How do I enable a buffer overflow?

Question

I just installed 12.04 (WUBI actually) and I wanted to learn a bit about buffer overflow. Unfortunately when I try to use a function like puts() and gets() in an incorrect manner (that is, to cause a buffer overflow), gcc tells me that it detected smashing the stack and terminate my program.

How do I enable stack overflow?

For more clarity, This is the program:

#include<stdio.h>

CanNeverExecute()
{
    printf("I can never execute\n");
    exit(0);
}

GetInput()
{
    char buffer[8];

    gets(buffer);
    puts(buffer);
}

main()
{
    GetInput();

    return 0;
}

Answer 1

I don't think what you are doing is a stack overflow. That is what happens when you recurse too deeply into a function, causing you to run out of stack frames.

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

What you are trying to achieve is a buffer overflow on the stack. I think you are hoping to write to the return address and then make it call CanNeverExecute.

Then you get stack smashing detected, from gcc's stack protector. You can disable it using gcc -fno-stack-protector. Of course, don't ever do that with programs you intend on running for production.

Answer 2

First of all, using any function in an incorrect manner is not recommended. Even if you do so, most of the times the code will not work.

Also, as far as I know "Stack Overflow" is a runtime error, which usually occurs when you try to store something which has a size larger than the size of the allotted stack.

Answer 3

You can not "enable stack overflow" - this is a name of a class of errors which can happen in C and other languages. See Wikipedia article for details.

So, basically, stack overflow is what's happening with your program and what makes the program to terminate.

In a simple program, either staring at the code long enough until you see the error or using a debugger (called gdb) to go through the program step by step should help you to find the problem.

Answer 4

This question on Stack Overflow lists almost all possible ways to cause Stack overflows in many languages.