you can't have in your subscription terms "don't distribute the [GPLed] patches".
A subscription can have exactly those terms; grsecurity would be far from the first to use them. You can't forbid redistribution, but you can terminate the contract if redistribution happens. I remember that even Richard Stallman has said that such terms are legitimate, though I can't find the reference now.
[^] # Re: Libre, pas libre, c'est douteux
Posté par gouttegd . En réponse au journal grsecurity abandonne le gratuit. Évalué à 10.
D’après la discussion sur LWN (voir notamment ce commentaire de Jonathan Corbet), ce serait exactement ça :