[PATCH net 1/6] smsc75xx: use skb_cow_head() to deal with cloned skbs

[Eric Dumazet]

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 <eduma...@google.com>
Cc: James Hughes <james.hug...@raspberrypi.org>
---
 drivers/net/usb/smsc75xx.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/smsc75xx.c b/drivers/net/usb/smsc75xx.c
index 
0b17b40d7a4fa2653caf21406c4a6b3b45d868b0..190de9a90f7387c5070c7f589aa18bb7d05ac5d7
 100644
--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -2203,13 +2203,9 @@ 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;
-- 
2.12.2.816.g2cccc81164-goog