Rewire

Rewire is a command line tool for Linux that allows code to alter the system call behavior of programs, without changing the programs themselves. It leverages ptrace to detect when executables perform system calls and provides a convenient interface to wire kits, user-written libraries that contain code to be executed on system call entries and exits.

Getting Started

This repository comes with a simple Makefile that does all the building for you. Rewire is written in a mixture of C and C++ and it requires compiler support for the C++-20 standard. It depends on no additional libraries.

Simply create a build directory, enter it and run cmake .. and then make. This yields rewire's main functionality in a shared library, a command line tool and an exemplary wire kit.

Wire kits must be installed before they can be used with the command line tool. This installation happens on a per-user basis. To install the provided example.so, use rewire install example.so. For convenience, rewire strips the .so from the name under which the installed wire kit is accessible, so this kit will be available under the name example. To prevent this, or to choose a different alias for the installation altogether, use rewire install example.so alias. No suffixes are truncated from aliases specified this way. A list of all installed wire kits can be printed with rewire list and each one can be removed using rewire uninstall kitName.

To run commands in rewire, it can be launched in one of two modes. It can either execute a single command with rewire kitName command arguments or be launched in shell mode using rewire kitName. The latter will initialize the wire kit once and listen for the user to input commands until exit is given.

To shorten commands, any executable can directly link to the rewire's shared library and internally decide which commands to execute in an altered environment.

Wire Kits

To work with rewire, wire kits have to implement a set of functions specified in rewire's wirekit.hpp.

• wirekit_prepare is called once (even in shell mode) when the kit is loaded.
• wirekit_command_start is called for every command that is executed. It can be used to reset kit-internal data between commands or initialize kit components based on the command and its arguments. Additionally, system call hooks should be installed from this function using e.g. rewire_syscall_hook (more information in wirekit.hpp).
• wirekit_command_exit is called when a command finishes execution. This means that the command main process and all its children have terminated. Use it to clear or reset kit-internal data. Providing an implementation for this function is optional.
• wirekit_subject_start is called whenever a new child thread or process, created under the current command, performs its first system call and thus becomes relevant to the wire kit. Implementing this function is optional.
• wirekit_subject_exit is called whenever a child process or thread, under the current command, terminates. Implementing this function is optional.

To get a better understanding of how to use these functions, have a look at the exemplary wire kits. Finally, each wire kit must be compiled as position-independent shared object, as done in the Makefile.