uvcvideo: prevent speculative execution

CVE-2017-5753
CVE-2017-5715

real commit text tbd
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(cherry picked from commit 5d9ab7231ea9f5a1b0c3cb612e20b0b486a5bdca)
Signed-off-by: Andy Whitcroft <apw@canonical.com>

drivers/media/usb/uvc/uvc_v4l2.c

@@ -811,6 +811,7 @@ static int uvc_ioctl_enum_input(struct file *file, void *fh,
 		}
 		pin = iterm->id;
 	} else if (index < selector->bNrInPins) {
+		gmb();
 		pin = selector->baSourceID[index];
 		list_for_each_entry(iterm, &chain->entities, chain) {
 			if (!UVC_ENTITY_IS_ITERM(iterm))