Buffer Overflow / Stack Smashing Example

buffer1.c

/*
	Written by Amit Seal Ami
*/

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

/*
Instructions
============
1. turn off Address space layout randomization (ASLR)(ASLR) by this command:

sudo echo 0 > /proc/sys/kernel/randomize_va_space

2. Next, compile this program using the switch to disable stack protector in the
 optimized build:

gcc buffer1.c -o buffer -fno-stack-protector

3. Give input, by default, each character array are given 16 byte space, even
though we used array of size 5 byte. So, a value larger than 16 bytes is entered
it will smash the stack - and you will be free from the eternal loop.

*/

int main(int argc, char const *argv[])
{
	/* code */
	int valid = 0;
	char str1[5];
	char str2[5];

	printf("locations: %p %p\n",  &str1, &str2);

	strcpy(str1,"START");

	while(valid==0){

		printf("Muhahaha, you are locked in while(1) lock! \n");
		printf("Enter your sinister stack smashing value: ");
		gets(str2);
		printf("before input: %s, %s\n", str1, str2);
		if(strncmp(str1, str2, 5)==0)
			valid = 1;	
		printf("after input: %s, %s\n", str1, str2, valid);
	}
	
	if(strncmp(str1,"START", 5) != 0){
		printf("aww, you broke from my eternal lock, you hacker :@\n");		
	}	
	else{
		printf("meh, you got out of it the usual way. Boring.\n");
	}
	return 0;
}