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Re: shellcoding on gentoo



ive written similar code recently using gentoo also, running on an amd 2200 XP:

i use GCC to build my assembler rather then nasm, could potentially be an issue there?
its also worth noting at&t syntax..

<snipped>
//close:
	"\x89\xf3"			// mov    %esi,%ebx
	"\x31\xc0"			// xor    %eax,%eax
	"\xb0\x06" 	                // mov    $0x6,%al
	"\xcd\x80"			// int    $0x80			;close

	"\x87\xf7"			// xchg   %esi,%edi
	"\x85\xc0"			// test   %eax,%eax
	"\x74\xf"			// jz     close

//exit:
	"\x31\xc0"			// xor    %eax,%eax
	"\xb0\x01"                              // mov    $0x1,%al
	"\xcd\x80"			// int    $0x80			;exit
<snipped>
----- Original Message ----- From: "Borja" <padre@xxxxxxxxxxxxx>
To: <vuln-dev@xxxxxxxxxxxxxxxxx>
Sent: Sunday, February 19, 2006 7:56 PM
Subject: Re: shellcoding on gentoo


Hi

Lot of ppl tell me that I did not proper zero the EAX register,so 3 MSB of eax corrupt trapping the syscall, but Its OK. I successfully run the shellcodes on a debian box,but in gentoo,allways SEGFAULT.

There is it, a new log:

------------------------------------------------------------------------------------------------------------------------------------------------------

petalo shellcode # cat 1.asm
BITS 32

;exit()
xor eax,eax
xor ebx,ebx
mov eax,1
int 0x80

petalo shellcode # nasm -g -f elf 1.asm
petalo shellcode # ld 1.o
ld: warning: cannot find entry symbol _start; defaulting to 00000000080480a0
petalo shellcode # ./a.out
Segmentation fault
petalo shellcode # gdb -q a.out
Using host libthread_db library "/lib/libthread_db.so.1".
(gdb) break 1
Breakpoint 1 at 0x80480a0: file 1.asm, line 1.
(gdb) r
Starting program: /root/code/shellcode/a.out

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
You can't do that without a process to debug.
(gdb) q

petalo shellcode #
Linux petalo 2.6.12-gentoo-r6 #9 Sat Dec 24 14:37:56 CET 2005 i686 AMD Athlon(tm) XP 1600+ AuthenticAMD GNU/Linux

------------------------------------------------------------------------------------------------------------------------------------------------------


I cant explain why SIGFAULT.
I did not edit any advanced kernel configurations rather than snd card and ethernet.

Thanks in advance.