Re: [PATCH net-next] kcm: do not attach sockets if sk_user_data is already used

From: Tom Herbert <redacted>
Date: Tue, 16 Jan 2018 09:36:41 -0800

sk_user_data is set with the sk_callback lock held in code below.
Should be able to take the lock earlier can do this check under the
lock.

csock, and this csk, is obtained from an arbitrary one of the
process's FDs.  It can be any socket type or family, and that socket's
family might set sk_user_data without the callback lock.

The only socket type check is making sure it is not another PF_KCM
socket.  So that doesn't help with this problem.