br2684: allow assign only on a connected socket

The br2684 does not check if used vcc is in connected state,
causing potential Oops in pppoatm_send() when vcc->send() is called
on not fully connected socket.

Now br2684 can be assigned only on connected sockets; otherwise
-EINVAL error is returned.
Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

net/atm/br2684.c

@@ -735,10 +735,13 @@ static int br2684_ioctl(struct socket *sock, unsigned int cmd,
 			return -ENOIOCTLCMD;
 		if (!capable(CAP_NET_ADMIN))
 			return -EPERM;
-		if (cmd == ATM_SETBACKEND)
+		if (cmd == ATM_SETBACKEND) {
+			if (sock->state != SS_CONNECTED)
+				return -EINVAL;
 			return br2684_regvcc(atmvcc, argp);
-		else
+		} else {
 			return br2684_create(argp);
+		}
 #ifdef CONFIG_ATM_BR2684_IPFILTER
 	case BR2684_SETFILT:
 		if (atmvcc->push != br2684_push)