patch "usb: misc: legousbtower: Fix NULL pointer deference" added to usb-next

This is a note to let you know that I've just added the patch titled

usb: misc: legousbtower: Fix NULL pointer deference

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From: Greg Kroah-Hartman <[email protected]>
Date: Mon, 19 Sep 2016 19:09:51 +0100
Subject: usb: misc: legousbtower: Fix NULL pointer deference

This patch fixes a NULL pointer dereference caused by a race codition in the probe function of the legousbtower driver. It re-structures the probe function to only register the interface after successfully reading the board's firmware ID.

The probe function does not deregister the usb interface after an error receiving the devices firmware ID. The device file registered (/dev/usb/legousbtower%d) may be read/written globally before the probe function returns. When tower_delete is called in the probe function (after an r/w has been initiated), core dev structures are deleted while the file operation functions are still running. If the 0 address is mappable on the machine, this vulnerability can be used to create a Local Priviege Escalation exploit via a write-what-where condition by remapping dev->interrupt_out_buffer in tower_write. A forged USB device and local program execution would be required for LPE. The USB device would have to delay the control message in tower_probe and accept the control urb in tower_open whilst guest code initiated a write to the device file as tower_delete is called from the error in tower_probe.

This bug has existed since 2003. Patch tested by emulated device.

---
 drivers/usb/misc/legousbtower.c | 35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

index ece9b3c1eaac..c8fbe7b739a0 100644
@@ -886,24 +886,6 @@ static int tower_probe (struct usb_interface *interface, const struct usb_device
 	dev->interrupt_in_interval = interrupt_in_interval ? interrupt_in_interval : dev->interrupt_in_endpoint->bInterval;
 	dev->interrupt_out_interval = interrupt_out_interval ? interrupt_out_interval : dev->interrupt_out_endpoint->bInterval;
 
-	/* we can register the device now, as it is ready */
-	usb_set_intfdata (interface, dev);
-
-	retval = usb_register_dev (interface, &tower_class);
-
-	if (retval) {
-		/* something prevented us from registering this driver */
-		dev_err(idev, "Not able to get a minor for this device.\n");
-		usb_set_intfdata (interface, NULL);
-		goto error;
-	}
-	dev->minor = interface->minor;
-
-	/* let the user know what node this device is now attached to */
-	dev_info(&interface->dev, "LEGO USB Tower #%d now attached to major "
-		 "%d minor %d\n", (dev->minor - LEGO_USB_TOWER_MINOR_BASE),
-		 USB_MAJOR, dev->minor);
-
 	/* get the firmware version and log it */
 	result = usb_control_msg (udev,
 				  usb_rcvctrlpipe(udev, 0),

@@ -924,6 +906,23 @@ static int tower_probe (struct usb_interface *interface, const struct usb_device
 		 get_version_reply.minor,
 		 le16_to_cpu(get_version_reply.build_no));
 
+	/* we can register the device now, as it is ready */
+	usb_set_intfdata (interface, dev);
+
+	retval = usb_register_dev (interface, &tower_class);
+
+	if (retval) {
+		/* something prevented us from registering this driver */
+		dev_err(idev, "Not able to get a minor for this device.\n");
+		usb_set_intfdata (interface, NULL);
+		goto error;
+	}
+	dev->minor = interface->minor;
+
+	/* let the user know what node this device is now attached to */
+	dev_info(&interface->dev, "LEGO USB Tower #%d now attached to major "
+		 "%d minor %d\n", (dev->minor - LEGO_USB_TOWER_MINOR_BASE),
+		 USB_MAJOR, dev->minor);
 
 exit:
 	return retval;

2.10.0