[PATCH net 5/6] ch9200: 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: 4a476bd6d1d9 ("usbnet: New driver for QinHeng CH9200 devices")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: James Hughes <james.hug...@raspberrypi.org>
Cc: Matthew Garrett <mj...@srcf.ucam.org>
---
 drivers/net/usb/ch9200.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/net/usb/ch9200.c b/drivers/net/usb/ch9200.c
index 
8a40202c0a1732850da1b2eb64af21470b9c85b4..c4f1c363e24b89404c6834312074f8a4451ded50
 100644
--- a/drivers/net/usb/ch9200.c
+++ b/drivers/net/usb/ch9200.c
@@ -254,14 +254,9 @@ static struct sk_buff *ch9200_tx_fixup(struct usbnet *dev, 
struct sk_buff *skb,
        tx_overhead = 0x40;
 
        len = skb->len;
-       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;
        }
 
        __skb_push(skb, tx_overhead);
-- 
2.12.2.816.g2cccc81164-goog