linux-kernel - Re: [PATCH net v3] net: ipv6: Fix a bug in ndisc_send

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Date:   Wed, 31 Jul 2019 15:42:01 -0600
From:   David Ahern <dsahern@...il.com>
To:     Su Yanjun <suyj.fnst@...fujitsu.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3] net: ipv6: Fix a bug in ndisc_send_ns when netdev
 only has a global address

On 7/30/19 7:52 PM, Su Yanjun wrote:
> When the egress interface does not have a link local address, it can
> not communicate with other hosts.
> 
> In RFC4861, 7.2.2 says
> "If the source address of the packet prompting the solicitation is the
> same as one of the addresses assigned to the outgoing interface, that
> address SHOULD be placed in the IP Source Address of the outgoing
> solicitation.  Otherwise, any one of the addresses assigned to the
> interface should be used."
> 
> In this patch we try get a global address if we get ll address failed.
> 
> Signed-off-by: Su Yanjun <suyj.fnst@...fujitsu.com>
> ---
> Changes since V2:
> 	- Let banned_flags under the scope of its use.
> ---
>  include/net/addrconf.h |  2 ++
>  net/ipv6/addrconf.c    | 34 ++++++++++++++++++++++++++++++++++
>  net/ipv6/ndisc.c       | 10 +++++++---
>  3 files changed, 43 insertions(+), 3 deletions(-)
> 


This change looks fine to me given the RFC reference, so for that part:
Reviewed-by: David Ahern <dsahern@...il.com>

Bigger picture is the issue Mark raised that a different RFC says all
links should have an LLA, so use of IN6_ADDR_GEN_MODE_NONE means
userspace is expected to create and add the LLA. Lack of an LLA is a
misconfigured system. If that is enforced via some to be developed
patch, then this patch would not be needed.