[ 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" <dsah...@gmail.com> 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 ||
>
>
>
>
