Crashing the Web UI in OpenWRT

The web user interface in OpenWRT is a reasonably good tool for configuring and managing OpenWRT devices. However it is possible to crash it with fairly innocuous behaviour.

If you're doing a large volume of changes to firewall rules via the web UI, it is tempting to use the Save option rather than Save & Apply, as it saves you a little time and spares service disconnections as the rules are reloaded.

In the top-right-hand corner you will see in red the number of unsaved changes that have been made and require Save & Apply to be pressed to commit persistently. If you store too many changes via Save, somewhere >50, before pressing Save & Apply you can crash the web UI.

You'll start to receive partial page loads or complete failures to load. You'll still be able to ssh in and poke around. If you do, top will tell you everything is fine and restarting uhttpd will not correct the problem.

I was pressed for time and the only way to resolve this I've found thus far is to reboot the device. Everything came good, except for the changes you've accumulated since the last Save & Apply.

The lesson here is to not rely on Save. When you're happy with how a ruleset works, press Save & Apply early and often.