[PATCH net 4/6] lan78xx: 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: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 
Ethernet device driver")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: James Hughes <james.hug...@raspberrypi.org>
Cc: Woojung Huh <woojung....@microchip.com>
---
 drivers/net/usb/lan78xx.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 
9889a70ff4f6fece5bfabbfb45a3470f721a5a32..636f48f19d1eacae67c050de4fc3e651bffdf825
 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -2607,14 +2607,9 @@ static struct sk_buff *lan78xx_tx_prep(struct 
lan78xx_net *dev,
 {
        u32 tx_cmd_a, tx_cmd_b;
 
-       if (skb_headroom(skb) < TX_OVERHEAD) {
-               struct sk_buff *skb2;
-
-               skb2 = skb_copy_expand(skb, TX_OVERHEAD, 0, flags);
+       if (skb_cow_head(skb, TX_OVERHEAD)) {
                dev_kfree_skb_any(skb);
-               skb = skb2;
-               if (!skb)
-                       return NULL;
+               return NULL;
        }
 
        if (lan78xx_linearize(skb) < 0)
-- 
2.12.2.816.g2cccc81164-goog