Heiher's Blog

/* fakemain.c
 * Heiher <admin@heiher.info>
 */
 
#include <stdio.h>
#include <stdlib.h>
 
#define __USE_GNU
#include <dlfcn.h>
 
int
__libc_start_main(int (*main)(int, char **, char **),
			int argc, char **ubp_av, void (*init)(void),
			void (*fini)(void), void (*rtld_fini)(void),
			void (*stack_end))
{
	int (*__libc_start_main_real)(int (*main) (int, char **, char **),
				int argc, char **ubp_av, void (*init)(void),
				void (*fini)(void), void (*rtld_fini)(void),
				void (*stack_end));
 
	unsetenv ("LD_PRELOAD");
	unsetenv ("LD_LIBRARY_PATH");
 
	__libc_start_main_real = dlsym(RTLD_NEXT, "__libc_start_main");
 
	return __libc_start_main_real(main, argc, ubp_av, init, fini,
				rtld_fini, stack_end);
}

gcc -fPIC -O3 -shared -o libfakemain.so fakemain.c -ldl

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
 
int
main (int argc, char *argv[])
{
	int i;
	char buf[1024], path[1024];
	char *str, *root, *args[512];
 
	/* get FAKE_ROOT */
	root = getenv ("FAKE_ROOT");
	if (!root) {
		fprintf (stderr, "Please set environment FAKE_ROOT!\n");
		return -1;
	}
 
	/* export PATH */
	str = getenv ("PATH");
	if (!str) {
		fprintf (stderr, "Get environment PATH failed!\n");
		return -2;
	}
	if (NULL == strstr (str, root)) {
		strcpy (buf, root);
		strcat (buf, "/bin:");
		strcat (buf, str);
		if (0 != setenv ("PATH", buf, 1)) {
			fprintf (stderr, "Set environment PATH failed!\n");
			return -3;
		}
	}
 
	/* export LD_PRELOAD */
	strcpy (buf, root);
	strcat (buf, "/lib64/libfakemain.so");
	if (0 != setenv ("LD_PRELOAD", buf, 1)) {
		fprintf (stderr, "Set environment LD_PRELOAD failed!\n");
		return -4;
	}
 
	/* export LD_LIBRARY_PATH */
	strcpy (buf, root);
	strcat (buf, "/lib64");
	if (0 != setenv ("LD_LIBRARY_PATH", buf, 1)) {
		fprintf (stderr, "Set environment LD_LIBRARY_PATH failed!\n");
		return -5;
	}
 
	/* set new path */
	strcpy (path, root);
	strcat (path, "/lib64/ld-2.20.so");
	args[0] = path;
 
	/* set real program path */
	strcpy (buf, root);
	strcat (buf, "/bin/");
	strcat (buf, argv[0]);
	strcat (buf, ".bin");
	args[1] = buf;
 
	/* copy arguments */
	for (i=1; i<argc; i++)
	      args[i+1] = argv[i];
	args[i+1] = NULL;
 
	/* run real program */
	return execv (path, args);;
}

gcc -O3 -o wrapper wrapper.c