Patching doesn't work [solved]

[Xcross87]

Hi MUsers,

 

I'm currently doing practices under Linux w/ blah crackmes:

Link: http://crackmes.de/users/lord/easy_linux_crackme/

 

This is the dump result:

 

blah:     file format elf32-i386


Disassembly of section .text:

08048094 <.text>:
8048094:	31 c0                	xor    %eax,%eax
8048096:	b8 2f 00 00 00       	mov    $0x2f,%eax
804809b:	cd 80                	int    $0x80
804809d:	3d ad de 00 00       	cmp    $0xdead,%eax
80480a2:	75 16                	jne    0x80480ba <-- I want to NOP this line
80480a4:	b8 04 00 00 00       	mov    $0x4,%eax
80480a9:	bb 01 00 00 00       	mov    $0x1,%ebx
80480ae:	b9 c4 90 04 08       	mov    $0x80490c4,%ecx
80480b3:	ba 06 00 00 00       	mov    $0x6,%edx
80480b8:	cd 80                	int    $0x80
80480ba:	31 c0                	xor    %eax,%eax
80480bc:	40                   	inc    %eax
80480bd:	31 db                	xor    %ebx,%ebx
80480bf:	cd 80                	int    $0x80

 

As I comment above, I want to patch that line by 2 - NOP bytes.

I wrote this code:

 

#include <stdio.h>

int
main( int argc, char *argv[] )
{
int offset[2] = { 0x75, 0x16 }; /* origin */
char patch[2] = { 0x90, 0x90 }; /* nop */
FILE *file;
int i;

file = fopen( "blah", "rb+" );
if( file != NULL ) {
	for( i = 0; i < 2; ++i ) {
		fseek( file, offset[i], SEEK_SET ); /* search */
		fprintf( file, "%c", patch[i] ); /* patch */			
	}
	printf("Patched Done.\n");
} else {
	printf("[Error]: file not found. \n");
}		
fclose( file );
return 0;
}

 

However, I don't know why it doesn't work???

May some1 help me this?

Edited August 5, 2009 by Xcross87

[Xcross87]

Problem found! ^^!