The kernel-development community has long had a tense relationship with
companies that create and ship proprietary loadable kernel modules. In the
view of many developers, such modules are a violation of the GPL and should
simply be disallowed. That has never happened, though; instead, the
community has pursued a policy of legal ambiguity and technical
inconvenience to discourage proprietary modules. A
“technical-inconvenience” patch that was merged nearly one year ago has
begun to show up in stable kernel releases, leading at least one
developer to complain that things have gone a little too far.

Source: LWN.net – [$] A stable bug fix bites proprietary modules