为什么GCC不会发生缓冲区溢出？

Question

I was just recently learning about buffer overflows. I was attempting to replicate it using GCC. Here's the code I wrote.

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

int main(int argc, char *argv[])
{
    int value = 5;
    char buffer_one[8], buffer_two[8];

    strcpy(buffer_one, "one");
    strcpy(buffer_two, "two");

    printf("[BEFORE] buffer_two is at %p and contains %s\n", buffer_two, buffer_two);
    printf("[BEFORE] buffer_one is at %p and contains %s\n", buffer_one, buffer_one);
    printf("[BEFORE] value is at %p and contains %d\n\n", value, value);

    printf("[STRCPY] copying %d bytes into buffer_two\n\n", strlen(argv[1]));
    strcpy(buffer_two, argv[1]);

    printf("[BEFORE] buffer_two is at %p and contains %s\n", buffer_two, buffer_two);
    printf("[BEFORE] buffer_one is at %p and contains %s\n", buffer_one, buffer_one);
    printf("[BEFORE] value is at %p and contains %d\n\n", value, value);

    return 0;
}

Seems like it should work, right? Buffer_two and buffer_one are adjacent from each other in memory.

[BEFORE] buffer_two is at 0x7fff56ff2b68 and contains two
[BEFORE] buffer_one is at 0x7fff56ff2b70 and contains one
[BEFORE] value is at 0x5 and contains 5

However, shortly following this…

[STRCPY] copying 14 bytes into buffer_two

Abort trap: 6

How come C recognizes this? And how can some hackers execute more complex buffer overflows that actually work?

Answer 1

In your case, you've successfuly produced a buffer overflow by attempting to write 14 char s in a memory region of 8 char s.

As soon as you write past the allocated memory, the behaviour goes undefined. So, the Abort message is there.

Related: undefined behaviour .

Answer 2

Why doesn't buffer overflow occur with GCC?

Well, it is happenning in your case. That's why, as a side effect you can see the Abort message.

Answer 3

What happens when a buffer overflow occurs is undefined . That means that anything might happen. For instance, demons may fly from your nose .

What happened here is that your program crashed. Rather boring.