Commit d8c444d5 authored Jun 18, 2019 by Shijie Luo Committed by David S. Miller Jun 24, 2019

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: d0daebc3 ("ipv4: Add interface option to enable routing of 127.0.0.0/8")

Signed-off-by: Shijie Luo <luoshijie1@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8bc81c57

net/ipv4/devinet.c

+5 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1287,6 +1287,7 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
	{		{
	const struct in_ifaddr *ifa;		const struct in_ifaddr *ifa;
	__be32 addr = 0;		__be32 addr = 0;
			unsigned char localnet_scope = RT_SCOPE_HOST;
	struct in_device *in_dev;		struct in_device *in_dev;
	struct net *net = dev_net(dev);		struct net *net = dev_net(dev);
	int master_idx;		int master_idx;
	@@ -1296,10 +1297,13 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
	if (!in_dev)		if (!in_dev)
	goto no_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) {		in_dev_for_each_ifa_rcu(ifa, in_dev) {
	if (ifa->ifa_flags & IFA_F_SECONDARY)		if (ifa->ifa_flags & IFA_F_SECONDARY)
	continue;		continue;
	if (ifa->ifa_scope > scope)		if (min(ifa->ifa_scope, localnet_scope) > scope)
	continue;		continue;
	if (!dst \|\| inet_ifa_match(dst, ifa)) {		if (!dst \|\| inet_ifa_match(dst, ifa)) {
	addr = ifa->ifa_local;		addr = ifa->ifa_local;

Admin message