README.md

Add more 420 to your files!

chemikadze@chemikadze:~/fakels$ make
gcc -shared -o lib420.so lib420.c
LD_PRELOAD=./lib420.so ls -l
total 16
-rw-rw-r-- 1 chemikadze chemikadze 1013 Apr 20 04:20 lib420.c
-rwxrwxr-x 1 chemikadze chemikadze 7816 Apr 20 04:20 lib420.so
-rw-rw-r-- 1 chemikadze chemikadze  137 Apr 20 04:20 Makefile

Illustrates hooking into existing binary by redefining existing dynamically-linked symbols.

lib420.c

#define _GNU_SOURCE
#include <unistd.h>
#include <dlfcn.h>
#include <sys/stat.h>

static int (*orig___lxstat)(int version, const char * __path, struct stat *__statbuf);

#define TIME_420 1555734000

void __attribute__ ((constructor)) resolve_dynamic_symbols(void) {
        *(void**)(&orig___lxstat) = dlsym(RTLD_NEXT, "__lxstat");
}

int __lxstat(int version, const char * __path, struct stat *__statbuf) {
        int res = orig___lxstat(version, __path, __statbuf);
        if (__statbuf != NULL) {
                __statbuf->st_mtime = TIME_420;
        }
        return res;
}

Makefile

demo: lib420.so
        LD_PRELOAD=./lib420.so ls -l
.PHONY: demo

lib420.so: lib420.c
        gcc -shared -o lib420.so lib420.c

clean:
        rm lib420.so