linux-kernel - Re: [PATCH][next] i2c: mediatek: fix integer overflow on an integer multiplication

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Date:   Mon, 18 May 2020 18:59:28 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Colin King <colin.king@...onical.com>, qii.wang@...iatek.com
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] i2c: mediatek: fix integer overflow on an integer
 multiplication

On Mon, May 18, 2020 at 05:55:29PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the calculation of sample_ns is using a 32 bit integer
> multiplication and can potentially overflow. Fix this by making the
> constant a long long to use a 64 bit multiply and hence
> avoid an overflow.
> 
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: 5f1ae73d538a ("i2c: mediatek: Add i2c ac-timing adjust support")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

CCing the patch author.

> ---
>  drivers/i2c/busses/i2c-mt65xx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
> index 702061805925..c93492b997ce 100644
> --- a/drivers/i2c/busses/i2c-mt65xx.c
> +++ b/drivers/i2c/busses/i2c-mt65xx.c
> @@ -551,7 +551,7 @@ static int mtk_i2c_check_ac_timing(struct mtk_i2c *i2c,
>  	const struct i2c_spec_values *spec;
>  	unsigned int su_sta_cnt, low_cnt, high_cnt, max_step_cnt;
>  	unsigned int sda_max, sda_min, clk_ns, max_sta_cnt = 0x3f;
> -	long long sample_ns = (1000000000 * (sample_cnt + 1)) / clk_src;
> +	long long sample_ns = (1000000000LL * (sample_cnt + 1)) / clk_src;
>  
>  	if (!i2c->dev_comp->timing_adjust)
>  		return 0;
> -- 
> 2.25.1
> 

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