Re: Issues during assigning addresses on point to point interfaces

From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Marek Behún" <kabel@kernel.org>,
	netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Alexey Kuznetsov" <kuznet@ms2.inr.ac.ru>,
	"Hideaki YOSHIFUJI" <yoshfuji@linux-ipv6.org>,
	linux-kernel@vger.kernel.org, "Andrew Lunn" <andrew@lunn.ch>,
	"Russell King" <rmk+kernel@armlinux.org.uk>,
	"Stephen Hemminger" <stephen@networkplumber.org>,
	"Phil Sutter" <phil@nwl.cc>
Subject: Re: Issues during assigning addresses on point to point interfaces
Date: Fri, 25 Jun 2021 17:06:21 +0200	[thread overview]
Message-ID: <d3dd210c-bf0f-7b48-6562-23e87c2ad55a@6wind.com> (raw)
In-Reply-To: <20210625084031.c33yovvximtabmf4@pali>

Le 25/06/2021 à 10:40, Pali Rohár a écrit :
> On Thursday 24 June 2021 14:57:41 Nicolas Dichtel wrote:
>> Le 24/06/2021 à 12:45, Marek Behún a écrit :
>>> On Sun, 6 Jun 2021 17:10:08 +0200
>>> Pali Rohár <pali@kernel.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.
> 
> Hello Nicolas!
> 
> See my original email where I put also rtnetlink packets (how strace see
> them). Seems that there is a bug in handling them (or bug in iproute2)
> as setting just peer (remote) IPv6 address is ignored:
> https://lore.kernel.org/netdev/20210606151008.7dwx5ukrlvxt4t3k@pali/
> 
> Do you have any idea if this is affected by that "issue in the uAPI"?
> And what is the way how to fix it?
What about forcing IFA_LOCAL address to :: in your case?