[media] usbvision: fix NULL-deref at probe

Make sure to check the number of endpoints to avoid dereferencing a
NULL-pointer or accessing memory beyond the endpoint array should a
malicious device lack the expected endpoints.

Fixes: 2a9f8b5d25be ("V4L/DVB (5206): Usbvision: set alternate interface
modification")

Cc: stable <stable@vger.kernel.org>     # 2.6.21
Cc: Thierry MERLE <thierry.merle@free.fr>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/usbvision/usbvision-video.c

@@ -1501,7 +1501,14 @@ static int usbvision_probe(struct usb_interface *intf,
 	}
 
 	for (i = 0; i < usbvision->num_alt; i++) {
-		u16 tmp = le16_to_cpu(uif->altsetting[i].endpoint[1].desc.
+		u16 tmp;
+
+		if (uif->altsetting[i].desc.bNumEndpoints < 2) {
+			ret = -ENODEV;
+			goto err_pkt;
+		}
+
+		tmp = le16_to_cpu(uif->altsetting[i].endpoint[1].desc.
 				      wMaxPacketSize);
 		usbvision->alt_max_pkt_size[i] =
 			(tmp & 0x07ff) * (((tmp & 0x1800) >> 11) + 1);