linux-kernel - Re: [PATCH] mtd: cast to u64 to avoid unexpected error

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Message-ID: <20181031145505.6b034b84@bbrezillon>
Date:   Wed, 31 Oct 2018 14:55:05 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Huijin Park <huijin.park@...sung.com>
Cc:     Marek Vasut <marek.vasut@...il.com>, linux-mtd@...ts.infradead.org,
        bbanghj.park@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: cast to u64 to avoid unexpected error

Hi Huijin,

Subject prefix should be "mtd: spi-nor: ...", and please replace
"unexpected error" by "unsigned int overflows".

On Thu, 23 Aug 2018 03:28:02 -0400
Huijin Park <huijin.park@...sung.com> wrote:

> From: "huijin.park" <huijin.park@...sung.com>
> 
> the params->size is defined as "u64"
> and, "info->sector_size" and "info->n_sectors" is defined as unsgined and u16

						 ^ are		^ unsigned

> thus, u64 data might have strange data(loss data) if data is overflow.

						    ^ if the result
overflows an unsigned int.

> this patch cast it to u64.

	     ^casts info->sector_size to an u64.

> 
> Signed-off-by: huijin.park <huijin.park@...sung.com>
> ---
>  drivers/mtd/spi-nor/spi-nor.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index d9c368c..527f281 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -2459,7 +2459,7 @@ static int spi_nor_init_params(struct spi_nor *nor,
>  	memset(params, 0, sizeof(*params));
>  
>  	/* Set SPI NOR sizes. */
> -	params->size = info->sector_size * info->n_sectors;
> +	params->size = (u64)info->sector_size * (u64)info->n_sectors;

						^ this cast is not needed.

BTW, I doubt we'll ever have to deal with NORs that are more than 4GB,
but making static code analysis tools happy and enforcing code
correctness is important too.

>  	params->page_size = info->page_size;
>  
>  	/* (Fast) Read settings. */

Regards,

Boris