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

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

[Oussama Ghorbel]

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;
 }
-- 
1.7.9.5

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

[Hannes Frederic Sowa]

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

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

[David Miller]

From: Hannes Frederic Sowa <hannes@stressinduktion.org>
Date: Fri, 4 Oct 2013 15:32:23 +0200

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

Applied, but please do not capitalize "IPv6" when using it as a subsystem
prefix in Subject lines.

Thanks.