Re: [PATCH net] gre: Fix MTU sizing check for gretap tunnels

[Eric Dumazet <eric.dumazet@gmail.com>]

On Thu, 2013-07-11 at 13:12 -0700, Alexander Duyck wrote:
> This change fixes an MTU sizing issue seen with gretap tunnels when non-gso
> packets are sent from the interface.
> 
> In my case I was able to reproduce the issue by simply sending a ping of
> 1421 bytes with the gretap interface created on a device with a standard
> 1500 mtu.
> 
> This fix is based on the fact that the tunnel mtu is already adjusted by
> dev->hard_header_len so it would make sense that any packets being compared
> against that mtu should also be adjusted by hard_header_len and the tunnel
> header instead of just the tunnel header.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
> ---
> 
>  net/ipv4/ip_tunnel.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index 945734b..ca1cb2d 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -476,7 +476,7 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb,
>  			    struct rtable *rt, __be16 df)
>  {
>  	struct ip_tunnel *tunnel = netdev_priv(dev);
> -	int pkt_size = skb->len - tunnel->hlen;
> +	int pkt_size = skb->len - tunnel->hlen - dev->hard_header_len;
>  	int mtu;
>  
>  

Reported-by: Cong Wang <amwang@redhat.com>

Acked-by: Eric Dumazet <edumazet@google.com>