Paranoid Penguin: Using iptables for Local Security
As you can see, the uses of --uid-owner and --gid-owner are pretty straightforward. One thing I haven't mentioned yet is that both options accept names, as I've shown in the examples, or numeric IDs.
Another issue I've dodged is TCP Wrappers-style access controls. On any system that uses TCP Wrappers (or whose stunnel binary was compiled with support for libwrapper), you must add appropriate entries to /etc/hosts.allow for Stunnel to work properly, whether you run Stunnel in client mode or dæmon mode on that host. This is a good thing; rather than being one more thing capable of preventing Stunnel from working, you should think of it as another layer of your security onion.
Finally, I'm leaving it to you to tinker with --pid-owner and --sid-owner. I will give you a hint, though. Many dæmons write their parent PID in a predictable place on startup, that is, /var/run/sshd.pid. By reading such a PID file into a variable in your iptables startup script, you can match packets originating from a specific process. Good luck!
Mick Bauer (email@example.com) is a network security consultant for Upstream Solutions, Inc., based in Minneapolis, Minnesota. He is the author of the upcoming O'Reilly book Building Secure Servers With Linux, composer of the “Network Engineering Polka” and a proud parent (of children).
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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