Update build.func

validate IPv4 CIDR address

misc/build.func

@@ -247,16 +247,25 @@ advanced_settings() {
     exit-script
   fi
 
-  if NET=$(whiptail --inputbox "Set a Static IPv4 CIDR Address(/24)" 8 58 dhcp --title "IP ADDRESS" 3>&1 1>&2 2>&3); then
+  while true; do
-    if [ -z $NET ]; then
+    NET=$(whiptail --inputbox "Set a Static IPv4 CIDR Address (/24)" 8 58 dhcp --title "IP ADDRESS" 3>&1 1>&2 2>&3)
-      NET="dhcp"
+    exit_status=$?
+    if [ $exit_status -eq 0 ]; then
+      if [ "$NET" = "dhcp" ]; then
         echo -e "${DGN}Using IP Address: ${BGN}$NET${CL}"
+        break
       else
+        if [[ "$NET" =~ ^([0-9]{1,3}\.){3}[0-9]{1,3}/([0-9]|[1-2][0-9]|3[0-2])$ ]]; then
           echo -e "${DGN}Using IP Address: ${BGN}$NET${CL}"
+          break
+        else
+          whiptail --msgbox "$NET is an invalid IPv4 CIDR address. Please enter a valid IPv4 CIDR address or 'dhcp'" 8 58
+        fi
       fi
     else
       exit-script
     fi
+  done
 
   if GATE1=$(whiptail --inputbox "Set a Gateway IP (mandatory if Static IP was used)" 8 58 --title "GATEWAY IP" 3>&1 1>&2 2>&3); then
     if [ -z $GATE1 ]; then