[PATCH 3.16 155/217] USB: mct_u232: add sanity checking in probe

[Ben Hutchings]

3.16.35-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Oliver Neukum <oneu...@suse.com>

commit 4e9a0b05257f29cf4b75f3209243ed71614d062e upstream.

An attack using the lack of sanity checking in probe is known. This
patch checks for the existence of a second port.

CVE-2016-3136

Signed-off-by: Oliver Neukum <oneu...@suse.com>
[johan: add error message ]
Signed-off-by: Johan Hovold <jo...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 drivers/usb/serial/mct_u232.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/usb/serial/mct_u232.c
+++ b/drivers/usb/serial/mct_u232.c
@@ -376,14 +376,21 @@ static void mct_u232_msr_to_state(struct
 
 static int mct_u232_port_probe(struct usb_serial_port *port)
 {
+       struct usb_serial *serial = port->serial;
        struct mct_u232_private *priv;
 
+       /* check first to simplify error handling */
+       if (!serial->port[1] || !serial->port[1]->interrupt_in_urb) {
+               dev_err(&port->dev, "expected endpoint missing\n");
+               return -ENODEV;
+       }
+
        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;
 
        /* Use second interrupt-in endpoint for reading. */
-       priv->read_urb = port->serial->port[1]->interrupt_in_urb;
+       priv->read_urb = serial->port[1]->interrupt_in_urb;
        priv->read_urb->context = port;
 
        spin_lock_init(&priv->lock);