From ccdb2d17df9f07c291d43b0aeea7c90e4c020489 Mon Sep 17 00:00:00 2001 From: Vincent Bernat Date: Sat, 15 Jul 2017 19:40:20 +0200 Subject: [PATCH] ip6: fix PMTU discovery when using /127 subnets The definition of an "anycast destination address" has been tweaked as a side-effect of commit 2647a9b07032 ("ipv6: Remove external dependency on rt6i_gateway and RTF_ANYCAST"). The first address of a point-to-point /127 subnet is now considered as an anycast address. This prevents ICMPv6 errors to be returned to a sender of such a subnet and breaks PMTU discovery. This can be reproduced with: ip link add name out6 type veth peer name in6 ip link add name out7 type veth peer name in7 ip link set mtu 1400 dev out7 ip link set mtu 1400 dev in7 ip netns add next-hop ip netns add next-next-hop ip link set netns next-hop dev in6 ip link set netns next-hop dev out7 ip link set netns next-next-hop dev in7 ip link set up dev out6 ip addr add 2001:db8:1::12/127 dev out6 ip netns exec next-hop ip link set up dev in6 ip netns exec next-hop ip link set up dev out7 ip netns exec next-hop ip addr add 2001:db8:1::13/127 dev in6 ip netns exec next-hop ip addr add 2001:db8:1::14/127 dev out7 ip netns exec next-hop ip route add default via 2001:db8:1::15 ip netns exec next-hop sysctl -qw net.ipv6.conf.all.forwarding=1 ip netns exec next-next-hop ip link set up dev in7 ip netns exec next-next-hop ip addr add 2001:db8:1::15/127 dev in7 ip netns exec next-next-hop ip addr add 2001:db8:1::50/128 dev in7 ip netns exec next-next-hop ip route add default via 2001:db8:1::14 ip netns exec next-next-hop sysctl -qw net.ipv6.conf.all.forwarding=1 ip route add 2001:db8:1::48/123 via 2001:db8:1::13 sleep 4 ping -M do -s 1452 -c 3 2001:db8:1::50 || true ip route get 2001:db8:1::50 Before the patch, we get: 2001:db8:1::50 from :: via 2001:db8:1::13 dev out6 src 2001:db8:1::12 metric 1024 pref medium After the patch, we get: 2001:db8:1::50 via 2001:db8:1::13 dev out6 src 2001:db8:1::12 metric 0 cache expires 578sec mtu 1400 pref medium Fixes: 2647a9b07032 ("ipv6: Remove external dependency on rt6i_gateway and RTF_ANYCAST") Signed-off-by: Vincent Bernat Signed-off-by: David S. Miller --- include/net/ip6_route.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h index 199056933dcb..907d39a42f6b 100644 --- a/include/net/ip6_route.h +++ b/include/net/ip6_route.h @@ -194,7 +194,7 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst, struct rt6_info *rt = (struct rt6_info *)dst; return rt->rt6i_flags & RTF_ANYCAST || - (rt->rt6i_dst.plen != 128 && + (rt->rt6i_dst.plen < 127 && ipv6_addr_equal(&rt->rt6i_dst.addr, daddr)); } -- 2.39.5