net: atm: fix use after free in lec_send()

The ->send() operation frees skb so save the length before calling
->send() to avoid a use after free.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/c751531d-4af4-42fe-affe-6104b34b791d@stanley.mountain
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/atm/lec.c

@@ -181,6 +181,7 @@ static void
 lec_send(struct atm_vcc *vcc, struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
+	unsigned int len = skb->len;
 
 	ATM_SKB(skb)->vcc = vcc;
 	atm_account_tx(vcc, skb);
@@ -191,7 +192,7 @@ lec_send(struct atm_vcc *vcc, struct sk_buff *skb)
 	}
 
 	dev->stats.tx_packets++;
-	dev->stats.tx_bytes += skb->len;
+	dev->stats.tx_bytes += len;
 }
 
 static void lec_tx_timeout(struct net_device *dev, unsigned int txqueue)