linux-kernel - [PATCH 3.16 072/305] media: cx231xx: fix potential sign-extension overflow on large shift

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Message-ID: <lsq.1549201508.768417032@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Mauro Carvalho Chehab" <mchehab+samsung@...nel.org>,
        "Colin Ian King" <colin.king@...onical.com>,
        "Hans Verkuil" <hverkuil@...all.nl>
Subject: [PATCH 3.16 072/305] media: cx231xx: fix potential sign-extension
 overflow on large shift

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Colin Ian King <colin.king@...onical.com>

commit 32ae592036d7aeaabcccb2b1715373a68639a768 upstream.

Shifting the u8 value[3] by an int can lead to sign-extension
overflow. For example, if value[3] is 0xff and the shift is 24 then it
is promoted to int and then the top bit is sign-extended so that all
upper 32 bits are set.  Fix this by casting value[3] to a u32 before
the shift.

Detected by CoverityScan, CID#1016522 ("Unintended sign extension")

Fixes: e0d3bafd0258 ("V4L/DVB (10954): Add cx231xx USB driver")

Signed-off-by: Colin Ian King <colin.king@...onical.com>
Signed-off-by: Hans Verkuil <hverkuil@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/media/usb/cx231xx/cx231xx-video.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/media/usb/cx231xx/cx231xx-video.c
+++ b/drivers/media/usb/cx231xx/cx231xx-video.c
@@ -1271,7 +1271,7 @@ int cx231xx_g_register(struct file *file
 		ret = cx231xx_read_ctrl_reg(dev, VRT_GET_REGISTER,
 				(u16)reg->reg, value, 4);
 		reg->val = value[0] | value[1] << 8 |
-			value[2] << 16 | value[3] << 24;
+			value[2] << 16 | (u32)value[3] << 24;
 		reg->size = 4;
 		break;
 	case 1:	/* AFE - read byte */