Sandstorm Blog

Updating Tiny Tiny RSS, Moving Sandstorm's Security Model Forward.

By Ian Denhardt - 08 Aug 2020

This past week I updated the Sandstorm package for Tiny Tiny RSS. In addition to updating to the latest upstream code, I’ve also made some improvements to the package’s integration with Sandstorm. In particular:

The latter of these is critical to enable Sandstorm’s goal of full network isolation for applications. It has always been the intent that apps running on a Sandstorm server should not be able to phone home or otherwise access the network without the user’s consent, but early on the team implemented some temporary hacks that apps could make use of until Sandstorm’s Powerbox API was actually available. Now it is, so it’s time to migrate existing code away from these legacy APIs. Once we’ve done that, we can remove the holes, and finally deliver on Sandstorm’s security promise of network isolation for server code.

In order to make this happen, I wrote a daemon that runs inside of the grain, intercepting HTTP traffic and making powerbox requests for access to the relevant hosts on-demand. The daemon is re-usable and could be used as a quick way to port other existing apps that have legitimate need to access a variety of different hosts at runtime, which are not known in advance.

Unfortunately, this transition does come with some growing pains, and there are a few things users should be aware of when upgrading.

First, since existing TTRSS grains will already have subscriptions to feeds that they haven’t requested access to, the first time you start the new version of TTRSS you’ll see a flood of requests for all of your existing feeds. This is annoying, but fortunately after this initial setup you’ll only need to grant access when adding new feeds.

Second, a more serious limitation of the current implementation is that it makes it impossible to add new feeds through mobile & desktop clients – at least without also having a browser window open somewhere. This is because, without the Sandstorm UI open, Sandstorm has no way of actually showing a user the powerbox dialog. We’d like to find ways to improve on this.

Finally, while the daemon is exciting for app packagers, in that it can make basic porting of apps not designed for Sandstorm much quicker, the integration is imperfect, resulting in a sub-par UX: as it stands, users will see an extra prompt (or two) when first subscribing to a feed.

Maintaining security while avoiding annoying extra prompts like this is one of the design goals of Sandstorm’s powerbox, but to fully take advantage of it will require more invasive changes to TTRSS; rather than prompting the user for a feed URL and then trying to fetch it (causing the daemon to request access), it should just ask Sandstorm for a feed directly. If you’re an enterprising PHP hacker and want to help make this happen, get in touch on the sandstorm-dev mailing list or the #sandstorm IRC channel on Freenode.