static unsigned int ffs_ep0_poll(struct file *file, poll_table *wait)
{
	struct ffs_data *ffs = file->private_data;
	unsigned int mask = POLLWRNORM;
	int ret;

	poll_wait(file, &ffs->ev.waitq, wait);

	ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
	if (unlikely(ret < 0))
		return mask;

	switch (ffs->state) {
	case FFS_READ_DESCRIPTORS:
	case FFS_READ_STRINGS:
		mask |= POLLOUT;
		break;

	case FFS_ACTIVE:
		switch (ffs->setup_state) {
		case FFS_NO_SETUP:
			if (ffs->ev.count)
				mask |= POLLIN;
			break;

		case FFS_SETUP_PENDING:
		case FFS_SETUP_CANCELLED:
			mask |= (POLLIN | POLLOUT);
			break;
		}
	case FFS_CLOSING:
		break;
	case FFS_DEACTIVATED:
		break;
	}

	mutex_unlock(&ffs->mutex);

	return mask;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.