USB: serial: ftdi_sio: fix latency-timer error handling

Make sure to detect short responses when reading the latency timer to
avoid using stale buffer data.

Note that no heap data would currently leak through sysfs as
ASYNC_LOW_LATENCY is set by default.

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

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 6dee20fc7e45..b064fad8e3ee 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1439,10 +1439,13 @@ static int read_latency_timer(struct usb_serial_port *port)
                              FTDI_SIO_GET_LATENCY_TIMER_REQUEST_TYPE,
                              0, priv->interface,
                              buf, 1, WDR_TIMEOUT);
-        if (rv < 0)
+        if (rv < 1) {
                 dev_err(&port->dev, "Unable to read latency timer: %i\n", rv);
-        else
+                if (rv >= 0)
+                        rv = -EIO;
+        } else {
                 priv->latency = buf[0];
+        }
 
         kfree(buf);