static ssize_t hiddev_read(struct file * file, char __user * buffer, size_t count, loff_t *ppos)
{
	DEFINE_WAIT(wait);
	struct hiddev_list *list = file->private_data;
	int event_size;
	int retval;

	event_size = ((list->flags & HIDDEV_FLAG_UREF) != 0) ?
		sizeof(struct hiddev_usage_ref) : sizeof(struct hiddev_event);

	if (count < event_size)
		return 0;

	/* lock against other threads */
	retval = mutex_lock_interruptible(&list->thread_lock);
	if (retval)
		return -ERESTARTSYS;

	while (retval == 0) {
		if (list->head == list->tail) {
			prepare_to_wait(&list->hiddev->wait, &wait, TASK_INTERRUPTIBLE);

			while (list->head == list->tail) {
				if (signal_pending(current)) {
					retval = -ERESTARTSYS;
					break;
				}
				if (!list->hiddev->exist) {
					retval = -EIO;
					break;
				}
				if (file->f_flags & O_NONBLOCK) {
					retval = -EAGAIN;
					break;
				}

				/* let O_NONBLOCK tasks run */
				mutex_unlock(&list->thread_lock);
				schedule();
				if (mutex_lock_interruptible(&list->thread_lock)) {
					finish_wait(&list->hiddev->wait, &wait);
					return -EINTR;
				}
				set_current_state(TASK_INTERRUPTIBLE);
			}
			finish_wait(&list->hiddev->wait, &wait);

		}

		if (retval) {
			mutex_unlock(&list->thread_lock);
			return retval;
		}


		while (list->head != list->tail &&
		       retval + event_size <= count) {
			if ((list->flags & HIDDEV_FLAG_UREF) == 0) {
				if (list->buffer[list->tail].field_index != HID_FIELD_INDEX_NONE) {
					struct hiddev_event event;

					event.hid = list->buffer[list->tail].usage_code;
					event.value = list->buffer[list->tail].value;
					if (copy_to_user(buffer + retval, &event, sizeof(struct hiddev_event))) {
						mutex_unlock(&list->thread_lock);
						return -EFAULT;
					}
					retval += sizeof(struct hiddev_event);
				}
			} else {
				if (list->buffer[list->tail].field_index != HID_FIELD_INDEX_NONE ||
				    (list->flags & HIDDEV_FLAG_REPORT) != 0) {

					if (copy_to_user(buffer + retval, list->buffer + list->tail, sizeof(struct hiddev_usage_ref))) {
						mutex_unlock(&list->thread_lock);
						return -EFAULT;
					}
					retval += sizeof(struct hiddev_usage_ref);
				}
			}
			list->tail = (list->tail + 1) & (HIDDEV_BUFFER_SIZE - 1);
		}

	}
	mutex_unlock(&list->thread_lock);

	return retval;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.