How to secure your Linux

How to secure your linux? (easily)

Now days computer security is on the top trending topics for several reasons, the pandemic confiment also boosted the search for this topic. So you have a linux, is it secure? Most likely yes, is it vulnerable, even if daily updated (also see how to speed up apt-update ) due to default values of some configurations.

An easy way to enhance Linux security or hardening Linux? Using lynis (also works on OSX)

What's hardening?  Basically is just tunning and configuring some features that by default might allow someone to exploit or use that as a vulnerability. (not just one feature per se, but some combined might create something exploitable)

How to install lynis on Linux?

There are two instalation methods, easy and easiest. The main difference is  the version you download from the Lynis site is always the latest one where the apt-get version might take sometime to get to the lastest. 

An example is allowing access to compilers, an intruder can pass a bunch of string and in the end compile them and there you go, someone uploaded some string and created an executable on your machine. Another example is not enforcing secure password, 1234, Joe, and Password aren't exactly secure passwords, but if the system won't allow anything rather than ex: JustATinny123Pass**Again is virtual impossible to guess or crack.

 

In ubuntu/mint lynis installation (easiest):

• sudo apt install lynis

In ubuntu/mint lynis installation (easy):

1. Go to Lynis webpage and download the rar
2. Unrar-It
3. Done  

How to run Lynis on your Linux machine?

Previous Note: You should always run it as root user 

• If the installation was done via apt-get the just type "lynis audit system" else, just go to the directory where you extracted Lynis and run "./lynis audit system".

This might take a while depending on our system ( 40sec plus). 

What do you get? Whell for start you get a score! 0-100points... if you use a default ubuntu 20 LTS from scratch you'll get around 65points depending on installed packages.

There's a list of issues to be solved, their solution (if possible in your system), solve one by one and in the end run it again. In the end you improve your score and harden your system.

Examples which I focus a LOT, since some of my machines are only accessible by network: sshd connections hardening.

Lenovo X250 tweeking in linux

Why the Lenovo X250?

My needs: a daily driver laptop, very cheap, light, small, upgradable and serviceable. (want to swap hdd, thermal paste etc) and Linux friendly. All things considered, I came up with a bargain on eBay, a 12.5"  Lenovo ThinkPad X250, i5 5300U with 8gb RAM, 128gb SSD, 2 batteries and HD screen with a barely noticeable bruise (which shall be swapped latter) for 130Euro.

X250 condition

X250 keyboard and screen

The Lenovo X250 in 2019 It's preparation for linux daily driver.

The batteries, yep no typo --two batteries-- this model has 2, one internal the other external were ~82% capacity each, the screen bruise is somehow noticeable, the fan and thermals were alright, yet first things to do; swap thermal paste for a top of the line one and swap the 128gb SSD for one bigger a 256SSD.  Keep in mind that there's a whitelist of LCD screens, if not on the list no brightness control on windows.

So price tag till now:

• X250 + Postage = 130Euro
• Grizzly  Kryonaut = 5Euro
• Western Digital Green SSD 256Gb = 33Euro
• FHD IPS screen ref ( ref MTM 20CLS0XA03 20CL)  = 75Euro

• Linux Mint19 = Free

X250 Interior

The thermal paste change settled the temperatures in full load (15min test) under 65 degrees, ( s-tui tool to monitor and stress CPU, sysbench to stress).

The i5-5300U CPU has a 'built in' GPU, the HD5500 and together both can consume up to 15w of power. When this power consumption threshold is exceeded the frequencies are lowered and the performance of the CPU, the GPU or both it takes a hit. The CPU/GPU throttling can also happen when the one of both achieves a certain temperature threshold, in the case of the X250 this doesn't happen due to good cooling. Even with default cooling/paste I could run stress tests at full CPU speed.

Undervolting Lenovo X250 and optimizing battery life

Next I decided to undervolt the CPU, this would allow even lower temperatures, more battery life and avoid package throttling, the 15watt limit! If both CPU and GPU consume less, less throttling will happen (duhh) and more performance one will get.
To undervolt I used undervolt python package, after a couple tests I could lower my voltages with the following values:

--core -100 --cache -100 --gpu -55 --uncore -70 --analogio -50

The values might get lower but I want full stability under all circumstances.

Hint: Don't just do stress tests, use the computer normally, and use it while doing the tests, I happen to pass lots of tests with -130mV in the core but crashed when opening firefox for example.

In order to test I installed sysbench and ran the following command:

sudo sysbench cpu --threads=4 --time=300 run

My results were the following, yet what matters is that the temperature didn't go above 63 degress Celcius.

CPU speed:
    events per second:  2675.87

General statistics:
    total time:                          300.0013s
    total number of events:              802769

Latency (ms):
         min:                                  1.09
         avg:                                  1.49
         max:                                 30.35
         95th percentile:                      1.52
         sum:                            1199489.59

Threads fairness:
    events (avg/stddev):           200692.2500/865.84
    execution time (avg/stddev):   299.8724/0.00

5 minutes after the test the temperatures drop to an very acceptable 37 degrees!

Battery life: depends a lot on what I do, compiling, watching youtube, browsing, screen brightness, but safe to say that at 50% screen brightness, light browsing 5 hours easily.

Now 2 important packages needed to be installed, these (basically) will tuneup the SO so it consumes a lot less energy, TLP will even make your fan be quieter in normal use: powertop and tlp

To install TLP:

$ sudo add-apt-repository ppa:linrunner/tlp
$ sudo apt-get update
$ sudo apt-get install tlp tlp-rdw 

$ sudo tlp start 

To install and configure powertop:

$ sudo apt-get update
$ sudo apt-get install powertop

$ sudo powertop --auto-tune 

On my lenovo X250 these steps gave me an extra 1h battery life and LOT quieter fan.