Logic for SNAT persistent handling introduced in 2.6.30 is inverted

Logic for SNAT persistent handling introduced in 2.6.30 is inverted

[Maximilian Engelhardt]

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Kernel 2.6.30 introduced a patch [1] for the persistent option in the 
netfilter SNAT target. This is exactly what we need here so I had a quick look 
at the code and noticed that the patch is wrong. The logic is simply inverted.
The patch below fixes this.
Also note that because of this the default behavior of the SNAT target has 
changed since kernel 2.6.30 as it now ignores the destination IP in choosing 
the source IP for nating (which should only be the case if the persistent 
option is set).

--- net/ipv4/netfilter/nf_nat_core.c.orig       2009-08-24 14:44:00.000000000 
+0200
+++ net/ipv4/netfilter/nf_nat_core.c    2009-08-24 14:44:43.000000000 +0200
@@ -212,7 +212,7 @@ find_best_ips_proto(struct nf_conntrack_
        maxip = ntohl(range->max_ip);
        j = jhash_2words((__force u32)tuple->src.u3.ip,
                         range->flags & IP_NAT_RANGE_PERSISTENT ?
-                               (__force u32)tuple->dst.u3.ip : 0, 0);
+                               0 : (__force u32)tuple->dst.u3.ip, 0);
        j = ((u64)j * (maxip - minip + 1)) >> 32;
        *var_ipp = htonl(minip + j);
 }

Signed-off-by: Maximilian Engelhardt <maxi@daemonizer.de>


Greetings,
Maximilian Engelhardt

[1] 
http://git.eu.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=98d500d66cb7940747b424b245fc6a51ecfbf005


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Re: Logic for SNAT persistent handling introduced in 2.6.30 is inverted

[Patrick McHardy]

Maximilian Engelhardt wrote:
> Kernel 2.6.30 introduced a patch [1] for the persistent option in the 
> netfilter SNAT target. This is exactly what we need here so I had a quick look 
> at the code and noticed that the patch is wrong. The logic is simply inverted.
> The patch below fixes this.

Good catch, applied. I'm wondering what the people who requested and
tested this change did actually test :)

> Also note that because of this the default behavior of the SNAT target has 
> changed since kernel 2.6.30 as it now ignores the destination IP in choosing 
> the source IP for nating (which should only be the case if the persistent 
> option is set).

It fortunately only affects NAT to a range of IPs, which isn't
used that much.