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 d3d6ec4551514c20880a059729ce401e08b1de34..848e4af6e10ebef5ad2a3d46f82fc06f1688e77b 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;
        }