Server crash with nuker (PlotSquared and/or possibly others) [DBO 980]

[asofold]

Seems NCP can't prevent a server crash 'out of memory', having a client use a block break nuker cheat. This only happens on PlotSquared plots where the player can NOT build.

Assumed reason is that another plugin (PlotSquared?) is getting interact/blockbreak events before NCP, with the plugin using a considerable lot of resources and cancelling the event, so that NCP doesn't check anything.

Suggested hack attempt (no feedback yet):

• Add a loadbefore: [PlotSquared] entry to the plugin.yml inside of the NoCheatPlus.jar with a zip/jar editor.

Suggestion for other plugin developers (without really being able to confirm this is the issue):

• Check for the events on LOW priority for region protection and more heavy checks. Have anti cheating be on lowest, thinking of simple checks like clicking wrong block/direction and event frequency.

What could be done in NCP:

• Still run checks for cancelled events, possibly configurable. THIS MIGHT NOT HELP, the other plugin will still receive events before NCP and use up resources, only kicking could help.
• Add the loadbefore entry to NCP by default - might help with this case.
• Add a packet level check for frequency of block breaking and interacting with blocks - might need some concept which type of checks to prefer (bukkit/packet).

[BOT-Neil]

Sorry for the late reply, I was not home until now. But adding "loadbefore: [PlotSquared]" to the plugin.yml doesn't affect it.

For the meantime I have removed the messages that PlotSquared sends when they don't have permission to build/break.

That seems to prevent the crashing, but the users still aren't being affected by NCP.

[asofold]

They possibly already do that on interaction - the interaction speed thresholds by NCP allow a lot - basically because we wanted to prevent crash-by-interact-only in the first place, without interfering with gameplay there. In that case, one would lower the threshold for blockinteract.frequency - by default it allows 60 interactions within 2 seconds.

I doubt 60 or even 120 at once is enough to crash a server, if it's just about sending messages. But looking at the code it's pretty old-style, i might want to redo those (unrelated though).

[BOT-Neil]

I don't want to seem too pushy, but would you consider making NCP compatible with PlotSquared or contacting the dev for PlotSquared?

[asofold]

Just ask/complain :). I'm afraid that compatibility from side of NCP won't really be possible, because PlotSquared receives events earlier than NCP.

Have you reported the issue to PlotSquared yet?
I suggest noting:

1. The message sending (as described above) seems to create a lot of overhead and should be throttled (once per second per player max. or so).
2. Further (my advice) they shouldn't listen on lowest priority to give anti cheating plugins a chance to detect stuff properly.

The other thing was the out of memory question - is your server running shortly underneath the limit with used memory?

[asofold]

Closing as 'can't fix', has to be fixed on the other plugin side (rate limit messages, not listen on lowest priortiy), possibly memory.

Things we could do is packet limiting, but that's already done by Spigot.