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.

Signed-off-by James Patrick-Evans <[email protected]>

---
drivers/usb/misc/legousbtower.c | 35 +++++++++++++++++------------------

1 file changed, 17 insertions(+), 18 deletions(-)

When you sent this the last time (back on Sept 2), I sent you a "simpler" patch, the same one below, and asked you if that worked instead. I never heard back, could you test this patch and see if it resolves the issue for you?

Quoted 4 lines · Greg KH

When you sent this the last time (back on Sept 2), I sent you a "simpler" patch, the same one below, and asked you if that worked instead. I never heard back, could you test this patch and see if it resolves the issue for you?

As far as I can tell, your patches are identical.

Quoted 7 lines · Oliver Neukum

Quoted 4 lines · Greg KH

When you sent this the last time (back on Sept 2), I sent you a "simpler" patch, the same one below, and asked you if that worked instead. I never heard back, could you test this patch and see if it resolves the issue for you?

As far as I can tell, your patches are identical.

Hah, so they are. James's original patch was not this one, sorry for not looking at it closer.

James, any reason why you are passing off my patch as yours here? Did you test mine and see that this did solve the problem? You did change your changelog text a bit, to reflect the change between mine and yours, so I'm guessing that you did?

thanks,

greg k-h

Hi greg,

Many appologies, I did not see your patch attached/forgot it existed when I
fixed this yesterday. I created this patch based on your
feedback from my original email on September 2nd. I have tested this patch with an emulated device and it fixes the vulnerability.
Again, applogies for the long delay and patch confusion.

From: Greg Kroah-Hartman <[email protected]>

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.

Reported-by James Patrick-Evans <[email protected]>

Tested-by James Patrick-Evans <[email protected]>

Signed-off-by James Patrick-Evans <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
drivers/usb/misc/legousbtower.c | 35 +++++++++++++++++------------------

1 file changed, 17 insertions(+), 18 deletions(-)

drivers/usb/misc/legousbtower.c +17 -18

index 7771be3..4dd531a 100644
@@ -898,24 +898,6 @@ 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),

@@ -936,6 +918,23 @@ 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;

--