netdev - [PATCH net 5/6] ch9200: use skb_cow_head() to deal with cloned skbs

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Message-Id: <20170419165926.30631-6-edumazet@google.com>
Date:   Wed, 19 Apr 2017 09:59:25 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        James Hughes <james.hughes@...pberrypi.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Matthew Garrett <mjg59@...f.ucam.org>
Subject: [PATCH net 5/6] ch9200: use skb_cow_head() to deal with cloned skbs

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@...gle.com>
Cc: James Hughes <james.hughes@...pberrypi.org>
Cc: Matthew Garrett <mjg59@...f.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