Re: RFC: Resumable clone based on hybrid "smart" and "dumb" HTTP

From: Jeff King <peff@peff.net>
Date: Feb 13, 2016, 17:00 UTC
Message-ID: <20160213170044.GB30144@sigill.intra.peff.net>
In-Reply-To: <CAP3OtXjyy+7cSi0S17FSsx8gnP1rKboeSAz_Hz1ZNVDuqcGASw@mail.gmail.com>

On Fri, Feb 12, 2016 at 07:40:43PM -0600, Blake Burkhart wrote:

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> On Wed, Feb 10, 2016 at 3:49 PM, Jeff King <peff@peff.net> wrote:
> >> 2. Servers that support resumable clone include a "resumable"
> >> capability in the advertisement.
> >
> > Because the magic happens in the git protocol, that would mean this does
> > not have to be limited to git-over-http. It could be "resumable=<url>"
> > to point the client anywhere (the same server over a different protocol,
> > another server, etc).
> 
> I'd like to call this out as a possible security issue before it gets
> implemented. Allowing the server to instruct the client what protocol
> to use is a security risk. This sounds like a fine feature, just do it
> carefully.

Thanks for mentioning this. I agree it's a potential issue, and we should use the same solution as submodules, as you pointed out:

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> To address this GIT_ALLOW_PROTOCOL was introduced, and git-submodule
> now uses it as of 33cfccb. This environment variable specifies a
> default whitelist of protocols. Whoever implements this should
> probably make use of GIT_ALLOW_PROTOCOL to limit resumable clones to
> the same default whitelist that git-submodule now uses.

-Peff