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SubjectRe: [PATCH] IPv6: Allow the MTU of ipip6 tunnel to be set below 1280
On Thu, Sep 26, 2013 at 03:51:48PM +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 <oghorbell@gmail.com>
> ---
> net/ipv6/ip6_tunnel.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
> index 1e55866..a66ead2 100644
> --- a/net/ipv6/ip6_tunnel.c
> +++ b/net/ipv6/ip6_tunnel.c
> @@ -1423,8 +1423,14 @@ 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 *t = netdev_priv(dev);
> +
> + if (t->parms.proto == IPPROTO_IPIP) {
> + if (new_mtu < 68)
> + return -EINVAL;

Maybe you could have a look at ip_tunnel_change_mtu in ipv4/ip_tunnel.c,
generalize this check as e.g. ip_tunnel_valid_mtu or something and use it
here? Maybe an af-independent ip_tunnel_max_mtu()?

> + } else {
> + if (new_mtu < IPV6_MIN_MTU)
> + return -EINVAL;

This check could also be used here, then.

> }
> dev->mtu = new_mtu;
> return 0;

Thanks,

Hannes



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