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>

1 files changed, 36 insertions, 0 deletions

diff --git a/target/linux/generic/patches-4.4/030-2-smsc75xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch b/target/linux/generic/patches-4.4/030-2-smsc75xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch
new file mode 100644
index 0000000..6312f0f
--- /dev/null
+++ b/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;