Input: pegasus_notetaker - fix endpoint sanity check

commit bcfcb7f9 upstream.

The driver was checking the number of endpoints of the first alternate
setting instead of the current one, something which could be used by a
malicious device (or USB descriptor fuzzer) to trigger a NULL-pointer
dereference.

Fixes: 1afca2b6 ("Input: add Pegasus Notetaker tablet driver")
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Martin Kepplinger <martink@posteo.de>
Acked-by: Vladis Dronov <vdronov@redhat.com>
Link: https://lore.kernel.org/r/20191210113737.4016-2-johan@kernel.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/input/tablet/pegasus_notetaker.c

@@ -274,7 +274,7 @@ static int pegasus_probe(struct usb_interface *intf,
 		return -ENODEV;
 
 	/* Sanity check that the device has an endpoint */
-	if (intf->altsetting[0].desc.bNumEndpoints < 1) {
+	if (intf->cur_altsetting->desc.bNumEndpoints < 1) {
 		dev_err(&intf->dev, "Invalid number of endpoints\n");
 		return -EINVAL;
 	}