# \[PATCH AUTOSEL 5.11 37/67\] media: mceusb: sanity check for prescaler value

- From: Sasha Levin \<sashal@kernel.org\>
- Date: 2021-02-24 13:06:42 
- List: stable
- Page: https://ratatoskr.run/stable/2021/02/6277710
- Thread: https://ratatoskr.run/stable/2021/02/6277678/t.md

```text
From: Sean Young <sean@mess.org>

[ Upstream commit 9dec0f48a75e0dadca498002d25ef4e143e60194 ]

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

Reported-by: <redacted>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/rc/mceusb.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/media/rc/mceusb.c b/drivers/media/rc/mceusb.c
index f1dbd059ed087..43d356251d051 100644
--- a/drivers/media/rc/mceusb.c
+++ b/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;
-- 
2.27.0

```