/*
 * ghQst - ElectronicSouls
 * tool to find hidden processes
 * works on 2.4.x kernels
 *
 * compile like this:
 * gcc -o psreal psreal.c -I/usr/src/linux/include/linux
 */


#define __KERNEL__
#include <linux/sched.h>
#undef __KERNEL__
#include <stdio.h>
#include <errno.h>

#define TASKSYMBOL  "init_task_union"
#define MAXPIDS    1024

unsigned long findtasksymbol(char *tasksymbol);
int checkproc(int pid);
int createpidlist(int *pidlist, int len);
int checkpidlist(int pid, int *pidlist, int len);


int main(int argc, char *argv[])
{
  int pidlist[MAXPIDS];
  struct task_struct task;
  char *tasksymb = TASKSYMBOL;
  unsigned long inittask, nexttask;
  int fd, rt, lstpid;

  if (argc > 2) {
    fprintf(stderr, "usage:\t%s <tasksymbol>\n", argv[0]); exit(1);
  }
  if (argc > 1) tasksymb = argv[1];

  lstpid = createpidlist(pidlist, MAXPIDS);
  if (lstpid == -1) return -1;
  if (lstpid >= MAXPIDS) {
    fprintf(stderr, "%s:\tpid buffer to small\n", argv[0]); exit(1);
  }

  inittask = findtasksymbol(tasksymb);
  if (inittask == -1) {
    fprintf(stderr, "%s:\tcouldnt find task symbol\n", argv[0]); exit(1);
  }
  printf("symbol %s found: 0x%.8x\n", tasksymb, inittask);

  fd = open("/dev/kmem", O_RDONLY);
  if (fd == -1) {
    perror("open"); exit(1);
  }

  nexttask = inittask;
  while (nexttask) {
    rt = lseek(fd, nexttask, SEEK_SET);
    if (rt != nexttask) {
      perror("lseek"); exit(1);
    }
    rt = read(fd, &task, sizeof(task));
    if (rt < 0) {
      perror("read"); exit(1);
    }
    if (checkproc(task.pid)) {
      printf("- process %u (%s) hidden by the kernel\n", task.pid, task.comm);
    } else if (checkpidlist(task.pid, pidlist, lstpid)) {
      printf("- process %u (%s) hidden by ps\n", task.pid, task.comm);
    }
    nexttask = (unsigned long)task.next_task;
    if (nexttask == inittask) break;
  }

  close(fd);
  return 0;
}

unsigned long findtasksymbol(char *tasksymbol)
{
  unsigned long addr;
  char buffer[1024];
  FILE *ksyms;
  char *p;

  ksyms = fopen("/proc/ksyms", "r");
  if (ksyms == NULL) {
    perror("findtasksymbol - fopen"); return -1;
  }

  bzero(buffer, sizeof(buffer));
  while (fgets(buffer, sizeof(buffer) - 1, ksyms)) {
    if (!(p = (char *)strchr(buffer, ' '))) continue;
    if (strstr(p+1, tasksymbol)) {
      *p = 0; addr = strtoul(buffer, NULL, 16);
      fclose(ksyms); return addr;
    }
  }

  fclose(ksyms);
  return -1;
}

int createpidlist(int *pidlist, int len)
{
  char buffer[1024];
  int rt, fd[2], lst;
  char *arg[3];
  FILE *ps;

  rt = pipe(fd);
  if (rt == -1) {
    perror("fork"); return -1;
  }

  rt = fork();
  switch (rt) {
  case -1:
    perror("fork"); return -1;
  case 0:
    close(fd[0]); dup2(fd[1], 1);
    arg[0] = "ps"; arg[1] = "-A"; arg[2] = NULL;
    execvp("/bin/ps", arg); exit(1);
  }

  close(fd[1]); lst = 0;
  if ((ps = fdopen(fd[0], "r")) == NULL) return -1;
  while (fgets(buffer, sizeof(buffer) - 1, ps) && lst < len) {
    buffer[6] = 0; pidlist[lst++] = atoi(buffer);
  }

  wait(NULL);
  return lst;
}


int checkproc(int pid)
{
  char buffer[1024];
  int fd;

  sprintf(buffer, "/proc/%d", pid);
  fd = open(buffer, O_RDONLY);
  if (fd == -1 && errno == ENOENT) return 1;
  close(fd);

  return 0;
}

int checkpidlist(int pid, int *pidlist, int len)
{
  int i;

  for (i=0; i<len; i++) {
    if (pidlist[i] == pid) return 0;
  }

  return 1;
}