Subject: Re: [PATCH net] ip_tunnels: Use skb-len to PMTU check.

From: Timo Teras <[email-masked]>
Date: Sun, 30 Jun 2013 10:50:03 +0300

On Sat, 29 Jun 2013 22:40:18 -0700
Pravin B Shelar <[email-masked]> wrote:

> In path mtu check, ip header total length works for gre device
> but not for gre-tap device.  Use skb len which is consistent
> for all tunneling types.  This also fixes bug introduced by
> commit c54419321455631079c7d (GRE: Refactor GRE tunneling code).
> 
> Reported-by: Timo Teras <[email-masked]>
> Signed-off-by: Pravin B Shelar <[email-masked]>
> ---
>  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 7fa8f08..4e9f530 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -595,7 +595,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct
> net_device *dev, 
>  		if (!skb_is_gso(skb) &&
>  		    (inner_iph->frag_off&htons(IP_DF)) &&
> -		     mtu < ntohs(inner_iph->tot_len)) {
> +		     mtu < skb->len) {
>  			icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu)); ip_rt_put(rt);
>  			goto tx_error;

I think icmp_send's mtu parameter should be adjusted too. Since it's
sent to the inner flow, but the mtu now is disregarding the possible
tunnel headers.

- Timo