USB: serial: spcp8x5: fix modem-status handling

commit 5ed8d41023751bdd3546f2fe4118304357efe8d2 upstream.

Make sure to detect short control transfers and return zero on success
when retrieving the modem status.

This fixes the TIOCMGET implementation which since e1ed212d8593 ("USB:
spcp8x5: add proper modem-status support") has returned TIOCM_LE on
successful retrieval, and avoids leaking bits from the stack on short
transfers.

This also fixes the carrier-detect implementation which since the above
mentioned commit unconditionally has returned true.

Fixes: e1ed212d8593 ("USB: spcp8x5: add proper modem-status support")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/serial/spcp8x5.c b/drivers/usb/serial/spcp8x5.c
index 475e6c31b266b013ed4749b482c0477eda4a3904..ddfd787c461cb5367c1f932b3edffb42c0812832 100644 (file)
--- a/drivers/usb/serial/spcp8x5.c
+++ b/drivers/usb/serial/spcp8x5.c
@@ -232,11 +232,17 @@ static int spcp8x5_get_msr(struct usb_serial_port *port, u8 *status)
        ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
                              GET_UART_STATUS, GET_UART_STATUS_TYPE,
                              0, GET_UART_STATUS_MSR, buf, 1, 100);
-       if (ret < 0)
+       if (ret < 1) {
                dev_err(&port->dev, "failed to get modem status: %d\n", ret);
+               if (ret >= 0)
+                       ret = -EIO;
+               goto out;
+       }
 
        dev_dbg(&port->dev, "0xc0:0x22:0:6  %d - 0x02%x\n", ret, *buf);
        *status = *buf;
+       ret = 0;
+out:
        kfree(buf);
 
        return ret;