Inject a shared library (i.e. arbitrary code) into a live linux process, without ptrace. Inspired by Cexigua and linux-inject, among other things.

Usage

    .___.__  .__            __               __
  __| _/|  | |__| ____     |__| ____   _____/  |_  ______ ___.__.
 / __ | |  | |  |/    \    |  |/ __ \_/ ___\   __\ \____ <   |  |
/ /_/ | |  |_|  |   |  \   |  \  ___/\  \___|  |   |  |_> >___  |
\____ | |____/__|___|  /\__|  |\___  >\___  >__| /\|   __// ____|
     \/              \/\______|    \/     \/     \/|__|   \/

source: https://github.com/DavidBuchanan314/dlinject

usage: dlinject.py [-h] [--stopmethod {sigstop,cgroup_freeze,none}]
                   pid /path/to/lib.so

Inject a shared library into a live process.

positional arguments:
  pid                   The pid of the target process
  /path/to/lib.so       Path of the shared library to load (note: must be
                        relative to the target process's cwd, or absolute)<   br/>
optional arguments:
  -h, --help            show this help message and exit
  --stopmethod {sigstop,cgroup_freeze,none}
                        How to stop the target process prior to shellcode
                        injection. SIGSTOP (default) can have side-effects.
                        cgroup freeze requires root. 'none' is likely to cause
                        race conditions.

Why?

Because I can.
There are various anti-ptrace techniques, which this evades by simply not using ptrace.
I don't like ptrace.
Using LD_PRELOAD can sometimes be fiddly or impossible, if the process you want to inject into is spawned by another process with a clean environment.

How it Works

Send the stop signal to the target process. (optional)
Locate the _dl_open() symbol.
Retreive RIP and RSP via /proc/[pid]/syscall.
Make a backup of part of the stack, and the code we're about to overwrite with our shellcode, by reading from /proc/[pid]/mem.
Generate primary and secondary shellcode buffers.
Insert primary shellcode at RIP, by writing to /proc/[pid]/mem.
The primary shellcode:
- Pushes common registers to the stack.
- Loads the secondary shellcode via mmap().
- Jumps to the secondary shellcode.
The secondary shellcode:
- Restores the stack and program code to their original states.
- Pivots the stack (so we don't touch the original one at all).
- Calls _dl_open() to load the user-specified library. Any constructors will be executed on load, as usual.
- Restores register state, un-pivots the stack, and jumps back to where it was at the time of the original SIGSTOP.

Limitations:

Sending SIGSTOP may cause unwanted side-effects, for example if another thread is waiting on waitpid(). The --stopmethod=cgroup_freeze option avoids this, but requires root (on most distros, at least).
I'm not entirely sure how this will interact with complex multi-threaded applications. There's certainly potential for breakage.
x86-64 Linux only (for now - 32-bit support could potentially be added).
Requires root, or relaxed YAMA configuration (echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope is useful when testing).
If the target process is sandboxed (e.g. seccomp filters), it might not have permission to mmap() the second stage shellcode, or to dlopen() the library.