add dynamic IP mapping for localhost

[f4rs1ght]

This PR aims to achieve the following goal:

1. Dynamically map MagicNet (240.x.x.x) addresses to corresponding loopback addresses (127.x.x.x) based on the original IP. For example, 240.0.0.5 will map to 127.0.0.5.

This way, by executing interface_add_route --name evil-cha --route 240.0.0.0/8 (after configuring the evil-cha interface) in the ligolo proxy terminal, the user will be able to access the entirety of the loopback CIDR of the target agent.

[nicocha30]

I have trouble understanding the purpose of this PR, knowing that 127.x.x.x always points to localhost? Do you have a case where this is necessary?

[f4rs1ght]

Let's assume we are hosting a website on the IP address 127.0.0.5 and port 80, using the command python3 -m http.server -b 127.0.0.5 80. This website is now only accessible via http://127.0.0.5 and not via http://127.0.0.1.

This means that if we point any IP in the CIDR range 240.0.0.0/8 to 127.0.0.1, we will not be able to access this website from the machine running the ligolo proxy. However, with this PR, we will be able to access it via http://240.0.0.5.

Open5Gs is a project that uses local IP addresses, such as 127.0.0.5 and 127.0.0.20, to run essential API services that are accessible only from the local machine running the project.

[nicocha30]

Thanks for the info. I wasn't aware that some programs use a local IP address other than 127.0.0.1!
There is one problem though. If there are two Ligolo-ng agents, and I want to access 127.0.0.1 on agent A, and then 127.0.0.1 on agent B, I can simply create two routes to 240.0.0.1 dev agentiface1 and 240.0.0.2 dev agentiface2.
Maybe we could use another unused subnet?

[f4rs1ght]

At first, I considered using 192.88.99.0/24 as another unused subnet. However, we do not need to since the problem you described is still solved with the current PR.

Since the 240.0.0.0/4 subnet that we use is larger than 127.0.0.0/8, we can access the localhost ip range of 2 agents by defining the routes as such:

From ligolo_proxy console:
interface_add_route --name agentiface1 --route 240.0.0.0/8
interface_add_route --name agentiface2 --route 241.0.0.0/8
Using ip command:
ip route add 240.0.0.0/8 dev agentiface1
ip route add 241.0.0.0/8 dev agentiface2

Now we can access 127.x.x.x of agent A with 240.x.x.x and 127.x.x.x of agent B with 241.x.x.x. This can work for up to 16 unique agents.