USB: serial: ftdi_sio: fix modem-status error handling

Make sure to detect short responses when fetching the modem status in
order to avoid parsing uninitialised buffer data and having bits of it
leak to user space.

Note that we still allow for short 1-byte responses.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 23d14b98ae2a778282ec186d7a80805ee2e103aa..6dee20fc7e455bb83834a371b2a9c90b2627c7f2 100644 (file)
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2428,8 +2428,12 @@ static int ftdi_get_modem_status(struct usb_serial_port *port,
                        FTDI_SIO_GET_MODEM_STATUS_REQUEST_TYPE,
                        0, priv->interface,
                        buf, len, WDR_TIMEOUT);
-       if (ret < 0) {
+
+       /* NOTE: We allow short responses and handle that below. */
+       if (ret < 1) {
                dev_err(&port->dev, "failed to get modem status: %d\n", ret);
+               if (ret >= 0)
+                       ret = -EIO;
                ret = usb_translate_errors(ret);
                goto out;
        }