Subject: Re: [PATCH v2] IP_GRE: Fix kernel panic in IP_GRE with GRE csum.

From: YOSHIFUJI Hideaki <[email-masked]>
Date: Wed, 23 Jan 2013 23:00:48 +0900

Pravin B Shelar wrote:
> Fixed code indentation according to comments from David Miller.
> 
> --8<--------------------------cut here-------------------------->8--
> Due to 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.
> 
> Signed-off-by: Pravin B Shelar <[email-masked]>
> ---
>  net/ipv4/ip_gre.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> index 303012a..8179e066 100644
> --- a/net/ipv4/ip_gre.c
> +++ b/net/ipv4/ip_gre.c
> @@ -964,7 +964,10 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
>  		}
>  		if (tunnel->parms.o_flags&GRE_CSUM) {
>  			*ptr = 0;
> -			*(__sum16 *)ptr = ip_compute_csum((void *)(iph+1), skb->len - sizeof(struct iphdr));
> +			*(__sum16 *)ptr = csum_fold(skb_checksum(skb,
> +						    skb_transport_offset(skb),
> +						    skb->len - skb_transport_offset(skb),
> +						    0));

IMHO, arguments for skb_checksum() should be aligned:

			*(__sum16 *)ptr = csum_fold(skb_checksum(skb,
								 skb_transport_offset(skb),
								 skb->len - skb_transport_offset(skb),
								 0));

--yoshfuji