netdev - Re: [PATCH] net: ipv6: don't generate link-local address in any addr_gen

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Date:   Tue, 6 Jul 2021 20:37:02 +0800
From:   Rocco Yue <rocco.yue@...iatek.com>
To:     David Ahern <dsahern@...il.com>
CC:     "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        <rocco.yue@...il.com>, <chao.song@...iatek.com>,
        <kuohong.wang@...iatek.com>, <zhuoliang.zhang@...iatek.com>,
        Rocco Yue <rocco.yue@...iatek.com>
Subject: Re: [PATCH] net: ipv6: don't generate link-local address in any addr_gen_mode

On Mon, 2021-07-05 at 10:35 -0600, David Ahern wrote:
> On 7/1/21 2:51 AM, Rocco Yue wrote:
>> On Wed, 2021-06-30 at 22:41 -0600, David Ahern wrote:
>> 
>> For mobile operators that don't need to support RFC7217, setting
>> addr_gen_mode == 1 is sufficient;
>> 
>> But for some other mobile operators that need to support RFC7217, such as AT&T,
>> the mobile device's addr_gen_mode will be switched to the
>> IN6_ADDR_GEN_MODE_STABLE_PRIVACY, instead of using IN6_ADDR_GEN_MODE_NONE.
>> The purpose is: in the IN6_ADDR_GEN_MODE_STABLE_PRIVACY mode, kernel can
>> gererate a stable privacy global ipv6 address after receiveing RA, and
>> network processes can use this global address to communicate with the
>> outside network.
>> 
>> Of course, mobile operators that need to support RFC7217 should also meet
>> the requirement of 3GPP TS 29.061, that is, MT should use IID assigned by
>> the GGSN to build its ipv6 link-local address and use this address to send RS.
>> We don't want the kernel to automatically generate an ipv6 link-local address
>> when addr_gen_mode == 2. Otherwise, using the stable privacy ipv6 link-local
>> address automatically generated by the kernel to send RS message, GGSN will
>> not be able to respond to the RS and reply a RA message.
>> 
>> Therefore, after this patch, kernel will not generate ipv6 link-local address
>> for the corresponding device when addr_gen_mode == 1 or addr_gen_mode == 2.
>> 
> 
> I think another addr_gen_mode is better than a separate sysctl. It looks
> like IN6_ADDR_GEN_MODE_STABLE_PRIVACY and IN6_ADDR_GEN_MODE_RANDOM are
> the ones used for RAs, so add something like:
> 
> IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
> IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,
> 
> to in6_addr_gen_mode.
> 

Hi David,

Thanks for your reply.

According to your suggestion, I checked the ipv6 code again. In my
opinion, adding another addr_gen_mode may not be suitable.

(1)
In the user space, the process enable the ipv6 stable privacy mode by
setting the "/proc/sys/net/ipv6/conf/<iface>/stable_secret".

In the kernel, the addr_gen_mode of a networking device is switched to
IN6_ADDR_GEN_MODE_STABLE_PRIVACY by judging the bool value of
"cnf.stable_secret.initialized".

So, although adding an additional IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
user space process has some trouble to let kernel switch the iface's
addr_gen_mode to the IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA.

This is not as flexible as adding a separate sysctl.

(2)
After adding "proc/sys/net/ipv6/<iface>/disable_gen_linklocal_addr",
so that kernel can keep the original code logic of the stable_secret
proc file, and expand when the subsequent kernel adds a new add_gen_mode
more flexibility and applicability.

And we only need to care about the networking device that do not
generate an ipv6 link-local address, and not the addr_gen_mode that
this device is using.

Maybe adding a separate sysctl is a better choice.
Looking forward to your professional reply again.

Thanks,
Rocco