[PATCH] s390/sclp: replace deprecated strncpy with strtomem

[PATCH] s390/sclp: replace deprecated strncpy with strtomem

[Justin Stitt]

Let's move away from using strncpy() as it is deprecated [1].

Instead use strtomem() as `e.id` is already marked as nonstring:
|       char id[4] __nonstring;

We don't need strtomem_pad() because `e` is already memset to 0 --
rendering any additional NUL-padding useless.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
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.

Found with: $ rg "strncpy\("
---
 drivers/s390/char/sclp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c
index 8f74db689a0c..486cf57a1605 100644
--- a/drivers/s390/char/sclp.c
+++ b/drivers/s390/char/sclp.c
@@ -81,7 +81,7 @@ static inline void sclp_trace(int prio, char *id, u32 a, u64 b, bool err)
 	struct sclp_trace_entry e;
 
 	memset(&e, 0, sizeof(e));
-	strncpy(e.id, id, sizeof(e.id));
+	strtomem(e.id, id);
 	e.a = a;
 	e.b = b;
 	debug_event(&sclp_debug, prio, &e, sizeof(e));

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-char-sclp-c-bb66226a7eaa

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

Re: [PATCH] s390/sclp: replace deprecated strncpy with strtomem

[Kees Cook]

On Mon, Oct 23, 2023 at 07:14:49PM +0000, Justin Stitt wrote:
> Let's move away from using strncpy() as it is deprecated [1].
> 
> Instead use strtomem() as `e.id` is already marked as nonstring:
> |       char id[4] __nonstring;

I'm surprised the compiler didn't complain about this -- I thought that
was the point of the __nonstring attribute: to diagnose when used with a
string function. Hmpf.

> 
> We don't need strtomem_pad() because `e` is already memset to 0 --
> rendering any additional NUL-padding useless.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> 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.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/s390/char/sclp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c
> index 8f74db689a0c..486cf57a1605 100644
> --- a/drivers/s390/char/sclp.c
> +++ b/drivers/s390/char/sclp.c
> @@ -81,7 +81,7 @@ static inline void sclp_trace(int prio, char *id, u32 a, u64 b, bool err)
>  	struct sclp_trace_entry e;
>  
>  	memset(&e, 0, sizeof(e));
> -	strncpy(e.id, id, sizeof(e.id));
> +	strtomem(e.id, id);

Looks right to me; thanks!

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

-Kees

>  	e.a = a;
>  	e.b = b;
>  	debug_event(&sclp_debug, prio, &e, sizeof(e));
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-s390-char-sclp-c-bb66226a7eaa
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

-- 
Kees Cook

Re: [PATCH] s390/sclp: replace deprecated strncpy with strtomem

[Kees Cook]

On Tue, Oct 24, 2023 at 04:46:04PM -0700, Kees Cook wrote:
> > Instead use strtomem() as `e.id` is already marked as nonstring:
> > |       char id[4] __nonstring;
> 
> I'm surprised the compiler didn't complain about this -- I thought that
> was the point of the __nonstring attribute: to diagnose when used with a
> string function. Hmpf.

Wow. GCC only warns if you call strlen() on it, but literally nothing
else... :(

-- 
Kees Cook

Re: [PATCH] s390/sclp: replace deprecated strncpy with strtomem

[Vasily Gorbik]

On Mon, Oct 23, 2023 at 07:14:49PM +0000, Justin Stitt wrote:
> Let's move away from using strncpy() as it is deprecated [1].
> 
> Instead use strtomem() as `e.id` is already marked as nonstring:
> |       char id[4] __nonstring;
> 
> We don't need strtomem_pad() because `e` is already memset to 0 --
> rendering any additional NUL-padding useless.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> 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.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/s390/char/sclp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thank you!