[PATCH] dm log userspace: replace deprecated strncpy with strscpy

[PATCH] dm log userspace: 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.

`lc` is already zero-allocated:
|       lc = kzalloc(sizeof(*lc), GFP_KERNEL);
... as such, any future NUL-padding is superfluous.

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

Let's also go with the more idiomatic `dest, src, sizeof(dest)` pattern
for destination buffers that the compiler can calculate the size for.

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
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.
---
 drivers/md/dm-log-userspace-base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
index 5aace6ee6d47..7e4f27e86150 100644
--- a/drivers/md/dm-log-userspace-base.c
+++ b/drivers/md/dm-log-userspace-base.c
@@ -224,7 +224,7 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 
 	lc->usr_argc = argc;
 
-	strncpy(lc->uuid, argv[0], DM_UUID_LEN);
+	strscpy(lc->uuid, argv[0], sizeof(lc->uuid));
 	argc--;
 	argv++;
 	spin_lock_init(&lc->flush_lock);

---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230925-strncpy-drivers-md-dm-log-userspace-base-c-857579d9834f

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

Re: [PATCH] dm log userspace: replace deprecated strncpy with strscpy

[Kees Cook]

On Mon, Sep 25, 2023 at 07:06:03AM +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.
> 
> `lc` is already zero-allocated:
> |       lc = kzalloc(sizeof(*lc), GFP_KERNEL);
> ... as such, any future NUL-padding is superfluous.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer without
> unnecessarily NUL-padding.
> 
> Let's also go with the more idiomatic `dest, src, sizeof(dest)` pattern
> for destination buffers that the compiler can calculate the size for.
> 
> 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
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Looks good to me. Thanks for the sizeof() replacement. :)

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

-Kees

> ---
> Note: build-tested only.
> ---
>  drivers/md/dm-log-userspace-base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
> index 5aace6ee6d47..7e4f27e86150 100644
> --- a/drivers/md/dm-log-userspace-base.c
> +++ b/drivers/md/dm-log-userspace-base.c
> @@ -224,7 +224,7 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
>  
>  	lc->usr_argc = argc;
>  
> -	strncpy(lc->uuid, argv[0], DM_UUID_LEN);
> +	strscpy(lc->uuid, argv[0], sizeof(lc->uuid));
>  	argc--;
>  	argv++;
>  	spin_lock_init(&lc->flush_lock);
> 
> ---
> base-commit: 6465e260f48790807eef06b583b38ca9789b6072
> change-id: 20230925-strncpy-drivers-md-dm-log-userspace-base-c-857579d9834f
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 

-- 
Kees Cook

Re: [PATCH] dm log userspace: replace deprecated strncpy with strscpy

[Kees Cook]

On Mon, 25 Sep 2023 07:06:03 +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.
> 
> `lc` is already zero-allocated:
> |       lc = kzalloc(sizeof(*lc), GFP_KERNEL);
> ... as such, any future NUL-padding is superfluous.
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] dm log userspace: replace deprecated strncpy with strscpy
      https://git.kernel.org/kees/c/f8cff5441800

Take care,

-- 
Kees Cook