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

[Vincent Bernat]

 ❦ 19 septembre 2016 06:58 CEST, David Miller  :

>> @@ -1808,6 +1808,30 @@ static struct rt6_info *ip6_nh_lookup_table(struct 
>> net *net,
>>  return rt;
>>  }
>>  
>> +static int ip6_nh_valid(struct rt6_info *grt,
>> +struct net_device **dev, struct inet6_dev **idev) {
>> +int ret = 0;
>
> First, this is not formatted properly.  The openning brace should start
> on a new line.
>
> Second, please use "bool", "true", and "false" for the return value.

Noted for the next time. However, the v3 version of the patch doesn't
have the function anymore.
-- 
Avoid temporary variables.
- The Elements of Programming Style (Kernighan & Plauger)

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

[David Miller]

From: Vincent Bernat 
Date: Fri, 16 Sep 2016 14:55:31 +0200

> @@ -1808,6 +1808,30 @@ static struct rt6_info *ip6_nh_lookup_table(struct net 
> *net,
>   return rt;
>  }
>  
> +static int ip6_nh_valid(struct rt6_info *grt,
> + struct net_device **dev, struct inet6_dev **idev) {
> + int ret = 0;

First, this is not formatted properly.  The openning brace should start
on a new line.

Second, please use "bool", "true", and "false" for the return value.

Thanks.

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
}
}

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

[Vincent Bernat]

 ❦ 16 septembre 2016 20:36 CEST, David Ahern  :

>> contained a non-connected route (like a default gateway) fails while it
>> was previously working:
>> 
>> $ ip link add eth0 type dummy
>> $ ip link set up dev eth0
>> $ ip addr add 2001:db8::1/64 dev eth0
>> $ ip route add ::/0 via 2001:db8::5 dev eth0 table 20
>> $ ip route add 2001:db8:cafe::1/128 via 2001:db8::6 dev eth0 table 20
>> RTNETLINK answers: No route to host
>> $ ip -6 route show table 20
>> default via 2001:db8::5 dev eth0  metric 1024  pref medium
>
> so your table 20 is not complete in that it lacks a connected route to
> resolve 2001:db8::6 as a nexthop, so you are relying on a fallback to
> other tables (main in this case).

Yes.

>> @@ -1991,33 +2015,15 @@ static struct rt6_info *ip6_route_info_create(struct 
>> fib6_config *cfg)
>>  if (!(gwa_type & IPV6_ADDR_UNICAST))
>>  goto out;
>>  
>> +err = -EHOSTUNREACH;
>>  if (cfg->fc_table)
>>  grt = ip6_nh_lookup_table(net, cfg, gw_addr);
>
> -8<-
>
>> -if (!(grt->rt6i_flags & RTF_GATEWAY))
>> -err = 0;
>
> This is the check that is failing for your use
> case. ip6_nh_lookup_table is returning the default route and nexthops
> can not rely on a gateway. Given that a simpler and more direct change
> is (whitespace mangled on paste):
>
> 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)?
-- 
"... an experienced, industrious, ambitious, and often quite often
picturesque liar."
-- Mark Twain

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

[David Ahern]

On 9/16/16 6:55 AM, Vincent Bernat wrote:
> Commit 8c14586fc320 ("net: ipv6: Use passed in table for nexthop
> lookups") introduced a regression: insertion of an IPv6 route in a table
> not containing the appropriate connected route for the gateway but which
> contained a non-connected route (like a default gateway) fails while it
> was previously working:
> 
> $ ip link add eth0 type dummy
> $ ip link set up dev eth0
> $ ip addr add 2001:db8::1/64 dev eth0
> $ ip route add ::/0 via 2001:db8::5 dev eth0 table 20
> $ ip route add 2001:db8:cafe::1/128 via 2001:db8::6 dev eth0 table 20
> RTNETLINK answers: No route to host
> $ ip -6 route show table 20
> default via 2001:db8::5 dev eth0  metric 1024  pref medium

so your table 20 is not complete in that it lacks a connected route to resolve 
2001:db8::6 as a nexthop, so you are relying on a fallback to other tables 
(main in this case).

-8<-

> @@ -1991,33 +2015,15 @@ static struct rt6_info *ip6_route_info_create(struct 
> fib6_config *cfg)
>   if (!(gwa_type & IPV6_ADDR_UNICAST))
>   goto out;
>  
> + err = -EHOSTUNREACH;
>   if (cfg->fc_table)
>   grt = ip6_nh_lookup_table(net, cfg, gw_addr);

-8<-

> - if (!(grt->rt6i_flags & RTF_GATEWAY))
> - err = 0;

This is the check that is failing for your use case. ip6_nh_lookup_table is 
returning the default route and nexthops can not rely on a gateway. Given that 
a simpler and more direct change is (whitespace mangled on paste):

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);