Dustin Kirkland writes: 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.
While the CDDL and GPLv2 are both "copyleft" licenses, they have different scope. The CDDL applies to all files under the CDDL, while the GPLv2 applies to derivative works. 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.