linux-kernel - Re: [PATCH] staging: iio: frequency: ad9834: Validate frequency parameter value

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Message-ID: <b7cc378d-11a8-44b6-a86f-baee12b5b1fa@suswa.mountain>
Date: Wed, 3 Jul 2024 15:29:52 +0200
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Aleksandr Mishin <amishin@...rgos.ru>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Jonathan Cameron <jic23@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Datta Shubhrajyoti <shubhrajyoti@...com>, linux-iio@...r.kernel.org,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH] staging: iio: frequency: ad9834: Validate frequency
 parameter value

On Wed, Jul 03, 2024 at 01:47:34PM +0300, Aleksandr Mishin wrote:
> In ad9834_write_frequency() clk_get_rate() can return 0. In such case
> ad9834_calc_freqreg() call will lead to division by zero. Checking
> 'if (fout > (clk_freq / 2))' doesn't protect in case of 'fout' is 0.
> ad9834_write_frequency() is called from ad9834_write(), where fout is
> taken from text buffer, which can contain any value.
> 
> Modify parameters checking.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 12b9d5bf76bf ("Staging: IIO: DDS: AD9833 / AD9834 driver")
> Signed-off-by: Aleksandr Mishin <amishin@...rgos.ru>
> ---
>  drivers/staging/iio/frequency/ad9834.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/iio/frequency/ad9834.c b/drivers/staging/iio/frequency/ad9834.c
> index a7a5cdcc6590..9e42129f44f7 100644
> --- a/drivers/staging/iio/frequency/ad9834.c
> +++ b/drivers/staging/iio/frequency/ad9834.c
> @@ -114,7 +114,7 @@ static int ad9834_write_frequency(struct ad9834_state *st,
>  
>  	clk_freq = clk_get_rate(st->mclk);
>  
> -	if (fout > (clk_freq / 2))
> +	if (!fout || fout > (clk_freq / 2))

So you don't want "clk_freq" to be zero so you check if "fout" can be
zero and do the algebra?  That's a lot of acrobatics.  Just check
if clk_freq == 0 directly.

regards,
dan carpenter

>  		return -EINVAL;
>  
>  	regval = ad9834_calc_freqreg(clk_freq, fout);
> -- 
> 2.30.2
>