netdev - Re: icmp_route_lookup returns wrong source address information

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Message-Id: <20110722.005904.2234780049605106051.davem@davemloft.net>
Date:	Fri, 22 Jul 2011 00:59:04 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	fw@...len.de
Cc:	netdev@...r.kernel.org
Subject: Re: icmp_route_lookup returns wrong source address information

From: Florian Westphal <fw@...len.de>
Date: Wed, 20 Jul 2011 21:22:58 +0200

> With linux-2.6 and net-next trees, whenever an icmp error message is
> sent in response to a to-be-forwarded packet, the destination address
> of the original packet is used as the IP header source address.
> 
> Example:
> $ traceroute breakpoint.cc
> traceroute to breakpoint.cc (85.10.199.196), 30 hops max, 40 byte packets
>  1  chamillionaire.breakpoint.cc (85.10.199.196)  0.476 ms  0.468 ms  0.793 ms
> 
> But the expected 1st hop is 192.168.20.7 in my setup.
> 
> I bisected this down to 77968b78242ee25e2a4d759f0fca8dd52df6d479
> ("ipv4: Pass flow keys down into datagram packet building engine.")
> 
> Specifically, it is caused by this hunk:
 ...
> Problem is that xfrm_decode_session_reverse() may rebuild fl4 from scratch.
> 
> In my setup, "goto relookup_failed" will be hit a bit later on, and fl4->saddr will
> be set to iph->daddr...

Thanks for the detailed report Florian, I'll look into this.
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