static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf,
				     size_t n)
{
	/*
	 * n cannot be bigger than ffs->ev.count, which cannot be bigger than
	 * size of ffs->ev.types array (which is four) so that's how much space
	 * we reserve.
	 */
	struct usb_functionfs_event events[ARRAY_SIZE(ffs->ev.types)];
	const size_t size = n * sizeof *events;
	unsigned i = 0;

	memset(events, 0, size);

	do {
		events[i].type = ffs->ev.types[i];
		if (events[i].type == FUNCTIONFS_SETUP) {
			events[i].u.setup = ffs->ev.setup;
			ffs->setup_state = FFS_SETUP_PENDING;
		}
	} while (++i < n);

	ffs->ev.count -= n;
	if (ffs->ev.count)
		memmove(ffs->ev.types, ffs->ev.types + n,
			ffs->ev.count * sizeof *ffs->ev.types);

	spin_unlock_irq(&ffs->ev.waitq.lock);
	mutex_unlock(&ffs->mutex);

	return unlikely(copy_to_user(buf, events, size)) ? -EFAULT : size;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.