`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

`dax_id->dev_name` is expected to be NUL-terminated and has been zero-allocated.

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on the destination buffer. Moreover, due to
`dax_id` being zero-allocated the padding behavior of `strncpy` is not
needed and a simple 1:1 replacement of strncpy -> strscpy should
suffice.

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/dax/bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 0ee96e6fc426..1659b787b65f 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -103,7 +103,7 @@ static ssize_t do_id_store(struct device_driver *drv, const char *buf,
 		if (action == ID_ADD) {
 			dax_id = kzalloc(sizeof(*dax_id), GFP_KERNEL);
 			if (dax_id) {
-				strncpy(dax_id->dev_name, buf, DAX_NAME_LEN);
+				strscpy(dax_id->dev_name, buf, DAX_NAME_LEN);
 				list_add(&dax_id->list, &dax_drv->ids);
 			} else
 				rc = -ENOMEM;

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230913-strncpy-drivers-dax-bus-c-f12e3153e44b

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

On Wed, Sep 13, 2023 at 01:10:24AM +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.
> 
> `dax_id->dev_name` is expected to be NUL-terminated and has been zero-allocated.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer. Moreover, due to
> `dax_id` being zero-allocated the padding behavior of `strncpy` is not
> needed and a simple 1:1 replacement of strncpy -> strscpy should
> suffice.
> 
> 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>

Looks correct to me.

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

-- 
Kees Cook

On 9/12/23 18:10, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> `dax_id->dev_name` is expected to be NUL-terminated and has been zero-allocated.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer. Moreover, due to
> `dax_id` being zero-allocated the padding behavior of `strncpy` is not
> needed and a simple 1:1 replacement of strncpy -> strscpy should
> suffice.
> 
> 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: Dave Jiang <dave.jiang@intel.com>
> ---
> Note: build-tested only.
> ---
>  drivers/dax/bus.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 0ee96e6fc426..1659b787b65f 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -103,7 +103,7 @@ static ssize_t do_id_store(struct device_driver *drv, const char *buf,
>  		if (action == ID_ADD) {
>  			dax_id = kzalloc(sizeof(*dax_id), GFP_KERNEL);
>  			if (dax_id) {
> -				strncpy(dax_id->dev_name, buf, DAX_NAME_LEN);
> +				strscpy(dax_id->dev_name, buf, DAX_NAME_LEN);
>  				list_add(&dax_id->list, &dax_drv->ids);
>  			} else
>  				rc = -ENOMEM;
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230913-strncpy-drivers-dax-bus-c-f12e3153e44b
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>