Code samples to go along with the blog post on how to run code at load/unload time when using LD_PRELOAD to inject libraries.
Blog: LD_PRELOAD: How to Run Code at Load Time
This repo is used to provide some code samples to go along side a tutorial in the Secure Ideas blog. This code repo will provide you with the code for:
- A simple hello world binary target
- The LD_PRELOAD injection code
- A make file to build it easily in a Kali VM.
The goal of this tutorial is to show how to use constructor and destructor attributes for running code at load/unload time with an LD_PRELOAD shared object to run code without hijacking a function call. In this case, It will demo this on a simple hello world binary
Once you clone the repo, simply change into the directory and run make or make all to build both the target and the LD_PRELOAD hijack shared object. The make file also includes a help option to show all of the build targets:
kali@kali:~$ make help
Default Target:
all => Build the default hello world & inject shared object.
Hello World Targets:
hello_world => Build the default hello world ELF binary.
Inject Targets:
inject.so => Build standard LD_PRELOAD inject.so shared object.
inject.so_nocolor => Build non-colorized LD_PRELOAD inject.so shared object.
Maintance Targets:
clean => delete the binaries.
kali@kali:~$
Standard Hello World build and usage:
kali@kali:~$ make hello_world
gcc -Wall -O3 -s src/hello_world.c -o hello_world
kali@kali:~$ ./hello_world
Hello World!
kali@kali:~$
kali@kali:~$ make inject.so
gcc -Wall -O3 -FPIC -shared src/inject.c -o inject.so
kali@kali:~$ ./hello_world
Hello World!
kali@kali:~$ LD_PRELOAD=./inject.so ./hello_world
[+] Inject.so Loaded!
[*] PID: 1445
[*] Process: /home/kali/src/ld_preload_load_time/hello_world
Hello World!
[-] Inject.so is being unloaded!
kali@kali:~$