Input: ims-psu - check if CDC union descriptor is sane

BugLink: http://bugs.launchpad.net/bugs/1744636

commit ea04efee upstream.

Before trying to use CDC union descriptor, try to validate whether that it
is sane by checking that intf->altsetting->extra is big enough and that
descriptor bLength is not too big and not too small.
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/input/misc/ims-pcu.c

@@ -1635,13 +1635,25 @@ ims_pcu_get_cdc_union_desc(struct usb_interface *intf)
 		return NULL;
 	}
 
-	while (buflen > 0) {
+	while (buflen >= sizeof(*union_desc)) {
 		union_desc = (struct usb_cdc_union_desc *)buf;
 
+		if (union_desc->bLength > buflen) {
+			dev_err(&intf->dev, "Too large descriptor\n");
+			return NULL;
+		}
+
 		if (union_desc->bDescriptorType == USB_DT_CS_INTERFACE &&
 		    union_desc->bDescriptorSubType == USB_CDC_UNION_TYPE) {
 			dev_dbg(&intf->dev, "Found union header\n");
-			return union_desc;
+
+			if (union_desc->bLength >= sizeof(*union_desc))
+				return union_desc;
+
+			dev_err(&intf->dev,
+				"Union descriptor to short (%d vs %zd\n)",
+				union_desc->bLength, sizeof(*union_desc));
+			return NULL;
 		}
 
 		buflen -= union_desc->bLength;