scm: Only support SCM_RIGHTS on unix domain sockets.

We use scm_send and scm_recv on both unix domain and
netlink sockets, but only unix domain sockets support
everything required for file descriptor passing,
so error if someone attempts to pass file descriptors
over netlink sockets.

Cc: stable@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/scm.c

@@ -156,6 +156,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 		switch (cmsg->cmsg_type)
 		{
 		case SCM_RIGHTS:
+			if (!sock->ops || sock->ops->family != PF_UNIX)
+				goto error;
 			err=scm_fp_copy(cmsg, &p->fp);
 			if (err<0)
 				goto error;