netdev - Re: [PATCH net-next 2/6] ipv6: Remove external dependency on rt6i_gateway and RTF

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Date:	Wed, 29 Apr 2015 11:28:46 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Martin KaFai Lau <kafai@...com>
cc:	netdev <netdev@...r.kernel.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	David Miller <davem@...emloft.net>,
	Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH net-next 2/6] ipv6: Remove external dependency on
 rt6i_gateway and RTF_ANYCAST


	Hello,

On Tue, 28 Apr 2015, Martin KaFai Lau wrote:

> -static inline struct in6_addr *rt6_nexthop(struct rt6_info *rt)
> +static inline struct in6_addr *rt6_nexthop(struct rt6_info *rt,
> +					   struct in6_addr *daddr)
>  {
> -	return &rt->rt6i_gateway;
> +	return (rt->rt6i_flags & RTF_GATEWAY) ? &rt->rt6i_gateway : daddr;
>  }

	Similar change in ipv4 caused problem for places
that request route to one nexthop but later the transmitted
IP header contains different destination. Such examples
were:

- net/ipv4/raw.c when hdrincl is used
- xt_TEE.c: I see that it has IPv6 support
- IPVS: request route to real server but send packet with
daddr=virtual IP (Direct Route method)

	For IPv4 link routes, callers can get a route
with rt_gateway=0 and rt_nexthop() can return daddr from
header.

	We then solved it with FLOWI_FLAG_KNOWN_NH flag which
forces a cached route where rt_gateway is filled with requested
nexthop address:

commit c27c9322d015
commit 2ad5b9e4bd31
commit ad4d3ef8b7eb

	Can you check if this series causes the same
problem for net/ipv6/raw.c (hdrincl=1), xt_TEE.c. IPVS code is
in __ip_vs_get_out_rt_v6() where the route is resolved
and then attached to skb with skb_dst_set_noref().

Regards

--
Julian Anastasov <ja@....bg>
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