USB: serial: pl2303: fix NULL-deref at open

commit 76ab439e upstream.

Fix NULL-pointer dereference in open() should a type-0 or type-1 device
lack the expected endpoints:

Unable to handle kernel NULL pointer dereference at virtual address 00000030
...
PC is at pl2303_open+0x38/0xec [pl2303]

Note that a missing interrupt-in endpoint would have caused open() to
fail.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/pl2303.c

@@ -185,10 +185,18 @@ static int pl2303_vendor_write(__u16 value, __u16 index,
 static int pl2303_startup(struct usb_serial *serial)
 {
 	struct pl2303_private *priv;
+	unsigned char num_ports = serial->num_ports;
 	enum pl2303_type type = type_0;
 	unsigned char *buf;
 	int i;
 
+	if (serial->num_bulk_in < num_ports ||
+			serial->num_bulk_out < num_ports ||
+			serial->num_interrupt_in < num_ports) {
+		dev_err(&serial->interface->dev, "missing endpoints\n");
+		return -ENODEV;
+	}
+
 	buf = kmalloc(10, GFP_KERNEL);
 	if (buf == NULL)
 		return -ENOMEM;