linux-kernel - Re: [PATCH] IPv6: Allow the MTU of ipip6 tunnel to be set below 1280

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Message-ID: <CA+ev270=P9txSvo7AZN0YcsopwhCYtJCgcZCPsdofEJ+BX+EUQ@mail.gmail.com>
Date:	Fri, 27 Sep 2013 11:45:48 +0100
From:	Oussama Ghorbel <oghorbell@...il.com>
To:	Oussama Ghorbel <oghorbell@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IPv6: Allow the MTU of ipip6 tunnel to be set below 1280

The ip6_tunnel.c module would be then dependent on ip_tunnel.c and may
be it would not be good thing?
As I have check in v3.10 there is no call from ip6_tunnel to ip_tunnel...

For information, there is no check for the maximum MTU for ipv4 in the
patch as this is not done for ipv6.

Regards,
Oussama

On Fri, Sep 27, 2013 at 9:37 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> 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@...il.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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