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

commit 427c3a95e3e29e65f59d99aaf320d7506f3eed57 upstream.

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")
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/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 6e9fc8bcc285d122c2148cefcb7c8f57ae6c4aa2..86cbb77be038041b7cbae88d4016aef07b825ba8 100644 (file)
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2433,8 +2433,12 @@ 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;
        }