BOF Sample

bof.c

#include <stdio.h>
#include <string.h>

/*
 *	Overly complex BOF example code.
 *		Leon Jacobs - 2014
 * 
 *	The reason for this is to try get some more useful assembly
 *	out of the program so that we can get some interesting POC's
 */

/* strlen code from http://fxr.watson.org/fxr/source/libkern/strlen.c?v=DFBSD */
size_t strlen(const char *str )
{

	const char *s;
	for (s = str; *s; ++s);
	return(s - str);
}

/* check that the string matches our minimum len requirement */
int check_string( const char *string_to_check )
{

	int len;
	len = strlen(string_to_check);

	if (len <= 5) {
		printf("The string is not long enoug! Provide at least 5 chars.\n");
		return 0;
	}
	return 1;
}

int main( int argc, char *argv[] )
{

	/* arg check */	
	if (argc < 2) {

		printf("You need to provide a string. Usage is %s <string>\n", argv[0]);
		return 1;
	}

	/* Copy 500 bytes into recieved */
	char received[500];
	strncpy(received, argv[1], 500);

	/* test this string meets min len */
	int len_ok = check_string(received);

	if (len_ok) {

		char buffer[20];
		strcpy(buffer, argv[1]); /* BOF! */

		printf("String is %d characters long and is: %s.\n", strlen(buffer), buffer);
	}
	return 0;
}