Re: [PATCH] iio: adc: stm32-adc: replace deprecated strncpy

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 23 Sep 2023 20:15:09 -0700
Kees Cook <keescook@chromium.org> wrote:

> On Thu, Sep 21, 2023 at 04:54:00AM +0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> > 
> > We should prefer more robust and less ambiguous string interfaces.
> > 
> > We expect adc->chan_name[val] to be NUL-terminated based on ch_name's
> > use within functions that expect NUL-terminated strings like strncmp and
> > printf-likes:
> > | 	if (!strncmp(stm32_adc_ic[i].name, ch_name, STM32_ADC_CH_SZ)) {
> > | 		/* Check internal channel availability */
> > | 		switch (i) {
> > | 		case STM32_ADC_INT_CH_VDDCORE:
> > | 			if (!adc->cfg->regs->or_vddcore.reg)
> > | 				dev_warn(&indio_dev->dev,
> > | 					 "%s channel not available\n", ch_name);
> > ...
> > 
> > There is no evidence that NUL-padding is needed either.  
> 
> Agreed -- it's used as a C string everywhere I can see.
> 
> > 
> > Considering the above, a suitable replacement is `strscpy` [2] due to
> > the fact that it guarantees NUL-termination on the destination buffer
> > without unnecessarily NUL-padding. If, for any reason, NUL-padding _is_
> > required we should go for `strscpy_pad`.
> > 
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> > Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> > Link: https://github.com/KSPP/linux/issues/90
> > Cc: linux-hardening@vger.kernel.org
> > Signed-off-by: Justin Stitt <justinstitt@google.com>
> > ---
> > Note: build-tested
> > ---
> >  drivers/iio/adc/stm32-adc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> > index f7613efb870d..9cdcf396d901 100644
> > --- a/drivers/iio/adc/stm32-adc.c
> > +++ b/drivers/iio/adc/stm32-adc.c
> > @@ -2209,7 +2209,7 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
> >  				ret = -EINVAL;
> >  				goto err;
> >  			}
> > -			strncpy(adc->chan_name[val], name, STM32_ADC_CH_SZ);
> > +			strscpy(adc->chan_name[val], name, STM32_ADC_CH_SZ);  
> 
> I still prefer sizeof($dst), but yes, these are the same:
> 
>         char chan_name[STM32_ADC_CH_MAX][STM32_ADC_CH_SZ];
> 
> If this needs a v2, please improve the Subject, but it is technically
> correct, so:

Hi Kees,

I can tweak the subject whilst applying.  What did you have in mind
as a better one?

Jonathan

> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 
> :)
> 
> -Kees
>