kernel: 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 Ethernet<->WiFi bridge for Raspberry Pi and probably other devices.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/generic/patches-4.4/030-1-smsc95xx-Use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,40 @@
+From e9156cd26a495a18706e796f02a81fee41ec14f4 Mon Sep 17 00:00:00 2001
+From: James Hughes <james.hughes@raspberrypi.org>
+Date: Wed, 19 Apr 2017 11:13:40 +0100
+Subject: [PATCH] smsc95xx: Use skb_cow_head to deal with cloned skbs
+
+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@raspberrypi.org>
+Acked-by: Eric Dumazet <edumazet@google.com>
+Acked-by: Woojung Huh <Woojung.Huh@microchip.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -1835,13 +1835,13 @@ 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) {

target/linux/generic/patches-4.4/030-2-smsc75xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,36 @@
+From b7c6d2675899cfff0180412c63fc9cbd5bacdb4d Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:21 -0700
+Subject: [PATCH] smsc75xx: 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: d0cad871703b ("smsc75xx: SMSC LAN75xx USB gigabit ethernet adapter driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -2193,13 +2193,9 @@ 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;

target/linux/generic/patches-4.4/030-3-cx82310_eth-use-skb_cow_head-to-deal-with-cloned-skb.patch

@@ -0,0 +1,35 @@
+From a9e840a2081ed28c2b7caa6a9a0041c950b3c37d Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:22 -0700
+Subject: [PATCH] cx82310_eth: 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: cc28a20e77b2 ("introduce cx82310_eth: Conexant CX82310-based ADSL router USB ethernet driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -293,12 +293,9 @@ 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);
+ 

target/linux/generic/patches-4.4/030-4-sr9700-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,37 @@
+From d532c1082f68176363ed766d09bf187616e282fe Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:23 -0700
+Subject: [PATCH] sr9700: 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: c9b37458e956 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/sr9700.c | 9 ++-------
+ 1 file changed, 2 insertions(+), 7 deletions(-)
+
+--- a/drivers/net/usb/sr9700.c
++++ b/drivers/net/usb/sr9700.c
+@@ -456,14 +456,9 @@ static struct sk_buff *sr9700_tx_fixup(s
+ 
+ 	len = skb->len;
+ 
+-	if (skb_headroom(skb) < SR_TX_OVERHEAD) {
+-		struct sk_buff *skb2;
+-
+-		skb2 = skb_copy_expand(skb, SR_TX_OVERHEAD, 0, flags);
++	if (skb_cow_head(skb, SR_TX_OVERHEAD)) {
+ 		dev_kfree_skb_any(skb);
+-		skb = skb2;
+-		if (!skb)
+-			return NULL;
++		return NULL;
+ 	}
+ 
+ 	__skb_push(skb, SR_TX_OVERHEAD);

target/linux/generic/patches-4.4/030-5-lan78xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,38 @@
+From d4ca73591916b760478d2b04334d5dcadc028e9c Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:24 -0700
+Subject: [PATCH] lan78xx: 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: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Cc: Woojung Huh <woojung.huh@microchip.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/lan78xx.c | 9 ++-------
+ 1 file changed, 2 insertions(+), 7 deletions(-)
+
+--- a/drivers/net/usb/lan78xx.c
++++ b/drivers/net/usb/lan78xx.c
+@@ -2050,14 +2050,9 @@ static struct sk_buff *lan78xx_tx_prep(s
+ {
+ 	u32 tx_cmd_a, tx_cmd_b;
+ 
+-	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;
+ 	}
+ 
+ 	if (lan78xx_linearize(skb) < 0)

target/linux/generic/patches-4.4/030-6-ch9200-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,38 @@
+From 6bc6895bdd6744e0136eaa4a11fbdb20a7db4e40 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:25 -0700
+Subject: [PATCH] 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@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Cc: Matthew Garrett <mjg59@srcf.ucam.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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);

target/linux/generic/patches-4.4/030-7-kaweth-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,43 @@
+From 39fba7835aacda65284a86e611774cbba71dac20 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:26 -0700
+Subject: [PATCH] kaweth: use skb_cow_head() to deal with cloned skbs
+
+We can use skb_cow_head() to properly deal with clones,
+especially the ones coming from TCP stack that allow their head being
+modified. This avoids a copy.
+
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/kaweth.c | 18 ++++++------------
+ 1 file changed, 6 insertions(+), 12 deletions(-)
+
+--- a/drivers/net/usb/kaweth.c
++++ b/drivers/net/usb/kaweth.c
+@@ -812,18 +812,12 @@ static netdev_tx_t kaweth_start_xmit(str
+ 	}
+ 
+ 	/* We now decide whether we can put our special header into the sk_buff */
+-	if (skb_cloned(skb) || skb_headroom(skb) < 2) {
+-		/* no such luck - we make our own */
+-		struct sk_buff *copied_skb;
+-		copied_skb = skb_copy_expand(skb, 2, 0, GFP_ATOMIC);
+-		dev_kfree_skb_irq(skb);
+-		skb = copied_skb;
+-		if (!copied_skb) {
+-			kaweth->stats.tx_errors++;
+-			netif_start_queue(net);
+-			spin_unlock_irq(&kaweth->device_lock);
+-			return NETDEV_TX_OK;
+-		}
++	if (skb_cow_head(skb, 2)) {
++		kaweth->stats.tx_errors++;
++		netif_start_queue(net);
++		spin_unlock_irq(&kaweth->device_lock);
++		dev_kfree_skb_any(skb);
++		return NETDEV_TX_OK;
+ 	}
+ 
+ 	private_header = (__le16 *)__skb_push(skb, 2);

target/linux/generic/patches-4.9/023-1-smsc95xx-Use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,40 @@
+From e9156cd26a495a18706e796f02a81fee41ec14f4 Mon Sep 17 00:00:00 2001
+From: James Hughes <james.hughes@raspberrypi.org>
+Date: Wed, 19 Apr 2017 11:13:40 +0100
+Subject: [PATCH] smsc95xx: Use skb_cow_head to deal with cloned skbs
+
+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@raspberrypi.org>
+Acked-by: Eric Dumazet <edumazet@google.com>
+Acked-by: Woojung Huh <Woojung.Huh@microchip.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -2001,13 +2001,13 @@ 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) {

target/linux/generic/patches-4.9/023-2-smsc75xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,36 @@
+From b7c6d2675899cfff0180412c63fc9cbd5bacdb4d Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:21 -0700
+Subject: [PATCH] smsc75xx: 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: d0cad871703b ("smsc75xx: SMSC LAN75xx USB gigabit ethernet adapter driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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;

target/linux/generic/patches-4.9/023-3-cx82310_eth-use-skb_cow_head-to-deal-with-cloned-skb.patch

@@ -0,0 +1,35 @@
+From a9e840a2081ed28c2b7caa6a9a0041c950b3c37d Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:22 -0700
+Subject: [PATCH] cx82310_eth: 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: cc28a20e77b2 ("introduce cx82310_eth: Conexant CX82310-based ADSL router USB ethernet driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -293,12 +293,9 @@ 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);
+ 

target/linux/generic/patches-4.9/023-4-sr9700-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,37 @@
+From d532c1082f68176363ed766d09bf187616e282fe Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:23 -0700
+Subject: [PATCH] sr9700: 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: c9b37458e956 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/sr9700.c | 9 ++-------
+ 1 file changed, 2 insertions(+), 7 deletions(-)
+
+--- a/drivers/net/usb/sr9700.c
++++ b/drivers/net/usb/sr9700.c
+@@ -456,14 +456,9 @@ static struct sk_buff *sr9700_tx_fixup(s
+ 
+ 	len = skb->len;
+ 
+-	if (skb_headroom(skb) < SR_TX_OVERHEAD) {
+-		struct sk_buff *skb2;
+-
+-		skb2 = skb_copy_expand(skb, SR_TX_OVERHEAD, 0, flags);
++	if (skb_cow_head(skb, SR_TX_OVERHEAD)) {
+ 		dev_kfree_skb_any(skb);
+-		skb = skb2;
+-		if (!skb)
+-			return NULL;
++		return NULL;
+ 	}
+ 
+ 	__skb_push(skb, SR_TX_OVERHEAD);

target/linux/generic/patches-4.9/023-5-lan78xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,38 @@
+From d4ca73591916b760478d2b04334d5dcadc028e9c Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:24 -0700
+Subject: [PATCH] lan78xx: 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: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Cc: Woojung Huh <woojung.huh@microchip.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/lan78xx.c | 9 ++-------
+ 1 file changed, 2 insertions(+), 7 deletions(-)
+
+--- a/drivers/net/usb/lan78xx.c
++++ b/drivers/net/usb/lan78xx.c
+@@ -2419,14 +2419,9 @@ static struct sk_buff *lan78xx_tx_prep(s
+ {
+ 	u32 tx_cmd_a, tx_cmd_b;
+ 
+-	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;
+ 	}
+ 
+ 	if (lan78xx_linearize(skb) < 0)

target/linux/generic/patches-4.9/023-6-ch9200-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,38 @@
+From 6bc6895bdd6744e0136eaa4a11fbdb20a7db4e40 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:25 -0700
+Subject: [PATCH] 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@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Cc: Matthew Garrett <mjg59@srcf.ucam.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ 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
+@@ -254,14 +254,9 @@ 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);

target/linux/generic/patches-4.9/023-7-kaweth-use-skb_cow_head-to-deal-with-cloned-skbs.patch

@@ -0,0 +1,43 @@
+From 39fba7835aacda65284a86e611774cbba71dac20 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 19 Apr 2017 09:59:26 -0700
+Subject: [PATCH] kaweth: use skb_cow_head() to deal with cloned skbs
+
+We can use skb_cow_head() to properly deal with clones,
+especially the ones coming from TCP stack that allow their head being
+modified. This avoids a copy.
+
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Cc: James Hughes <james.hughes@raspberrypi.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/usb/kaweth.c | 18 ++++++------------
+ 1 file changed, 6 insertions(+), 12 deletions(-)
+
+--- a/drivers/net/usb/kaweth.c
++++ b/drivers/net/usb/kaweth.c
+@@ -803,18 +803,12 @@ static netdev_tx_t kaweth_start_xmit(str
+ 	}
+ 
+ 	/* We now decide whether we can put our special header into the sk_buff */
+-	if (skb_cloned(skb) || skb_headroom(skb) < 2) {
+-		/* no such luck - we make our own */
+-		struct sk_buff *copied_skb;
+-		copied_skb = skb_copy_expand(skb, 2, 0, GFP_ATOMIC);
+-		dev_kfree_skb_irq(skb);
+-		skb = copied_skb;
+-		if (!copied_skb) {
+-			kaweth->stats.tx_errors++;
+-			netif_start_queue(net);
+-			spin_unlock_irq(&kaweth->device_lock);
+-			return NETDEV_TX_OK;
+-		}
++	if (skb_cow_head(skb, 2)) {
++		kaweth->stats.tx_errors++;
++		netif_start_queue(net);
++		spin_unlock_irq(&kaweth->device_lock);
++		dev_kfree_skb_any(skb);
++		return NETDEV_TX_OK;
+ 	}
+ 
+ 	private_header = (__le16 *)__skb_push(skb, 2);