From: Shijie Luo <luoshij...@huawei.com>
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 <luoshij...@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqian...@huawei.com>
---
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 c6bd0f7a020a..08c6c7c41749 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1254,6 +1254,7 @@ static __be32 in_dev_select_addr(const struct in_device
*in_dev,
__be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
{
__be32 addr = 0;
+ unsigned char localnet_scope = RT_SCOPE_HOST;
struct in_device *in_dev;
struct net *net = dev_net(dev);
int master_idx;
@@ -1263,8 +1264,11 @@ __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;
+
for_primary_ifa(in_dev) {
- 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;
--
2.19.1
