Clients Crashing Server...

[bubbajames]

Recently we've been plagued with random clients logging on which causes server to lockup -- CPU is max on one CPU and everyone's connection gets dropped. When started with Oracle JDK, I could attach using jstack and saw all threads in BLOCKED state.

Resetting the world/player data does not help! Enabling White-List works which prevents the 'general public' from connecting, but we'd prefer to not enable white-list permanently.

Using OpenJDK 7 vs Oracle JDK 7 makes no difference.

I suspect some clients are sending malicious packets causing a buffer overflow or corrupting memory.

What, if anything, can we do to protect against such issues?

 

[DZCreeper]

Let people on, until the server starts having these issues. All the people that were on, and/or the person that joined last then need to be filtered to find who did it.

Also, MineCraft is single threaded, make sure your server is not simply having problems with too many people at 1 time. Same goes for memory usage, if it maxes out, assign more.

Edit: Not sure if this will help: http://forum.feed-the-beast.com/threads/mytown-aperf-server-protection-and-performance-mods.8054/

Look at "aPerf". Here is a little snip.

• Packet limiting - for those who have to play on a 3g mobile internet and still want to build advanced stuff. Disable duplicate packet sending or just send every 5th redpower pipe content update packet. Customizable filters, saved per user. Can turn on/off ingame. (needs currently nallar's ThreadTicking to set the needed hooks in minecrafts tcpconnection class)
• Packet sniffer - Check what packets are sent to a specific player (or yourself) and on what amout (speed) to find the spam you may not need (like rp's tube item updates or extrabees unknown spam). (depends on packet limiter)

I am thinking this could help with seeing what the server is sending to each player, help rule out troublesome people. Also, it says you can do packet limiting per player, so if you find the server sending weird packets back to player, start limiting those packets for that player, if it solves the problem, that person gets the HAMMER!