[NET]: Avoid copying writable clones in tunnel drivers

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -809,7 +809,8 @@ static int ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	max_headroom = LL_RESERVED_SPACE(tdev) + gre_hlen;
 
-	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
+	if (skb_headroom(skb) < max_headroom || skb_shared(skb)||
+	    (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
 		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
 		if (!new_skb) {
 			ip_rt_put(rt);

net/ipv4/ipip.c

@@ -595,7 +595,8 @@ static int ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 	 */
 	max_headroom = (LL_RESERVED_SPACE(tdev)+sizeof(struct iphdr));
 
-	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
+	if (skb_headroom(skb) < max_headroom || skb_shared(skb) ||
+	    (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
 		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
 		if (!new_skb) {
 			ip_rt_put(rt);

net/ipv6/ip6_tunnel.c

@@ -883,8 +883,8 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
 	 */
 	max_headroom += LL_RESERVED_SPACE(tdev);
 
-	if (skb_headroom(skb) < max_headroom ||
-	    skb_cloned(skb) || skb_shared(skb)) {
+	if (skb_headroom(skb) < max_headroom || skb_shared(skb) ||
+	    (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
 		struct sk_buff *new_skb;
 
 		if (!(new_skb = skb_realloc_headroom(skb, max_headroom)))

net/ipv6/sit.c

@@ -532,7 +532,8 @@ static int ipip6_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 	 */
 	max_headroom = LL_RESERVED_SPACE(tdev)+sizeof(struct iphdr);
 
-	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
+	if (skb_headroom(skb) < max_headroom || skb_shared(skb) ||
+	    (skb_cloned(skb) && !skb_clone_writable(skb, 0))) {
 		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
 		if (!new_skb) {
 			ip_rt_put(rt);