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List:       linux-iio
Subject:    Re: [PATCH] iio: adc: stm32-adc: replace deprecated strncpy
From:       Kees Cook <keescook () chromium ! org>
Date:       2023-09-30 17:57:03
Message-ID: 202309301056.5A21C37D5 () keescook
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On Sat, Sep 30, 2023 at 06:41:18PM +0100, Jonathan Cameron wrote:
> 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?

I would use "iio: adc: stm32-adc: Replace deprecated strncpy() with strscpy()"

Thanks!

-Kees

-- 
Kees Cook


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