Grieco
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