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

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Date: Mon, 25 Sep 2023 11:20:18 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
	dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] dm log userspace: replace deprecated strncpy with strscpy

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@...r.kernel.org
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

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

Reviewed-by: Kees Cook <keescook@...omium.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@...gle.com>
> 

-- 
Kees Cook