Ubiquiti devices are great.

They could be amazing if you can add stuff missing, like TPROXY support in iptables.
Here is a tutorial on how you could compile a single module that can be installed into your ubiquity devices.
In this article, I'm going to compile the missing tproxy module for iptables as an example.

Prepare environment

System

Debian 10 (buster) is preferred, although Debian 7 (stretch) can do the same job.
Debian 8 and 9 are not ideal for this task since gcc for mips is missing in their respective repos.

add

deb http://packages.debian.org/debian/ buster main
deb-src http://packages.debian.org/debian/ buster main

to your /etc/apt/source.list if it is not there.
For Debian 7:

deb http://packages.debian.org/debian/ oldstable main
deb-src http://packages.debian.org/debian/ oldstable main

is what you need.

Compilers

Install all the required compile tools with
apt install -y autoconf automake libtool gettext pkg-config g++-mipsel-linux-gnu gcc-mipsel-linux-gnu g++-mips64-linux-gnuabi64 gcc-mips64-linux-gnuabi64 build-essential upx

Environment variables

Create a shell script and paste

export ARCH=mips
export host=mipsel-linux-gnu
export strip=mipsel-linux-gnu-strip
export CROSS_COMPILE=mipsel-linux-gnu-

You don't need to apply the executable attribute to it.
Apply it to the current console with source you.file.sh

Get the source

Figure out the router version

Login to your router and check the firmware version. It should be displayed on the top left of the page.

Once you know the version number (and device model of course), head over to DOWNLOAD SECTION, find the version you're on, and make sure you clicked the right link.
20191010151210.png
The archive could be huge, ~500MB+ or you're downloading the wrong thing.

Get the kernel source

Open the archive with an archiver and look for a file with kernel in its name.
Extract it and copy it to your prepared linux environment.

Once you get it there and have set up a warm home for it, extract it by tar -xf kernel-source-archive-filename.tgz.
Let's presume you put the kernel in /usr/local/kernel/kernel

Compile

Prepare for the module

Create another folder for your module and copy all required files into it.
I created /usr/local/kernel/tproxy for my module and copied kernel/net/netfilter/xt_TPROXY.c into it.

Create a makefile for it. It's unbelievably simple.

obj-m:=xt_TPROXY.o

That's it.

Prepare for compiling

CD to the kernel folder and do make oldconfig && make prepare && make scripts
This should be enough to generate everything required to compile a module.

No question should be prompted. If it does, you set your environment variable incorrectly and you are compiling the source for your current Linux.

Compile the module

Now, the most exciting part: Compiling

make -s -C ../kernel/ ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- M=`pwd` EXTRA_CFLAGS+=-fno-pie  modules

Change the ../kernel/ part accordingly to the position you rest your kernel source in.

If everything is right, a xt_TPROXY.ko file should be in the same folder you're in. Copy it to your router or other types of devices.

Install mod

Install and load the module

The rests are simple.

  • Copy the .ko file to where it should be (/lib/modules/{kernel version}/kernel/net/netfiler/ in my case)
  • run insmod /absolute/path/to/your/kofile to install it
  • run depmod to deploy it
  • run mobprobe yourko to load it.

Congratulations! You made it.

There is another easier way to make modules but limited to the builtin modules only. For third-party modules or modules you write, You have to follow the method above mentioned.

This method is very simple:

make oldconfig && make menuconfig

This will make a sample .config for kernel and pops up a config dialog to fiddle the kernel options.
Load the .config via load button and tick all the modules you want to build. Remember to set the compiling status to <M> instead of <*> which will build modules into the kernel instead of a separate .ko file.

Save your new .config and run make modules.
It will take a while and you'll find a lot of .ko files in their respective folders.