[PATCH 3.2 85/95] smsc75xx: use skb_cow_head() to deal with cloned skbs

[Ben Hutchings]

3.2.91-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit b7c6d2675899cfff0180412c63fc9cbd5bacdb4d upstream.

We need to ensure there is enough headroom to push extra header,
but we also need to check if we are allowed to change headers.

skb_cow_head() is the proper helper to deal with this.

Fixes: d0cad871703b ("smsc75xx: SMSC LAN75xx USB gigabit ethernet adapter driver")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: James Hughes <james.hughes@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/net/usb/smsc75xx.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -1170,13 +1170,9 @@ static struct sk_buff *smsc75xx_tx_fixup
 {
 	u32 tx_cmd_a, tx_cmd_b;
 
-	if (skb_headroom(skb) < SMSC75XX_TX_OVERHEAD) {
-		struct sk_buff *skb2 =
-			skb_copy_expand(skb, SMSC75XX_TX_OVERHEAD, 0, flags);
+	if (skb_cow_head(skb, SMSC75XX_TX_OVERHEAD)) {
 		dev_kfree_skb_any(skb);
-		skb = skb2;
-		if (!skb)
-			return NULL;
+		return NULL;
 	}
 
 	tx_cmd_a = (u32)(skb->len & TX_CMD_A_LEN) | TX_CMD_A_FCS;