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

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Message-Id: <6eb7d811-5c0a-4d0a-84f4-57323fd794e0@app.fastmail.com>
Date: Fri, 19 Jul 2024 16:28:19 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Bartosz Golaszewski" <brgl@...ev.pl>, "Arnd Bergmann" <arnd@...nel.org>
Cc: "Linus Walleij" <linus.walleij@...aro.org>,
 "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: virtuser: avoid non-constant format string

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