Canonical developers have been talking up their inclusion of ZFS file-system support in Ubuntu 16.04 as one of the new features of interest to containers/server/workstation users. The ZFS support is available via their default kernel and they have published they don't believe there is any licensing issue. Relayed by Canonical's Dustin Kirkland, "We at Canonical have conducted a legal review, including discussion with the industry's leading software freedom legal counsel, of the licenses that apply to the Linux kernel and to ZFS. And in doing so, we have concluded that we are acting within the rights granted and in compliance with their terms of both of those licenses...The CDDL cannot apply to the Linux kernel because zfs.ko is a self-contained file system module -- the kernel itself is quite obviously not a derivative work of this new file system. And zfs.ko, as a self-contained file system module, is clearly not a derivative work of the Linux kernel but rather quite obviously a derivative work of OpenZFS and OpenSolaris. Equivalent exceptions have existed for many years, for various other stand alone, self-contained, non-GPL kernel modules. Our conclusion is good for Ubuntu users, good for Linux, and good for all of free and open source software."
However, Karen Sandler and Bradley Kuhn with the Software Freedom Conservancy have a different opinion. They jointly posted an article today entitled GPL Violations Related to Combining ZFS and Linux. They concluded, "We are sympathetic to Canonical's frustration in this desire to easily support more features for their users. However, as set out below, we have concluded that their distribution of zfs.ko violates the GPL. We have written this statement to answer, from the point of view of many key Linux copyright holders, the community questions that we've seen on this matter. Specifically, we provide our detailed analysis of the incompatibility between CDDLv1 and GPLv2 — and its potential impact on the trajectory of free software development — below. However, our conclusion is simple: Conservancy and the Linux copyright holders in the GPL Compliance Project for Linux Developers believe that distribution of ZFS binaries is a GPL violation and infringes Linux's copyright. We are also concerned that it may infringe Oracle's copyrights in ZFS. As such, we again ask Oracle to respect community norms against license proliferation and simply relicense its copyrights in ZFS under a GPLv2-compatible license."
While they don't call their new article legal advice, their case is laid out in the aforelinked article for those interested.