From: Jeff King <peff@peff.net>
Date: Thu, 29 Mar 2018 21:55:02 GMT
Subject: Re: [RFC/PATCH] upload-pack: disable object filtering when disabled by config
Message-ID: <20180329215502.GK2939@sigill.intra.peff.net>
In-Reply-To: <20180328203303.GA260688@aiede.svl.corp.google.com>

On Wed, Mar 28, 2018 at 01:33:03PM -0700, Jonathan Nieder wrote:

> When upload-pack gained partial clone support (v2.17.0-rc0~132^2~12,
> 2017-12-08), it was guarded by the uploadpack.allowFilter config item
> to allow server operators to control when they start supporting it.
> 
> That config item didn't go far enough, though: it controls whether the
> 'filter' capability is advertised, but if a (custom) client ignores
> the capability advertisement and passes a filter specification anyway,
> the server would handle that despite allowFilter being false.
> 
> This is particularly significant if a security bug is discovered in
> this new experimental partial clone code.  Installations without
> uploadpack.allowFilter ought not to be affected since they don't
> intend to support partial clone, but they would be swept up into being
> vulnerable.
> 
> Simplify and limit the attack surface by making uploadpack.allowFilter
> disable the feature, not just the advertisement of it.

Great catch. If I understand correctly, this is an issue in the 2.17.0
release candidates. Is this worth delaying the release?

It's a funny situation. The presence of a security bug is theoretical
here, so nobody _should_ need to care, and this is just hardening. But
it does make me a little nervous, given the experimental-ness of the new
feature.

-Peff