linux-kernel - Re: [PATCH] MTD SPI-NOR: BUG FIX of divide by zero in new n

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Date:   Wed, 17 May 2023 08:10:11 +0100
From:   Tudor Ambarus <tudor.ambarus@...aro.org>
To:     Todd Brandt <todd.e.brandt@...el.com>, miquel.raynal@...tlin.com,
        linux-kernel@...r.kernel.org
Cc:     todd.e.brandt@...ux.intel.com, pratyush@...nel.org,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH] MTD SPI-NOR: BUG FIX of divide by zero in new n_banks
 value

Hi, Todd,

On 5/16/23 23:51, Todd Brandt wrote:
> While testing 6.4-rc1 on our Lenovo Thinkpad X1 I discovered
> that freeze, suspend, and shutdown, all hang the system. I bisected
> it to an addition made to the MTD spi-nor code.
> 
> The new "n_banks" value is being divided into without a proper check..
> Thus on certain systems this causes a divide by zero hang.
> 
> Reported-and-tested-by: Todd Brandt <todd.e.brandt@...ux.intel.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217448
> Fixes: 9d6c5d64f028 ("mtd: spi-nor: Introduce the concept of bank")
> Signed-off-by: Todd Brandt <todd.e.brandt@...el.com>
> ---
>  drivers/mtd/spi-nor/core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 0bb0ad14a2fc..084117959be4 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -2921,7 +2921,10 @@ static void spi_nor_late_init_params(struct spi_nor *nor)
>  	if (nor->flags & SNOR_F_HAS_LOCK && !nor->params->locking_ops)
>  		spi_nor_init_default_locking_ops(nor);
>  
> -	nor->params->bank_size = div64_u64(nor->params->size, nor->info->n_banks);
> +	if (nor->info->n_banks > 0)
> +		nor->params->bank_size = div64_u64(nor->params->size, nor->info->n_banks);
> +	else
> +		nor->params->bank_size = 0;
>  }
>  
>  /**

Indeed, thanks for the report and patch. You probably use the
spi-nor-generic driver, don't you?

Can you try the following change instead?

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
                      index 0bb0ad14a2fc..37f750bd7bfb 100644
--- a/drivers/mtd/spi-nor/core.cdrivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.cdrivers/mtd/spi-nor/core.c
@@ -2018,6 +2018,7 @@ static const struct spi_nor_manufacturer
*manufacturers[] = {

 static const struct flash_info spi_nor_generic_flash = {
        .name = "spi-nor-generic",
+       .n_banks = 1,
        /*
         * JESD216 rev A doesn't specify the page size, therefore we need a
         * sane default.