netdev - Re: [Patch net v3] ipv6: check for ip6_null_entry in __ip6_del_rt

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Message-ID: <20170302004215.3ohf6smlrxodd3mn@kafai-mba.local>
Date:   Wed, 1 Mar 2017 16:42:15 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     David Ahern <dsa@...ulusnetworks.com>
CC:     Cong Wang <xiyou.wangcong@...il.com>, <netdev@...r.kernel.org>,
        <andreyknvl@...gle.com>, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [Patch net v3] ipv6: check for ip6_null_entry in
 __ip6_del_rt_siblings()

On Wed, Mar 01, 2017 at 04:07:38PM -0800, David Ahern wrote:
> On 3/1/17 3:16 PM, Martin KaFai Lau wrote:
> > [ An unrelated topic.  I wonder ip -6 r del xyz::/0 would delete
> >   the gateway route...]
>
> a very related question ...
>
> ip -6 r del x::/0 comes down to the kernel as delete '::/0' (plen is 0,
> so cfg->fc_dst is 0). It ends up on the null_entry from fib6_locate b/c
> of the 0 prefix length, so it is another variant of 'ip -6 ro del ::/0'
Agree on the plen == 0 part.

I actually meant if 'ip -6 r del xyz::/0' would delete any _default_
_gateway_ also.  By looking at ip6_route_del() alone, it seems it only
checks ipv6_addr_equal(&cfg->fc_gateway, &rt->rt6i_gateway) if
(cfg->fc_flags & RTF_GATEWAY) is true.  Your test case makes
me think about this possibility but it is not related
to what this patch is trying to fix.  I should have started
another thread for this :p