USB: serial: io_edgeport: fix slab-out-of-bounds read in edge_interrupt_callback

Fix slab-out-of-bounds read in the interrupt-URB completion handler.

The boundary condition should be (length - 1) as we access
data[position + 1].

Reported-and-tested-by: [email protected]
Signed-off-by: Qiujun Huang <[email protected]>
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>

Author: Qiujun Huang

drivers/usb/serial/io_edgeport.c

@@ -710,7 +710,7 @@ static void edge_interrupt_callback(struct urb *urb)
 		/* grab the txcredits for the ports if available */
 		position = 2;
 		portNumber = 0;
-		while ((position < length) &&
+		while ((position < length - 1) &&
 				(portNumber < edge_serial->serial->num_ports)) {
 			txCredits = data[position] | (data[position+1] << 8);
 			if (txCredits) {