That I agree might be a problem. If the case ends up being decided in favor of Christoph Hellwig based on that then I wonder if what happens isn't just that companies gets a third party to distribute a modified kernel (as source code) with the interfaces they need added and then use that. It may still technically be a violation, but judging intent isn't easy.

I think the question is really what resolution you would get. Consider the fictional situation where Company A makes a derived work of the novel Harry Potter without permission. They then sell a license to Company B to make derived works of their work. Company B writes a novel in the Harry Potter world, thinking they have a license to do so.

When Company B is sued by the copyright holder of Harry Potter, they hold up their license and say, "See. We have permission". My (very limited) understanding of copyright law is that the court would quickly find the license invalid since Company A never had the ability to grant the license. Company B would lose the lawsuit, pay some money and have an injunction against distributing their work. They would then be invited to sue Company A to recover their costs.