[PATCH] isdn: replace deprecated strncpy with strscpy

[PATCH] isdn: replace deprecated strncpy with strscpy

[Justin Stitt]

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

We expect `iclock->name` to be NUL-terminated based on its use within
printk:
|	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
|	       iclock->pri);

`iclock` is zero-initialized and as such is already NUL-padded which
means strncpy is doing extra work here by eagerly NUL-padding the
destination buffer.

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.

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/isdn/mISDN/clock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/isdn/mISDN/clock.c b/drivers/isdn/mISDN/clock.c
index 01d878168ef2..f71eb61db131 100644
--- a/drivers/isdn/mISDN/clock.c
+++ b/drivers/isdn/mISDN/clock.c
@@ -96,7 +96,7 @@ struct mISDNclock
 		printk(KERN_ERR "%s: No memory for clock entry.\n", __func__);
 		return NULL;
 	}
-	strncpy(iclock->name, name, sizeof(iclock->name) - 1);
+	strscpy(iclock->name, name, sizeof(iclock->name));
 	iclock->pri = pri;
 	iclock->priv = priv;
 	iclock->ctl = ctl;

---
base-commit: 2cf0f715623872823a72e451243bbf555d10d032
change-id: 20230922-strncpy-drivers-isdn-misdn-clock-c-2d32a23b8c2d

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

Re: [PATCH] isdn: replace deprecated strncpy with strscpy

[Kees Cook]

On Fri, Sep 22, 2023 at 11:58:06AM +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.
> 
> We expect `iclock->name` to be NUL-terminated based on its use within
> printk:
> |	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
> |	       iclock->pri);
> 
> `iclock` is zero-initialized and as such is already NUL-padded which
> means strncpy is doing extra work here by eagerly NUL-padding the
> destination buffer.
> 
> 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.
> 
> 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>

Yup, looks like a clean replacement.

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

-- 
Kees Cook

Re: [PATCH] isdn: replace deprecated strncpy with strscpy

[Kees Cook]

On Fri, 22 Sep 2023 11:58:06 +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.
> 
> We expect `iclock->name` to be NUL-terminated based on its use within
> printk:
> |	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
> |	       iclock->pri);
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] isdn: replace deprecated strncpy with strscpy
      https://git.kernel.org/kees/c/a9b065a6751b

Take care,

-- 
Kees Cook