maanantai 17. elokuuta 2015

Proposal for a dependency security scheme for sandboxed apps

Perhaps the main disadvantage of embedding external projects as source code rather than using distro packages is the loss of security. Linux distributions have lots of people working on keeping distro packages up to date and safe. With embedded source code this is no longer the case. The developer is in charge of keeping the application up to date. Some developers are better at it than others.

What makes this worse is the fact that if you embed (and especially statically link) your dependencies it is impossible to know what versions of which libraries you are using. If this information were available, then the host operating system could verify the list of embedded dependencies against a known white- or blacklist. The packaging format simply does not have this information.

So let's put it there.

A merge proposal has just recently been proposed to Meson. This makes it create (and optionally install) a dependency manifest for each generated binary. This manifest is simply a JSON file that lists all the embedded dependencies that each given binary uses. Its proposed format looks like this.

{
  "type": "dependency manifest",
  "version": 1,
  "dependencies":
  {
    "entity": "1.0"
  }
}

In this case the executable has only one dependency, the project entity version 1.0. Other such dependencies could include zlib version 1.2.8 or openssl version 1.0.2d. The project names and releases would mirror upstream releases. This manifest would make it easy to guard against binaries that have embedded unsafe versions of their dependencies.

But wait, it gets better.

All dependencies that are provided by the Wrap database would (eventually ;) expose this information and thus would generate the manifest automatically. The developer does not need to do anything to get it built, only to say he wants to have it installed. It is simply a byproduct of using the dependency.

As the Linux application installation experience keeps moving away from distro packages and towards things such as xdg-app, snappy and the like, the need to increase security becomes ever trickier. This is one such proposal that is already working and testable today. Hopefully it will see adoption among the community.

Single question mini-faq

What happens if someone creates a fraudulent or empty manifest file for their app?

The exact same thing as now when there is no manifest info of any kind. This scheme is not meant to protect against Macchiavelli, only against Murphy.

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