socket_wrapper

A library that overrides the socket options set by any pre-existing application

Linux shared libraries (with extension .so) are load and unload dynamically in system memory as needed. This project demonstrates how any method contained in a shared library can be override at run-time to execute arbitrary code before that shared library is loaded into memory.

This library specifically modify socket options for any new TCP connection that is about to be created by any preexisting program. The program is not aware of those options nor able to react to them unless it is modified and recompiled.

Use Cases:

1. To set specific ToS and QoS values for critical network communication programs such as SSH, WebRTC and DB cluster services etc.

2. To enable TCP extensions such as Multi-Path TCP (MPTCP) for pre-existing programs, provided that the newer socket library (i.e. with MPTCP support) is backward compatible. This means e.g. an SSH client application linked against older GNU C shared library (without MPTCP support) can utilize MPTCP capabilities of newer GNU C shared library without having to be modified and recompiled.

3. It can be extended to analyze, hack or reverse engineer any existing program.

Build Steps

Dependencies

• C compiler (C99 compliant)
• REDIS C API library hiredis (optional)
• Linux kernel MPTCP user API headers (optional)

Compilation

There are multiple ways to compile,

• Simply run make. It will generate libsocket_wrapper.so file with MPTCP support.
• To compile with REDIS support (to load TCP options from redis), run make with_redis.
• To compile without MPTCP (and redis) support run make without_mptcp.

Usage

Set the environment variable LD_PRELOAD with full path to libsocket_wrapper.so before running the program.

e.g.

LD_PRELOAD=/home/shahzad/shari/socket_wrapper/libsocket_wrapper.so ssh localhost

This will print logs like below in stderr, indicating the socket methods that have been successfully applied on the program.

Loading __close => 0x7f83be2308c0
Loading __read => 0x7f83be230070
Loading __socket => 0x7f83be242ec0
Loading __connect => 0x7f83be2428a0
Loading __setsockopt => 0x7f83be242e60
Loading __write => 0x7f83be230140

Copyright

Copyright (c) 2019 Muhammad Shahzad Shafi [email protected]