media: mceusb: sanity check for prescaler value

commit 9dec0f4 upstream.

prescaler larger than 8 would mean the carrier is at most 152Hz,
which does not make sense for IR carriers.

Reported-by: syzbot+6d31bf169a8265204b8d@syzkaller.appspotmail.com
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/media/rc/mceusb.c

@@ -701,11 +701,18 @@ static void mceusb_dev_printdata(struct mceusb_dev *ir, u8 *buf, int buf_len,
 				data[0], data[1]);
 			break;
 		case MCE_RSP_EQIRCFS:
+			if (!data[0] && !data[1]) {
+				dev_dbg(dev, "%s: no carrier", inout);
+				break;
+			}
+			// prescaler should make sense
+			if (data[0] > 8)
+				break;
 			period = DIV_ROUND_CLOSEST((1U << data[0] * 2) *
 						   (data[1] + 1), 10);
 			if (!period)
 				break;
-			carrier = (1000 * 1000) / period;
+			carrier = USEC_PER_SEC / period;
 			dev_dbg(dev, "%s carrier of %u Hz (period %uus)",
 				 inout, carrier, period);
 			break;