econet: disallow NULL remote addr for sendmsg(), fixes CVE-2010-3849

Later parts of econet_sendmsg() rely on saddr != NULL, so return early
with EINVAL if NULL was passed otherwise an oops may occur.
Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/econet/af_econet.c

@@ -297,15 +297,7 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
 
 	mutex_lock(&econet_mutex);
 
-	if (saddr == NULL) {
-		struct econet_sock *eo = ec_sk(sk);
-
-		addr.station = eo->station;
-		addr.net     = eo->net;
-		port	     = eo->port;
-		cb	     = eo->cb;
-	} else {
-		if (msg->msg_namelen < sizeof(struct sockaddr_ec)) {
+        if (saddr == NULL || msg->msg_namelen < sizeof(struct sockaddr_ec)) {
                 mutex_unlock(&econet_mutex);
                 return -EINVAL;
         }
@@ -313,7 +305,6 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
         addr.net = saddr->addr.net;
         port = saddr->port;
         cb = saddr->cb;
-	}
 
 	/* Look for a device with the right network number. */
 	dev = net2dev_map[addr.net];
@@ -351,7 +342,6 @@ static int econet_sendmsg(struct kiocb *iocb, struct socket *sock,
 
 		eb = (struct ec_cb *)&skb->cb;
 
-		/* BUG: saddr may be NULL */
 		eb->cookie = saddr->cookie;
 		eb->sec = *saddr;
 		eb->sent = ec_tx_done;