Re: [PATCHv2] IPv6: Allow the MTU of ipip6 tunnel to be set below 1280

[Hannes Frederic Sowa <hannes@stressinduktion.org>]

On Thu, Oct 03, 2013 at 02:49:26PM +0100, Oussama Ghorbel wrote:
> The (inner) MTU of a ipip6 (IPv4-in-IPv6) tunnel cannot be set below 1280, which is the minimum MTU in IPv6.
> However, there should be no IPv6 on the tunnel interface at all, so the IPv6 rules should not apply.
> More info at https://bugzilla.kernel.org/show_bug.cgi?id=15530
> 
> This patch allows to check the minimum MTU for ipv6 tunnel according to these rules:
> -In case the tunnel is configured with ipip6 mode the minimum MTU is 68.
> -In case the tunnel is configured with ip6ip6 or any mode the minimum MTU is 1280.
> 
> Signed-off-by: Oussama Ghorbel <ou.ghorbel@gmail.com>
> ---
>  net/ipv6/ip6_tunnel.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
> index 46ba243..4b51b03 100644
> --- a/net/ipv6/ip6_tunnel.c
> +++ b/net/ipv6/ip6_tunnel.c
> @@ -1429,9 +1429,17 @@ ip6_tnl_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
>  static int
>  ip6_tnl_change_mtu(struct net_device *dev, int new_mtu)
>  {
> -	if (new_mtu < IPV6_MIN_MTU) {
> -		return -EINVAL;
> +	struct ip6_tnl *tnl = netdev_priv(dev);
> +
> +	if (tnl->parms.proto == IPPROTO_IPIP) {
> +		if (new_mtu < 68)
> +			return -EINVAL;
> +	} else {
> +		if (new_mtu < IPV6_MIN_MTU)
> +			return -EINVAL;
>  	}
> +	if (new_mtu > 0xFFF8 - dev->hard_header_len)
> +		return -EINVAL;
>  	dev->mtu = new_mtu;
>  	return 0;
>  }

Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

Anytime soon we should replace all the FFF8 with a symbolic constant.

Thanks,

  Hannes