linux-kernel - Re: [PATCH] rtc: rtc-ds1672: fix unintended sign extension

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Message-ID: <20190205215939.GJ24598@piout.net>
Date:   Tue, 5 Feb 2019 22:59:39 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: rtc-ds1672: fix unintended sign extension

On 05/02/2019 18:04:49+0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Shifting a u8 by 24 will cause the value to be promoted to an integer. If
> the top bit of the u8 is set then the following conversion to an unsigned
> long will sign extend the value causing the upper 32 bits to be set in
> the result.
> 
> Fix this by casting the u8 value to an unsigned long before the shift.
> 
> Detected by CoverityScan, CID#138801 ("Unintended sign extension")
> 
> Fixes: edf1aaa31fc5 ("[PATCH] RTC subsystem: DS1672 driver")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/rtc/rtc-ds1672.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
Applied, thanks.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com