[PATCH] gpio: virtuser: avoid non-constant format string

[PATCH] gpio: virtuser: avoid non-constant format string

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Using a string variable as an sprintf format is potentially
dangerous, and gcc can warn about this:

drivers/gpio/gpio-virtuser.c: In function 'gpio_virtuser_dbgfs_init_line_attrs':
drivers/gpio/gpio-virtuser.c:808:9: error: format not a string literal and no format arguments [-Werror=format-security]
  808 |         sprintf(data->consumer, id);
      |         ^~~~~~~

Change this instance to use a "%s" format instead to print the string
argument.

Fixes: 91581c4b3f29 ("gpio: virtuser: new virtual testing driver for the GPIO API")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpio/gpio-virtuser.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-virtuser.c b/drivers/gpio/gpio-virtuser.c
index 0e0d55da4f01..c55b72e426c7 100644
--- a/drivers/gpio/gpio-virtuser.c
+++ b/drivers/gpio/gpio-virtuser.c
@@ -805,7 +805,7 @@ static int gpio_virtuser_dbgfs_init_line_attrs(struct device *dev,
 		return -ENOMEM;
 
 	data->ad.desc = desc;
-	sprintf(data->consumer, id);
+	sprintf(data->consumer, "%s", id);
 	atomic_set(&data->irq, 0);
 	atomic_set(&data->irq_count, 0);
 
-- 
2.39.2

Re: [PATCH] gpio: virtuser: avoid non-constant format string

[Bartosz Golaszewski]

On Fri, Jul 19, 2024 at 1:46 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> Using a string variable as an sprintf format is potentially
> dangerous, and gcc can warn about this:
>
> drivers/gpio/gpio-virtuser.c: In function 'gpio_virtuser_dbgfs_init_line_attrs':
> drivers/gpio/gpio-virtuser.c:808:9: error: format not a string literal and no format arguments [-Werror=format-security]
>   808 |         sprintf(data->consumer, id);
>       |         ^~~~~~~
>
> Change this instance to use a "%s" format instead to print the string
> argument.
>
> Fixes: 91581c4b3f29 ("gpio: virtuser: new virtual testing driver for the GPIO API")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpio/gpio-virtuser.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-virtuser.c b/drivers/gpio/gpio-virtuser.c
> index 0e0d55da4f01..c55b72e426c7 100644
> --- a/drivers/gpio/gpio-virtuser.c
> +++ b/drivers/gpio/gpio-virtuser.c
> @@ -805,7 +805,7 @@ static int gpio_virtuser_dbgfs_init_line_attrs(struct device *dev,
>                 return -ENOMEM;
>
>         data->ad.desc = desc;
> -       sprintf(data->consumer, id);
> +       sprintf(data->consumer, "%s", id);
>         atomic_set(&data->irq, 0);
>         atomic_set(&data->irq_count, 0);
>
> --
> 2.39.2
>

I know this should not happen as the string is checked for length when
it is set over configfs but while we're at it: maybe make it 100%
correct by using snprintf(data->consumer, sizeof(data->consumer), ...
?

Bart

Re: [PATCH] gpio: virtuser: avoid non-constant format string

[Arnd Bergmann]

On Fri, Jul 19, 2024, at 16:10, Bartosz Golaszewski wrote:
>> diff --git a/drivers/gpio/gpio-virtuser.c b/drivers/gpio/gpio-virtuser.c
>> index 0e0d55da4f01..c55b72e426c7 100644
>> --- a/drivers/gpio/gpio-virtuser.c
>> +++ b/drivers/gpio/gpio-virtuser.c
>> @@ -805,7 +805,7 @@ static int gpio_virtuser_dbgfs_init_line_attrs(struct device *dev,
>>                 return -ENOMEM;
>>
>>         data->ad.desc = desc;
>> -       sprintf(data->consumer, id);
>> +       sprintf(data->consumer, "%s", id);
>>         atomic_set(&data->irq, 0);
>>         atomic_set(&data->irq_count, 0);
>>
>> --
>> 2.39.2
>>
>
> I know this should not happen as the string is checked for length when
> it is set over configfs but while we're at it: maybe make it 100%
> correct by using snprintf(data->consumer, sizeof(data->consumer), ...?

Actually I now think this should just be

     strscpy(data->consumer, id);

There was never a reason to use sprintf() here at all.
strscpy() does both the correct size check and avoids
treating it as a format string.

      Arnd

Re: [PATCH] gpio: virtuser: avoid non-constant format string

[Bartosz Golaszewski]

On Fri, Jul 19, 2024 at 4:28 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Jul 19, 2024, at 16:10, Bartosz Golaszewski wrote:
> >> diff --git a/drivers/gpio/gpio-virtuser.c b/drivers/gpio/gpio-virtuser.c
> >> index 0e0d55da4f01..c55b72e426c7 100644
> >> --- a/drivers/gpio/gpio-virtuser.c
> >> +++ b/drivers/gpio/gpio-virtuser.c
> >> @@ -805,7 +805,7 @@ static int gpio_virtuser_dbgfs_init_line_attrs(struct device *dev,
> >>                 return -ENOMEM;
> >>
> >>         data->ad.desc = desc;
> >> -       sprintf(data->consumer, id);
> >> +       sprintf(data->consumer, "%s", id);
> >>         atomic_set(&data->irq, 0);
> >>         atomic_set(&data->irq_count, 0);
> >>
> >> --
> >> 2.39.2
> >>
> >
> > I know this should not happen as the string is checked for length when
> > it is set over configfs but while we're at it: maybe make it 100%
> > correct by using snprintf(data->consumer, sizeof(data->consumer), ...?
>
> Actually I now think this should just be
>
>      strscpy(data->consumer, id);
>
> There was never a reason to use sprintf() here at all.
> strscpy() does both the correct size check and avoids
> treating it as a format string.
>
>       Arnd

Even better!

Bart