[PATCH 4.4 34/60] USB: serial: ftdi_sio: fix latency-timer error handling

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

commit e3e574ad85a208cb179f33720bb5f12b453de33c upstream.

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/serial/ftdi_sio.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- 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
 			     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);