linux-kernel - [PATCH 4.9 52/58] smsc95xx: Use skb_cow

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Date:   Mon, 18 Feb 2019 14:44:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        James Hughes <james.hughes@...pberrypi.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Woojung Huh <Woojung.Huh@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH 4.9 52/58] smsc95xx: Use skb_cow_head to deal with cloned skbs

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

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

From: James Hughes <james.hughes@...pberrypi.org>

commit e9156cd26a495a18706e796f02a81fee41ec14f4 upstream.

The driver was failing to check that the SKB wasn't cloned
before adding checksum data.
Replace existing handling to extend/copy the header buffer
with skb_cow_head.

Signed-off-by: James Hughes <james.hughes@...pberrypi.org>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Woojung Huh <Woojung.Huh@...rochip.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/usb/smsc95xx.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -2011,13 +2011,13 @@ static struct sk_buff *smsc95xx_tx_fixup
 	/* We do not advertise SG, so skbs should be already linearized */
 	BUG_ON(skb_shinfo(skb)->nr_frags);
 
-	if (skb_headroom(skb) < overhead) {
-		struct sk_buff *skb2 = skb_copy_expand(skb,
-			overhead, 0, flags);
+	/* Make writable and expand header space by overhead if required */
+	if (skb_cow_head(skb, overhead)) {
+		/* Must deallocate here as returning NULL to indicate error
+		 * means the skb won't be deallocated in the caller.
+		 */
 		dev_kfree_skb_any(skb);
-		skb = skb2;
-		if (!skb)
-			return NULL;
+		return NULL;
 	}
 
 	if (csum) {