[PPPOL2TP]: Fix use-after-free

Don't use skb->len after passing it to ip_queue_xmit.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/pppol2tp.c

@@ -824,6 +824,7 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
 	struct pppol2tp_session *session;
 	struct pppol2tp_tunnel *tunnel;
 	struct udphdr *uh;
+	unsigned int len;
 
 	error = -ENOTCONN;
 	if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
@@ -912,14 +913,15 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
 	}
 
 	/* Queue the packet to IP for output */
+	len = skb->len;
 	error = ip_queue_xmit(skb, 1);
 
 	/* Update stats */
 	if (error >= 0) {
 		tunnel->stats.tx_packets++;
-		tunnel->stats.tx_bytes += skb->len;
+		tunnel->stats.tx_bytes += len;
 		session->stats.tx_packets++;
-		session->stats.tx_bytes += skb->len;
+		session->stats.tx_bytes += len;
 	} else {
 		tunnel->stats.tx_errors++;
 		session->stats.tx_errors++;
@@ -958,6 +960,7 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 	__wsum csum = 0;
 	struct sk_buff *skb2 = NULL;
 	struct udphdr *uh;
+	unsigned int len;
 
 	if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
 		goto abort;
@@ -1050,14 +1053,15 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 	skb2->dst = sk_dst_get(sk_tun);
 
 	/* Queue the packet to IP for output */
+	len = skb2->len;
 	rc = ip_queue_xmit(skb2, 1);
 
 	/* Update stats */
 	if (rc >= 0) {
 		tunnel->stats.tx_packets++;
-		tunnel->stats.tx_bytes += skb2->len;
+		tunnel->stats.tx_bytes += len;
 		session->stats.tx_packets++;
-		session->stats.tx_bytes += skb2->len;
+		session->stats.tx_bytes += len;
 	} else {
 		tunnel->stats.tx_errors++;
 		session->stats.tx_errors++;