IP_GRE: Fix kernel panic in IP_GRE with GRE csum.

Due to IP_GRE GSO support, GRE can recieve non linear skb which
results in panic in case of GRE_CSUM.  Following patch fixes it by
using correct csum API.

Bug introduced in commit 6b78f16e4bdde3936b (gre: add GSO support)

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 303012adf9e6..e81b1caf2ea2 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -963,8 +963,12 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
                         ptr--;
                 }
                 if (tunnel->parms.o_flags&GRE_CSUM) {
+                        int offset = skb_transport_offset(skb);
+
                         *ptr = 0;
-                        *(__sum16 *)ptr = ip_compute_csum((void *)(iph+1), skb->len - sizeof(struct iphdr));
+                        *(__sum16 *)ptr = csum_fold(skb_checksum(skb, offset,
+                                                                 skb->len - offset,
+                                                                 0));
                 }
         }