USB: serial: omninet: fix NULL-derefs at open and disconnect

Fix NULL-pointer dereferences at open() and disconnect() should the
device lack the expected bulk-out endpoints:

Unable to handle kernel NULL pointer dereference at virtual address 000000b4
...
[c0170ff0>] (__lock_acquire) from [<c0172f00>] (lock_acquire+0x108/0x264)
[<c0172f00>] (lock_acquire) from [<c06a5090>] (_raw_spin_lock_irqsave+0x58/0x6c)
[<c06a5090>] (_raw_spin_lock_irqsave) from [<c0470684>] (tty_port_tty_set+0x28/0xa4)
[<c0470684>] (tty_port_tty_set) from [<bf08d384>] (omninet_open+0x30/0x40 [omninet])
[<bf08d384>] (omninet_open [omninet]) from [<bf07c118>] (serial_port_activate+0x68/0x98 [usbserial])

Unable to handle kernel NULL pointer dereference at virtual address 00000234
...
[<bf01f418>] (omninet_disconnect [omninet]) from [<bf0016c0>] (usb_serial_disconnect+0xe4/0x100 [usbserial])

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/omninet.c

@@ -38,6 +38,7 @@ static int  omninet_write(struct tty_struct *tty, struct usb_serial_port *port,
 				const unsigned char *buf, int count);
 static int  omninet_write_room(struct tty_struct *tty);
 static void omninet_disconnect(struct usb_serial *serial);
+static int omninet_attach(struct usb_serial *serial);
 static int omninet_port_probe(struct usb_serial_port *port);
 static int omninet_port_remove(struct usb_serial_port *port);
 
@@ -56,6 +57,7 @@ static struct usb_serial_driver zyxel_omninet_device = {
 	.description =		"ZyXEL - omni.net lcd plus usb",
 	.id_table =		id_table,
 	.num_ports =		1,
+	.attach =		omninet_attach,
 	.port_probe =		omninet_port_probe,
 	.port_remove =		omninet_port_remove,
 	.open =			omninet_open,
@@ -104,6 +106,17 @@ struct omninet_data {
 	__u8	od_outseq;	/* Sequence number for bulk_out URBs */
 };
 
+static int omninet_attach(struct usb_serial *serial)
+{
+	/* The second bulk-out endpoint is used for writing. */
+	if (serial->num_bulk_out < 2) {
+		dev_err(&serial->interface->dev, "missing endpoints\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
 static int omninet_port_probe(struct usb_serial_port *port)
 {
 	struct omninet_data *od;