netdev - Re: [PATCH] net: ipv6: fallback to full lookup if table lookup is unsuitable

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Date:   Fri, 16 Sep 2016 13:38:46 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Vincent Bernat <vincent@...nat.im>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: ipv6: fallback to full lookup if table lookup is
 unsuitable

On 9/16/16 1:15 PM, Vincent Bernat wrote:
>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>> index ad4a7ff301fc..48bae2ee2e18 100644
>> --- a/net/ipv6/route.c
>> +++ b/net/ipv6/route.c
>> @@ -1991,9 +1991,19 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
>>                         if (!(gwa_type & IPV6_ADDR_UNICAST))
>>                                 goto out;
>>
>> -                       if (cfg->fc_table)
>> +                       if (cfg->fc_table) {
>>                                 grt = ip6_nh_lookup_table(net, cfg, gw_addr);
>>
>> +                               /* a nexthop lookup can not go through a gw.
>> +                                * if this happens on a table based lookup
>> +                                * then fallback to a full lookup
>> +                                */
>> +                               if (grt && grt->rt6i_flags & RTF_GATEWAY) {
>> +                                       ip6_rt_put(grt);
>> +                                       grt = NULL;
>> +                               }
>> +                       }
>> +
>>                         if (!grt)
>>                                 grt = rt6_lookup(net, gw_addr, NULL,
>>                                                  cfg->fc_ifindex, 1);
> 
> OK. Should the dev check be dismissed or do we add "dev && dev !=
> grt->dst.dev" just as a safety net (this would be a convulated setup,
> but the correct direct route could be in an ip rule with higher priority
> while the one in this table is incorrect)?
> 

yes. So the validity check becomes:

	grt = ip6_nh_lookup_table(net, cfg, gw_addr);
	if (grt) {
		if (grt->rt6i_flags & RTF_GATEWAY ||
		    dev && dev != grt->dst.dev) {
			ip6_rt_put(grt);
			grt = NULL;            <---- causes the full rt6_lookup
		}
	}