Commit message: USB: yurex: fix out-of-bounds uaccess in read handler

In general, accessing userspace memory beyond the length of the supplied
buffer in VFS read/write handlers can lead to both kernel memory corruption
(via kernel_read()/kernel_write(), which can e.g. be triggered via
sys_splice()) and privilege escalation inside userspace.

Fix it by using simple_read_from_buffer() instead of custom logic.

Fixes: 6bc235a2e24a ("USB: add driver for Meywa-Denki & Kayac YUREX")
Signed-off-by: Jann Horn <jannh@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE: CVE-2018-16276
CWE: CWE-20
Vulnerability description: An issue was discovered in yurex_read in drivers/usb/misc/yurex.c in the Linux kernel before 4.17.7. Local attackers could use user access read/writes with incorrect bounds checking in the yurex USB driver to crash the kernel or potentially escalate privileges.

Project: linux
File: yurex.c

static void yurex_delete(struct kref *kref)
{
	struct usb_yurex *dev = to_yurex_dev(kref);

	dev_dbg(&dev->interface->dev, "%s\n", __func__);

	usb_put_dev(dev->udev);
	if (dev->cntl_urb) {
		usb_kill_urb(dev->cntl_urb);
		kfree(dev->cntl_req);
		if (dev->cntl_buffer)
			usb_free_coherent(dev->udev, YUREX_BUF_SIZE,
				dev->cntl_buffer, dev->cntl_urb->transfer_dma);
		usb_free_urb(dev->cntl_urb);
	}
	if (dev->urb) {
		usb_kill_urb(dev->urb);
		if (dev->int_buffer)
			usb_free_coherent(dev->udev, YUREX_BUF_SIZE,
				dev->int_buffer, dev->urb->transfer_dma);
		usb_free_urb(dev->urb);
	}
	kfree(dev);
}

Project: linux
File: yurex.c

static void yurex_disconnect(struct usb_interface *interface)
{
	struct usb_yurex *dev;
	int minor = interface->minor;

	dev = usb_get_intfdata(interface);
	usb_set_intfdata(interface, NULL);

	/* give back our minor */
	usb_deregister_dev(interface, &yurex_class);

	/* prevent more I/O from starting */
	mutex_lock(&dev->io_mutex);
	dev->interface = NULL;
	mutex_unlock(&dev->io_mutex);

	/* wakeup waiters */
	kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
	wake_up_interruptible(&dev->waitq);

	/* decrement our usage count */
	kref_put(&dev->kref, yurex_delete);

	dev_info(&interface->dev, "USB YUREX #%d now disconnected\n", minor);
}

Project: linux
File: yurex.c

static int yurex_fasync(int fd, struct file *file, int on)
{
	struct usb_yurex *dev;

	dev = file->private_data;
	return fasync_helper(fd, file, on, &dev->async_queue);
}

Project: linux
File: yurex.c

static int yurex_open(struct inode *inode, struct file *file)
{
	struct usb_yurex *dev;
	struct usb_interface *interface;
	int subminor;
	int retval = 0;

	subminor = iminor(inode);

	interface = usb_find_interface(&yurex_driver, subminor);
	if (!interface) {
		printk(KERN_ERR "%s - error, can't find device for minor %d",
		       __func__, subminor);
		retval = -ENODEV;
		goto exit;
	}

	dev = usb_get_intfdata(interface);
	if (!dev) {
		retval = -ENODEV;
		goto exit;
	}

	/* increment our usage count for the device */
	kref_get(&dev->kref);

	/* save our object in the file's private structure */
	mutex_lock(&dev->io_mutex);
	file->private_data = dev;
	mutex_unlock(&dev->io_mutex);

exit:
	return retval;
}

Project: linux
File: yurex.c

static int yurex_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
	struct usb_yurex *dev;
	struct usb_host_interface *iface_desc;
	struct usb_endpoint_descriptor *endpoint;
	int retval = -ENOMEM;
	DEFINE_WAIT(wait);
	int res;

	/* allocate memory for our device state and initialize it */
	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		goto error;
	kref_init(&dev->kref);
	mutex_init(&dev->io_mutex);
	spin_lock_init(&dev->lock);
	init_waitqueue_head(&dev->waitq);

	dev->udev = usb_get_dev(interface_to_usbdev(interface));
	dev->interface = interface;

	/* set up the endpoint information */
	iface_desc = interface->cur_altsetting;
	res = usb_find_int_in_endpoint(iface_desc, &endpoint);
	if (res) {
		dev_err(&interface->dev, "Could not find endpoints\n");
		retval = res;
		goto error;
	}

	dev->int_in_endpointAddr = endpoint->bEndpointAddress;

	/* allocate control URB */
	dev->cntl_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->cntl_urb)
		goto error;

	/* allocate buffer for control req */
	dev->cntl_req = kmalloc(YUREX_BUF_SIZE, GFP_KERNEL);
	if (!dev->cntl_req)
		goto error;

	/* allocate buffer for control msg */
	dev->cntl_buffer = usb_alloc_coherent(dev->udev, YUREX_BUF_SIZE,
					      GFP_KERNEL,
					      &dev->cntl_urb->transfer_dma);
	if (!dev->cntl_buffer) {
		dev_err(&interface->dev, "Could not allocate cntl_buffer\n");
		goto error;
	}

	/* configure control URB */
	dev->cntl_req->bRequestType = USB_DIR_OUT | USB_TYPE_CLASS |
				      USB_RECIP_INTERFACE;
	dev->cntl_req->bRequest	= HID_REQ_SET_REPORT;
	dev->cntl_req->wValue	= cpu_to_le16((HID_OUTPUT_REPORT + 1) << 8);
	dev->cntl_req->wIndex	= cpu_to_le16(iface_desc->desc.bInterfaceNumber);
	dev->cntl_req->wLength	= cpu_to_le16(YUREX_BUF_SIZE);

	usb_fill_control_urb(dev->cntl_urb, dev->udev,
			     usb_sndctrlpipe(dev->udev, 0),
			     (void *)dev->cntl_req, dev->cntl_buffer,
			     YUREX_BUF_SIZE, yurex_control_callback, dev);
	dev->cntl_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;


	/* allocate interrupt URB */
	dev->urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->urb)
		goto error;

	/* allocate buffer for interrupt in */
	dev->int_buffer = usb_alloc_coherent(dev->udev, YUREX_BUF_SIZE,
					GFP_KERNEL, &dev->urb->transfer_dma);
	if (!dev->int_buffer) {
		dev_err(&interface->dev, "Could not allocate int_buffer\n");
		goto error;
	}

	/* configure interrupt URB */
	usb_fill_int_urb(dev->urb, dev->udev,
			 usb_rcvintpipe(dev->udev, dev->int_in_endpointAddr),
			 dev->int_buffer, YUREX_BUF_SIZE, yurex_interrupt,
			 dev, 1);
	dev->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
	if (usb_submit_urb(dev->urb, GFP_KERNEL)) {
		retval = -EIO;
		dev_err(&interface->dev, "Could not submitting URB\n");
		goto error;
	}

	/* save our data pointer in this interface device */
	usb_set_intfdata(interface, dev);
	dev->bbu = -1;

	/* we can register the device now, as it is ready */
	retval = usb_register_dev(interface, &yurex_class);
	if (retval) {
		dev_err(&interface->dev,
			"Not able to get a minor for this device.\n");
		usb_set_intfdata(interface, NULL);
		goto error;
	}

	dev_info(&interface->dev,
		 "USB YUREX device now attached to Yurex #%d\n",
		 interface->minor);

	return 0;

error:
	if (dev)
		/* this frees allocated memory */
		kref_put(&dev->kref, yurex_delete);
	return retval;
}

Project: linux
File: yurex.c

static int yurex_release(struct inode *inode, struct file *file)
{
	struct usb_yurex *dev;

	dev = file->private_data;
	if (dev == NULL)
		return -ENODEV;

	/* decrement the count on our device */
	kref_put(&dev->kref, yurex_delete);
	return 0;
}

Project: linux
File: yurex.c

 static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
			   size_t count, loff_t *ppos)
{
	struct usb_yurex *dev;
	int i, set = 0, retval = 0;
	char buffer[16];
	char *data = buffer;
	unsigned long long c, c2 = 0;
	signed long timeout = 0;
	DEFINE_WAIT(wait);

	count = min(sizeof(buffer), count);
	dev = file->private_data;

	/* verify that we actually have some data to write */
	if (count == 0)
		goto error;

	mutex_lock(&dev->io_mutex);
	if (!dev->interface) {		/* already disconnected */
		mutex_unlock(&dev->io_mutex);
		retval = -ENODEV;
		goto error;
	}

	if (copy_from_user(buffer, user_buffer, count)) {
		mutex_unlock(&dev->io_mutex);
		retval = -EFAULT;
		goto error;
	}
	memset(dev->cntl_buffer, CMD_PADDING, YUREX_BUF_SIZE);

	switch (buffer[0]) {
	case CMD_ANIMATE:
	case CMD_LED:
		dev->cntl_buffer[0] = buffer[0];
		dev->cntl_buffer[1] = buffer[1];
		dev->cntl_buffer[2] = CMD_EOF;
		break;
	case CMD_READ:
	case CMD_VERSION:
		dev->cntl_buffer[0] = buffer[0];
		dev->cntl_buffer[1] = 0x00;
		dev->cntl_buffer[2] = CMD_EOF;
		break;
	case CMD_SET:
		data++;
		/* FALL THROUGH */
	case '0' ... '9':
		set = 1;
		c = c2 = simple_strtoull(data, NULL, 0);
		dev->cntl_buffer[0] = CMD_SET;
		for (i = 1; i < 6; i++) {
			dev->cntl_buffer[i] = (c>>32) & 0xff;
			c <<= 8;
		}
		buffer[6] = CMD_EOF;
		break;
	default:
		mutex_unlock(&dev->io_mutex);
		return -EINVAL;
	}

	/* send the data as the control msg */
	prepare_to_wait(&dev->waitq, &wait, TASK_INTERRUPTIBLE);
	dev_dbg(&dev->interface->dev, "%s - submit %c\n", __func__,
		dev->cntl_buffer[0]);
	retval = usb_submit_urb(dev->cntl_urb, GFP_KERNEL);
	if (retval >= 0)
		timeout = schedule_timeout(YUREX_WRITE_TIMEOUT);
	finish_wait(&dev->waitq, &wait);

	mutex_unlock(&dev->io_mutex);

	if (retval < 0) {
		dev_err(&dev->interface->dev,
			"%s - failed to send bulk msg, error %d\n",
			__func__, retval);
		goto error;
	}
	if (set && timeout)
		dev->bbu = c2;
	return timeout ? count : -EIO;

error:
	return retval;
}