safe malloc and free with tag

my_free.c

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

#define MAGIC_TAG 0x11223344

inline static void* my_malloc(int size) {
    void* ptr = malloc(size + sizeof(MAGIC_TAG));
    int *p = (int *) ptr;
    *p = MAGIC_TAG;
    return p + 1;
}

inline static void my_free(void *ptr) {
    if (ptr == NULL) return;
    int *p = (int *) ptr - 1;
    if (*p == MAGIC_TAG) {
        *p = 0;
        free(p);
    }
}

int main() {
    char *ptr = my_malloc(100);
    my_free(ptr);
    my_free(ptr);
    my_free(ptr);
    ptr = NULL;
    my_free(ptr);

    return 0;
}