atm: idt77252: prevent use after free in dequeue_rx()

[ Upstream commit a9a18e8f770c9b0703dab93580d0b02e199a4c79 ]

We can't dereference "skb" after calling vcc->push() because the skb
is released.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/atm/idt77252.c

@@ -1118,8 +1118,8 @@ dequeue_rx(struct idt77252_dev *card, struct rsq_entry *rsqe)
 	rpp->len += skb->len;
 
 	if (stat & SAR_RSQE_EPDU) {
+		unsigned int len, truesize;
 		unsigned char *l1l2;
-		unsigned int len;
 
 		l1l2 = (unsigned char *) ((unsigned long) skb->data + skb->len - 6);
 
@@ -1189,14 +1189,15 @@ dequeue_rx(struct idt77252_dev *card, struct rsq_entry *rsqe)
 		ATM_SKB(skb)->vcc = vcc;
 		__net_timestamp(skb);
 
+		truesize = skb->truesize;
 		vcc->push(vcc, skb);
 		atomic_inc(&vcc->stats->rx);
 
-		if (skb->truesize > SAR_FB_SIZE_3)
+		if (truesize > SAR_FB_SIZE_3)
 			add_rx_skb(card, 3, SAR_FB_SIZE_3, 1);
-		else if (skb->truesize > SAR_FB_SIZE_2)
+		else if (truesize > SAR_FB_SIZE_2)
 			add_rx_skb(card, 2, SAR_FB_SIZE_2, 1);
-		else if (skb->truesize > SAR_FB_SIZE_1)
+		else if (truesize > SAR_FB_SIZE_1)
 			add_rx_skb(card, 1, SAR_FB_SIZE_1, 1);
 		else
 			add_rx_skb(card, 0, SAR_FB_SIZE_0, 1);