netdev - Re: [PATCH 2/3] route: set iif and oif information in flowi struct

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Date:	Wed, 30 Nov 2011 18:21:52 +0100
From:	Ulrich Weber <ulrich.weber@...hos.com>
To:	Julian Anastasov <ja@....bg>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH 2/3] route: set iif and oif information in flowi struct

On 29.11.2011 00:53, Julian Anastasov wrote:
>
> 	May be setting flowi4_oif unconditionally here is more
> correct because ip_route_output_slow fills flowi4_oif with
> the selected oif, it can even change the provided original
> oif in flowi4_oif. What about this?:
>
> 			flp4->flowi4_oif = rth->dst.dev->ifindex;
>
> 	OTOH, rt_iif has some complex semantic: original oif
> or the selected oif. May be you prefer flowi4_oif to hold
> the selected oif, right?
I wasn't aware the ip_route_output_slow() might change the original oif.
You know why this might happen? Shouldn't fib_lookup only return
a route matching the given oif?

Anyway, if thats the case your code above is more correct. The packet
should always match the xfrm policy where it was originally routed.

> 	I see one dangerous place that must be checked:
> icmp_route_lookup. Before now __ip_route_output_key was
> called after xfrm_decode_session_reverse with 0 in
> flowi4_oif, i.e. no oif binding was used. But now when
> decode_session sets flowi4_oif we will restrict the route
> via this interface?
Thanks for the hint! Yes the current patch will force the ICMP packet
over the received interface.

Will add "fl4_dec.flowi4_oif = 0;" in case the saddr is local, so the
behavior will be the same. fl4_dec.flowi4_oif will then be set in
_ip_route_output_key() again.

Cheers
Ulrich

-- 
Ulrich Weber | ulrich.weber@...hos.com | Senior Software Engineer
Astaro - a Sophos company | Amalienbadstr 41 | 76227 Karlsruhe | Germany
Phone +49-721-25516-0 | Fax –200 | www.astaro.com

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