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Date:   Tue, 14 May 2019 09:32:32 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
Cc:     netdev@...r.kernel.org, Dan Winship <danw@...hat.com>
Subject: Re: [PATCH net v2] rtnetlink: always put ILFA_LINK for links with a
 link-netnsid

Le 13/05/2019 à 23:46, Sabrina Dubroca a écrit :
> 2019-05-13, 17:13:36 +0200, Nicolas Dichtel wrote:
>> Le 13/05/2019 à 17:08, Sabrina Dubroca a écrit :
>>> 2019-05-13, 16:50:51 +0200, Nicolas Dichtel wrote:
>>>> Le 13/05/2019 à 15:47, Sabrina Dubroca a écrit :
>>>>> Currently, nla_put_iflink() doesn't put the IFLA_LINK attribute when
>>>>> iflink == ifindex.
>>>>>
>>>>> In some cases, a device can be created in a different netns with the
>>>>> same ifindex as its parent. That device will not dump its IFLA_LINK
>>>>> attribute, which can confuse some userspace software that expects it.
>>>>> For example, if the last ifindex created in init_net and foo are both
>>>>> 8, these commands will trigger the issue:
>>>>>
>>>>>     ip link add parent type dummy                   # ifindex 9
>>>>>     ip link add link parent netns foo type macvlan  # ifindex 9 in ns foo
>>>>>
>>>>> So, in case a device puts the IFLA_LINK_NETNSID attribute in a dump,
>>>>> always put the IFLA_LINK attribute as well.
>>>>>
>>>>> Thanks to Dan Winship for analyzing the original OpenShift bug down to
>>>>> the missing netlink attribute.
>>>>>
>>>>> Analyzed-by: Dan Winship <danw@...hat.com>
>>>>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>>>> I would say:
>>>> Fixes: 5e6700b3bf98 ("sit: add support of x-netns")
>>>>
>>>> Because before this patch, there was no device with an iflink that can be put in
>>>> another netns.
>>>
>>> That tells us how far back we might want to backport this fix, but not
>>> which commit introduced the bug. I think Fixes should refer to the
>>> introduction of the faulty code, not to what patch made it visible (if
>>> we can find both).
>> No sure to follow you. The problem you describe cannot happen before commit
>> 5e6700b3bf98, so there cannot be a "faulty" patch before that commit.
> 
> What about macvlan devices?
> 
> From commit b863ceb7ddce ("[NET]: Add macvlan driver"):
> 
> static int macvlan_init(struct net_device *dev)
> {
> ...
>         dev->iflink             = lowerdev->ifindex;
> ...
> }
> 
> vlan devices also had an iflink assigned since commit ddd7bf9fe4e5.
> 
> What am I missing?
You miss the fact that netns have been introduced after both commits.

What about this one?
Fixes: d8a5ec672768 ("[NET]: netlink support for moving devices between network
namespaces.")



Regards,
Nicolas

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