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

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Date:   Tue, 13 Nov 2018 01:12:48 +0900
From:   Huijin Park <bbanghj.park@...il.com>
To:     boris.brezillon@...tlin.com
Cc:     huijin.park@...sung.com, marek.vasut@...il.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: cast to u64 to avoid unexpected error

Hi Boris

Thanks for review.
I will send patch again.

On Wed, Oct 31, 2018 at 10:55 PM Boris Brezillon
<boris.brezillon@...tlin.com> wrote:
>
> 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.
>

I agree that enforcing code correctness is important as your said too.

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

Thanks & best regards,

Huijin