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    Subject[PATCH 3.16 056/306] usb: misc: legousbtower: Fix NULL pointer deference
    3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    commit 2fae9e5a7babada041e2e161699ade2447a01989 upstream.

    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 <james@jmp-e.com>
    Tested-by: James Patrick-Evans <james@jmp-e.com>
    Signed-off-by: James Patrick-Evans <james@jmp-e.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/usb/misc/legousbtower.c | 35 +++++++++++++++++------------------
    1 file changed, 17 insertions(+), 18 deletions(-)

    --- a/drivers/usb/misc/legousbtower.c
    +++ b/drivers/usb/misc/legousbtower.c
    @@ -898,24 +898,6 @@ static int tower_probe (struct usb_inter
    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_inter
    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;
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