netdev - Re: [PATCH] ipv4: fix inet_select_addr() when enable route

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Date:   Fri, 14 Jun 2019 19:00:27 -0600
From:   David Ahern <dsahern@...il.com>
To:     luoshijie <luoshijie1@...wei.com>, davem@...emloft.net,
        tgraf@...g.ch
Cc:     netdev@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: [PATCH] ipv4: fix inet_select_addr() when enable route_localnet

On 6/14/19 10:55 AM, luoshijie wrote:
> From: Shijie Luo <luoshijie1@...wei.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.

Since you already have the commands, create a test script in
tools/testing/selftests/net that uses network namespaces for host1 and
host2 and demonstrates the problem. There quite a few examples in that
directory to use as a template. eg., see icmp_redirect.sh

> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index ea4bd8a52..325fafd4b 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1249,14 +1249,19 @@ __be32 inet_select_addr(const struct net_device *dev, __be32 dst, int scope)
>  	struct in_device *in_dev;
>  	struct net *net = dev_net(dev);
>  	int master_idx;
> +	unsigned char localnet_scope = RT_SCOPE_HOST;

net code uses reverse xmas tree ordering. ie., move that up.

>  
>  	rcu_read_lock();
>  	in_dev = __in_dev_get_rcu(dev);
>  	if (!in_dev)
>  		goto no_in_dev;
>  
> +	if (unlikely(IN_DEV_ROUTE_LOCALNET(in_dev))) {
> +		localnet_scope = RT_SCOPE_LINK;
> +	}
> +

brackets are not needed.


>  	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;
>