[rtcweb] Please require user consent for data channels

[Daniel Roesler <[e-mail]>]

Howdy all, this is mostly a re-surfacing of the discussion about IP
address leaking back in April[1], which unfortunately I did not
discover until recently.

One of the items in the new proposal was "WebRTC already requires
permission to access getUserMedia. Why not use that permission to
control interface enumeration?" That item didn't really get discussed
much in the thread, but I think it's one of the most important issues.

Why? There is now a documented case where a third party on nytimes.com
is using a fake webRTC datachannel to silently gather user local (and
potentially "real" ISP) IP addresses.

https://twitter.com/incloud/status/619624021123010560

So I'd like to voice my support for adding a consent requirement that
would prevent this type of silent behavior. A user that is
purposefully visiting a site that has a legitimate reason for using a
webRTC data channel will have the necessary context to give consent,
just like they have to get consent on getUserMedia.

I'm really unclear on why it's so important to have the silent webRTC
data channel behavior. P2P data connections should be held to the same
consent requirements just like P2P video and voice connections. In
addition to the silent third party local IP tracking, a silent P2P
data channel opens up users to silently becoming nodes in a web-based
file sharing network. For example, webtorrent[2] can be silently
embedded on a website so that all of the users to that website start
seeding content they don't know they are seeding.

Possible fix:

1. Require user consent before calling the callback on createOffer().
2. If the user has already given consent via getUserMedia, the user
consent requirement is satisfied.
3. If there's no previous gUM consent, then ask the user for consent.

This implementation requires no updates to current webRTC demos, since
you have to wait for a callback on createOffer anyway. I'm open to
other ways, such as making createDataChannel asynchronous like gUM,
but that would require updates to existing apps that use
createDataChannel.

Thanks!
Daniel Roesler

[1]: https://www.ietf.org/mail-archive/web/rtcweb/current/msg14494.htm
[2]: https://github.com/feross/webtorrent