It's not an issue of GPL virality because the CDDL-ed code is not derivative of GPLed code and thus out of scope for GPL.
The problem is, IIRC, that GPLv2 does not allow creating a combined work where part of it is covered by license that has stricter requirements than GPL.
This is the same reason why you can't submit GPLv3 code to Linux kernel, because GPLv3 falls under the same issue, and IIRC even on the same kind of clause (mandatory patent licensing)
> The problem is, IIRC, that GPLv2 does not allow creating a combined work where part of it is covered by license that has stricter requirements than GPL
That is part of the virality: the combined work is under the terms of the GPL and therefore cannot have additional restrictions placed on it. If the GPL wasn't viral then the GPL code and CDDL code would both be under their respective licenses and leave each other alone. The GPL decided to apply itself to the combined work which causes the problems.