USB: serial: mct_u232: fix modem-status error handling

commit 36356a669eddb32917fc4b5c2b9b8bf80ede69de upstream.

Make sure to detect short control-message transfers so that errors are
logged when reading the modem status at open.

Note that while this also avoids initialising the modem status using
uninitialised heap data, these bits could not leak to user space as they
are currently not used.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/serial/mct_u232.c b/drivers/usb/serial/mct_u232.c
index a7e7ba65a6112e1e41280c2b0b5029c7f0076457..801c697148eff979fc44afbe93ddd1e3591742fc 100644 (file)
--- a/drivers/usb/serial/mct_u232.c
+++ b/drivers/usb/serial/mct_u232.c
@@ -385,9 +385,13 @@ static int mct_u232_get_modem_stat(struct usb_serial *serial,
                        MCT_U232_GET_REQUEST_TYPE,
                        0, 0, buf, MCT_U232_GET_MODEM_STAT_SIZE,
                        WDR_TIMEOUT);
-       if (rc < 0) {
+       if (rc < MCT_U232_GET_MODEM_STAT_SIZE) {
                dev_err(&serial->dev->dev,
                        "Get MODEM STATus failed (error = %d)\n", rc);
+
+               if (rc >= 0)
+                       rc = -EIO;
+
                *msr = 0;
        } else {
                *msr = buf[0];