[PATCH 4.18 002/145] net: 6lowpan: fix reserved space for single frames

[Greg Kroah-Hartman]

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

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

From: Alexander Aring <aring@xxxxxxxxxxxx>

commit ac74f87c789af40936a80131c4759f3e72579c3a upstream.

This patch fixes patch add handling to take care tail and headroom for
single 6lowpan frames. We need to be sure we have a skb with the right
head and tailroom for single frames. This patch do it by using
skb_copy_expand() if head and tailroom is not enough allocated by upper
layer.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=195059
Reported-by: David Palma <david.palma@xxxxxxx>
Reported-by: Rabi Narayan Sahoo <rabinarayans0828@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Alexander Aring <aring@xxxxxxxxxxxx>
Signed-off-by: Stefan Schmidt <stefan@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/ieee802154/6lowpan/tx.c |   21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

--- a/net/ieee802154/6lowpan/tx.c
+++ b/net/ieee802154/6lowpan/tx.c
@@ -265,9 +265,24 @@ netdev_tx_t lowpan_xmit(struct sk_buff *
 	/* We must take a copy of the skb before we modify/replace the ipv6
 	 * header as the header could be used elsewhere
 	 */
-	skb = skb_unshare(skb, GFP_ATOMIC);
-	if (!skb)
-		return NET_XMIT_DROP;
+	if (unlikely(skb_headroom(skb) < ldev->needed_headroom ||
+		     skb_tailroom(skb) < ldev->needed_tailroom)) {
+		struct sk_buff *nskb;
+
+		nskb = skb_copy_expand(skb, ldev->needed_headroom,
+				       ldev->needed_tailroom, GFP_ATOMIC);
+		if (likely(nskb)) {
+			consume_skb(skb);
+			skb = nskb;
+		} else {
+			kfree_skb(skb);
+			return NET_XMIT_DROP;
+		}
+	} else {
+		skb = skb_unshare(skb, GFP_ATOMIC);
+		if (!skb)
+			return NET_XMIT_DROP;
+	}
 
 	ret = lowpan_header(skb, ldev, &dgram_size, &dgram_offset);
 	if (ret < 0) {