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Defeating a Ninja

I was recently asked if I had ever used Ninja on any of my machines. I had not even heard of such a thing. I found that it was available in the Lucid repository, so I installed it and configured it for my system. The two changes I made were to have it constantly poll, instead of waiting 1 second between polls; and to kill the offending tasks, instead of merely warning about them. I whipped up a little back door application that gets root. I ran it and sure enough, it was instantly killed by the Ninja. But how instantly? There is a race there to be sure. I had my w00t process run 'killall -9 ninja' instead of giving me a root shell. Sure enough, my hack was faster than the Ninja. It must only be a wannabe or maybe a Ninja Apprentice. Whatever it is, I defeated the Ninja in less than ten minutes. Without even breaking a sweat.

Ninja may be good in concept, but poor in execution (I'm so punny!!!) The race window that exists is wide enough to easily defeat it. What it needs to do is something along these lines:

1) Run the critical section in the kernel as a kprobe parked on the fork, exec, setuid, setgid syscalls.
2) On each watched syscall, check for escalation and pause execution while we pop out to userspace (probably via the kprobe print functions) and do a bit of testing.
3) If we pass muster, let the task go, otherwise kill it.

This way, we can pause the questionable tasks in the kernel before they get a chance to do anything malicious.

Right now, all Ninja does is make you think you are safe, while really, it does very little for you.