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

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Message-ID: <202309301056.5A21C37D5@keescook>
Date: Sat, 30 Sep 2023 10:57:03 -0700
From: Kees Cook <keescook@...omium.org>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Justin Stitt <justinstitt@...gle.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	linux-iio@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] iio: adc: stm32-adc: replace deprecated strncpy

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@...omium.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@...r.kernel.org
> > > Signed-off-by: Justin Stitt <justinstitt@...gle.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