netdev - Re: 5.1 `ip route get addr/cidr` regression

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Message-ID: <2e6749cb-3a7a-242a-bd60-5fa7a8e724db@gmail.com>
Date:   Fri, 17 May 2019 09:17:51 -0600
From:   David Ahern <dsahern@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        emersonbernier@...anota.com, Netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        David Miller <davem@...emloft.net>
Cc:     piraty1@...ox.ru
Subject: Re: 5.1 `ip route get addr/cidr` regression

On 5/17/19 4:22 AM, Jason A. Donenfeld wrote:
> Hi,
> 
> I'm back now and catching up with a lot of things. A few people have
> mentioned to me that wg-quick(8), a bash script that makes a bunch of
> iproute2 invocations, appears to be broken on 5.1. I've distilled the
> behavior change down to the following.
> 
> Behavior on 5.0:
> 
> + ip link add wg0 type dummy
> + ip address add 192.168.50.2/24 dev wg0
> + ip link set mtu 1420 up dev wg0
> + ip route get 192.168.50.0/24
> broadcast 192.168.50.0 dev wg0 src 192.168.50.2 uid 0
>    cache <local,brd>
> 
> Behavior on 5.1:
> 
> + ip link add wg0 type dummy
> + ip address add 192.168.50.2/24 dev wg0
> + ip link set mtu 1420 up dev wg0
> + ip route get 192.168.50.0/24
> RTNETLINK answers: Invalid argument

This is a 5.1 change.
a00302b607770 ("net: ipv4: route: perform strict checks also for doit
handlers")

Basically, the /24 is unexpected. I'll send a patch.

> 
> Upon investigating, I'm not sure that `ip route get` was ever suitable
> for getting details on a particular route. So I'll adjust the

'ip route get <prefix> fibmatch' will show the fib entry.