From fb56be83e43d0bb0cc9e8c35a6a9cac853231ba2 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Maciej=20=C5=BBenczykowski?= Date: Fri, 4 Nov 2016 14:51:54 -0700 Subject: [PATCH] net-ipv6: on device mtu change do not add mtu to mtu-less routes MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Routes can specify an mtu explicitly or inherit the mtu from the underlying device - this inheritance is implemented in dst->ops->mtu handlers ip6_mtu() and ip6_blackhole_mtu(). Currently changing the mtu of a device adds mtu explicitly to routes using that device. ie. # ip link set dev lo mtu 65536 # ip -6 route add local 2000::1 dev lo # ip -6 route get 2000::1 local 2000::1 dev lo table local src ... metric 1024 pref medium # ip link set dev lo mtu 65535 # ip -6 route get 2000::1 local 2000::1 dev lo table local src ... metric 1024 mtu 65535 pref medium # ip link set dev lo mtu 65536 # ip -6 route get 2000::1 local 2000::1 dev lo table local src ... metric 1024 mtu 65536 pref medium # ip -6 route del local 2000::1 After this patch the route entry no longer changes unless it already has an mtu. There is no need: this inheritance is already done in ip6_mtu() # ip link set dev lo mtu 65536 # ip -6 route add local 2000::1 dev lo # ip -6 route add local 2000::2 dev lo mtu 2000 # ip -6 route get 2000::1; ip -6 route get 2000::2 local 2000::1 dev lo table local src ... metric 1024 pref medium local 2000::2 dev lo table local src ... metric 1024 mtu 2000 pref medium # ip link set dev lo mtu 65535 # ip -6 route get 2000::1; ip -6 route get 2000::2 local 2000::1 dev lo table local src ... metric 1024 pref medium local 2000::2 dev lo table local src ... metric 1024 mtu 2000 pref medium # ip link set dev lo mtu 1501 # ip -6 route get 2000::1; ip -6 route get 2000::2 local 2000::1 dev lo table local src ... metric 1024 pref medium local 2000::2 dev lo table local src ... metric 1024 mtu 1501 pref medium # ip link set dev lo mtu 65536 # ip -6 route get 2000::1; ip -6 route get 2000::2 local 2000::1 dev lo table local src ... metric 1024 pref medium local 2000::2 dev lo table local src ... metric 1024 mtu 65536 pref medium # ip -6 route del local 2000::1 # ip -6 route del local 2000::2 This is desirable because changing device mtu and then resetting it to the previous value shouldn't change the user visible routing table. Signed-off-by: Maciej Żenczykowski CC: Eric Dumazet Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- net/ipv6/route.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 7403d90dcb38..1b57e11e6e0d 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -2761,6 +2761,7 @@ static int rt6_mtu_change_route(struct rt6_info *rt, void *p_arg) PMTU discouvery. */ if (rt->dst.dev == arg->dev && + dst_metric_raw(&rt->dst, RTAX_MTU) && !dst_metric_locked(&rt->dst, RTAX_MTU)) { if (rt->rt6i_flags & RTF_CACHE) { /* For RTF_CACHE with rt6i_pmtu == 0 -- 2.20.1