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Date:   Tue, 24 Oct 2023 17:30:11 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org
Subject: Re: [PATCH] scsi: ch: replace deprecated strncpy with strscpy
Message-ID: <202310241729.1740ED4F@keescook>
References: <20231023-strncpy-drivers-scsi-ch-c-v1-1-dc67ba8075a3@google.com>
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In-Reply-To: <20231023-strncpy-drivers-scsi-ch-c-v1-1-dc67ba8075a3@google.com>
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On Mon, Oct 23, 2023 at 08:20:14PM +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.
> 
> These labels get copied out to the user so lets make sure they are
> NUL-terminated and NUL-padded.
> 
> vparams is already memset to 0 so we don't need to do any NUL-padding
> (like what strncpy() is doing).
> 
> 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.
> 
> Let's also opt to use the more idiomatic strscpy() usage of:
> (dest, src, sizeof(dest)) as this more closely ties the destination
> buffer to the length.
> 
> 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, these all look correct. I can confirm the open-coded "16" matches
the now-used sizeof().

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

-Kees

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/scsi/ch.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/ch.c b/drivers/scsi/ch.c
> index cb0a399be1cc..2b864061e073 100644
> --- a/drivers/scsi/ch.c
> +++ b/drivers/scsi/ch.c
> @@ -659,19 +659,23 @@ static long ch_ioctl(struct file *file,
>  		memset(&vparams,0,sizeof(vparams));
>  		if (ch->counts[CHET_V1]) {
>  			vparams.cvp_n1  = ch->counts[CHET_V1];
> -			strncpy(vparams.cvp_label1,vendor_labels[0],16);
> +			strscpy(vparams.cvp_label1, vendor_labels[0],
> +				sizeof(vparams.cvp_label1));
>  		}
>  		if (ch->counts[CHET_V2]) {
>  			vparams.cvp_n2  = ch->counts[CHET_V2];
> -			strncpy(vparams.cvp_label2,vendor_labels[1],16);
> +			strscpy(vparams.cvp_label2, vendor_labels[1],
> +				sizeof(vparams.cvp_label2));
>  		}
>  		if (ch->counts[CHET_V3]) {
>  			vparams.cvp_n3  = ch->counts[CHET_V3];
> -			strncpy(vparams.cvp_label3,vendor_labels[2],16);
> +			strscpy(vparams.cvp_label3, vendor_labels[2],
> +				sizeof(vparams.cvp_label3));
>  		}
>  		if (ch->counts[CHET_V4]) {
>  			vparams.cvp_n4  = ch->counts[CHET_V4];
> -			strncpy(vparams.cvp_label4,vendor_labels[3],16);
> +			strscpy(vparams.cvp_label4, vendor_labels[3],
> +				sizeof(vparams.cvp_label4));
>  		}
>  		if (copy_to_user(argp, &vparams, sizeof(vparams)))
>  			return -EFAULT;
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-scsi-ch-c-23b1cdac43cc
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

-- 
Kees Cook