static ssize_t wdm_read
(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
	int rv, cntr;
	int i = 0;
	struct wdm_device *desc = file->private_data;


	rv = mutex_lock_interruptible(&desc->rlock); /*concurrent reads */
	if (rv < 0)
		return -ERESTARTSYS;

	cntr = ACCESS_ONCE(desc->length);
	if (cntr == 0) {
		desc->read = 0;
retry:
		if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
 			rv = -ENODEV;
 			goto err;
 		}
		if (test_bit(WDM_OVERFLOW, &desc->flags)) {
			clear_bit(WDM_OVERFLOW, &desc->flags);
			rv = -ENOBUFS;
			goto err;
		}
 		i++;
 		if (file->f_flags & O_NONBLOCK) {
 			if (!test_bit(WDM_READ, &desc->flags)) {
				rv = cntr ? cntr : -EAGAIN;
				goto err;
			}
			rv = 0;
		} else {
			rv = wait_event_interruptible(desc->wait,
				test_bit(WDM_READ, &desc->flags));
		}

		/* may have happened while we slept */
		if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
			rv = -ENODEV;
			goto err;
		}
		if (test_bit(WDM_RESETTING, &desc->flags)) {
			rv = -EIO;
			goto err;
		}
		usb_mark_last_busy(interface_to_usbdev(desc->intf));
		if (rv < 0) {
			rv = -ERESTARTSYS;
			goto err;
		}

		spin_lock_irq(&desc->iuspin);

		if (desc->rerr) { /* read completed, error happened */
			desc->rerr = 0;
			spin_unlock_irq(&desc->iuspin);
			rv = -EIO;
			goto err;
		}
		/*
		 * recheck whether we've lost the race
		 * against the completion handler
		 */
		if (!test_bit(WDM_READ, &desc->flags)) { /* lost race */
 			spin_unlock_irq(&desc->iuspin);
 			goto retry;
 		}

 		if (!desc->reslength) { /* zero length read */
 			dev_dbg(&desc->intf->dev, "%s: zero length - clearing WDM_READ\n", __func__);
 			clear_bit(WDM_READ, &desc->flags);
			spin_unlock_irq(&desc->iuspin);
			goto retry;
		}
		cntr = desc->length;
		spin_unlock_irq(&desc->iuspin);
	}

	if (cntr > count)
		cntr = count;
	rv = copy_to_user(buffer, desc->ubuf, cntr);
	if (rv > 0) {
		rv = -EFAULT;
		goto err;
	}

	spin_lock_irq(&desc->iuspin);

	for (i = 0; i < desc->length - cntr; i++)
		desc->ubuf[i] = desc->ubuf[i + cntr];

	desc->length -= cntr;
	/* in case we had outstanding data */
	if (!desc->length)
		clear_bit(WDM_READ, &desc->flags);

	spin_unlock_irq(&desc->iuspin);

	rv = cntr;

err:
	mutex_unlock(&desc->rlock);
	return rv;
}

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.