How to hook into (hijack) linux kernel functions via LKM

It’s about time I post a detailed explanation about how my tpe-lkm module is able to enforce its security policy. This post is very technical, readers beware. Note that this writeup is based on the code as it was the latest commit, which was of this writing, was the one on Dec 10th, 2011. I’ll keep all the links relative to that date.

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Monitor time drift with nagios and snmp

The other day I threw together a check_snmp_time.pl script that simply checks the remote’s time against the monitor host’s time. It’s fairly straight forward, and will alert you when host’s time drift too much, indicating that your ntpd configuration is bad. I had to do some custimizations to it, because not all hosts have the HOST-RESOURCES-MIB::hrSystemDate.0 option. For hosts that don’t it falls-back to the UCD-SNMP-MIB::versionCDate.0 option.

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An agent, auditor, and bodyguard walk into a bar…

This evening I wasted a bunch of time on what turned out to be a simple problem. I really hate it when that happens.

I fixed a bug in tpe-lkm where users weren’t seeing all of their processes, and updated my servers with the new module. Suddenly, my phone starts buzzing off the desk; nagios was complaining that some daemons were down. This data is retrieved via snmp, and upon further investigation, I noticed that the daemons were in-fact up.

So it was a snmp problem.

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tpe-lkm “hardcoded_path” feature

This evening I implemented the optional hardcoded_path feature for tpe-lkm. It’s a way to be very strict on what on the system can be executed. When set, anything outside of the given path can’t be executed, regardless of permissions or ownership. This includes shared libraries, so use this feature with caution. Read the entry in the FAQ about it.

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