HID: multitouch: handle faulty Elo touch device

commit 81bcbad5 upstream.

Since kernel v5.0, one single win8 touchscreen device failed.
And it turns out this is because it reports 2 InRange usage per touch.

It's a first, and I *really* wonder how this was allowed by Microsoft in
the first place. But IIRC, Breno told me this happened *after* a firmware
upgrade...

Anyway, better be safe for those crappy devices, and make sure we have
a full slot before jumping to the next.
This won't prevent all crappy devices to fail here, but at least we will
have a safeguard as long as the contact ID and the X and Y coordinates
are placed in the report after the grabage.

Fixes: 01eaac7e ("HID: multitouch: remove one copy of values")
CC: stable@vger.kernel.org # v5.0+
Reported-and-tested-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hid/hid-multitouch.c

@@ -641,6 +641,13 @@ static void mt_store_field(struct hid_device *hdev,
 	if (*target != DEFAULT_TRUE &&
 	    *target != DEFAULT_FALSE &&
 	    *target != DEFAULT_ZERO) {
+		if (usage->contactid == DEFAULT_ZERO ||
+		    usage->x == DEFAULT_ZERO ||
+		    usage->y == DEFAULT_ZERO) {
+			hid_dbg(hdev,
+				"ignoring duplicate usage on incomplete");
+			return;
+		}
 		usage = mt_allocate_usage(hdev, application);
 		if (!usage)
 			return;