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[PATCH] iio: sx9324: replace deprecated strncpy

Justin Stitt posted 1 patch 2 years, 2 months ago 
drivers/iio/proximity/sx9324.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
[PATCH] iio: sx9324: replace deprecated strncpy
Posted by Justin Stitt 2 years, 2 months ago 
`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

`prop` is defined as this string literal with size 30 (including null):
|       #define SX9324_PROXRAW_DEF "semtech,ph01-proxraw-strength"
|      	char prop[] = SX9324_PROXRAW_DEF;

Each of the strncpy->strscpy replacements involve string literals with a
size less than 30 which means there are no current problems with how
strncpy is used. However, let's move away from using strncpy entirely.

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on the destination buffer without
unnecessarily NUL-padding.

Moreover, let's opt for the more conventional `sizeof()` as opposed to
`ARRAY_SIZE` for these simple strings.

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>
---
FWIW: It seems fragile to base future `prop` stores on the
size of it's default string.

Note: build-tested
---
 drivers/iio/proximity/sx9324.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
index 438f9c9aba6e..25ac2733bcef 100644
--- a/drivers/iio/proximity/sx9324.c
+++ b/drivers/iio/proximity/sx9324.c
@@ -937,11 +937,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
 	case SX9324_REG_AFE_CTRL4:
 	case SX9324_REG_AFE_CTRL7:
 		if (reg_def->reg == SX9324_REG_AFE_CTRL4)
-			strncpy(prop, "semtech,ph01-resolution",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph01-resolution", sizeof(prop));
 		else
-			strncpy(prop, "semtech,ph23-resolution",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph23-resolution", sizeof(prop));
 
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
@@ -1012,11 +1010,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
 	case SX9324_REG_PROX_CTRL0:
 	case SX9324_REG_PROX_CTRL1:
 		if (reg_def->reg == SX9324_REG_PROX_CTRL0)
-			strncpy(prop, "semtech,ph01-proxraw-strength",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph01-proxraw-strength", sizeof(prop));
 		else
-			strncpy(prop, "semtech,ph23-proxraw-strength",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph23-proxraw-strength", sizeof(prop));
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
 			break;

---
base-commit: 2cf0f715623872823a72e451243bbf555d10d032
change-id: 20230921-strncpy-drivers-iio-proximity-sx9324-c-8c3437676039

Best regards,
--
Justin Stitt <justinstitt@google.com>
Re: [PATCH] iio: sx9324: replace deprecated strncpy
Posted by Jonathan Cameron 2 years, 2 months ago 
On Thu, 21 Sep 2023 07:01:01 +0000
Justin Stitt <justinstitt@google.com> wrote:

> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> `prop` is defined as this string literal with size 30 (including null):
> |       #define SX9324_PROXRAW_DEF "semtech,ph01-proxraw-strength"
> |      	char prop[] = SX9324_PROXRAW_DEF;
> 
> Each of the strncpy->strscpy replacements involve string literals with a
> size less than 30 which means there are no current problems with how
> strncpy is used. However, let's move away from using strncpy entirely.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer without
> unnecessarily NUL-padding.
> 
> Moreover, let's opt for the more conventional `sizeof()` as opposed to
> `ARRAY_SIZE` for these simple strings.
> 
> 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>
> ---
> FWIW: It seems fragile to base future `prop` stores on the
> size of it's default string.

Agreed - can we just get rid of the copying?  Just set a const char *
to point to appropriate string instead and use that?

The dance is just about reasonable for the case where there is
a string format being used to fill in the numbers, here I can't see any
advantage at all. (for the other case, a kasprintf() or similar is probably
more appropriate anyway) given this isn't a particular hot path.

Jonathan
> 
> Note: build-tested
> ---
>  drivers/iio/proximity/sx9324.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
> index 438f9c9aba6e..25ac2733bcef 100644
> --- a/drivers/iio/proximity/sx9324.c
> +++ b/drivers/iio/proximity/sx9324.c
> @@ -937,11 +937,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
>  	case SX9324_REG_AFE_CTRL4:
>  	case SX9324_REG_AFE_CTRL7:
>  		if (reg_def->reg == SX9324_REG_AFE_CTRL4)
> -			strncpy(prop, "semtech,ph01-resolution",
> -				ARRAY_SIZE(prop));
> +			strscpy(prop, "semtech,ph01-resolution", sizeof(prop));
>  		else
> -			strncpy(prop, "semtech,ph23-resolution",
> -				ARRAY_SIZE(prop));
> +			strscpy(prop, "semtech,ph23-resolution", sizeof(prop));
>  
>  		ret = device_property_read_u32(dev, prop, &raw);
>  		if (ret)
> @@ -1012,11 +1010,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
>  	case SX9324_REG_PROX_CTRL0:
>  	case SX9324_REG_PROX_CTRL1:
>  		if (reg_def->reg == SX9324_REG_PROX_CTRL0)
> -			strncpy(prop, "semtech,ph01-proxraw-strength",
> -				ARRAY_SIZE(prop));
> +			strscpy(prop, "semtech,ph01-proxraw-strength", sizeof(prop));
>  		else
> -			strncpy(prop, "semtech,ph23-proxraw-strength",
> -				ARRAY_SIZE(prop));
> +			strscpy(prop, "semtech,ph23-proxraw-strength", sizeof(prop));
>  		ret = device_property_read_u32(dev, prop, &raw);
>  		if (ret)
>  			break;
> 
> ---
> base-commit: 2cf0f715623872823a72e451243bbf555d10d032
> change-id: 20230921-strncpy-drivers-iio-proximity-sx9324-c-8c3437676039
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>
Re: [PATCH] iio: sx9324: replace deprecated strncpy
Posted by Justin Stitt 2 years, 1 month ago 
Hi Jonathan,

On Sat, Sep 23, 2023 at 10:47 AM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Thu, 21 Sep 2023 07:01:01 +0000
> Justin Stitt <justinstitt@google.com> wrote:
>
> > `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> >
> > We should prefer more robust and less ambiguous string interfaces.
> >
> > `prop` is defined as this string literal with size 30 (including null):
> > |       #define SX9324_PROXRAW_DEF "semtech,ph01-proxraw-strength"
> > |             char prop[] = SX9324_PROXRAW_DEF;
> >
> > Each of the strncpy->strscpy replacements involve string literals with a
> > size less than 30 which means there are no current problems with how
> > strncpy is used. However, let's move away from using strncpy entirely.
> >
> > A suitable replacement is `strscpy` [2] due to the fact that it
> > guarantees NUL-termination on the destination buffer without
> > unnecessarily NUL-padding.
> >
> > Moreover, let's opt for the more conventional `sizeof()` as opposed to
> > `ARRAY_SIZE` for these simple strings.
> >
> > 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>
> > ---
> > FWIW: It seems fragile to base future `prop` stores on the
> > size of it's default string.
>
> Agreed - can we just get rid of the copying?  Just set a const char *
> to point to appropriate string instead and use that?
>
> The dance is just about reasonable for the case where there is
> a string format being used to fill in the numbers, here I can't see any
> advantage at all. (for the other case, a kasprintf() or similar is probably
> more appropriate anyway) given this isn't a particular hot path.

I sent a [v2]! Can you see if this matches your vision here?

>
> Jonathan
> >
> > Note: build-tested
> > ---
> >  drivers/iio/proximity/sx9324.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
> > index 438f9c9aba6e..25ac2733bcef 100644
> > --- a/drivers/iio/proximity/sx9324.c
> > +++ b/drivers/iio/proximity/sx9324.c
> > @@ -937,11 +937,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
> >       case SX9324_REG_AFE_CTRL4:
> >       case SX9324_REG_AFE_CTRL7:
> >               if (reg_def->reg == SX9324_REG_AFE_CTRL4)
> > -                     strncpy(prop, "semtech,ph01-resolution",
> > -                             ARRAY_SIZE(prop));
> > +                     strscpy(prop, "semtech,ph01-resolution", sizeof(prop));
> >               else
> > -                     strncpy(prop, "semtech,ph23-resolution",
> > -                             ARRAY_SIZE(prop));
> > +                     strscpy(prop, "semtech,ph23-resolution", sizeof(prop));
> >
> >               ret = device_property_read_u32(dev, prop, &raw);
> >               if (ret)
> > @@ -1012,11 +1010,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
> >       case SX9324_REG_PROX_CTRL0:
> >       case SX9324_REG_PROX_CTRL1:
> >               if (reg_def->reg == SX9324_REG_PROX_CTRL0)
> > -                     strncpy(prop, "semtech,ph01-proxraw-strength",
> > -                             ARRAY_SIZE(prop));
> > +                     strscpy(prop, "semtech,ph01-proxraw-strength", sizeof(prop));
> >               else
> > -                     strncpy(prop, "semtech,ph23-proxraw-strength",
> > -                             ARRAY_SIZE(prop));
> > +                     strscpy(prop, "semtech,ph23-proxraw-strength", sizeof(prop));
> >               ret = device_property_read_u32(dev, prop, &raw);
> >               if (ret)
> >                       break;
> >
> > ---
> > base-commit: 2cf0f715623872823a72e451243bbf555d10d032
> > change-id: 20230921-strncpy-drivers-iio-proximity-sx9324-c-8c3437676039
> >
> > Best regards,
> > --
> > Justin Stitt <justinstitt@google.com>
> >
>

[v2]: https://lore.kernel.org/r/20231026-strncpy-drivers-iio-proximity-sx9324-c-v2-1-cee6e5db700c@google.com

Thanks
Justin

Patchew 2.1-devel-b67e4c2

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