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

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


From: Pravin B Shelar <redacted>

[ Upstream commit 5465740ace36f179de5bb0ccb5d46ddeb945e309 ]

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 <redacted>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/ip_gre.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c

@@ -972,8 +972,12 @@ static netdev_tx_t ipgre_tunnel_xmit(str
 			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));
 		}
 	}