Re: [PATCH] ACPI: fan: Use scnprintf() for avoiding potential buffer overflow

["Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>]

On Wednesday, March 11, 2020 8:08:51 AM CET Takashi Iwai wrote:
> Since snprintf() returns the would-be-output size instead of the
> actual output size, the succeeding calls may go beyond the given
> buffer limit.  Fix it by replacing with scnprintf().
> 
> Also adjust the argument to really match with the actually remaining
> buffer size.
> 
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
>  drivers/acpi/fan.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/acpi/fan.c b/drivers/acpi/fan.c
> index aaf4e8f348cf..873e039ad4b7 100644
> --- a/drivers/acpi/fan.c
> +++ b/drivers/acpi/fan.c
> @@ -276,29 +276,29 @@ static ssize_t show_state(struct device *dev, struct device_attribute *attr, cha
>  	int count;
>  
>  	if (fps->control == 0xFFFFFFFF || fps->control > 100)
> -		count = snprintf(buf, PAGE_SIZE, "not-defined:");
> +		count = scnprintf(buf, PAGE_SIZE, "not-defined:");
>  	else
> -		count = snprintf(buf, PAGE_SIZE, "%lld:", fps->control);
> +		count = scnprintf(buf, PAGE_SIZE, "%lld:", fps->control);
>  
>  	if (fps->trip_point == 0xFFFFFFFF || fps->trip_point > 9)
> -		count += snprintf(&buf[count], PAGE_SIZE, "not-defined:");
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "not-defined:");
>  	else
> -		count += snprintf(&buf[count], PAGE_SIZE, "%lld:", fps->trip_point);
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "%lld:", fps->trip_point);
>  
>  	if (fps->speed == 0xFFFFFFFF)
> -		count += snprintf(&buf[count], PAGE_SIZE, "not-defined:");
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "not-defined:");
>  	else
> -		count += snprintf(&buf[count], PAGE_SIZE, "%lld:", fps->speed);
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "%lld:", fps->speed);
>  
>  	if (fps->noise_level == 0xFFFFFFFF)
> -		count += snprintf(&buf[count], PAGE_SIZE, "not-defined:");
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "not-defined:");
>  	else
> -		count += snprintf(&buf[count], PAGE_SIZE, "%lld:", fps->noise_level * 100);
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "%lld:", fps->noise_level * 100);
>  
>  	if (fps->power == 0xFFFFFFFF)
> -		count += snprintf(&buf[count], PAGE_SIZE, "not-defined\n");
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "not-defined\n");
>  	else
> -		count += snprintf(&buf[count], PAGE_SIZE, "%lld\n", fps->power);
> +		count += scnprintf(&buf[count], PAGE_SIZE - count, "%lld\n", fps->power);
>  
>  	return count;
>  }
> 

Applied as 5.7 material, thanks!