gre: Call gso_make_checksum

Call gso_make_checksum. This should have the benefit of using a
checksum that may have been previously computed for the packet.

This also adds NETIF_F_GSO_GRE_CSUM to differentiate devices that
offload GRE GSO with and without the GRE checksum offloaed.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 2 deletions

diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index f1d32280cb54..24deb3928b9e 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -42,6 +42,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
                                   SKB_GSO_DODGY |
                                   SKB_GSO_TCP_ECN |
                                   SKB_GSO_GRE |
+                                  SKB_GSO_GRE_CSUM |
                                   SKB_GSO_IPIP)))
                 goto out;
 
@@ -55,6 +56,8 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
                 goto out;
 
         csum = !!(greh->flags & GRE_CSUM);
+        if (csum)
+                skb->encap_hdr_csum = 1;
 
         if (unlikely(!pskb_may_pull(skb, ghl)))
                 goto out;
@@ -94,10 +97,13 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
                                 }
                         }
 
-                        greh = (struct gre_base_hdr *)(skb->data);
+                        skb_reset_transport_header(skb);
+
+                        greh = (struct gre_base_hdr *)
+                            skb_transport_header(skb);
                         pcsum = (__be32 *)(greh + 1);
                         *pcsum = 0;
-                        *(__sum16 *)pcsum = csum_fold(skb_checksum(skb, 0, skb->len, 0));
+                        *(__sum16 *)pcsum = gso_make_checksum(skb, 0);
                 }
                 __skb_push(skb, tnl_hlen - ghl);