From df23bb18b44b9a1f2b54358201730e710a9df57f Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Tue, 4 Aug 2020 07:53:42 +0200 Subject: ipv4: route: Ignore output interface in FIB lookup for PMTU route Currently, processes sending traffic to a local bridge with an encapsulation device as a port don't get ICMP errors if they exceed the PMTU of the encapsulated link. David Ahern suggested this as a hack, but it actually looks like the correct solution: when we update the PMTU for a given destination by means of updating or creating a route exception, the encapsulation might trigger this because of PMTU discovery happening either on the encapsulation device itself, or its lower layer. This happens on bridged encapsulations only. The output interface shouldn't matter, because we already have a valid destination. Drop the output interface restriction from the associated route lookup. For UDP tunnels, we will now have a route exception created for the encapsulation itself, with a MTU value reflecting its headroom, which allows a bridge forwarding IP packets originated locally to deliver errors back to the sending socket. The behaviour is now consistent with IPv6 and verified with selftests pmtu_ipv{4,6}_br_{geneve,vxlan}{4,6}_exception introduced later in this series. v2: - reset output interface only for bridge ports (David Ahern) - add and use netif_is_any_bridge_port() helper (David Ahern) Suggested-by: David Ahern Signed-off-by: Stefano Brivio Reviewed-by: David Ahern Signed-off-by: David S. Miller --- net/ipv4/route.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'net') diff --git a/net/ipv4/route.c b/net/ipv4/route.c index a01efa062f6b..8ca6bcab7b03 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1050,6 +1050,11 @@ static void ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk, struct flowi4 fl4; ip_rt_build_flow_key(&fl4, sk, skb); + + /* Don't make lookup fail for bridged encapsulations */ + if (skb && netif_is_any_bridge_port(skb->dev)) + fl4.flowi4_oif = 0; + __ip_rt_update_pmtu(rt, &fl4, mtu); } -- cgit v1.2.3