linux-kernel - Re: [PATCH] iio: dac: ad3552r-hs: fix out-of-bound write in ad3552r_hs_write_data

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Message-ID: <aQB8PRlaBY_9-L8d@smile.fi.intel.com>
Date: Tue, 28 Oct 2025 10:18:05 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Miaoqian Lin <linmq006@...il.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	Angelo Dureghello <adureghello@...libre.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] iio: dac: ad3552r-hs: fix out-of-bound write in
 ad3552r_hs_write_data_source

On Mon, Oct 27, 2025 at 11:07:13PM +0800, Miaoqian Lin wrote:
> When simple_write_to_buffer() succeeds, it returns the number of bytes
> actually copied to the buffer, which may be less than the requested
> 'count' if the buffer size is insufficient. However, the current code
> incorrectly uses 'count' as the index for null termination instead of
> the actual bytes copied, leading to out-of-bound write.
> 
> Add a check for the count and use the return value as the index.

...

> +	if (count >= sizeof(buf))
> +		return -ENOSPC;

But this makes the validation too strict now.

>  	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf,
>  				     count);

You definitely failed to read the code that implements the above.

>  	if (ret < 0)
>  		return ret;
>  
> -	buf[count] = '\0';
> +	buf[ret] = '\0';

NAK.

This patch is an unneeded churn.

-- 
With Best Regards,
Andy Shevchenko