`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

ethtool_sprintf() is designed specifically for get_strings() usage.
Let's replace strncpy in favor of this more robust and easier to
understand interface.

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 only.
---
 drivers/net/dsa/realtek/rtl8365mb.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
index 41ea3b5a42b1..d171c18dd354 100644
--- a/drivers/net/dsa/realtek/rtl8365mb.c
+++ b/drivers/net/dsa/realtek/rtl8365mb.c
@@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
 
 	for (i = 0; i < RTL8365MB_MIB_END; i++) {
 		struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
-
-		strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
+		ethtool_sprintf(&data, "%s", mib->name);
 	}
 }
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231009-strncpy-drivers-net-dsa-realtek-rtl8365mb-c-bb106e4c110c

Best regards,
--
Justin Stitt <justinstitt@google.com>

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 09 Oct 2023 22:43:59 +0000 you wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> ethtool_sprintf() is designed specifically for get_strings() usage.
> Let's replace strncpy in favor of this more robust and easier to
> understand interface.
> 
> [...]

Here is the summary with links:
  - net: dsa: realtek: rtl8365mb: replace deprecated strncpy with ethtool_sprintf
    https://git.kernel.org/netdev/net-next/c/e5f061d5e340

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

On Mon, Oct 09, 2023 at 10:43:59PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> ethtool_sprintf() is designed specifically for get_strings() usage.
> Let's replace strncpy in favor of this more robust and easier to
> understand interface.
> 
> 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>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Hello Justin,

On Mon, Oct 09, 2023 at 10:43:59PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> ethtool_sprintf() is designed specifically for get_strings() usage.
> Let's replace strncpy in favor of this more robust and easier to
> understand interface.
> 
> 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 only.
> ---
>  drivers/net/dsa/realtek/rtl8365mb.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
> index 41ea3b5a42b1..d171c18dd354 100644
> --- a/drivers/net/dsa/realtek/rtl8365mb.c
> +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> @@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
>  
>  	for (i = 0; i < RTL8365MB_MIB_END; i++) {
>  		struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
> -
> -		strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
> +		ethtool_sprintf(&data, "%s", mib->name);

Is there any particular reason why you opted for the "%s" printf format
specifier when you could have simply given mib->name as the single
argument? This comment applies to all the ethtool_sprintf() patches
you've submitted.

On Tue, Oct 10, 2023 at 02:07:17PM +0300, Vladimir Oltean wrote:
> Hello Justin,
> 
> On Mon, Oct 09, 2023 at 10:43:59PM +0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings
> > [1] and as such we should prefer more robust and less ambiguous string
> > interfaces.
> > 
> > ethtool_sprintf() is designed specifically for get_strings() usage.
> > Let's replace strncpy in favor of this more robust and easier to
> > understand interface.
> > 
> > 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 only.
> > ---
> >  drivers/net/dsa/realtek/rtl8365mb.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
> > index 41ea3b5a42b1..d171c18dd354 100644
> > --- a/drivers/net/dsa/realtek/rtl8365mb.c
> > +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> > @@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
> >  
> >  	for (i = 0; i < RTL8365MB_MIB_END; i++) {
> >  		struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
> > -
> > -		strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
> > +		ethtool_sprintf(&data, "%s", mib->name);
> 
> Is there any particular reason why you opted for the "%s" printf format
> specifier when you could have simply given mib->name as the single
> argument? This comment applies to all the ethtool_sprintf() patches
> you've submitted.

The primary reason is that without the "%s", any format specifiers in
mib->name will be processed by sprintf(), which could lead to very
unexpected results. One never wants to just pass a string directly to
the sprintf-family of functions for this reason. "%s" is needed to keep
things safe.

-Kees

-- 
Kees Cook

On Tue, Oct 10, 2023 at 4:07 AM Vladimir Oltean <olteanv@gmail.com> wrote:
>
> Hello Justin,
>
> On Mon, Oct 09, 2023 at 10:43:59PM +0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings
> > [1] and as such we should prefer more robust and less ambiguous string
> > interfaces.
> >
> > ethtool_sprintf() is designed specifically for get_strings() usage.
> > Let's replace strncpy in favor of this more robust and easier to
> > understand interface.
> >
> > 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 only.
> > ---
> >  drivers/net/dsa/realtek/rtl8365mb.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
> > index 41ea3b5a42b1..d171c18dd354 100644
> > --- a/drivers/net/dsa/realtek/rtl8365mb.c
> > +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> > @@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
> >
> >       for (i = 0; i < RTL8365MB_MIB_END; i++) {
> >               struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
> > -
> > -             strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
> > +             ethtool_sprintf(&data, "%s", mib->name);
>
> Is there any particular reason why you opted for the "%s" printf format
> specifier when you could have simply given mib->name as the single
> argument? This comment applies to all the ethtool_sprintf() patches
> you've submitted.

Yeah, it causes a -Wformat-security warning for me. I briefly mentioned it
in one of my first patches like this [1].

[1]: https://lore.kernel.org/all/20231005-strncpy-drivers-net-dsa-lan9303-core-c-v2-1-feb452a532db@google.com/

On Tue, Oct 10, 2023 at 10:36 AM Justin Stitt <justinstitt@google.com> wrote:
>
> On Tue, Oct 10, 2023 at 4:07 AM Vladimir Oltean <olteanv@gmail.com> wrote:
> >
> > Hello Justin,
> >
> > On Mon, Oct 09, 2023 at 10:43:59PM +0000, Justin Stitt wrote:
> > > `strncpy` is deprecated for use on NUL-terminated destination strings
> > > [1] and as such we should prefer more robust and less ambiguous string
> > > interfaces.
> > >
> > > ethtool_sprintf() is designed specifically for get_strings() usage.
> > > Let's replace strncpy in favor of this more robust and easier to
> > > understand interface.
> > >
> > > 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 only.
> > > ---
> > >  drivers/net/dsa/realtek/rtl8365mb.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
> > > index 41ea3b5a42b1..d171c18dd354 100644
> > > --- a/drivers/net/dsa/realtek/rtl8365mb.c
> > > +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> > > @@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_switch *ds, int port, u32 stringset
> > >
> > >       for (i = 0; i < RTL8365MB_MIB_END; i++) {
> > >               struct rtl8365mb_mib_counter *mib = &rtl8365mb_mib_counters[i];
> > > -
> > > -             strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRING_LEN);
> > > +             ethtool_sprintf(&data, "%s", mib->name);
> >
> > Is there any particular reason why you opted for the "%s" printf format
> > specifier when you could have simply given mib->name as the single
> > argument? This comment applies to all the ethtool_sprintf() patches
> > you've submitted.
>
> Yeah, it causes a -Wformat-security warning for me. I briefly mentioned it
> in one of my first patches like this [1].

For more context, here's some warnings in the wild:
https://lore.kernel.org/netdev/20231003183603.3887546-3-jesse.brandeburg@intel.com/

>
> [1]: https://lore.kernel.org/all/20231005-strncpy-drivers-net-dsa-lan9303-core-c-v2-1-feb452a532db@google.com/

On Tue, Oct 10, 2023 at 02:48:07PM -0700, Justin Stitt wrote:
> On Tue, Oct 10, 2023 at 10:36 AM Justin Stitt <justinstitt@google.com> wrote:
> > > Is there any particular reason why you opted for the "%s" printf format
> > > specifier when you could have simply given mib->name as the single
> > > argument? This comment applies to all the ethtool_sprintf() patches
> > > you've submitted.
> >
> > Yeah, it causes a -Wformat-security warning for me. I briefly mentioned it
> > in one of my first patches like this [1].
> 
> For more context, here's some warnings in the wild:
> https://lore.kernel.org/netdev/20231003183603.3887546-3-jesse.brandeburg@intel.com/
> 
> >
> > [1]: https://lore.kernel.org/all/20231005-strncpy-drivers-net-dsa-lan9303-core-c-v2-1-feb452a532db@google.com/

Yeah, ok. It's a false positive warning, but I guess it would be too
hard for the compiler to figure that out.

On 10/9/23 15:43, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> ethtool_sprintf() is designed specifically for get_strings() usage.
> Let's replace strncpy in favor of this more robust and easier to
> understand interface.
> 
> 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>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
-- 
Florian