Unprivileged Docker Builds – A Proof of Concept

zwischenzugs

I work at a very ‘locked-down’ enterprise, where direct access to Docker is effectively verboten.

This, fundamentally, is because access to Docker is effectively giving users root. From Docker’s own pages:

First of all, only trusted users should be allowed to control your Docker daemon.

Most home users get permissions in their account (at least in Linux) by adding themselves to the docker group, which may as well be root. In Mac, installing Docker also gives you root-like power if you know what you’re doing.

Platform Proxies

Many Docker platforms (like OpenShift) work around this by putting an API between the user and the Docker socket.

However, for untrusted usersthis creates a potentially painful dev experience thatcontrasts badly with their experience at home:

  • Push change to git repo
  • Wait for OpenShift to detect the change
  • Wait for OpenShift to pull the repo
  • Wait for OpenShift…

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Taking a Stroll Between The Pixels

The blog at the bottom of the sea

This post relates to a paper I wrote which talks about (ab)using linear texture interpolation to calculate points on Bezier curves. Extensions generalize it to Bezier surfaces and (multivariate) polynomials. All that can be found here: https://blog.demofox.org/2016/02/22/gpu-texture-sampler-bezier-curve-evaluation/

The original observation was that if you sample along the diagonal of a 2×2 texture, that as output you get points on a quadratic Bezier curve with the control points of the curve being the values of the pixels like in the image below. When I say you get a quadratic Bezier curve, I mean it literally, and exactly. One way of looking at what’s going on is that the texture interpolation is literally performing the De Casteljau algorithm. (Note: if the “B” values are not equal in the setup below, the 2nd control point will be the average of these two values, which an extension abuses to fit more curves into a…

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