Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135Ab3JEOGk (ORCPT ); Sat, 5 Oct 2013 10:06:40 -0400 Received: from order.stressinduktion.org ([87.106.68.36]:42272 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751492Ab3JEOGi (ORCPT ); Sat, 5 Oct 2013 10:06:38 -0400 Date: Sat, 5 Oct 2013 16:06:36 +0200 From: Hannes Frederic Sowa To: Oussama Ghorbel Cc: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix the upper MTU limit in ipv6 GRE tunnel Message-ID: <20131005140636.GA25076@order.stressinduktion.org> Mail-Followup-To: Oussama Ghorbel , "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <1380880333-3546-1-git-send-email-ou.ghorbel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1380880333-3546-1-git-send-email-ou.ghorbel@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1966 Lines: 52 On Fri, Oct 04, 2013 at 10:52:13AM +0100, Oussama Ghorbel wrote: > Unlike ipv4, the struct member hlen holds the length of the GRE and ipv6 > headers. This length is also counted in dev->hard_header_len. > Perhaps, it's more clean to modify the hlen to count only the GRE header > without ipv6 header as the variable name suggest, but the simple way to fix > this without regression risk is simply modify the calculation of the limit > in ip6gre_tunnel_change_mtu function. > Verified in kernel version v3.11. > > Signed-off-by: Oussama Ghorbel > --- > net/ipv6/ip6_gre.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c > index 90747f1..41487ab 100644 > --- a/net/ipv6/ip6_gre.c > +++ b/net/ipv6/ip6_gre.c > @@ -1175,9 +1175,8 @@ done: > > static int ip6gre_tunnel_change_mtu(struct net_device *dev, int new_mtu) > { > - struct ip6_tnl *tunnel = netdev_priv(dev); > if (new_mtu < 68 || > - new_mtu > 0xFFF8 - dev->hard_header_len - tunnel->hlen) > + new_mtu > 0xFFF8 - dev->hard_header_len) > return -EINVAL; > dev->mtu = new_mtu; > return 0; Hmmm... dev->hard_header_len is initialized to LL_MAX_HEADER + sizeof(struct ipv6hdr) + 4 but won't include the additional head space needed for GRE_SEQ, GRE_KEY etc. if at time of tunnel creation the routing table did not had a good guess for the outgoing device. To make this correct we would have to refactor the usage of the variables a bit as is done in ipv4/ip_tunnel.c. The safest thing would be to leave this check as-is currently although we exclude some allowed mtus. Perhaps you want to take a look how to achieve that? ;) Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/