[bug report] usbip: fix stub_rx: harden CMD_SUBMIT path to handle malicious input

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Shuah Khan,

The patch c6688ef9f297: "usbip: fix stub_rx: harden CMD_SUBMIT path
to handle malicious input" from Dec 7, 2017, leads to the following
static checker warning:

    drivers/usb/usbip/stub_rx.c:346 get_pipe()
    warn: impossible condition '(pdu->u.cmd_submit.transfer_buffer_length > ((~0 >> 1))) => (s32min-s32max > s32max)'
    drivers/usb/usbip/stub_rx.c:486 stub_recv_cmd_submit()
    warn: always true condition '(pdu->u.cmd_submit.transfer_buffer_length <= ((~0 >> 1))) => (s32min-s32max <= s32max)'

drivers/usb/usbip/stub_rx.c
   343          epd = &ep->desc;
   344  
   345          /* validate transfer_buffer_length */
   346          if (pdu->u.cmd_submit.transfer_buffer_length > INT_MAX) {
                                      ^^^^^^^^^^^^^^^^^^^^^^
This is an int.

   347                  dev_err(&sdev->udev->dev,
   348                          "CMD_SUBMIT: -EMSGSIZE transfer_buffer_length %d\n",
   349                          pdu->u.cmd_submit.transfer_buffer_length);
   350                  return -1;
   351          }


[ snip ]


   479          if (!priv->urb) {
   480                  usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
   481                  return;
   482          }
   483  
   484          /* allocate urb transfer buffer, if needed */
   485          if (pdu->u.cmd_submit.transfer_buffer_length > 0 &&
   486              pdu->u.cmd_submit.transfer_buffer_length <= INT_MAX) {
                                      ^^^^^^^^^^^^^^^^^^^^^^
   487                  priv->urb->transfer_buffer =
   488                          kzalloc(pdu->u.cmd_submit.transfer_buffer_length,
   489                                  GFP_KERNEL);
   490                  if (!priv->urb->transfer_buffer) {
   491                          usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
   492                          return;
   493                  }
   494          }

regards,
dan carpenter
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