linux-kernel - [PATCH 4.9 28/96] smsc75xx: use skb_cow

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Message-Id: <20180115123406.890643427@linuxfoundation.org>
Date:   Mon, 15 Jan 2018 13:34:27 +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, Eric Dumazet <edumazet@...gle.com>,
        James Hughes <james.hughes@...pberrypi.org>,
        "David S. Miller" <davem@...emloft.net>,
        Oliver Neukum <oneukum@...e.com>
Subject: [PATCH 4.9 28/96] smsc75xx: use skb_cow_head() to deal with cloned skbs

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

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

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

commit b7c6d2675899cfff0180412c63fc9cbd5bacdb4d 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: d0cad871703b ("smsc75xx: SMSC LAN75xx USB gigabit ethernet adapter 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: Oliver Neukum <oneukum@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/usb/smsc75xx.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/drivers/net/usb/smsc75xx.c
+++ b/drivers/net/usb/smsc75xx.c
@@ -2205,13 +2205,9 @@ static struct sk_buff *smsc75xx_tx_fixup
 {
 	u32 tx_cmd_a, tx_cmd_b;

-	if (skb_headroom(skb) < SMSC75XX_TX_OVERHEAD) {
-		struct sk_buff *skb2 =
-			skb_copy_expand(skb, SMSC75XX_TX_OVERHEAD, 0, flags);
+	if (skb_cow_head(skb, SMSC75XX_TX_OVERHEAD)) {
 		dev_kfree_skb_any(skb);
-		skb = skb2;
-		if (!skb)
-			return NULL;
+		return NULL;
 	}

 	tx_cmd_a = (u32)(skb->len & TX_CMD_A_LEN) | TX_CMD_A_FCS;