Overwriting a function pointer in global memory, see detail on https://blog.gypsyengineer.com/fun/security/global-buffer-overflows.html

gbo.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
 
void do_something(void) {
    printf("this is not a secret\n");
}
 
void print_secret(void) {
    printf("this is a secret\n");
}
 
// uninitialized function pointer
void (*func)(void);
 
// a buffer for password
char buffer[16];
 
int main(int argc, char **argv) {
    if(argc < 2) {
        printf("pass a password\n");
        exit(-1);
    }
 
    func = &do_something;
 
    // copy pass phrase to the buffer
    strcpy(buffer, argv[1]);
 
    // check if the password is correct
    if (strcmp(buffer, "password") == 0) {
        printf("access granted\n");
        func = &print_secret;
    }
 
    func();
}