linux-kernel - [PATCH 3.16 163/178] cx82310_eth: use skb_cow

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Date:   Sun, 16 Jul 2017 14:56:46 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "James Hughes" <james.hughes@...pberrypi.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>
Subject: [PATCH 3.16 163/178] cx82310_eth: use skb_cow_head() to deal with
 cloned skbs

3.16.46-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@...gle.com>

commit a9e840a2081ed28c2b7caa6a9a0041c950b3c37d 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: cc28a20e77b2 ("introduce cx82310_eth: Conexant CX82310-based ADSL router USB ethernet driver")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: James Hughes <james.hughes@...pberrypi.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/usb/cx82310_eth.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/net/usb/cx82310_eth.c
+++ b/drivers/net/usb/cx82310_eth.c
@@ -275,12 +275,9 @@ static struct sk_buff *cx82310_tx_fixup(
 {
 	int len = skb->len;
 
-	if (skb_headroom(skb) < 2) {
-		struct sk_buff *skb2 = skb_copy_expand(skb, 2, 0, flags);
+	if (skb_cow_head(skb, 2)) {
 		dev_kfree_skb_any(skb);
-		skb = skb2;
-		if (!skb)
-			return NULL;
+		return NULL;
 	}
 	skb_push(skb, 2);