linux-kernel - Re: [PATCH] firmware: ti_sci: Fix an off-by-one in ti_sci_debugfs

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Message-ID: <6fa05bc4-55ad-4173-9af0-9db713b4d148@kadam.mountain>
Date:   Mon, 30 Oct 2023 11:00:59 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Tero Kristo <t-kristo@...com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] firmware: ti_sci: Fix an off-by-one in
 ti_sci_debugfs_create()

On Sun, Oct 29, 2023 at 08:52:36AM +0100, Christophe JAILLET wrote:
> The ending NULL is not taken into account by strncat(), so switch to
> strlcat() to correctly compute the size of the available memory when
> building 'debug_name'.
> 
> Because of the difference in the return type between strncat() and
> strlcat(), some code shuffling is needed.
> 
> Fixes: aa276781a64a ("firmware: Add basic support for TI System Control Interface (TI-SCI) protocol")

The fixes tag isn't really required.

> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/firmware/ti_sci.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/firmware/ti_sci.c b/drivers/firmware/ti_sci.c
> index 7041befc756a..1036c6b0f3eb 100644
> --- a/drivers/firmware/ti_sci.c
> +++ b/drivers/firmware/ti_sci.c
> @@ -181,10 +181,9 @@ static int ti_sci_debugfs_create(struct platform_device *pdev,
>  	/* Setup NULL termination */
>  	info->debug_buffer[info->debug_region_size] = 0;
>  
> -	info->d = debugfs_create_file(strncat(debug_name, dev_name(dev),
> -					      sizeof(debug_name) -
> -					      sizeof("ti_sci_debug@")),
> -				      0444, NULL, info, &ti_sci_debug_fops);
> +	strlcat(debug_name, dev_name(dev), sizeof(debug_name));

Eventually we are going to want to get rid for the strlcat() as well,
right?  Everyone hates strl* functions because they do a strlen() on
the src string.  It's fine if the src string is a string constant, I
suppose.  Here we basically trust dev_name() to be reasonable so either
strncat and strlcpy() are fine I guess...

But it's is more readable if the we use snprintf().

        snprintf(debug_name, sizeof(debug_name),
                 "ti_sci_debug@%s", dev_name(dev));

regards,
dan carpenter

> +	info->d = debugfs_create_file(debug_name, 0444, NULL, info,
> +				      &ti_sci_debug_fops);
>  	if (IS_ERR(info->d))
>  		return PTR_ERR(info->d);
>  
> -- 
> 2.34.1
>