netdev - Re: Issues during assigning addresses on point to point interfaces

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Message-ID: <d3995a21-d9fe-9393-a10e-8eddccec2f47@6wind.com>
Date:   Thu, 24 Jun 2021 14:57:41 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Marek Behún <kabel@...nel.org>,
        Pali Rohár <pali@...nel.org>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        linux-kernel@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Phil Sutter <phil@....cc>
Subject: Re: Issues during assigning addresses on point to point interfaces

Le 24/06/2021 à 12:45, Marek Behún a écrit :
> On Sun, 6 Jun 2021 17:10:08 +0200
> Pali Rohár <pali@...nel.org> wrote:
> 
>> Hello!
>>
>> Seems that there is a bug during assigning IP addresses on point to
>> point interfaces.
>>
>> Assigning just one local address works fine:
>>
>>     ip address add fe80::6 dev ppp1 --> inet6 fe80::6/128 scope link
>>
>> Assigning both local and remote peer address also works fine:
>>
>>     ip address add fe80::7 peer fe80::8 dev ppp1 ---> inet6 fe80::7
>> peer fe80::8/128 scope link
>>
>> But trying to assign just remote peer address does not work. Moreover
>> "ip address" call does not fail, it returns zero but instead of
>> setting remote peer address, it sets local address:
>>
>>     ip address add peer fe80::5 dev ppp1 --> inet6 fe80::5/128 scope
>> link
>>
> 
> Adding some other people to Cc in order to get their opinions.
> 
> It seems this bug is there from the beginning, from commit
> caeaba79009c2 ("ipv6: add support of peer address")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=caeaba79009c2
> 
> Maybe some older user-space utilities use IFA_ADDRESS instead of
> IFA_LOCAL, and this was done in order to be compatible with them?
If I remember well, there was an issue in the uAPI.
IFA_LOCAL is supposed to be the address of the interface and IFA_ADDRESS is
supposed to be the endpoint of a point-to-point interface.
However, in case of IPv6, it was not the case. In netlink messages generated by
the kernel, IFA_ADDRESS was used instead of IFA_LOCAL.
The patch tried to keep the backward compatibility and the symmetry between msg
from userland and notification from the kernel.


Regards,
Nicolas