Re: [PATCH net 0/3] ipv6: use rt6i_gateway as nexthop

To: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH net 0/3] ipv6: use rt6i_gateway as nexthop
Cc: David Miller <davem@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
From: Julian Anastasov <ja@xxxxxx>
Date: Mon, 21 Oct 2013 23:02:57 +0300 (EEST)

On Mon, 21 Oct 2013, Hannes Frederic Sowa wrote:

> Not related to the patch:
> That reminds me that Yoshifuji had the idea to cache the results for
> ipv6_addr_type in IP6CB to avoid calling this function over and over again.
> Maybe we can do the same for rt6_infos to save some cycles here and there.

        Yes, ipv6_addr_type has little price. May be only
DNAT and IPSec can complicate such caching.

> Also, what do you think about this site:
> net/ipv6/ip6_output.c:
>     411 
>     412                 rt = (struct rt6_info *) dst;
>     413                 if (rt->rt6i_flags & RTF_GATEWAY)
>     414                         target = &rt->rt6i_gateway;
>     415                 else
>     416                         target = &hdr->daddr;
>     417 
> Our provided skb_dst should come from ip6_route_input, thus ip6_pol_route. So
> I assume we have rt6i_gateway == hdr->daddr there, too. It is a bit more
> complicated because of possible routing extension headers. Maybe you already
> looked at this already?

        Yes, I checked every site that uses rt6i_gateway but
not with the perspective to use rt6_nexthop(). It seems
this is a rt6_nexthop() candidate.

> I just found it while searching which other code paths do emit packets
> while xt_TEE is processing (generation of redirects) and could also lead
> to stack exhaustion. But the path in ip6_forward seems fine.

        Yes. I found only one place more dangerous:
fib6_add_rt2node(). But I think its checks are still valid.


Julian Anastasov <ja@xxxxxx>
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