netdev - Re: [PATCH net] ipv6: addrconf: fix Juniper SSL VPN client regression

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Date:	Mon, 11 Jul 2016 09:17:19 -0400
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	netdev@...r.kernel.org, Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Jonas Lippuner <jonas@...puner.ca>,
	吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
Subject: Re: [PATCH net] ipv6: addrconf: fix Juniper SSL VPN client regression

On 09.07.2016 19:23, Bjørn Mork wrote:
> Hannes Frederic Sowa <hannes@...essinduktion.org> writes:
>> On Sat, Jul 9, 2016, at 23:13, Bjørn Mork wrote:
>>> The Juniper SSL VPN client use a "tun" interface and seems to
>>> be picky about visible changes.to it. Commit cc9da6cc4f56
>>> ("ipv6: addrconf: use stable address generator for ARPHRD_NONE")
>>> made such interfaces get an auto-generated IPv6 link local address
>>> by default, similar to most other interface types. This made the
>>> Juniper SSL VPN client fail for unknown reasons.
>>>
>>> Fixing this regression by effectively reverting the behaviour to
>>> what we had before, while keeping the new "addrgenmode random"
>>> feature.
>>
>> I wonder if we can simply add a flag, something like
>> IFF_SUPPRESS_AUTO_IPV6_LL, to net_device->priv_flags and use that. So we
>> can keep behavior for qmi, vxlan-gpe and gre. tun is the only device
>> that is really user space facing, so maybe we just limit it to this?
> 
> Sounds good to me, but I don't know if the use case really qualifies as
> 
>  "* You should have a pretty good reason to be extending these flags."
> 
> 
> The automatic address is certainly nice to have, but "good reason"?  I
> don't know...  We can always just configure those devices for automatic
> LL addresses using "ip link set foo addrgen random" or similar.

I do think it is important enough to include it into priv_flags,
especially if you compare it to other flags in there. We also can easily
add new priv_flags member or enlarge to long if we run out in the long term.

I would slightly prefer if tunnels keep the behavior we introduced one
release(?) ago.

Thanks,
Hannes