Quoting russell@coker.com.au (russell@coker.com.au):
What rights do the Linux kernel coders have in this regard?
Copyright title conferring ownership of the abstract right of distribution of derivative works. If you're going to go around alleging that in-kernel filesystems are not derivative works of the Linux kernel, good luck with that. To quote a saying from Damon Runyon, riffing off Ecclesiastes 9:11, 'The race is not to the swift, nor the battle to the strong..., but that's the way to bet.'
If you knowingly infringe then that's the case. If you believe that Canonical and Oracle have sorted things out then you are clear.
In one of the two USA copyright cases commonly cited for contributory copyright infringement, Metro-Goldwyn-Mayer Studios Inc. v. Grokster, Ltd., 545 U.S. 913 (2005), respondent Grokster was found to have actual knowledge of infringement. However, in the other case commonly cited, Sony Corp. v. Universal City Studios, Inc., 464 U.S. 417 (1984), the court found Sony to have had 'constructive knowledge', which is to say not actual knowledge but circumstances where Sony should have known. So, no.