Re: [RFC net-next 1/2] net: allow user to set IPv6 nexthop for IPv4 route

Julian Anastasov
2015-03-26T23:13:21Z

Hello,

On Thu, 26 Mar 2015, Andy Gospodarek wrote:

> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index 66c1e4f..7de2924 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -1033,6 +1041,9 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
> if (fi->fib_nh->nh_oif &&
> nla_put_u32(skb, RTA_OIF, fi->fib_nh->nh_oif))
> goto nla_put_failure;
> + if (!ipv6_addr_any(&fi->fib_nh->nh_gw6) &&
> + nla_put(skb, RTA_GATEWAY, 16, &fi->fib_nh->nh_gw6))

RTA_GATEWAY6

> + goto nla_put_failure;
> #ifdef CONFIG_IP_ROUTE_CLASSID
> if (fi->fib_nh[0].nh_tclassid &&
> nla_put_u32(skb, RTA_FLOW, fi->fib_nh[0].nh_tclassid))
> @@ -1060,6 +1071,9 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
> if (nh->nh_gw &&
> nla_put_be32(skb, RTA_GATEWAY, nh->nh_gw))
> goto nla_put_failure;
> + if (!ipv6_addr_any(&nh->nh_gw6) &&
> + nla_put(skb, RTA_GATEWAY, 16, &nh->nh_gw6))

RTA_GATEWAY6

> @@ -193,10 +196,27 @@ static inline int ip_finish_output2(struct sk_buff *skb)
> }
>
> rcu_read_lock_bh();
> - nexthop = (__force u32) rt_nexthop(rt, ip_hdr(skb)->daddr);
> - neigh = __ipv4_neigh_lookup_noref(dev, nexthop);
> - if (unlikely(!neigh))
> - neigh = __neigh_create(&arp_tbl, &nexthop, dev, false);
> +
> +#if IS_ENABLED(CONFIG_IPV6)
> + /* If there is an ipv6 gateway specified, use it */
> + if (!rt->rt_gateway && !ipv6_addr_any(&rt->rt_gateway6)) {

DST_NOCACHE routes can fill rt_gateway even when
nh_gw=0 (rt_set_nexthop), so above check can be:

if (rt->rt_uses_gateway && !ipv6_addr_any(&rt->rt_gateway6)) {

Not sure, some places may prefer to see rt_uses_gateway=1
for v4 and rt_uses_gateway=2 for v6 nexthop. Then above check
can be just 'if (rt->rt_uses_gateway == 2) {'.

> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index be8703d..c654b41 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1400,6 +1400,10 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
> rt->rt_gateway = nh->nh_gw;
> rt->rt_uses_gateway = 1;
> }
> + if (!ipv6_addr_any(&nh->nh_gw6)) {
> + memcpy(&rt->rt_gateway6, &nh->nh_gw6, sizeof(struct in6_addr));
> + rt->rt_uses_gateway = 1;
> + }
> dst_init_metrics(&rt->dst, fi->fib_metrics, true);
> #ifdef CONFIG_IP_ROUTE_CLASSID
> rt->dst.tclassid = nh->nh_tclassid;
> @@ -1417,6 +1421,10 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
> rt->dst.flags |= DST_NOCACHE;
> if (!rt->rt_gateway)
> rt->rt_gateway = daddr;
> + if (ipv6_addr_any(&rt->rt_gateway6)) {
> + memcpy(&rt->rt_gateway6, &nh->nh_gw6, sizeof(struct in6_addr));
> + rt->rt_uses_gateway = 1;
> + }

Above hunk is not needed, rt_gateway6 is set above.

> rt_add_uncached_list(rt);
> }
> } else
> @@ -1488,6 +1496,7 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
> rth->rt_pmtu = 0;
> rth->rt_gateway = 0;
> rth->rt_uses_gateway = 0;
> + memset(&rth->rt_gateway6, 0, sizeof(struct in6_addr));

We can remove such initializations if
rt_uses_gateway=2 is used as v6 indication, for example:

rt_uses_gateway rt_gateway nh_gw nh_gw6 DST_NOCACHE What
===============================================================================
0 0 0/LOCAL N N Non-gatewayed, cached
0 DADDR 0/LOCAL N Y Non-gatewayed, not cached
2 0 0 GW6 N Gatewayed, cached
2 DADDR 0 GW6 Y Gatewayed, not cached
1 GW GW N Y/N Gatewayed

May be more places need to be changed:

- fib_check_nh: validate v6 address type, set nh_dev,
allow only nh->nh_scope == RT_SCOPE_LINK (I assume
we do not plan to use local v6 address in nh_gw6).
- nh_comp: needs nh_gw6 comparison
- fib_create_info: more checks are needed around
'if (cfg->fc_scope == RT_SCOPE_HOST) {' check

There are other places that use rt_uses_gateway
and rt_gateway.

Regards

--
Julian Anastasov <ja@ssi.bg>