USB: serial: ti_usb_3410_5052: fix array underflow in completion handler

BugLink: https://bugs.launchpad.net/bugs/1798587

commit 5dfdd24e upstream.

Similarly to a recently reported bug in io_ti, a malicious USB device
could set port_number to a negative value and we would underflow the
port array in the interrupt completion handler.

As these devices only have one or two ports, fix this by making sure we
only consider the seventh bit when determining the port number (and
ignore bits 0xb0 which are typically set to 0x30).

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/usb/serial/ti_usb_3410_5052.h

@@ -227,7 +227,7 @@ struct ti_interrupt {
 } __attribute__((packed));
 
 /* Interrupt codes */
-#define TI_GET_PORT_FROM_CODE(c)	(((c) >> 4) - 3)
+#define TI_GET_PORT_FROM_CODE(c)	(((c) >> 6) & 0x01)
 #define TI_GET_FUNC_FROM_CODE(c)	((c) & 0x0f)
 #define TI_CODE_HARDWARE_ERROR		0xFF
 #define TI_CODE_DATA_ERROR		0x03