From d8c444d540beaa39aff834c5b83df7e86a1ae765 Mon Sep 17 00:00:00 2001 From: Shijie Luo Date: Tue, 18 Jun 2019 15:14:03 +0000 Subject: [PATCH] ipv4: fix inet_select_addr() when enable route_localnet Suppose we have two interfaces eth0 and eth1 in two hosts, follow the same steps in the two hosts: # sysctl -w net.ipv4.conf.eth1.route_localnet=1 # sysctl -w net.ipv4.conf.eth1.arp_announce=2 # ip route del 127.0.0.0/8 dev lo table local and then set ip to eth1 in host1 like: # ifconfig eth1 127.25.3.4/24 set ip to eth2 in host2 and ping host1: # ifconfig eth1 127.25.3.14/24 # ping -I eth1 127.25.3.4 Well, host2 cannot connect to host1. When set a ip address with head 127, the scope of the address defaults to RT_SCOPE_HOST. In this situation, host2 will use arp_solicit() to send a arp request for the mac address of host1 with ip address 127.25.3.14. When arp_announce=2, inet_select_addr() cannot select a correct saddr with condition ifa->ifa_scope > scope, because ifa_scope is RT_SCOPE_HOST and scope is RT_SCOPE_LINK. Then, inet_select_addr() will go to no_in_dev to lookup all interfaces to find a primary ip and finally get the primary ip of eth0. Here I add a localnet_scope defaults to RT_SCOPE_HOST, and when route_localnet is enabled, this value changes to RT_SCOPE_LINK to make inet_select_addr() find a correct primary ip as saddr of arp request. Fixes: d0daebc3d622 ("ipv4: Add interface option to enable routing of 127.0.0.0/8") Signed-off-by: Shijie Luo Signed-off-by: Zhiqiang Liu Signed-off-by: David S. Miller --- net/ipv4/devinet.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c index 914ccc7f192a..6fd4628d10b9 100644 --- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -1287,6 +1287,7 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope) { const struct in_ifaddr *ifa; __be32 addr = 0; + unsigned char localnet_scope = RT_SCOPE_HOST; struct in_device *in_dev; struct net *net = dev_net(dev); int master_idx; @@ -1296,10 +1297,13 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope) if (!in_dev) goto no_in_dev; + if (unlikely(IN_DEV_ROUTE_LOCALNET(in_dev))) + localnet_scope = RT_SCOPE_LINK; + in_dev_for_each_ifa_rcu(ifa, in_dev) { if (ifa->ifa_flags & IFA_F_SECONDARY) continue; - if (ifa->ifa_scope > scope) + if (min(ifa->ifa_scope, localnet_scope) > scope) continue; if (!dst || inet_ifa_match(dst, ifa)) { addr = ifa->ifa_local; -- 2.34.1