netdev - Re: [PATCH net] ipv6: no need to return rt->dst.error if it is not null entry.

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Date:   Wed, 26 Jul 2017 11:18:10 -0600
From:   David Ahern <dsahern@...il.com>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        network dev <netdev@...r.kernel.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net] ipv6: no need to return rt->dst.error if it is not
 null entry.

On 7/25/17 1:32 AM, Hangbin Liu wrote:
> On Mon, Jul 24, 2017 at 09:28:07PM -0600, David Ahern wrote:
>> On 7/24/17 6:08 PM, Hangbin Liu wrote:
>>> That's why I think we should remove both rt->dst.error and ip6_null_entry
>>> check in inet6_rtm_getroute(). And even further, remove the ip6_null_entry
>>> check in rt6_dump_route().
>>
>> git blame net/ipv6/route.c
>>
>> find the commits and review.
> 
> Hi David,
> 
> Sorry, would you like to give me more hints?
> 
> I saw your commit 1f17e2f2c8a8 ("net: ipv6: ignore null_entry on route
> dumps"). But I think this issue has been fixed by
> 
> 2f460933f58e ("ipv6: initialize route null entry in addrconf_init()") and
> 242d3a49a2a1 ("ipv6: reorder ip6_route_dev_notifier after ipv6_dev_notf")
> 
> I use a reproducer which add unreachable route in netns with lo down. And I
> could not trigger Panic in the fixed kernel. That's why I think we could
> remove ip6_null_entry check in rt6_dump_route().

Understood. Cong's patch to fix the intialization order (lo device
before route init) makes sure the idev is not null. That said, the
null_entry route is internal ipv6 logic and is not a route entry to be
returned to userspace.