Kernelroll LD_PRELOAD version

kernelroll.c

/***********************************************************************
 *                    KernelRoll, LD_PRELOAD version.                  *
 *                    ===============================                  *
 *                                                                     *
 * Compile with: gcc -o kernelroll.so kernelroll.c -shared -fPIC -ldl  *
 * Run with: LD_PRELOAD=./kernelroll.so some_file.mp3                  *
 *                                                                     *
 * Remember to change SONG constant in this file                       *
 *                                                                     *
 * Authors: Roger Duran                                                *
 * Contributors: j0hn                                                  *
 ***********************************************************************/

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdarg.h>
#include <assert.h>

#if defined(RTLD_NEXT)
#define REAL_LIBC RTLD_NEXT
#else
#define REAL_LIBC ((void*) -1L)
#endif

/* CHANG ME */
#define SONG "/path/to/roll/file"

static int lib_start = 0;

static int (*real_open)(const char *path, int flags, ...);
static int (*real_open64)(const char *path, int flags, ...);

void _start_lib()
{
    if (!lib_start){
        assert(real_open = dlsym(REAL_LIBC, "open"));
        assert(real_open64 = dlsym(REAL_LIBC, "open64"));
        lib_start++;
    }
}

int _open(int type, const char *path, int flags, va_list arg)
{
    char *ext = NULL;
    mode_t mode;

    _start_lib();

    if(flags & O_CREAT) {
        mode = va_arg(arg, mode_t);
    }

    ext = (char *)(path + strlen(path) - 4);

    if(strcmp(ext, ".mp3") == 0){
        if(type == 64){
            return real_open64(SONG, flags, mode);
        } else {
            return real_open(SONG, flags, mode);
        }
    }

    if(type == 64){
        return real_open64(path, flags, mode);
    } else {
        return real_open(path, flags, mode);
    }
}

int open(const char *path, int flags, ...)
{
    int result = 0;
    va_list arg;

    va_start(arg, flags);
    result = _open(32, path, flags, arg);
    va_end(arg);

    return result;
}

int open64(const char* path, int flags, ...)
{
    int result = 0;
    va_list arg;

    va_start(arg, flags);
    result = _open(64, path, flags, arg);
    va_end(arg);

    return result;
}