[PATCH] ipt_REDIRECT: only change dest-ip if not local ip

[Bas van Sisseren <bas@quarantainenet.nl>]

Hello,

When redirecting, the destination address is replaced by the first
ip-address on the receiving interface.

If the packet originally was sent to the second ip-address (or third,
fourth, etc..), this patch doesn't change the destination ip.

============
--- linux.orig/net/ipv4/netfilter/ipt_REDIRECT.c
+++ linux/net/ipv4/netfilter/ipt_REDIRECT.c
@@ -78,7 +78,21 @@
        rcu_read_lock();
        indev = __in_dev_get_rcu((*pskb)->dev);
        if (indev && (ifa = indev->ifa_list))
+       {
+           struct in_ifaddr *ifa_cur; // interface ip-list cursor
+
+           // set current destination ip
+           newdst = ((struct iphdr*)skb_network_header(*pskb))->daddr;
+
+           // iterate through interface ip list
+           for (ifa_cur = ifa; ifa_cur; ifa_cur = ifa_cur->ifa_next)
+               if (newdst == ifa_cur->ifa_local)
+                   goto newdst_is_local;
+
+           // set new destination to first ip of this interface
            newdst = ifa->ifa_local;
+       }
+   newdst_is_local:
        rcu_read_unlock();

        if (!newdst)
============

Kind regards,

Bas van Sisseren

-- 
Bas van Sisseren <bas@quarantainenet.nl>
Quarantainenet