License

• PDX-License-Identifier: GPL-2.0-or-later
• @author Stephan Leemburg stephan@it-functions.nl
• @copyright Copyright (c) 2020, IT Functions

Description

This code can monitor cheap Huawei HiLink USB modems. It can be used as a SMS repeater. So any SMS received on the SIM in the modem will be repeated to a list of other recipients. This can be SMS, Email, Signal (or anything else that you can implement, even MQTT).

It can also be used as a fallback router. Sending a SMS with 'connect' will enable the mobile data on the modem and can then alter routes or start a program.

I use it on two different locations. One location as a SMS 'gateway' and on the other location as both a SMS gateway and a 'emergency' remote reverse SSH access method.

The last one has a prepaid SIM, so I only want to enable mobile data when needed and disable it as soon as it is not needed anymore

Modems known to work

• E3372: Huawei Technologies Co., Ltd. E33372 LTE/UMTS/GSM HiLink Modem/Networkcard
• E3372h-320: Huawei Technologies Co., Ltd. E353/E3131
• E3531: Huawei Technologies Co.,

Requirements

apt install php-cli php-curl php-xml php-json

Why PHP?

Because I am rather fluent in writing php code. I am also fluent in C, but I prefer the higher level languages that relieve me from memory management issues and performance is not an issue with this code and setup.

As I want to become a fluent python coder, I will rewrite the code in python as soon as I get to it.

Installation

Clone this repository to the system you want to run it on. It can run as any user, as long as the user is able to run certain commands, for example with the help of sudo.

Note that I run it as root within unpriviliged, dedicated Proxmox containers.

Then copy the hlmon/config/hlmon-config-example.php file to hlmon/config/hlmon.php and edit the hlmon/config/hlmon.php so it reflects your situation. The example config file is annotated and should be self documenting.

The hlmon/examples contains some example scripts that may be of use.

So in short:

[ -d /opt ] || mkdir -m02775 /opt
cd /opt && git clone https://github.com/sleemburg/hlmon.git
cd hlmon
cp config/hlmon-config-example.php config/hlmon.php
vi config/hlmon.php # adjust to you liking

After that the systemd hlmon unit file can be installed and enabled with

bash examples/hlmon-unit.sh

Commands

There are two 'commands':

• /opt/hlmon/hlmon.php : this is the monitoring code
• /opt/hlmon/hlcmd.php : this is the cli for sending manual sms and (dis)connecting manually

Recomended setup

• Run autossh to connect to your reverse shell target
• Run hlmon to enable mobile data and change the routing
• Use ip addresses if DNS can become unavailable when an outage occurs

Modem mode of operation

The modem is used in the 'network device modus'. In this mode it manifests itself as a USB Ethernet device.

It may be nescessary to use usb_modeswitch to set the modem in this mode. On debian this can be found in the usb-modeswitch package.

For the below 'remote modem', the command for this is:

usb_modeswitch -J -W -v 0x12d1 -V 0x12d -p 0x1f01 -P 0x14dc

For the 'Local backup modem', I used:

usb_modeswitch -N -v 0x12d1 -V 0x12d1 -p 0x1465 -P 0x14dc

Tested devices

I have tested the code on my own 2 Huawei USB modems, these are:

• Remote modem.

  This one has a prepaid SIM in it, so mobile data needs to be switched on and off every time a connection is required.

  Device name: E3372

  Hardware version: CL2E3372HM

  Software version: 22.317.01.00.778

  lsusb output: ID 12d1:14dc Huawei Technologies Co., Ltd. E33372 LTE/UMTS/GSM HiLink Modem/Networkcard

• Local backup modem.

  This one has an unlimited data SIM, so mobile data can remain on. No route switching or commands are required. Only sms gateway.

  Device name: E3372h-320

  Hardwareversion: CL4E3372HM

  Softwareversion: 10.0.3.1(H192SP1C983)

  lsusb output: ID 12d1:14db Huawei Technologies Co., Ltd. E353/E3131

• Modem of a friend

  Device name: E3531

Testing without sending a sms

The basic commands: {connect, disconnect, reset} can be tested by echoing the command to the hlmon directory into a file named commands.txt. For example to force a connect:

echo connect > /opt/hlmon/commands.txt

And to have it disconnect again:

echo disconnect > /opt/hlmon/commands.txt

Usage scenarios

For the both setups, I use autossh. See the examples below.

On the prepaid SIM modem, when the connection is activated, the mobile data is switched on. Then a route specific to the reverse SSH tunnel address is inserted. No command is being run, as I have autossh always running.

On the unlimited data SIM, no connection activation takes place. The system has it's default route via the modem. So the autossh connections are already in place. My firewall switches it's default routes over my main line and if that drops over the modem.

The modem on the unlimited data SIM is for what hlmon is concerned only used as a SMS gateway to enable multiple receivers for SMS data (or signal or mail).

In the autossh configuration ip addresses are used, in stead of FQDN. This is to avoid resolving issues when a failover connection is required and maybe DNS is disfunctional at that moment.

Proxmox container installation

For proxmox unpriviliged based containers, it is nescessary to give the device to the container. In your /etc/pve/lxc/$CTID.conf you should add:

lxc.net.1.type: phys
lxc.net.1.link: eth1
lxc.net.1.name: eth1
lxc.net.1.flags: up

Also, I noticed that one of the modems - the E3372h-320 - sometimes restarts and then 'vanishes' from the container. So I have a udev rule for that:

cat /etc/udev/rules.d/10-dynamic-network.rules
KERNEL=="eth1", SUBSYSTEM=="net", ACTION=="add", RUN+="/root/bin/restart-gw3.sh"

cat /root/bin/restart-gw3
#!/bin/bash

export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

pct stop 102
pct start 102

echo "Restarted gw3 due to modem reset" | mail -s "GW3 restart" root@my.domain

exit 0

See also

In the examples directory are various example scripts and configurations.