Actually, if I understand what Linus says here[1] correctly, porting modules from other OSes to work with linux seems to be ok, writing closed source modules specifically for linux kernel is not ok. But overall still a gray area.<p>Other kernel devs indeed claim that everything that links with a kernel is a derivative work and EXPORT_SYMBOL &#x2F; EXPORT_SYMBOL_GPL distinction means nothing.<p>[1] <a href="https:&#x2F;&#x2F;lkml.org&#x2F;lkml&#x2F;2003&#x2F;12&#x2F;3&#x2F;228" rel="nofollow">https:&#x2F;&#x2F;lkml.org&#x2F;lkml&#x2F;2003&#x2F;12&#x2F;3&#x2F;228</a>