From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ahern Subject: Re: PMTU discovery broken in Linux for UDP/raw application if the socket is not bound to a device Date: Tue, 9 Oct 2018 10:23:37 -0600 Message-ID: <6ebc8ad8-7e08-7d94-73d8-3dd9feb8b0f3@gmail.com> References: <811A4496-322E-443D-9B07-46E6BC406C38@juniper.net> <4138E416-D846-47B2-AA9F-593313041E6F@juniper.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Reji Thomas , Yogesh Ankolekar , "netdev@vger.kernel.org" To: Preethi Ramachandra Return-path: Received: from mail-pl1-f193.google.com ([209.85.214.193]:35042 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbeJIXlX (ORCPT ); Tue, 9 Oct 2018 19:41:23 -0400 Received: by mail-pl1-f193.google.com with SMTP id f8-v6so1090456plb.2 for ; Tue, 09 Oct 2018 09:23:40 -0700 (PDT) In-Reply-To: <4138E416-D846-47B2-AA9F-593313041E6F@juniper.net> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: [ adding netdev so others know ] On 10/9/18 3:38 AM, Preethi Ramachandra wrote: > Hi David, > > I tested your fix, Linux is updating PMTU successfully. ok, I'll send a formal patch > > Thanks, > Preethi > > On 10/7/18, 8:59 AM, "David Ahern" wrote: > > The correct mailing list is netdev@vger.kernel.org (added) > > non-text emails will be rejected. > > > On 10/3/18 10:15 PM, Preethi Ramachandra wrote: > > Hi, > > > > > > > > While testing the PMTU discovery for UDP/raw applications, Linux is not > > doing PMTU discovery if the UDP server socket is not bound to a device. > > In the scenario we are testing there could be multiple VRF devices > > created and an application like UDP/RAW can use a common socket for all > > vrf devices. While sending packet IP_PKTINFO socket option can be used > > to specify the vrf interface through which packet will be sent out. In > > this case, when packet too big icmp6 error message comes back to Linux > > on a vrf device, a route lookup is done on default routing-table(0) for > > src/dst address which case, the route will not be found and packet is > > dropped. If the route lookup happened with proper VRF device (packet’s > > incoming index), the route lookup succeeds, PMTU discovery is successful. > > > > > > > > This might need a fix, please take a look. > > > > > > > > *Linux version * > > > > > > > > Linux 4.8.24 > > > > > > > > *Code flow * > > > > > > > > Linux code where it expects socket’s bound device in order for PMTU > > discovery to happen. > > > > *void ip6_sk_update_pmtu*(struct sk_buff *skb, struct sock *sk, __be32 mtu) > > > > { > > > > struct dst_entry *dst; > > > > > > > > ip6_update_pmtu(skb, sock_net(sk), mtu, > > > > > > sk->sk_bound_dev_if, sk->sk_mark, sk->sk_uid);*<<<<< This is the point > > where it expects socket’s sk_bound_dev_if to be set. In our testing this > > is actually 0, since the socket is not really bound to a vrf device.* > > Try this based on top of tree for 4.19-next (whitespace damaged on paste > so you'll need to manually apply and handle differences with 4.8): > > diff --git a/net/ipv6/route.c b/net/ipv6/route.c > index 6c1d817151ca..50b95b48b911 100644 > --- a/net/ipv6/route.c > +++ b/net/ipv6/route.c > @@ -2360,10 +2360,13 @@ EXPORT_SYMBOL_GPL(ip6_update_pmtu); > > void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu) > { > + int oif = sk->sk_bound_dev_if; > struct dst_entry *dst; > > - ip6_update_pmtu(skb, sock_net(sk), mtu, > - sk->sk_bound_dev_if, sk->sk_mark, sk->sk_uid); > + if (!oif && skb->dev) > + oif = l3mdev_master_ifindex(skb->dev); > + > + ip6_update_pmtu(skb, sock_net(sk), mtu, oif, sk->sk_mark, > sk->sk_uid); > > dst = __sk_dst_get(sk); > if (!dst || !dst->obsolete || > > > >