NETLINK_URELEASE non-bound socket problem (was: [PATCH] Fix local DoS in cfg80211 subsystem)

Hi Dmitrijs,

Thanks for reporting this problem.

The patch below corrects this problem in kernel space. 

I don't think that this is correct, there are four more users of
NETLINK_URELEASE (nfnetlink, NFC), and afaict all of them have the same
bug as nl80211.

Rather than fix all of them, I think we should simply not report
NETLINK_URELEASE for netlink sockets that weren't bound; if any user
comes up that requires them later we could add a new event instead.

I can't find what commit introduced this code, it goes back before git
history, so I don't have the commit log. Maybe it was done for
nfnetlink log/queue? Certainly both nl80211 and NFC are much newer.

Also, it is
recommended to ensure that user-space applications are not using
user-supplied port_id for netlink sockets (which is default in
libnl-tiny for example).

This I think we should remove from the commit log - it's misleading and
there's no point.

johannes