[PATCH 4.4 140/143] ch9200: use skb_cow_head() to deal with cloned skbs

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit 6bc6895bdd6744e0136eaa4a11fbdb20a7db4e40 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: 4a476bd6d1d9 ("usbnet: New driver for QinHeng CH9200 devices")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: James Hughes <james.hughes@xxxxxxxxxxxxxxx>
Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/usb/ch9200.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/drivers/net/usb/ch9200.c
+++ b/drivers/net/usb/ch9200.c
@@ -255,14 +255,9 @@ static struct sk_buff *ch9200_tx_fixup(s
 	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);