Re: [PATCH RFC 1/6] net: rfkill: gpio: fix gpio name buffer size off by 1

[Chen-Yu Tsai <wens-jdAy2FN1RRM@public.gmane.org>]

On Fri, Jan 17, 2014 at 5:46 PM, David Laight <David.Laight-JxhZ9S5GRejQT0dZR+AlfA@public.gmane.org> wrote:
> From: Chen-Yu Tsai
>> snprintf should be passed the complete size of the buffer, including
>> the space for '\0'. The previous code resulted in the *_reset and
>> *_shutdown strings being truncated.
> ...
>> diff --git a/net/rfkill/rfkill-gpio.c b/net/rfkill/rfkill-gpio.c
> ...
>> -     snprintf(rfkill->reset_name, len + 6 , "%s_reset", rfkill->name);
>> -     snprintf(rfkill->shutdown_name, len + 9, "%s_shutdown", rfkill->name);
>> +     snprintf(rfkill->reset_name, len + 7 , "%s_reset", rfkill->name);
>> +     snprintf(rfkill->shutdown_name, len + 10, "%s_shutdown", rfkill->name);
>
> I can't find the context for the above, but they look very dubious.
> I'd expect: snprintf(foo, sizeof foo, ...).
> If you are trying to truncate rfkill->name you need to use %.*s.

The driver allocates these buffers on the fly, a few lines above:

        len = strlen(rfkill->name);
        rfkill->reset_name = devm_kzalloc(&pdev->dev, len + 7, GFP_KERNEL);
        rfkill->shutdown_name = devm_kzalloc(&pdev->dev, len + 10, GFP_KERNEL);

I am not trying to truncate rfkill->name. Rather, the buffer length passed
to snprintf was wrong, so the resulting name was truncated by one character.


Thanks,
ChenYu