ATM: CVE-2008-5079: duplicate listen() on socket corrupts the vcc table

As reported by Hugo Dias that it is possible to cause a local denial
of service attack by calling the svc_listen function twice on the same
socket and reading /proc/net/atm/*vc

Signed-off-by: Chas Williams <chas@cmf.nrl.navy.mil>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/svc.c

@@ -293,7 +293,10 @@ static int svc_listen(struct socket *sock,int backlog)
 		error = -EINVAL;
 		goto out;
 	}
-	vcc_insert_socket(sk);
+	if (test_bit(ATM_VF_LISTEN, &vcc->flags)) {
+		error = -EADDRINUSE;
+		goto out;
+        }
 	set_bit(ATM_VF_WAITING, &vcc->flags);
 	prepare_to_wait(sk->sk_sleep, &wait, TASK_UNINTERRUPTIBLE);
 	sigd_enq(vcc,as_listen,NULL,NULL,&vcc->local);
@@ -307,6 +310,7 @@ static int svc_listen(struct socket *sock,int backlog)
 		goto out;
 	}
 	set_bit(ATM_VF_LISTEN,&vcc->flags);
+	vcc_insert_socket(sk);
 	sk->sk_max_ack_backlog = backlog > 0 ? backlog : ATM_BACKLOG_DEFAULT;
 	error = -sk->sk_err;
 out: