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

[David Ahern]

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
                }
        }