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

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Date:   Fri, 17 May 2019 11:40:31 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        emersonbernier@...anota.com, Netdev <netdev@...r.kernel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        David Miller <davem@...emloft.net>, piraty1@...ox.ru
Subject: Re: 5.1 `ip route get addr/cidr` regression

On 5/17/19 11:35 AM, Stephen Hemminger wrote:
> On Fri, 17 May 2019 09:17:51 -0600
> David Ahern <dsahern@...il.com> wrote:
> 
>> 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.

oh, and I think changing iproute2 to ignore the /24 and always set to 32
is better than changing the kernel to allow a prefix length that is ignored.