linux-hardening - Re: [PATCH] aoe: refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 20:21:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Justin Sanders <justin@...aid.com>, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Xu Panda <xu.panda@....com.cn>,
        Yang Yang <yang.yang29@....com>
Subject: Re: [PATCH] aoe: refactor deprecated strncpy

On Mon, Sep 11, 2023 at 09:09:07PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> `aoe_iflist` is expected to be NUL-terminated which is evident by its
> use with string apis later on like `strspn`:
> | 	p = aoe_iflist + strspn(aoe_iflist, WHITESPACE);
> 
> It also seems `aoe_iflist` does not need to be NUL-padded which means
> `strscpy` [2] is a suitable replacement due to the fact that it
> guarantees NUL-termination on the destination buffer while not
> 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@...r.kernel.org
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Xu Panda <xu.panda@....com.cn>
> Cc: Yang Yang <yang.yang29@....com>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Agreed, truncation is the current behavior, and padding isn't needed.
(Or more precisely, it's already zeroed and this function is called
once.)

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

> ---
> Note: This exact same patch exists [3] but seemed to die so I'm
> resending. If it was actually picked-up somewhere then we can ignore
> this patch.
> 
> [3]: https://lore.kernel.org/all/202212051930256039214@zte.com.cn/

Ah, weird. Well, I think this current one has a more complete commit
log, so let's use this one.

-Kees

> ---
>  drivers/block/aoe/aoenet.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
> index 63773a90581d..c51ea95bc2ce 100644
> --- a/drivers/block/aoe/aoenet.c
> +++ b/drivers/block/aoe/aoenet.c
> @@ -39,8 +39,7 @@ static struct ktstate kts;
>  #ifndef MODULE
>  static int __init aoe_iflist_setup(char *str)
>  {
> -	strncpy(aoe_iflist, str, IFLISTSZ);
> -	aoe_iflist[IFLISTSZ - 1] = '\0';
> +	strscpy(aoe_iflist, str, IFLISTSZ);
>  	return 1;
>  }
>  
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230911-strncpy-drivers-block-aoe-aoenet-c-024debad6105
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Kees Cook