network in NAT mode, processing packets only with the destination (ds…

…t) set to the container IP can prevent packets coming out of the QEMU virtual machine through eth0 from being incorrectly DNAT

run/network.sh

@@ -146,10 +146,13 @@ configureNAT () {
 
   ip link set dev "${VM_NET_TAP}" master dockerbridge
 
+
   # Add internet connection to the VM
+  IP=$(ip address show dev "${VM_NET_DEV}" | grep inet | awk '/inet / { print $2 }' | cut -f1 -d/)
+
   iptables -t nat -A POSTROUTING -o "${VM_NET_DEV}" -j MASQUERADE
-  iptables -t nat -A PREROUTING -i "${VM_NET_DEV}" -p tcp  -j DNAT --to $VM_NET_IP
-  iptables -t nat -A PREROUTING -i "${VM_NET_DEV}" -p udp  -j DNAT --to $VM_NET_IP
+  iptables -t nat -A PREROUTING -i "${VM_NET_DEV}" -d "${IP}" -p tcp  -j DNAT --to $VM_NET_IP
+  iptables -t nat -A PREROUTING -i "${VM_NET_DEV}" -d "${IP}" -p udp  -j DNAT --to $VM_NET_IP
 
   if (( KERNEL > 4 )); then
     # Hack for guest VMs complaining about "bad udp checksums in 5 packets"