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

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

[Takashi Iwai]

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@suse.de>
---
 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;
 }
-- 
2.16.4

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

[Rafael J. Wysocki]

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@suse.de>
> ---
>  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!