smsc75xx: use skb_cow_head() to deal with cloned skbs

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@google.com>
Cc: James Hughes <james.hughes@raspberrypi.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index c41b42b..afd06e8 100644 (file)
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -1170,13 +1170,9 @@ static struct sk_buff *smsc75xx_tx_fixup(struct usbnet *dev,
 {
        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;