[NETFILTER]: Fix DHCP + MASQUERADE problem

In 2.6.13-rcX the MASQUERADE target was changed not to exclude local
packets for better source address consistency. This breaks DHCP clients
using UDP sockets when the DHCP requests are caught by a MASQUERADE rule
because the MASQUERADE target drops packets when no address is configured
on the outgoing interface. This patch makes it ignore packets with a
source address of 0.

Thanks to Rusty for this suggestion.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/ipv4/netfilter/ipt_MASQUERADE.c b/net/ipv4/netfilter/ipt_MASQUERADE.c
index 2f3e181c8e97..275a174c6fe6 100644
--- a/net/ipv4/netfilter/ipt_MASQUERADE.c
+++ b/net/ipv4/netfilter/ipt_MASQUERADE.c
@@ -90,6 +90,12 @@ masquerade_target(struct sk_buff **pskb,
         IP_NF_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
                             || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
 
+        /* Source address is 0.0.0.0 - locally generated packet that is
+         * probably not supposed to be masqueraded.
+         */
+        if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip == 0)
+                return NF_ACCEPT;
+
         mr = targinfo;
         rt = (struct rtable *)(*pskb)->dst;
         newsrc = inet_select_addr(out, rt->rt_gateway, RT_SCOPE_UNIVERSE);