RE: Re-routing packets via netfilter (ip_rt_bug)

["Yair Itzhaki" <Yair@arx.com>]

Can anyone propose a patch that I can start checking?

I have come up with the following:

--- net/core/netfilter.c.orig   2005-04-18 21:55:30.000000000 +0300
+++ net/core/netfilter.c        2005-05-02 17:35:20.000000000 +0300
@@ -622,9 +622,10 @@
        /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
         * packets with foreign saddr to appear on the NF_IP_LOCAL_OUT hook.
         */
-       if (inet_addr_type(iph->saddr) == RTN_LOCAL) {
+       if ((inet_addr_type(iph->saddr) == RTN_LOCAL) ||
+           (inet_addr_type(iph->daddr) == RTN_LOCAL)) {
                fl.nl_u.ip4_u.daddr = iph->daddr;
-               fl.nl_u.ip4_u.saddr = iph->saddr;
+               fl.nl_u.ip4_u.saddr = 0;
                fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
                fl.oif = (*pskb)->sk ? (*pskb)->sk->sk_bound_dev_if : 0;
 #ifdef CONFIG_IP_ROUTE_FWMARK

Please advise,
Yair


> -----Original Message-----
> From: Patrick McHardy [mailto:kaber@trash.net]
> Sent: Wednesday, April 27, 2005 14:05
> To: Herbert Xu
> Cc: Jozsef Kadlecsik; netdev@oss.sgi.com; 
> netfilter-devel@lists.netfilter.org; Yair Itzhaki; 
> linux-kernel@vger.kernel.org
> Subject: Re: Re-routing packets via netfilter (ip_rt_bug)
> 
> 
> Herbert Xu wrote:
> > Here is another reason why these packets should go through FORWARD.
> > They were generated in response to packets in INPUT/FORWARD/OUTPUT.
> > The original packet has not undergone SNAT in any of these cases.
> > 
> > However, if we feed the response packet through LOCAL_OUT it will
> > be subject to DNAT.  This creates a NAT asymmetry and we may end
> > up with the wrong destination address.
> > 
> > By pushing it through FORWARD it will only undergo SNAT which is
> > correct since the original packet would have undergone DNAT.
> 
> This is only a problem since the recent NAT changes, but I agree
> that we should fix it by moving these packets to FORWARD.
> 
> Regards
> Patrick
>